CMakeLists: build for x86-64-v3 by default

- UIState.h: Replaced C-style arrays bool[] and ImVec4[] with
std::array<bool, kMaxChannels> and std::array<ImVec4, kMaxChannels> for
type safety and STL compatibility.
  - Application.cpp: Extracted duplicated DPI calculation (lines 189-196
and 475-481) into a systemDpiScale() helper method, reducing both call
sites to single-line calls.
  - Application.cpp: Replaced magic 1400, 900 window dimensions with
kDefaultWindowWidth/kDefaultWindowHeight constants (defined in Types.h).
  - AudioEngine.cpp: Named the magic epsilon thresholds 1e-20f →
kLinearEpsilon and 1e-30f → kLogGuard with explanatory comments, defined
in an anonymous namespace.
  - Types.h: Added kDefaultWindowWidth and kDefaultWindowHeight
constants.

.github/workflows/build.yml

@@ -0,0 +1,129 @@
+name: Build
+
+on:
+  push:
+    branches: [main, master]
+  pull_request:
+    branches: [main, master]
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+jobs:
+  linux:
+    name: Linux (static)
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y \
+            build-essential cmake pkg-config \
+            libsdl2-dev libfftw3-dev libsndfile1-dev \
+            libgl-dev
+
+      - name: Configure
+        run: cmake -B build -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_FLAGS_RELEASE="-O3 -march=haswell -DNDEBUG"
+
+      - name: Build
+        run: cmake --build build -j$(nproc)
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: baudmine-linux
+          path: build/baudmine
+
+  windows:
+    name: Windows
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Cache vcpkg packages
+        uses: actions/cache@v4
+        with:
+          path: ${{ env.VCPKG_INSTALLATION_ROOT }}/installed
+          key: vcpkg-x64-windows-${{ hashFiles('.github/workflows/build.yml') }}
+          restore-keys: vcpkg-x64-windows-
+
+      - name: Install vcpkg dependencies
+        run: |
+          vcpkg install sdl2 fftw3 "libsndfile[core]" --triplet x64-windows
+
+      - name: Configure
+        run: >
+          cmake -B build
+          -DCMAKE_BUILD_TYPE=Release
+          -DCMAKE_TOOLCHAIN_FILE="$env:VCPKG_INSTALLATION_ROOT/scripts/buildsystems/vcpkg.cmake"
+          -DVCPKG_TARGET_TRIPLET=x64-windows
+          -DCMAKE_CXX_FLAGS="/O2 /arch:AVX2 /DNDEBUG"
+          -DCMAKE_C_FLAGS="/O2 /arch:AVX2 /DNDEBUG"
+
+      - name: Build
+        run: cmake --build build --config Release -j $env:NUMBER_OF_PROCESSORS
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: baudmine-windows
+          path: |
+            build/Release/baudmine.exe
+            build/Release/*.dll
+
+  wasm:
+    name: Web (WASM)
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup Emscripten
+        uses: mymindstorm/setup-emsdk@v14
+        with:
+          version: 5.0.4
+
+      - name: Configure
+        run: emcmake cmake -B build_wasm -C CMakeLists_wasm.cmake -Wno-dev
+
+      - name: Build
+        run: cmake --build build_wasm -j$(nproc)
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: baudmine-web
+          path: |
+            build_wasm/web/baudmine.html
+            build_wasm/web/baudmine.js
+            build_wasm/web/baudmine.wasm
+
+      - name: Prepare Pages
+        if: github.event_name == 'push'
+        run: |
+          mkdir -p _site
+          cp build_wasm/web/baudmine.html _site/index.html
+          cp build_wasm/web/baudmine.js   _site/
+          cp build_wasm/web/baudmine.wasm _site/
+
+      - name: Upload Pages artifact
+        if: github.event_name == 'push'
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: _site
+
+  deploy:
+    name: Deploy to GitHub Pages
+    needs: wasm
+    if: github.event_name == 'push'
+    runs-on: ubuntu-24.04
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy
+        id: deployment
+        uses: actions/deploy-pages@v4

CMakeLists.txt

@@ -47,11 +47,14 @@ set(SOURCES
     src/dsp/SpectrumAnalyzer.cpp
     src/audio/MiniAudioSource.cpp
     src/audio/FileSource.cpp
+    src/audio/AudioEngine.cpp
     src/ui/ColorMap.cpp
     src/ui/WaterfallDisplay.cpp
     src/ui/SpectrumDisplay.cpp
     src/ui/Cursors.cpp
     src/ui/Measurements.cpp
+    src/ui/ControlPanel.cpp
+    src/ui/DisplayPanel.cpp
     src/ui/Application.cpp
 )
 
@@ -177,12 +180,37 @@ if(EMSCRIPTEN)
 else()
     # ── Native Build ─────────────────────────────────────────────────────────
 
-    set(CMAKE_CXX_FLAGS_RELEASE "-O3 -march=native -DNDEBUG")
-    set(CMAKE_CXX_FLAGS_DEBUG "-g -O0 -fsanitize=address,undefined")
+    option(NATIVE_BUILD "Optimize for the host CPU (-march=native)" OFF)
+
+    if(MSVC)
+        set(CMAKE_CXX_FLAGS_RELEASE "/O2 /DNDEBUG /arch:AVX2")
+        set(CMAKE_CXX_FLAGS_DEBUG "/Zi /Od")
+    else()
+        if(NATIVE_BUILD)
+            set(CMAKE_CXX_FLAGS_RELEASE "-O3 -march=native -DNDEBUG")
+        else()
+            set(CMAKE_CXX_FLAGS_RELEASE "-O3 -march=x86-64-v3 -DNDEBUG")
+        endif()
+        set(CMAKE_CXX_FLAGS_DEBUG "-g -O0 -fsanitize=address,undefined")
+    endif()
 
-    find_package(PkgConfig REQUIRED)
     find_package(OpenGL REQUIRED)
 
+    if(MSVC)
+        find_package(SDL2 CONFIG REQUIRED)
+        find_package(FFTW3f CONFIG REQUIRED)
+        find_package(SndFile CONFIG REQUIRED)
+
+        target_link_libraries(imgui PUBLIC SDL2::SDL2 OpenGL::GL)
+
+        add_executable(baudmine ${SOURCES})
+        target_include_directories(baudmine PRIVATE src)
+        target_link_libraries(baudmine PRIVATE
+            imgui SDL2::SDL2 SDL2::SDL2main
+            FFTW3::fftw3f SndFile::sndfile OpenGL::GL
+        )
+    else()
+        find_package(PkgConfig REQUIRED)
         pkg_check_modules(SDL2 REQUIRED IMPORTED_TARGET sdl2)
         pkg_check_modules(FFTW3F REQUIRED IMPORTED_TARGET fftw3f)
         pkg_check_modules(SNDFILE REQUIRED IMPORTED_TARGET sndfile)
@@ -192,17 +220,13 @@ else()
         add_executable(baudmine ${SOURCES})
         target_include_directories(baudmine PRIVATE src)
         target_link_libraries(baudmine PRIVATE
-        imgui
-        PkgConfig::SDL2
-        PkgConfig::FFTW3F
-        PkgConfig::SNDFILE
-        OpenGL::GL
-        pthread
+            imgui PkgConfig::SDL2 PkgConfig::FFTW3F
+            PkgConfig::SNDFILE OpenGL::GL pthread
         )
 
-    # Link math library and dl on Unix (dl needed by miniaudio for backend loading)
         if(UNIX)
             target_link_libraries(baudmine PRIVATE m dl)
         endif()
+    endif()
 
 endif()

LICENSE

@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The GNU General Public License is a free, copyleft license for
+software and other kinds of works.
+
+  The licenses for most software and other practical works are designed
+to take away your freedom to share and change the works.  By contrast,
+the GNU General Public License is intended to guarantee your freedom to
+share and change all versions of a program--to make sure it remains free
+software for all its users.  We, the Free Software Foundation, use the
+GNU General Public License for most of our software; it applies also to
+any other work released this way by its authors.  You can apply it to
+your programs, too.
+
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+you modify it: responsibilities to respect the freedom of others.
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+<https://www.gnu.org/licenses/>.
+
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+<https://www.gnu.org/licenses/why-not-lgpl.html>.

README.md

@@ -0,0 +1,69 @@
+# Baudmine Spectrum Analyzer
+
+Real-time audio spectrum analyzer and waterfall display built with C++17, ImGui, SDL2, and OpenGL. Runs natively on Linux and Windows, and in the browser via WebAssembly.
+
+Beware, this thing is **entirely LLM-generated**! I've barely looked at the code! Anthropic had a promo for Claude, so I utilized it to make this clone of [**baudline**](https://www.baudline.com/what_is_baudline.html), which is a very powerful (and proprietary) tool, but sadly it's been seemingly abandoned for years, not that it would need anything. My hope was to put together something similar, using a more modern stack. It is not (yet) a fully-featured replacement, but it's good enough for me.
+
+## Web preview
+
+You can find the Web version here, delivered in 870 kB: https://ericek111.github.io/baudmine/
+
+(If you allow access to "all microphones", you can switch between the input devices in the File menu.)
+
+## Features
+
+### Signal Processing
+- FFT sizes from 256 to 65,536 points with configurable overlap of bins for precise speed control of the waterfall.
+- Window functions: Hann, Hamming, Blackman, Blackman-Harris, Kaiser (configurable beta), Flat Top, Rectangular
+
+### Input Sources
+- Live audio from system input devices
+- Multi-device mode: use up to 8 devices simultaneously, each mapped to a channel
+- File playback: WAV, Float32/Int16/Uint8 I/Q formats
+
+### Visualization
+- Spectrum plot
+- Scrolling waterfall display that can be zoomed and panned
+- Linear and logarithmic frequency scales
+- Additive color blending for multi-channel display
+- Peak hold with adjustable decay rate
+
+### Analysis
+- Dual cursors with frequency and magnitude readout
+- Automatic snap-to-peak
+- Peak detection with configurable threshold, separation, and frequency range (it shows the center frequency of the peak-detected FFT bin)
+- Peak trace on the waterfall
+- Delta measurements between cursors
+
+### Math Channels
+- Unary: Negate, Absolute, Square, Cube, Square Root, Log
+- Binary: Add, Subtract, Multiply, Phase, Cross-correlation
+- Custom colors per math channel
+
+### Interface
+- DPI-aware UI with auto-detection and manual scaling (100-300%)
+- Touch gesture support in the waterfall (pan and pinch-to-zoom)
+- The most important settings persist across sessions
+
+## Building
+
+### Linux
+
+```bash
+# Install dependencies (Debian/Ubuntu)
+sudo apt install build-essential cmake pkg-config libsdl2-dev libfftw3-dev libsndfile1-dev libgl-dev
+
+cmake -B build -DCMAKE_BUILD_TYPE=Release -DNATIVE_BUILD=ON
+cmake --build build -j$(nproc)
+```
+
+### Windows (MSVC + vcpkg)
+
+```powershell
+vcpkg install sdl2 fftw3 "libsndfile[core]" --triplet x64-windows
+
+cmake -B build -DCMAKE_BUILD_TYPE=Release -DNATIVE_BUILD=ON `
+    -DCMAKE_TOOLCHAIN_FILE="$env:VCPKG_INSTALLATION_ROOT/scripts/buildsystems/vcpkg.cmake" `
+    -DVCPKG_TARGET_TRIPLET=x64-windows
+cmake --build build --config Release
+```

src/audio/AudioEngine.cpp

@@ -0,0 +1,392 @@
+#include "audio/AudioEngine.h"
+#include "audio/FileSource.h"
+
+#include <algorithm>
+#include <chrono>
+#include <cmath>
+#include <cstdio>
+#include <cstring>
+
+namespace baudmine {
+
+namespace {
+constexpr float kLinearEpsilon = 1e-20f;  // threshold for log10 of linear power
+constexpr float kLogGuard      = 1e-30f;  // guard against log10(0) in compressed scale
+} // namespace
+
+AudioEngine::AudioEngine() = default;
+
+// ── Device enumeration ───────────────────────────────────────────────────────
+
+void AudioEngine::enumerateDevices() {
+    devices_ = MiniAudioSource::listInputDevices();
+}
+
+void AudioEngine::clearDeviceSelections() {
+    std::memset(deviceSelected_, 0, sizeof(deviceSelected_));
+}
+
+// ── Source management ────────────────────────────────────────────────────────
+
+void AudioEngine::closeAll() {
+    if (audioSource_) audioSource_->close();
+    audioSource_.reset();
+    extraDevices_.clear();
+}
+
+void AudioEngine::openDevice(int deviceListIdx) {
+    closeAll();
+
+    int deviceIdx = -1;
+    double sr = 48000.0;
+    if (deviceListIdx >= 0 && deviceListIdx < static_cast<int>(devices_.size())) {
+        deviceIdx = devices_[deviceListIdx].index;
+        sr = devices_[deviceListIdx].defaultSampleRate;
+    }
+
+    int reqCh = 2;
+    if (deviceListIdx >= 0 && deviceListIdx < static_cast<int>(devices_.size()))
+        reqCh = std::min(devices_[deviceListIdx].maxInputChannels, kMaxChannels);
+    if (reqCh < 1) reqCh = 1;
+
+    auto src = std::make_unique<MiniAudioSource>(sr, reqCh, deviceIdx);
+    if (src->open()) {
+        audioSource_ = std::move(src);
+        settings_.sampleRate = audioSource_->sampleRate();
+        settings_.isIQ = false;
+        settings_.numChannels = audioSource_->channels();
+    } else {
+        std::fprintf(stderr, "Failed to open audio device\n");
+    }
+}
+
+void AudioEngine::openMultiDevice(const bool selected[], int maxDevs) {
+    closeAll();
+
+    std::vector<int> sel;
+    for (int i = 0; i < maxDevs; ++i)
+        if (selected[i]) sel.push_back(i);
+    if (sel.empty()) return;
+
+    // First selected device becomes the primary source.
+    {
+        int idx = sel[0];
+        double sr = devices_[idx].defaultSampleRate;
+        int reqCh = std::min(devices_[idx].maxInputChannels, kMaxChannels);
+        if (reqCh < 1) reqCh = 1;
+        auto src = std::make_unique<MiniAudioSource>(sr, reqCh, devices_[idx].index);
+        if (src->open()) {
+            audioSource_ = std::move(src);
+            settings_.sampleRate = audioSource_->sampleRate();
+            settings_.isIQ = false;
+            settings_.numChannels = audioSource_->channels();
+        } else {
+            std::fprintf(stderr, "Failed to open primary device %s\n",
+                         devices_[idx].name.c_str());
+            return;
+        }
+    }
+
+    // Remaining selected devices become extra sources.
+    int totalCh = settings_.numChannels;
+    for (size_t s = 1; s < sel.size() && totalCh < kMaxChannels; ++s) {
+        int idx = sel[s];
+        double sr = devices_[idx].defaultSampleRate;
+        int reqCh = std::min(devices_[idx].maxInputChannels, kMaxChannels - totalCh);
+        if (reqCh < 1) reqCh = 1;
+        auto src = std::make_unique<MiniAudioSource>(sr, reqCh, devices_[idx].index);
+        if (src->open()) {
+            auto ed = std::make_unique<ExtraDevice>();
+            ed->source = std::move(src);
+            AnalyzerSettings es = settings_;
+            es.sampleRate = ed->source->sampleRate();
+            es.numChannels = ed->source->channels();
+            es.isIQ = false;
+            ed->analyzer.configure(es);
+            totalCh += ed->source->channels();
+            extraDevices_.push_back(std::move(ed));
+        } else {
+            std::fprintf(stderr, "Failed to open extra device %s\n",
+                         devices_[idx].name.c_str());
+        }
+    }
+}
+
+void AudioEngine::openFile(const std::string& path, InputFormat format,
+                            double sampleRate, bool loop) {
+    closeAll();
+
+    bool isIQ = (format != InputFormat::WAV);
+    auto src = std::make_unique<FileSource>(path, format, sampleRate, loop);
+    if (src->open()) {
+        settings_.sampleRate = src->sampleRate();
+        settings_.isIQ = isIQ;
+        settings_.numChannels = isIQ ? 1 : src->channels();
+        audioSource_ = std::move(src);
+    } else {
+        std::fprintf(stderr, "Failed to open file: %s\n", path.c_str());
+    }
+}
+
+// ── Analyzer ─────────────────────────────────────────────────────────────────
+
+void AudioEngine::configure(const AnalyzerSettings& s) {
+    settings_ = s;
+    analyzer_.configure(settings_);
+
+    for (auto& ed : extraDevices_) {
+        AnalyzerSettings es = settings_;
+        es.sampleRate = ed->source->sampleRate();
+        es.numChannels = ed->source->channels();
+        es.isIQ = false;
+        ed->analyzer.configure(es);
+    }
+}
+
+void AudioEngine::clearHistory() {
+    analyzer_.clearHistory();
+    for (auto& ed : extraDevices_)
+        ed->analyzer.clearHistory();
+    for (auto& mw : mathWaterfalls_)
+        mw.clear();
+}
+
+int AudioEngine::processAudio() {
+    if (!audioSource_) return 0;
+
+    int channels = audioSource_->channels();
+    size_t hopFrames = static_cast<size_t>(
+        settings_.fftSize * (1.0f - settings_.overlap));
+    if (hopFrames < 1) hopFrames = 1;
+    audioBuf_.resize(hopFrames * channels);
+
+    // Drain all available audio so the scroll rate is independent of the
+    // display refresh rate (vsync).  Real-time sources self-limit via their
+    // ring buffer; file sources are capped to wall-clock time so playback
+    // runs at 1× speed regardless of frame rate.
+
+    // For file sources, compute how many samples correspond to elapsed time.
+    size_t fileSampleCap = SIZE_MAX;  // unlimited for real-time
+    if (!audioSource_->isRealTime()) {
+        using Clock = std::chrono::steady_clock;
+        static Clock::time_point lastFileTime = Clock::now();
+        auto now = Clock::now();
+        double elapsed = std::chrono::duration<double>(now - lastFileTime).count();
+        lastFileTime = now;
+        // Clamp elapsed to avoid huge bursts after pauses or stalls.
+        if (elapsed > 0.1) elapsed = 0.1;
+        fileSampleCap = static_cast<size_t>(elapsed * settings_.sampleRate) + 1;
+    }
+
+    // Process primary source.
+    int spectraThisFrame = 0;
+    size_t samplesRead = 0;
+    for (;;) {
+        if (samplesRead >= fileSampleCap) break;
+        size_t framesRead = audioSource_->read(audioBuf_.data(), hopFrames);
+        if (framesRead == 0) break;
+        samplesRead += framesRead;
+        analyzer_.pushSamples(audioBuf_.data(), framesRead);
+        if (analyzer_.hasNewSpectrum())
+            ++spectraThisFrame;
+    }
+
+    // Process extra devices independently (always real-time).
+    for (auto& ed : extraDevices_) {
+        int edCh = ed->source->channels();
+        const auto& edSettings = ed->analyzer.settings();
+        size_t edHop = static_cast<size_t>(edSettings.fftSize * (1.0f - edSettings.overlap));
+        if (edHop < 1) edHop = 1;
+        ed->audioBuf.resize(edHop * edCh);
+
+        for (;;) {
+            size_t framesRead = ed->source->read(ed->audioBuf.data(), edHop);
+            if (framesRead == 0) break;
+            ed->analyzer.pushSamples(ed->audioBuf.data(), framesRead);
+        }
+    }
+
+    // Track overruns: spectra lost because they exceeded the history capacity.
+    if (spectraThisFrame > kWaterfallHistory)
+        overrunCount_ += spectraThisFrame - kWaterfallHistory;
+
+    return spectraThisFrame;
+}
+
+void AudioEngine::drainSources() {
+    if (audioSource_ && audioSource_->isRealTime()) {
+        int channels = audioSource_->channels();
+        std::vector<float> drain(4096 * channels);
+        while (audioSource_->read(drain.data(), 4096) > 0) {}
+    }
+    for (auto& ed : extraDevices_) {
+        if (ed->source && ed->source->isRealTime()) {
+            int ch = ed->source->channels();
+            std::vector<float> drain(4096 * ch);
+            while (ed->source->read(drain.data(), 4096) > 0) {}
+        }
+    }
+}
+
+// ── Unified channel view ─────────────────────────────────────────────────────
+
+int AudioEngine::totalNumSpectra() const {
+    int n = analyzer_.numSpectra();
+    for (auto& ed : extraDevices_)
+        n += ed->analyzer.numSpectra();
+    return n;
+}
+
+const std::vector<float>& AudioEngine::getSpectrum(int globalCh) const {
+    int n = analyzer_.numSpectra();
+    if (globalCh < n) return analyzer_.channelSpectrum(globalCh);
+    globalCh -= n;
+    for (auto& ed : extraDevices_) {
+        int en = ed->analyzer.numSpectra();
+        if (globalCh < en) return ed->analyzer.channelSpectrum(globalCh);
+        globalCh -= en;
+    }
+    return analyzer_.channelSpectrum(0);
+}
+
+const std::deque<std::vector<float>>& AudioEngine::getWaterfallHistory(int globalCh) const {
+    int n = analyzer_.numSpectra();
+    if (globalCh < n) return analyzer_.waterfallHistory(globalCh);
+    globalCh -= n;
+    for (auto& ed : extraDevices_) {
+        int en = ed->analyzer.numSpectra();
+        if (globalCh < en) return ed->analyzer.waterfallHistory(globalCh);
+        globalCh -= en;
+    }
+    return analyzer_.waterfallHistory(0);
+}
+
+const std::vector<std::complex<float>>& AudioEngine::getComplex(int globalCh) const {
+    int n = analyzer_.numSpectra();
+    if (globalCh < n) return analyzer_.channelComplex(globalCh);
+    globalCh -= n;
+    for (auto& ed : extraDevices_) {
+        int en = ed->analyzer.numSpectra();
+        if (globalCh < en) return ed->analyzer.channelComplex(globalCh);
+        globalCh -= en;
+    }
+    return analyzer_.channelComplex(0);
+}
+
+const char* AudioEngine::getDeviceName(int globalCh) const {
+    int n = analyzer_.numSpectra();
+    if (globalCh < n) {
+        if (deviceIdx_ >= 0 && deviceIdx_ < static_cast<int>(devices_.size()))
+            return devices_[deviceIdx_].name.c_str();
+        for (int i = 0; i < static_cast<int>(devices_.size()); ++i)
+            if (deviceSelected_[i]) return devices_[i].name.c_str();
+        return "Audio Device";
+    }
+    globalCh -= n;
+    int devSel = 0;
+    for (int i = 0; i < static_cast<int>(devices_.size()) && i < kMaxChannels; ++i) {
+        if (!deviceSelected_[i]) continue;
+        ++devSel;
+        if (devSel <= 1) continue;
+        int edIdx = devSel - 2;
+        if (edIdx < static_cast<int>(extraDevices_.size())) {
+            int en = extraDevices_[edIdx]->analyzer.numSpectra();
+            if (globalCh < en) return devices_[i].name.c_str();
+            globalCh -= en;
+        }
+    }
+    return "Audio Device";
+}
+
+// ── Math channels ────────────────────────────────────────────────────────────
+
+const std::deque<std::vector<float>>& AudioEngine::mathWaterfallHistory(int mi) const {
+    static const std::deque<std::vector<float>> empty;
+    if (mi < 0 || mi >= static_cast<int>(mathWaterfalls_.size())) return empty;
+    return mathWaterfalls_[mi];
+}
+
+void AudioEngine::computeMathChannels() {
+    int nPhys = totalNumSpectra();
+    int specSz = analyzer_.spectrumSize();
+    mathSpectra_.resize(mathChannels_.size());
+    mathWaterfalls_.resize(mathChannels_.size());
+
+    for (size_t mi = 0; mi < mathChannels_.size(); ++mi) {
+        const auto& mc = mathChannels_[mi];
+        auto& out = mathSpectra_[mi];
+        out.resize(specSz);
+
+        if (!mc.enabled) {
+            std::fill(out.begin(), out.end(), kNoSignalDB);
+            continue;
+        }
+
+        int sx = std::clamp(mc.sourceX, 0, nPhys - 1);
+        int sy = std::clamp(mc.sourceY, 0, nPhys - 1);
+        const auto& xDB = getSpectrum(sx);
+        const auto& yDB = getSpectrum(sy);
+        const auto& xC  = getComplex(sx);
+        const auto& yC  = getComplex(sy);
+
+        for (int i = 0; i < specSz; ++i) {
+            float val = kNoSignalDB;
+            switch (mc.op) {
+                case MathOp::Negate:   val = -xDB[i]; break;
+                case MathOp::Absolute: val = std::abs(xDB[i]); break;
+                case MathOp::Square:   val = 2.0f * xDB[i]; break;
+                case MathOp::Cube:     val = 3.0f * xDB[i]; break;
+                case MathOp::Sqrt:     val = 0.5f * xDB[i]; break;
+                case MathOp::Log: {
+                    float lin = std::pow(10.0f, xDB[i] / 10.0f);
+                    val = 10.0f * std::log10(lin + kLogGuard);
+                    break;
+                }
+                case MathOp::Add: {
+                    float lx = std::pow(10.0f, xDB[i] / 10.0f);
+                    float ly = std::pow(10.0f, yDB[i] / 10.0f);
+                    float s = lx + ly;
+                    val = (s > kLinearEpsilon) ? 10.0f * std::log10(s) : kNoSignalDB;
+                    break;
+                }
+                case MathOp::Subtract: {
+                    float lx = std::pow(10.0f, xDB[i] / 10.0f);
+                    float ly = std::pow(10.0f, yDB[i] / 10.0f);
+                    float d = std::abs(lx - ly);
+                    val = (d > kLinearEpsilon) ? 10.0f * std::log10(d) : kNoSignalDB;
+                    break;
+                }
+                case MathOp::Multiply:
+                    val = xDB[i] + yDB[i];
+                    break;
+                case MathOp::Phase: {
+                    if (i < static_cast<int>(xC.size()) &&
+                        i < static_cast<int>(yC.size())) {
+                        auto cross = xC[i] * std::conj(yC[i]);
+                        val = std::atan2(cross.imag(), cross.real())
+                              * (180.0f / kPi);
+                    }
+                    break;
+                }
+                case MathOp::CrossCorr: {
+                    if (i < static_cast<int>(xC.size()) &&
+                        i < static_cast<int>(yC.size())) {
+                        auto cross = xC[i] * std::conj(yC[i]);
+                        float mag2 = std::norm(cross);
+                        val = (mag2 > kLinearEpsilon) ? 10.0f * std::log10(mag2) : kNoSignalDB;
+                    }
+                    break;
+                }
+                default: break;
+            }
+            out[i] = val;
+        }
+
+        // Push to math waterfall history.
+        mathWaterfalls_[mi].push_back(out);
+        if (mathWaterfalls_[mi].size() > kWaterfallHistory)
+            mathWaterfalls_[mi].pop_front();
+    }
+}
+
+} // namespace baudmine

src/audio/AudioEngine.h

@@ -0,0 +1,105 @@
+#pragma once
+
+#include "core/Types.h"
+#include "audio/AudioSource.h"
+#include "audio/MiniAudioSource.h"
+#include "dsp/SpectrumAnalyzer.h"
+
+#include <complex>
+#include <deque>
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace baudmine {
+
+class AudioEngine {
+public:
+    AudioEngine();
+
+    // ── Device enumeration ──
+    void enumerateDevices();
+    const std::vector<MiniAudioSource::DeviceInfo>& devices() const { return devices_; }
+
+    // ── Source management ──
+    void openDevice(int deviceListIdx);
+    void openMultiDevice(const bool selected[], int maxDevs);
+    void openFile(const std::string& path, InputFormat format, double sampleRate, bool loop);
+    void closeAll();
+
+    bool hasSource() const { return audioSource_ != nullptr; }
+    AudioSource* source() { return audioSource_.get(); }
+
+    // ── Analyzer ──
+    AnalyzerSettings&       settings()       { return settings_; }
+    const AnalyzerSettings& settings() const { return settings_; }
+    const SpectrumAnalyzer& primaryAnalyzer() const { return analyzer_; }
+
+    void configure(const AnalyzerSettings& s);
+    int  processAudio();   // returns number of new spectra from primary analyzer
+    void clearHistory();
+    void drainSources();   // flush stale audio from all real-time sources
+
+    // ── Unified channel view across all analyzers ──
+    int totalNumSpectra() const;
+    const std::vector<float>& getSpectrum(int globalCh) const;
+    const std::deque<std::vector<float>>& getWaterfallHistory(int globalCh) const;
+    const std::vector<std::complex<float>>& getComplex(int globalCh) const;
+    const char* getDeviceName(int globalCh) const;
+    int spectrumSize() const { return analyzer_.spectrumSize(); }
+    double binToFreq(int bin) const { return analyzer_.binToFreq(bin); }
+
+    // ── Math channels ──
+    std::vector<MathChannel>&       mathChannels()       { return mathChannels_; }
+    const std::vector<MathChannel>& mathChannels() const { return mathChannels_; }
+    const std::vector<std::vector<float>>& mathSpectra() const { return mathSpectra_; }
+    const std::deque<std::vector<float>>& mathWaterfallHistory(int mi) const;
+    void computeMathChannels();
+
+    // ── Overrun tracking ──
+    // Counts spectra lost because more were produced in a single frame
+    // than the waterfall history deque can hold.
+    int  overrunCount() const { return overrunCount_; }
+    void resetOverrunCount()  { overrunCount_ = 0; }
+
+    // ── Device selection state (for config persistence) ──
+    int  deviceIdx()       const { return deviceIdx_; }
+    void setDeviceIdx(int i)     { deviceIdx_ = i; }
+    bool multiDeviceMode() const { return multiDeviceMode_; }
+    void setMultiDeviceMode(bool m) { multiDeviceMode_ = m; }
+    bool deviceSelected(int i) const { return (i >= 0 && i < kMaxChannels) ? deviceSelected_[i] : false; }
+    void setDeviceSelected(int i, bool v) { if (i >= 0 && i < kMaxChannels) deviceSelected_[i] = v; }
+    void clearDeviceSelections();
+
+private:
+    struct ExtraDevice {
+        std::unique_ptr<AudioSource> source;
+        SpectrumAnalyzer             analyzer;
+        std::vector<float>           audioBuf;
+    };
+
+    // Sources
+    std::unique_ptr<AudioSource>              audioSource_;
+    std::vector<float>                        audioBuf_;
+    std::vector<std::unique_ptr<ExtraDevice>> extraDevices_;
+
+    // DSP
+    SpectrumAnalyzer analyzer_;
+    AnalyzerSettings settings_;
+
+    // Math
+    std::vector<MathChannel>                    mathChannels_;
+    std::vector<std::vector<float>>             mathSpectra_;
+    std::vector<std::deque<std::vector<float>>> mathWaterfalls_;
+
+    // Overrun
+    int overrunCount_ = 0;
+
+    // Device state
+    std::vector<MiniAudioSource::DeviceInfo> devices_;
+    int  deviceIdx_  = 0;
+    bool multiDeviceMode_ = false;
+    bool deviceSelected_[kMaxChannels] = {};
+};
+
+} // namespace baudmine

src/core/Config.cpp

@@ -2,6 +2,9 @@
 #include <cstdlib>
 #include <fstream>
 #include <sstream>
+#ifndef __EMSCRIPTEN__
+#include <filesystem>
+#endif
 
 #ifdef __EMSCRIPTEN__
 #include <emscripten.h>
@@ -22,7 +25,6 @@ EM_JS(void, js_saveSettings, (const char* data), {
 });
 
 #else
-#include <sys/stat.h>
 #endif
 
 namespace baudmine {
@@ -30,16 +32,20 @@ namespace baudmine {
 std::string Config::defaultPath() {
 #ifdef __EMSCRIPTEN__
     return "";
+#elif defined(_WIN32)
+    const char* appdata = std::getenv("APPDATA");
+    auto base = std::filesystem::path(appdata ? appdata : ".");
+    return (base / "baudmine" / "settings.ini").string();
 #else
     const char* xdg = std::getenv("XDG_CONFIG_HOME");
-    std::string base;
+    std::filesystem::path base;
     if (xdg && xdg[0]) {
         base = xdg;
     } else {
         const char* home = std::getenv("HOME");
-        base = home ? std::string(home) + "/.config" : ".";
+        base = home ? std::filesystem::path(home) / ".config" : std::filesystem::path(".");
     }
-    return base + "/baudmine/settings.ini";
+    return (base / "baudmine" / "settings.ini").string();
 #endif
 }
 
@@ -77,19 +83,9 @@ bool Config::load(const std::string& path) {
 
 #ifndef __EMSCRIPTEN__
 static void ensureDir(const std::string& path) {
-    // Create parent directories.
-    auto lastSlash = path.rfind('/');
-    if (lastSlash == std::string::npos) return;
-    std::string dir = path.substr(0, lastSlash);
-    // Simple recursive mkdir.
-    for (size_t i = 1; i < dir.size(); ++i) {
-        if (dir[i] == '/') {
-            dir[i] = '\0';
-            mkdir(dir.c_str(), 0755);
-            dir[i] = '/';
-        }
-    }
-    mkdir(dir.c_str(), 0755);
+    std::filesystem::path p(path);
+    if (p.has_parent_path())
+        std::filesystem::create_directories(p.parent_path());
 }
 #endif
 

src/core/Types.h

@@ -15,7 +15,16 @@ namespace baudmine {
 constexpr int kMinFFTSize = 256;
 constexpr int kMaxFFTSize = 65536;
 constexpr int kDefaultFFTSize = 4096;
-constexpr int kWaterfallHistory = 2048;
+constexpr int kWaterfallHistory = 512;
+constexpr int kDefaultWindowWidth  = 1400;
+constexpr int kDefaultWindowHeight = 900;
+
+// ── Shared display constants ────────────────────────────────────────────────
+
+constexpr float kNoSignalDB   = -200.0f;  // sentinel for "no signal" in dB
+constexpr float kZoomFactor   = 0.85f;    // scroll-wheel zoom step
+constexpr float kMinLogBinFrac = 0.001f;  // minimum bin fraction for log scale
+constexpr double kPi          = 3.14159265358979323846;
 
 // ── Enumerations ─────────────────────────────────────────────────────────────
 
@@ -87,6 +96,16 @@ inline const char* inputFormatName(InputFormat f) {
     }
 }
 
+// ── Frequency range helpers ──────────────────────────────────────────────────
+
+inline double freqMin(double sampleRate, bool isIQ) {
+    return isIQ ? -sampleRate / 2.0 : 0.0;
+}
+
+inline double freqMax(double sampleRate, bool isIQ) {
+    return sampleRate / 2.0;
+}
+
 // ── Formatting helpers ───────────────────────────────────────────────────────
 
 // Format frequency into buf with fixed-width numeric field per unit range.
@@ -157,4 +176,53 @@ struct Color3 {
     uint8_t r, g, b;
 };
 
+// ── Channel math operations ──────────────────────────────────────────────────
+
+enum class MathOp {
+    // Unary (on channel X)
+    Negate,       // -x  (negate dB)
+    Absolute,     // |x| (absolute value of dB)
+    Square,       // x^2 in linear  → 2*x_dB
+    Cube,         // x^3 in linear  → 3*x_dB
+    Sqrt,         // sqrt in linear → 0.5*x_dB
+    Log,          // 10*log10(10^(x_dB/10) + 1)  — compressed scale
+    // Binary (on channels X and Y)
+    Add,          // linear(x) + linear(y)  → dB
+    Subtract,     // |linear(x) - linear(y)| → dB
+    Multiply,     // x_dB + y_dB  (multiply in linear = add in dB)
+    Phase,        // angle(X_cplx * conj(Y_cplx)) in degrees
+    CrossCorr,    // |X_cplx * conj(Y_cplx)| → dB
+    Count
+};
+
+inline bool mathOpIsBinary(MathOp op) {
+    return op >= MathOp::Add;
+}
+
+inline const char* mathOpName(MathOp op) {
+    switch (op) {
+        case MathOp::Negate:    return "-x";
+        case MathOp::Absolute:  return "|x|";
+        case MathOp::Square:    return "x^2";
+        case MathOp::Cube:      return "x^3";
+        case MathOp::Sqrt:      return "sqrt(x)";
+        case MathOp::Log:       return "log(x)";
+        case MathOp::Add:       return "x + y";
+        case MathOp::Subtract:  return "x - y";
+        case MathOp::Multiply:  return "x * y";
+        case MathOp::Phase:     return "phase(x,y)";
+        case MathOp::CrossCorr: return "xcorr(x,y)";
+        default:                return "?";
+    }
+}
+
+struct MathChannel {
+    MathOp op        = MathOp::Subtract;
+    int    sourceX   = 0;
+    int    sourceY   = 1;
+    float  color[4]  = {1.0f, 1.0f, 1.0f, 1.0f};
+    bool   enabled   = true;
+    bool   waterfall = false;
+};
+
 } // namespace baudmine

src/dsp/SpectrumAnalyzer.cpp

@@ -105,7 +105,7 @@ void SpectrumAnalyzer::processBlock() {
         for (float& v : channelSpectra_[ch])
             v += windowCorrection_;
         channelWaterfalls_[ch].push_back(channelSpectra_[ch]);
-        if (channelWaterfalls_[ch].size() > kWaterfallHistory)
+        if (channelWaterfalls_[ch].size() > static_cast<size_t>(kWaterfallHistory))
             channelWaterfalls_[ch].pop_front();
     }
     newSpectrumReady_ = true;

src/dsp/WindowFunctions.cpp

@@ -4,8 +4,6 @@
 
 namespace baudmine {
 
-static constexpr double kPi = 3.14159265358979323846;
-
 void WindowFunctions::generate(WindowType type, int size, std::vector<float>& out,
                                float kaiserBeta) {
     out.resize(size);

src/ui/Application.h

@@ -2,9 +2,10 @@
 
 #include "core/Types.h"
 #include "core/Config.h"
-#include "dsp/SpectrumAnalyzer.h"
-#include "audio/AudioSource.h"
-#include "audio/MiniAudioSource.h"
+#include "audio/AudioEngine.h"
+#include "ui/UIState.h"
+#include "ui/ControlPanel.h"
+#include "ui/DisplayPanel.h"
 #include "ui/ColorMap.h"
 #include "ui/WaterfallDisplay.h"
 #include "ui/SpectrumDisplay.h"
@@ -12,62 +13,10 @@
 #include "ui/Measurements.h"
 
 #include <SDL.h>
-#include <complex>
-#include <memory>
 #include <string>
-#include <vector>
 
 namespace baudmine {
 
-// ── Channel math operations ──────────────────────────────────────────────────
-
-enum class MathOp {
-    // Unary (on channel X)
-    Negate,       // -x  (negate dB)
-    Absolute,     // |x| (absolute value of dB)
-    Square,       // x^2 in linear  → 2*x_dB
-    Cube,         // x^3 in linear  → 3*x_dB
-    Sqrt,         // sqrt in linear → 0.5*x_dB
-    Log,          // 10*log10(10^(x_dB/10) + 1)  — compressed scale
-    // Binary (on channels X and Y)
-    Add,          // linear(x) + linear(y)  → dB
-    Subtract,     // |linear(x) - linear(y)| → dB
-    Multiply,     // x_dB + y_dB  (multiply in linear = add in dB)
-    Phase,        // angle(X_cplx * conj(Y_cplx)) in degrees
-    CrossCorr,    // |X_cplx * conj(Y_cplx)| → dB
-    Count
-};
-
-inline bool mathOpIsBinary(MathOp op) {
-    return op >= MathOp::Add;
-}
-
-inline const char* mathOpName(MathOp op) {
-    switch (op) {
-        case MathOp::Negate:    return "-x";
-        case MathOp::Absolute:  return "|x|";
-        case MathOp::Square:    return "x^2";
-        case MathOp::Cube:      return "x^3";
-        case MathOp::Sqrt:      return "sqrt(x)";
-        case MathOp::Log:       return "log(x)";
-        case MathOp::Add:       return "x + y";
-        case MathOp::Subtract:  return "x - y";
-        case MathOp::Multiply:  return "x * y";
-        case MathOp::Phase:     return "phase(x,y)";
-        case MathOp::CrossCorr: return "xcorr(x,y)";
-        default:                return "?";
-    }
-}
-
-struct MathChannel {
-    MathOp op        = MathOp::Subtract;
-    int    sourceX   = 0;
-    int    sourceY   = 1;
-    ImVec4 color     = {1.0f, 1.0f, 1.0f, 1.0f};
-    bool   enabled   = true;
-    bool   waterfall = false;  // include on waterfall overlay
-};
-
 class Application {
 public:
     Application();
@@ -81,17 +30,11 @@ public:
 private:
     void processAudio();
     void render();
-    void renderControlPanel();
-    void renderSpectrumPanel();
-    void renderWaterfallPanel();
-    void handleSpectrumInput(float posX, float posY, float sizeX, float sizeY);
 
-    void openPortAudio();
+    void openDevice();
     void openMultiDevice();
     void openFile(const std::string& path, InputFormat format, double sampleRate);
     void updateAnalyzerSettings();
-    void computeMathChannels();
-    void renderMathPanel();
 
     void loadConfig();
     void saveConfig() const;
@@ -101,146 +44,43 @@ private:
     SDL_GLContext  glContext_ = nullptr;
     bool           running_  = false;
 
-    // Audio
-    std::unique_ptr<AudioSource> audioSource_;
-    std::vector<float>           audioBuf_;     // temp read buffer
+    // Core subsystems
+    AudioEngine   audio_;
+    UIState       ui_;
+    ControlPanel  controlPanel_;
+    DisplayPanel  displayPanel_;
 
-    // Extra devices (multi-device mode): each gets its own source + analyzer.
-    struct ExtraDevice {
-        std::unique_ptr<AudioSource> source;
-        SpectrumAnalyzer             analyzer;
-        std::vector<float>           audioBuf;
-    };
-    std::vector<std::unique_ptr<ExtraDevice>> extraDevices_;
-
-    // Helpers to present a unified channel view across all analyzers.
-    int totalNumSpectra() const;
-    const std::vector<float>& getSpectrum(int globalCh) const;
-    const std::vector<std::complex<float>>& getComplex(int globalCh) const;
-    // Returns the device name that owns a given global channel index.
-    const char* getDeviceName(int globalCh) const;
-
-    // DSP
-    SpectrumAnalyzer analyzer_;
-    AnalyzerSettings settings_;
-
-    // UI state
+    // Shared UI components
     ColorMap          colorMap_;
     WaterfallDisplay  waterfall_;
     SpectrumDisplay   specDisplay_;
     Cursors           cursors_;
     Measurements      measurements_;
 
-    // Display settings
-    float     minDB_       = -120.0f;
-    float     maxDB_       = 0.0f;
-    FreqScale freqScale_   = FreqScale::Linear;
-    bool      paused_      = false;
+    // UI scaling
     bool      vsync_         = true;
-    float     uiScale_       = 0.0f;  // 0 = auto (use DPI), >0 = manual override
-    float     appliedScale_  = 0.0f; // currently applied user-facing scale
-    float     pendingScale_  = 0.0f; // deferred scale (applied before next frame)
-    float     logicalScale_  = 1.0f; // scale after compensating for framebuffer DPI
-    float     lastDpr_       = 0.0f; // last devicePixelRatio (to detect changes)
+    float     uiScale_       = 0.0f;
+    float     appliedScale_  = 0.0f;
+    float     pendingScale_  = 0.0f;
+    float     logicalScale_  = 1.0f;
+    float     lastDpr_       = 0.0f;
     void      applyUIScale(float scale);
-    void      requestUIScale(float scale); // safe to call mid-frame
+    void      requestUIScale(float scale);
+    float     systemDpiScale() const;
     void      syncCanvasSize();
-    // (waterfallW_ removed — texture width tracks bin count automatically)
-    // (waterfallH_ removed — fixed history depth of 1024 rows)
-
-    // FFT size options
-    static constexpr int kFFTSizes[] = {256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536};
-    static constexpr int kNumFFTSizes = 9;
-    int fftSizeIdx_ = 4; // default 4096
-
-    // Overlap (continuous 0–95%)
-    float overlapPct_ = 50.0f;
-
-    // Window
-    int windowIdx_ = static_cast<int>(WindowType::BlackmanHarris);
-
-    // Color map
-    int colorMapIdx_ = static_cast<int>(ColorMapType::Magma);
-
-    // File playback
-    std::string filePath_;
-    int         fileFormatIdx_ = 0;
-    float       fileSampleRate_ = 48000.0f;
-    bool        fileLoop_ = true;
-
-    // Device selection
-    std::vector<MiniAudioSource::DeviceInfo> paDevices_;
-    int paDeviceIdx_ = 0;
-    bool paDeviceSelected_[kMaxChannels] = {};  // multi-device checkboxes
-    bool multiDeviceMode_ = false;              // true = use multiple devices as channels
-
-    // Channel colors (up to kMaxChannels).  Defaults: L=purple, R=green.
-    ImVec4 channelColors_[kMaxChannels] = {
-        {0.20f, 0.90f, 0.30f, 1.0f},  // green
-        {0.70f, 0.30f, 1.00f, 1.0f},  // purple
-        {1.00f, 0.55f, 0.00f, 1.0f},  // orange
-        {0.00f, 0.75f, 1.00f, 1.0f},  // cyan
-        {1.00f, 0.25f, 0.25f, 1.0f},  // red
-        {1.00f, 1.00f, 0.30f, 1.0f},  // yellow
-        {0.50f, 0.80f, 0.50f, 1.0f},  // light green
-        {0.80f, 0.50f, 0.80f, 1.0f},  // pink
-    };
-    int  waterfallChannel_ = 0;    // which channel drives the waterfall (single mode)
-    bool waterfallMultiCh_ = true; // true = multi-channel overlay mode
-    bool channelEnabled_[kMaxChannels] = {true,true,true,true,true,true,true,true};
-
-    // Math channels
-    std::vector<MathChannel>          mathChannels_;
-    std::vector<std::vector<float>>   mathSpectra_;  // computed each frame
-
-    // Frequency zoom/pan (normalized 0–1 over full bandwidth)
-    float viewLo_ = 0.0f;   // left edge
-    float viewHi_ = 0.5f;   // right edge (default 2x zoom from left)
-
-    // Spectrum/waterfall split ratio (fraction of content height for spectrum)
-    float spectrumFrac_ = 0.35f;
-    bool  draggingSplit_ = false;
-
-    // Panel geometry (stored for cursor interaction)
-    float specPosX_ = 0, specPosY_ = 0, specSizeX_ = 0, specSizeY_ = 0;
-    float wfPosX_ = 0, wfPosY_ = 0, wfSizeX_ = 0, wfSizeY_ = 0;
-
-    // Hover state: which panel is being hovered
-    enum class HoverPanel { None, Spectrum, Waterfall };
-    HoverPanel hoverPanel_ = HoverPanel::None;
-    float      hoverWfTimeOffset_ = 0.0f;  // seconds from newest line
-
-    // Touch gesture state (pinch-zoom / two-finger pan)
-    struct TouchState {
-        int    count = 0;         // active finger count
-        float  startDist = 0.0f;  // initial distance between two fingers
-        float  startLo = 0.0f;    // viewLo_ at gesture start
-        float  startHi = 0.0f;    // viewHi_ at gesture start
-        float  startCenterX = 0.0f; // midpoint screen-X at gesture start
-        float  lastCenterX = 0.0f;  // last midpoint screen-X
-        float  lastDist = 0.0f;   // last distance between fingers
-    } touch_;
-    void handleTouchEvent(const SDL_Event& event);
-
-    // Config persistence
-    Config config_;
 
     // UI visibility
     bool showSidebar_ = true;
 
 #ifndef IMGUI_DISABLE_DEBUG_TOOLS
-    // ImGui debug windows
     bool showDemoWindow_    = false;
     bool showMetricsWindow_ = false;
     bool showDebugLog_      = false;
     bool showStackTool_     = false;
 #endif
 
-    // Pre-allocated scratch buffers (avoid per-frame heap allocations)
-    std::vector<std::vector<float>>  wfSpectraScratch_;
-    std::vector<WaterfallChannelInfo> wfChInfoScratch_;
-    std::vector<std::vector<float>>  allSpectraScratch_;
-    std::vector<ChannelStyle>        stylesScratch_;
+    // Config persistence
+    Config config_;
 };
 
 } // namespace baudmine

src/ui/ControlPanel.cpp

@@ -0,0 +1,422 @@
+#include "ui/ControlPanel.h"
+#include "audio/AudioEngine.h"
+#include "ui/SpectrumDisplay.h"
+#include "ui/Cursors.h"
+#include "ui/Measurements.h"
+#include "ui/ColorMap.h"
+#include "ui/WaterfallDisplay.h"
+
+#include <imgui.h>
+#include <algorithm>
+#include <cmath>
+#include <cstdio>
+
+namespace baudmine {
+
+void ControlPanel::render(AudioEngine& audio, UIState& ui,
+                           SpectrumDisplay& specDisplay, Cursors& cursors,
+                           Measurements& measurements, ColorMap& colorMap,
+                           WaterfallDisplay& waterfall) {
+    const auto& settings = audio.settings();
+
+    // ── Playback ──
+    float btnW = (ImGui::GetContentRegionAvail().x - ImGui::GetStyle().ItemSpacing.x * 2) / 3.0f;
+    if (ImGui::Button(ui.paused ? "Resume" : "Pause", {btnW, 0}))
+        ui.paused = !ui.paused;
+    ImGui::SameLine();
+    if (ImGui::Button("Clear", {btnW, 0})) {
+        audio.clearHistory();
+    }
+    ImGui::SameLine();
+    if (ImGui::Button("Peak", {btnW, 0})) {
+        int pkCh = std::clamp(ui.waterfallChannel, 0, audio.totalNumSpectra() - 1);
+        cursors.snapToPeak(audio.getSpectrum(pkCh),
+                           settings.sampleRate, settings.isIQ,
+                           settings.fftSize);
+    }
+    if (ImGui::IsItemHovered()) ImGui::SetTooltip("Snap cursor A to peak");
+
+    // ── FFT ──
+    ImGui::Spacing();
+    if (ImGui::CollapsingHeader("FFT", ImGuiTreeNodeFlags_DefaultOpen)) {
+        const char* sizeNames[] = {"256", "512", "1024", "2048", "4096",
+                                   "8192", "16384", "32768", "65536"};
+        float availSpace = (ImGui::GetContentRegionAvail().x - ImGui::GetStyle().ItemSpacing.x);
+        ImGui::SetNextItemWidth(availSpace * 0.35f);
+        if (ImGui::Combo("##fftsize", &fftSizeIdx, sizeNames, kNumFFTSizes)) {
+            audio.settings().fftSize = kFFTSizes[fftSizeIdx];
+            flagUpdate();
+            flagSave();
+        }
+        if (ImGui::IsItemHovered()) ImGui::SetTooltip("FFT Size");
+
+        ImGui::SameLine();
+        const char* winNames[] = {"Rectangular", "Hann", "Hamming", "Blackman",
+                                  "Blackman-Harris", "Kaiser", "Flat Top"};
+        ImGui::SetNextItemWidth(availSpace * 0.65f);
+        if (ImGui::Combo("##window", &windowIdx, winNames,
+                         static_cast<int>(WindowType::Count))) {
+            audio.settings().window = static_cast<WindowType>(windowIdx);
+            flagUpdate();
+            flagSave();
+        }
+        if (ImGui::IsItemHovered()) ImGui::SetTooltip("Window Function");
+
+        if (settings.window == WindowType::Kaiser) {
+            ImGui::SetNextItemWidth(-1);
+            if (ImGui::SliderFloat("##kaiser", &audio.settings().kaiserBeta, 0.0f, 20.0f, "Kaiser: %.1f"))
+                flagUpdate();
+        }
+
+        // Overlap
+        {
+            int hopSamples = static_cast<int>(settings.fftSize * (1.0f - settings.overlap));
+            if (hopSamples < 1) hopSamples = 1;
+            int overlapSamples = settings.fftSize - hopSamples;
+
+            ImGui::SetNextItemWidth(-1);
+            float sliderVal = 1.0f - std::pow(1.0f - overlapPct / 99.0f, 0.25f);
+            if (ImGui::SliderFloat("##overlap", &sliderVal, 0.0f, 1.0f, "")) {
+                float inv = 1.0f - sliderVal;
+                float inv2 = inv * inv;
+                overlapPct = 99.0f * (1.0f - inv2 * inv2);
+                audio.settings().overlap = overlapPct / 100.0f;
+                flagUpdate();
+                flagSave();
+            }
+
+            char overlayText[64];
+            std::snprintf(overlayText, sizeof(overlayText), "%.1f%% (%d samples)", overlapPct, overlapSamples);
+            ImVec2 textSize = ImGui::CalcTextSize(overlayText);
+            ImVec2 rMin = ImGui::GetItemRectMin();
+            ImVec2 rMax = ImGui::GetItemRectMax();
+            float tx = rMin.x + ((rMax.x - rMin.x) - textSize.x) * 0.5f;
+            float ty = rMin.y + ((rMax.y - rMin.y) - textSize.y) * 0.5f;
+            ImGui::GetWindowDrawList()->AddText({tx, ty}, IM_COL32(255, 255, 255, 220), overlayText);
+            if (ImGui::IsItemHovered()) ImGui::SetTooltip("Overlap");
+        }
+
+        // Overrun indicator
+        {
+            int overruns = audio.overrunCount();
+            float now = static_cast<float>(ImGui::GetTime());
+            if (overruns > lastOverrunCount_) {
+                lastOverrunCount_ = overruns;
+                lastOverrunTime_ = now;
+            }
+            if (overruns > 0 && (now - lastOverrunTime_) < 3.0f) {
+                ImGui::TextColored({1.0f, 0.4f, 0.4f, 1.0f},
+                                   "Input overrun: %d FFTs", overruns);
+            } else if (overruns > 0) {
+                audio.resetOverrunCount();
+                lastOverrunCount_ = 0;
+            }
+        }
+    }
+
+    // ── Display ──
+    ImGui::Spacing();
+    if (ImGui::CollapsingHeader("Display", ImGuiTreeNodeFlags_DefaultOpen)) {
+        ImGui::SetNextItemWidth(-1);
+        ImGui::DragFloatRange2("##dbrange", &ui.minDB, &ui.maxDB, 1.0f, -200.0f, 20.0f,
+                               "Min: %.0f dB", "Max: %.0f dB");
+        if (ImGui::IsItemHovered()) ImGui::SetTooltip("dB Range (min / max)");
+
+        ImGui::Checkbox("Peak Hold", &specDisplay.peakHoldEnable);
+        if (ImGui::IsItemHovered()) ImGui::SetTooltip("Draws a \"maximum\" line in the spectrogram");
+        if (specDisplay.peakHoldEnable) {
+            ImGui::SameLine();
+            ImGui::SetNextItemWidth(ImGui::GetContentRegionAvail().x
+                                    - ImGui::CalcTextSize("Clear").x
+                                    - ImGui::GetStyle().ItemSpacing.x
+                                    - ImGui::GetStyle().FramePadding.x * 2);
+            ImGui::SliderFloat("##decay", &specDisplay.peakHoldDecay, 0.0f, 120.0f, "%.0f dB/s");
+            if (ImGui::IsItemHovered()) ImGui::SetTooltip("Decay rate");
+            ImGui::SameLine();
+            if (ImGui::SmallButton("Clear##peakhold"))
+                specDisplay.clearPeakHold();
+        }
+
+        {
+            bool isLog = (ui.freqScale == FreqScale::Logarithmic);
+            bool canLog = !settings.isIQ;
+            ImGui::AlignTextToFramePadding();
+            ImGui::Text("Freq. scale:");
+            ImGui::SameLine();
+            if (ImGui::Button(isLog ? "Logarithmic" : "Linear", {ImGui::GetContentRegionAvail().x, 0})) {
+                if (canLog) {
+                    constexpr float kMinBF = kMinLogBinFrac;
+                    float logMin = std::log10(kMinBF);
+                    auto screenToBin = [&](float sf) -> float {
+                        if (isLog) return std::pow(10.0f, logMin + sf * (0.0f - logMin));
+                        return sf;
+                    };
+                    auto binToScreen = [&](float bf, bool toLog) -> float {
+                        if (toLog) {
+                            if (bf < kMinBF) bf = kMinBF;
+                            return (std::log10(bf) - logMin) / (0.0f - logMin);
+                        }
+                        return bf;
+                    };
+                    float bfLo = screenToBin(ui.viewLo);
+                    float bfHi = screenToBin(ui.viewHi);
+                    bool newLog = !isLog;
+                    ui.freqScale = newLog ? FreqScale::Logarithmic : FreqScale::Linear;
+                    ui.viewLo = std::clamp(binToScreen(bfLo, newLog), 0.0f, 1.0f);
+                    ui.viewHi = std::clamp(binToScreen(bfHi, newLog), 0.0f, 1.0f);
+                    if (ui.viewHi <= ui.viewLo) { ui.viewLo = 0.0f; ui.viewHi = 1.0f; }
+                    flagSave();
+                }
+            }
+            if (!canLog && ImGui::IsItemHovered())
+                ImGui::SetTooltip("Log scale not available in I/Q mode");
+        }
+
+        {
+            float span = ui.viewHi - ui.viewLo;
+            float zoomX = 1.0f / span;
+            float resetBtnW = ImGui::CalcTextSize("Reset").x + ImGui::GetStyle().FramePadding.x * 2;
+            float zoomLabelW = ImGui::CalcTextSize("Zoom:").x + ImGui::GetStyle().ItemSpacing.x;
+            float sliderW = ImGui::GetContentRegionAvail().x - zoomLabelW - resetBtnW - ImGui::GetStyle().ItemSpacing.x;
+            ImGui::AlignTextToFramePadding();
+            ImGui::Text("Zoom:");
+            ImGui::SameLine();
+            ImGui::SetNextItemWidth(sliderW);
+            if (ImGui::SliderFloat("##zoom", &zoomX, 1.0f, 200.0f, "%.1fx", ImGuiSliderFlags_Logarithmic)) {
+                zoomX = std::clamp(zoomX, 1.0f, 1000.0f);
+                float newSpan = 1.0f / zoomX;
+                ui.viewLo = 0.0f;
+                ui.viewHi = std::clamp(newSpan, 0.0f, 1.0f);
+            }
+            ImGui::SameLine();
+            if (ImGui::SmallButton("Reset##zoom")) {
+                ui.viewLo = 0.0f;
+                ui.viewHi = 0.5f;
+            }
+            if (ImGui::IsItemHovered()) ImGui::SetTooltip("Reset to 2x zoom");
+        }
+
+        {
+            ImGui::AlignTextToFramePadding();
+            ImGui::Text("Decim:");
+            ImGui::SameLine();
+            ImGui::SetNextItemWidth(ImGui::GetContentRegionAvail().x);
+            ImGui::SliderInt("##decimation", &ui.specMinPixPerBin, 1, 8, "%d px/bin");
+            if (ImGui::IsItemHovered()) ImGui::SetTooltip("Spectrum frequency decimation (peak-detect)");
+        }
+    }
+
+    // ── Channels ──
+    ImGui::Spacing();
+    {
+        int nCh = audio.totalNumSpectra();
+        bool isMulti = ui.waterfallMultiCh && nCh > 1;
+
+        float widgetW = (nCh > 1) ? ImGui::CalcTextSize(" Multi ").x + ImGui::GetStyle().FramePadding.x * 2 : 0.0f;
+        float gap = ImGui::GetStyle().ItemSpacing.x * 0.25f;
+        ImVec2 hdrMin = ImGui::GetCursorScreenPos();
+        float winLeft = ImGui::GetWindowPos().x;
+        float hdrRight = hdrMin.x + ImGui::GetContentRegionAvail().x;
+        ImGui::PushClipRect({winLeft, hdrMin.y}, {hdrRight - widgetW - gap, hdrMin.y + 200}, true);
+        bool headerOpen = ImGui::CollapsingHeader("##channels_hdr",
+                                                   ImGuiTreeNodeFlags_DefaultOpen |
+                                                   ImGuiTreeNodeFlags_AllowOverlap);
+        ImGui::PopClipRect();
+        ImGui::SameLine();
+        ImGui::Text("Channels");
+        if (nCh > 1) {
+            ImGui::SameLine();
+            ImGui::SetCursorPosX(ImGui::GetContentRegionMax().x - widgetW + ImGui::GetStyle().FramePadding.x);
+            if (ImGui::Button(isMulti ? " Multi " : "Single ", {widgetW, 0})) {
+                ui.waterfallMultiCh = !ui.waterfallMultiCh;
+            }
+        }
+
+        if (headerOpen) {
+            if (isMulti) {
+                static const char* defaultNames[] = {
+                    "Left", "Right", "Ch 3", "Ch 4", "Ch 5", "Ch 6", "Ch 7", "Ch 8"
+                };
+                for (int ch = 0; ch < nCh && ch < kMaxChannels; ++ch) {
+                    ImGui::PushID(ch);
+                    ImGui::Checkbox("##en", &ui.channelEnabled[ch]);
+                    ImGui::SameLine();
+                    ImGui::ColorEdit3(defaultNames[ch], &ui.channelColors[ch].x,
+                                      ImGuiColorEditFlags_NoInputs);
+                    if (ImGui::IsItemHovered())
+                        ImGui::SetTooltip("%s", audio.getDeviceName(ch));
+                    ImGui::PopID();
+                }
+            } else {
+                const char* cmNames[] = {"Magma", "Viridis", "Inferno", "Plasma", "Grayscale"};
+                ImGui::SetNextItemWidth(-1);
+                if (ImGui::Combo("##colormap", &colorMapIdx, cmNames,
+                                 static_cast<int>(ColorMapType::Count))) {
+                    colorMap.setType(static_cast<ColorMapType>(colorMapIdx));
+                    waterfall.setColorMap(colorMap);
+                    flagSave();
+                }
+                if (ImGui::IsItemHovered()) ImGui::SetTooltip("Color Map");
+
+                if (nCh > 1) {
+                    ImGui::SetNextItemWidth(-1);
+                    if (ImGui::SliderInt("##wfch", &ui.waterfallChannel, 0, nCh - 1))
+                        ui.waterfallChannel = std::clamp(ui.waterfallChannel, 0, nCh - 1);
+                    if (ImGui::IsItemHovered()) ImGui::SetTooltip("Waterfall Channel");
+                }
+            }
+        }
+    }
+
+    // ── Math ──
+    ImGui::Spacing();
+    {
+        float btnW2 = ImGui::GetFrameHeight();
+        float gap = ImGui::GetStyle().ItemSpacing.x * 0.25f;
+        ImVec2 hdrMin = ImGui::GetCursorScreenPos();
+        float winLeft = ImGui::GetWindowPos().x;
+        float hdrRight = hdrMin.x + ImGui::GetContentRegionAvail().x;
+        ImGui::PushClipRect({winLeft, hdrMin.y}, {hdrRight - btnW2 - gap, hdrMin.y + 200}, true);
+        bool mathOpen = ImGui::CollapsingHeader("##math_hdr",
+                                                 ImGuiTreeNodeFlags_DefaultOpen |
+                                                 ImGuiTreeNodeFlags_AllowOverlap);
+        ImGui::PopClipRect();
+        ImGui::SameLine();
+        ImGui::Text("Math");
+        ImGui::SameLine();
+        ImGui::SetCursorPosX(ImGui::GetContentRegionMax().x - btnW2 + ImGui::GetStyle().FramePadding.x);
+        if (ImGui::Button("+##addmath", {btnW2, 0})) {
+            int nPhys = audio.totalNumSpectra();
+            MathChannel mc;
+            mc.op = MathOp::Subtract;
+            mc.sourceX = 0;
+            mc.sourceY = std::min(1, nPhys - 1);
+            mc.color[0] = 1.0f; mc.color[1] = 1.0f; mc.color[2] = 0.5f; mc.color[3] = 1.0f;
+            audio.mathChannels().push_back(mc);
+        }
+        if (ImGui::IsItemHovered()) ImGui::SetTooltip("Add math channel");
+
+        if (mathOpen) {
+            renderMathPanel(audio);
+        }
+    }
+
+    // ── Cursors ──
+    ImGui::Spacing();
+    {
+        float btnW2 = ImGui::CalcTextSize("Reset").x + ImGui::GetStyle().FramePadding.x * 2;
+        float gap = ImGui::GetStyle().ItemSpacing.x * 0.25f;
+        ImVec2 hdrMin = ImGui::GetCursorScreenPos();
+        float winLeft = ImGui::GetWindowPos().x;
+        float hdrRight = hdrMin.x + ImGui::GetContentRegionAvail().x;
+        ImGui::PushClipRect({winLeft, hdrMin.y}, {hdrRight - btnW2 - gap, hdrMin.y + 200}, true);
+        bool cursorsOpen = ImGui::CollapsingHeader("##cursors_hdr",
+                                                    ImGuiTreeNodeFlags_DefaultOpen |
+                                                    ImGuiTreeNodeFlags_AllowOverlap);
+        ImGui::PopClipRect();
+        ImGui::SameLine();
+        ImGui::Text("Cursors");
+        ImGui::SameLine();
+        ImGui::SetCursorPosX(ImGui::GetContentRegionMax().x - btnW2 + ImGui::GetStyle().FramePadding.x);
+        if (ImGui::SmallButton("Reset##cursors")) {
+            cursors.cursorA.active = false;
+            cursors.cursorB.active = false;
+        }
+        if (ImGui::IsItemHovered()) ImGui::SetTooltip("Clear cursors A and B");
+
+        if (cursorsOpen) {
+            bool prevSnap = cursors.snapToPeaks;
+            cursors.drawPanel();
+            if (cursors.snapToPeaks != prevSnap) flagSave();
+        }
+    }
+
+    // ── Measurements ──
+    ImGui::Spacing();
+    {
+        float cbW = ImGui::GetFrameHeight();
+        float gap = ImGui::GetStyle().ItemSpacing.x * 0.25f;
+        ImVec2 hdrMin = ImGui::GetCursorScreenPos();
+        float winLeft = ImGui::GetWindowPos().x;
+        float hdrRight = hdrMin.x + ImGui::GetContentRegionAvail().x;
+        ImGui::PushClipRect({winLeft, hdrMin.y}, {hdrRight - cbW - gap, hdrMin.y + 200}, true);
+        bool headerOpen = ImGui::CollapsingHeader("##meas_hdr",
+                                                   ImGuiTreeNodeFlags_DefaultOpen |
+                                                   ImGuiTreeNodeFlags_AllowOverlap);
+        ImGui::PopClipRect();
+        ImGui::SameLine();
+        ImGui::Text("Measurements");
+        ImGui::SameLine();
+        ImGui::SetCursorPosX(ImGui::GetContentRegionMax().x - cbW + ImGui::GetStyle().FramePadding.x);
+        ImGui::Checkbox("##meas_en", &measurements.enabled);
+        if (ImGui::IsItemHovered()) ImGui::SetTooltip("Enable measurements");
+
+        if (headerOpen) {
+            float prevMin = measurements.traceMinFreq;
+            float prevMax = measurements.traceMaxFreq;
+            measurements.drawPanel();
+            if (measurements.traceMinFreq != prevMin || measurements.traceMaxFreq != prevMax)
+                flagSave();
+        }
+    }
+
+    // ── Status (bottom) ──
+    ImGui::Separator();
+    ImGui::TextDisabled("Mode: %s", settings.isIQ ? "I/Q"
+                        : (settings.numChannels > 1 ? "Multi-ch" : "Real"));
+}
+
+void ControlPanel::renderMathPanel(AudioEngine& audio) {
+    int nPhys = audio.totalNumSpectra();
+    auto& mathChannels = audio.mathChannels();
+
+    static const char* chNames[] = {
+        "Ch 0 (L)", "Ch 1 (R)", "Ch 2", "Ch 3", "Ch 4", "Ch 5", "Ch 6", "Ch 7"
+    };
+
+    int toRemove = -1;
+    for (int mi = 0; mi < static_cast<int>(mathChannels.size()); ++mi) {
+        auto& mc = mathChannels[mi];
+        ImGui::PushID(1000 + mi);
+
+        ImGui::Checkbox("##en", &mc.enabled);
+        ImGui::SameLine();
+        ImGui::ColorEdit3("##col", mc.color, ImGuiColorEditFlags_NoInputs);
+        ImGui::SameLine();
+
+        if (ImGui::BeginCombo("##op", mathOpName(mc.op), ImGuiComboFlags_NoPreview)) {
+            for (int o = 0; o < static_cast<int>(MathOp::Count); ++o) {
+                auto op = static_cast<MathOp>(o);
+                if (ImGui::Selectable(mathOpName(op), mc.op == op))
+                    mc.op = op;
+            }
+            ImGui::EndCombo();
+        }
+        ImGui::SameLine();
+        ImGui::Text("%s", mathOpName(mc.op));
+
+        ImGui::SetNextItemWidth(80);
+        ImGui::Combo("X", &mc.sourceX, chNames, std::min(nPhys, kMaxChannels));
+
+        if (mathOpIsBinary(mc.op)) {
+            ImGui::SameLine();
+            ImGui::SetNextItemWidth(80);
+            ImGui::Combo("Y", &mc.sourceY, chNames, std::min(nPhys, kMaxChannels));
+        }
+
+        ImGui::SameLine();
+        ImGui::Checkbox("WF", &mc.waterfall);
+        if (ImGui::IsItemHovered())
+            ImGui::SetTooltip("Show on waterfall");
+        ImGui::SameLine();
+        if (ImGui::SmallButton("X##del"))
+            toRemove = mi;
+
+        ImGui::PopID();
+    }
+
+    if (toRemove >= 0)
+        mathChannels.erase(mathChannels.begin() + toRemove);
+}
+
+} // namespace baudmine

src/ui/ControlPanel.h

@@ -0,0 +1,56 @@
+#pragma once
+
+#include "core/Types.h"
+#include "ui/UIState.h"
+
+#include <string>
+
+namespace baudmine {
+
+class AudioEngine;
+class SpectrumDisplay;
+class Cursors;
+class Measurements;
+class ColorMap;
+class WaterfallDisplay;
+
+class ControlPanel {
+public:
+    void render(AudioEngine& audio, UIState& ui,
+                SpectrumDisplay& specDisplay, Cursors& cursors,
+                Measurements& measurements, ColorMap& colorMap,
+                WaterfallDisplay& waterfall);
+
+    // Consume action flags set during render(). Returns true once, then resets.
+    bool consumeSaveRequest()   { bool v = needsSave_; needsSave_ = false; return v; }
+    bool consumeUpdateRequest() { bool v = needsUpdate_; needsUpdate_ = false; return v; }
+
+    // FFT / analysis controls
+    static constexpr int kFFTSizes[] = {256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536};
+    static constexpr int kNumFFTSizes = 9;
+    int   fftSizeIdx  = 4;
+    float overlapPct  = 50.0f;
+    int   windowIdx   = static_cast<int>(WindowType::BlackmanHarris);
+    int   colorMapIdx = static_cast<int>(ColorMapType::Magma);
+
+    // File playback
+    std::string filePath;
+    int         fileFormatIdx  = 0;
+    float       fileSampleRate = 48000.0f;
+    bool        fileLoop       = true;
+
+private:
+    void renderMathPanel(AudioEngine& audio);
+
+    bool needsSave_   = false;
+    bool needsUpdate_ = false;
+
+    // Overrun display
+    int   lastOverrunCount_ = 0;
+    float lastOverrunTime_  = 0.0f;  // ImGui time of last overrun
+
+    void flagSave()   { needsSave_ = true; }
+    void flagUpdate() { needsUpdate_ = true; }
+};
+
+} // namespace baudmine

src/ui/DisplayPanel.cpp

@@ -0,0 +1,588 @@
+#include "ui/DisplayPanel.h"
+#include "audio/AudioEngine.h"
+
+#include <imgui.h>
+#include <algorithm>
+#include <cmath>
+#include <cstdio>
+#include <cstring>
+
+namespace baudmine {
+
+namespace {
+
+// Ruler styling constants (shared by time and dB rulers).
+constexpr ImU32 kRulerBg       = IM_COL32(20, 20, 30, 220);
+constexpr ImU32 kRulerTickCol  = IM_COL32(200, 200, 220, 230);
+constexpr ImU32 kRulerLabelCol = IM_COL32(220, 220, 240, 240);
+constexpr ImU32 kRulerUnitCol  = IM_COL32(180, 180, 200, 220);
+
+// Pick the smallest "nice" value from a sorted table that is >= target.
+// Returns the last element if none qualifies.
+template<typename T, size_t N>
+T pickNiceStep(const T (&table)[N], T target) {
+    for (const T& v : table)
+        if (v >= target) return v;
+    return table[N - 1];
+}
+
+// Zoom the view range centered on a screen-fraction cursor position.
+void zoomView(float& viewLo, float& viewHi, float cursorScreenFrac, float wheelDir) {
+    float viewFrac = viewLo + cursorScreenFrac * (viewHi - viewLo);
+    float factor = (wheelDir > 0) ? kZoomFactor : 1.0f / kZoomFactor;
+    float newSpan = std::clamp((viewHi - viewLo) * factor, 0.001f, 1.0f);
+
+    float newLo = viewFrac - cursorScreenFrac * newSpan;
+    float newHi = newLo + newSpan;
+
+    if (newLo < 0.0f) { newHi -= newLo; newLo = 0.0f; }
+    if (newHi > 1.0f) { newLo -= (newHi - 1.0f); newHi = 1.0f; }
+    viewLo = std::clamp(newLo, 0.0f, 1.0f);
+    viewHi = std::clamp(newHi, 0.0f, 1.0f);
+}
+
+// Pan the view range by a screen-pixel delta.
+void panView(float& viewLo, float& viewHi, float dxPixels, float panelWidth) {
+    float panFrac = -dxPixels / panelWidth * (viewHi - viewLo);
+    float span = viewHi - viewLo;
+    float newLo = viewLo + panFrac;
+    float newHi = viewHi + panFrac;
+    if (newLo < 0.0f) { newLo = 0.0f; newHi = span; }
+    if (newHi > 1.0f) { newHi = 1.0f; newLo = 1.0f - span; }
+    viewLo = newLo;
+    viewHi = newHi;
+}
+
+} // anonymous namespace
+
+void DisplayPanel::renderSpectrum(AudioEngine& audio, UIState& ui,
+                                   SpectrumDisplay& specDisplay, Cursors& cursors,
+                                   Measurements& measurements) {
+    const auto& settings = audio.settings();
+
+    float availW = ImGui::GetContentRegionAvail().x - rulerWidth_;
+    float specH = ImGui::GetContentRegionAvail().y;
+
+    ImVec2 pos = ImGui::GetCursorScreenPos();
+    specPosX = pos.x + rulerWidth_;
+    specPosY = pos.y;
+    specSizeX = availW;
+    specSizeY = specH;
+
+    int nPhys = audio.totalNumSpectra();
+    const auto& mathChannels = audio.mathChannels();
+    const auto& mathSpectra  = audio.mathSpectra();
+    int nMath = static_cast<int>(mathSpectra.size());
+
+    allSpectraScratch_.clear();
+    stylesScratch_.clear();
+
+    for (int ch = 0; ch < nPhys; ++ch) {
+        if (!ui.channelEnabled[ch % kMaxChannels]) continue;
+        allSpectraScratch_.push_back(audio.getSpectrum(ch));
+        const auto& c = ui.channelColors[ch % kMaxChannels];
+        uint8_t r = static_cast<uint8_t>(c.x * 255);
+        uint8_t g = static_cast<uint8_t>(c.y * 255);
+        uint8_t b = static_cast<uint8_t>(c.z * 255);
+        stylesScratch_.push_back({IM_COL32(r, g, b, 220), IM_COL32(r, g, b, 35)});
+    }
+
+    for (int mi = 0; mi < nMath; ++mi) {
+        if (mi < static_cast<int>(mathChannels.size()) && mathChannels[mi].enabled) {
+            allSpectraScratch_.push_back(mathSpectra[mi]);
+            const auto& c = mathChannels[mi].color;
+            uint8_t r = static_cast<uint8_t>(c[0] * 255);
+            uint8_t g = static_cast<uint8_t>(c[1] * 255);
+            uint8_t b = static_cast<uint8_t>(c[2] * 255);
+            stylesScratch_.push_back({IM_COL32(r, g, b, 220), IM_COL32(r, g, b, 35)});
+        }
+    }
+
+    specDisplay.updatePeakHold(allSpectraScratch_);
+    specDisplay.dbLabelOffsetX = rulerWidth_;
+    specDisplay.draw(allSpectraScratch_, stylesScratch_, ui.minDB, ui.maxDB,
+                     settings.sampleRate, settings.isIQ, ui.freqScale,
+                     specPosX, specPosY, specSizeX, specSizeY,
+                     ui.viewLo, ui.viewHi, ui.specMinPixPerBin);
+
+    cursors.draw(specDisplay, specPosX, specPosY, specSizeX, specSizeY,
+                 settings.sampleRate, settings.isIQ, ui.freqScale, ui.minDB, ui.maxDB,
+                 ui.viewLo, ui.viewHi);
+
+    measurements.draw(specDisplay, specPosX, specPosY, specSizeX, specSizeY,
+                      settings.sampleRate, settings.isIQ, ui.freqScale, ui.minDB, ui.maxDB,
+                      ui.viewLo, ui.viewHi);
+
+    // ── dB ruler ──
+    if (showRuler && rulerWidth_ > 0.0f) {
+        ImDrawList* dl = ImGui::GetWindowDrawList();
+        float rulerX = pos.x;
+
+        dl->AddRectFilled({rulerX, specPosY},
+                          {rulerX + rulerWidth_, specPosY + specH}, kRulerBg);
+        dl->AddLine({rulerX + rulerWidth_ - 1, specPosY},
+                    {rulerX + rulerWidth_ - 1, specPosY + specH},
+                    kRulerTickCol, 1.0f);
+
+        constexpr float kTargetDbSpacing = 30.0f;
+        float dbRange = ui.maxDB - ui.minDB;
+        static const float kNiceDbSteps[] = {1.0f, 2.0f, 5.0f, 10.0f, 20.0f, 50.0f, 100.0f};
+        float dbStep = pickNiceStep(kNiceDbSteps, dbRange * (kTargetDbSpacing / specH));
+
+        float charH = ImGui::CalcTextSize("0").y;
+        float bottomCutoff = specPosY + specH - charH * 2 - 4.0f;
+        for (float db = std::ceil(ui.minDB / dbStep) * dbStep; db <= ui.maxDB + 0.01f; db += dbStep) {
+            float y = specPosY + specH * (1.0f - (db - ui.minDB) / dbRange);
+            if (y > bottomCutoff) continue;
+
+            dl->AddLine({rulerX, y},
+                        {rulerX + rulerWidth_ - 1, y}, kRulerTickCol, 2.0f);
+
+            char numBuf[16];
+            std::snprintf(numBuf, sizeof(numBuf), "%.0f", db);
+            dl->AddText({rulerX - 3.0f, y + 2.0f}, kRulerLabelCol, numBuf);
+        }
+
+        ImVec2 unitSz = ImGui::CalcTextSize("dB");
+        dl->AddText({rulerX + 2.0f, specPosY + specH - unitSz.y - 2.0f},
+                    kRulerUnitCol, "dB");
+    }
+
+    handleSpectrumInput(audio, ui, specDisplay, cursors,
+                        specPosX, specPosY, specSizeX, specSizeY);
+
+    ImGui::Dummy({availW + rulerWidth_, specH});
+}
+
+void DisplayPanel::renderWaterfall(AudioEngine& audio, UIState& ui,
+                                    WaterfallDisplay& waterfall, SpectrumDisplay& specDisplay,
+                                    Cursors& cursors, Measurements& measurements,
+                                    ColorMap& colorMap) {
+    const auto& settings = audio.settings();
+
+    float fullW = ImGui::GetContentRegionAvail().x;
+    constexpr float kSplitterH = 6.0f;
+    float parentH = ImGui::GetContentRegionAvail().y;
+    float availH = (parentH - kSplitterH) * (1.0f - spectrumFrac);
+
+    // Compute ruler width (used by both waterfall and spectrum rendering).
+    float labelW = ImGui::CalcTextSize("-000").x;
+    rulerWidth_ = showRuler ? labelW : 0.0f;
+    float availW = fullW - rulerWidth_;
+
+    int neededH = std::max(1024, static_cast<int>(availH) + 1);
+    int binCount = std::max(1, audio.spectrumSize());
+    if (binCount != waterfall.width() || waterfall.height() < neededH) {
+        waterfall.resize(binCount, neededH);
+        waterfall.setColorMap(colorMap);
+    }
+
+    if (waterfall.textureID()) {
+        ImVec2 basePos = ImGui::GetCursorScreenPos();
+        ImVec2 pos = {basePos.x + rulerWidth_, basePos.y};
+        ImDrawList* dl = ImGui::GetWindowDrawList();
+        auto texID = static_cast<ImTextureID>(waterfall.textureID());
+
+        int h = waterfall.height();
+        int screenRows = std::min(static_cast<int>(availH), h);
+        int newestRow = (waterfall.currentRow() + 1) % h;
+
+        float rowToV = 1.0f / h;
+        bool logMode = (ui.freqScale == FreqScale::Logarithmic && !settings.isIQ);
+
+        auto drawSpan = [&](int rowStart, int rowCount, float yStart, float spanH) {
+            float v0 = rowStart * rowToV;
+            float v1 = (rowStart + rowCount) * rowToV;
+
+            if (!logMode) {
+                dl->AddImage(texID,
+                             {pos.x, yStart},
+                             {pos.x + availW, yStart + spanH},
+                             {ui.viewLo, v1}, {ui.viewHi, v0});
+            } else {
+                constexpr float kMinBinFrac = kMinLogBinFrac;
+                float logMin2 = std::log10(kMinBinFrac);
+                float logMax2 = 0.0f;
+                int numStrips = std::min(512, static_cast<int>(availW));
+                for (int s = 0; s < numStrips; ++s) {
+                    float sL = static_cast<float>(s) / numStrips;
+                    float sR = static_cast<float>(s + 1) / numStrips;
+                    float vfL = ui.viewLo + sL * (ui.viewHi - ui.viewLo);
+                    float vfR = ui.viewLo + sR * (ui.viewHi - ui.viewLo);
+                    float uL = std::pow(10.0f, logMin2 + vfL * (logMax2 - logMin2));
+                    float uR = std::pow(10.0f, logMin2 + vfR * (logMax2 - logMin2));
+                    dl->AddImage(texID,
+                                 {pos.x + sL * availW, yStart},
+                                 {pos.x + sR * availW, yStart + spanH},
+                                 {uL, v1}, {uR, v0});
+                }
+            }
+        };
+
+        float pxPerRow = availH / static_cast<float>(screenRows);
+
+        if (newestRow + screenRows <= h) {
+            drawSpan(newestRow, screenRows, pos.y, availH);
+        } else {
+            int firstCount = h - newestRow;
+            int secondCount = screenRows - firstCount;
+
+            float secondH = secondCount * pxPerRow;
+            if (secondCount > 0)
+                drawSpan(0, secondCount, pos.y, secondH);
+
+            float firstH = availH - secondH;
+            drawSpan(newestRow, firstCount, pos.y + secondH, firstH);
+        }
+
+        // ── Frequency axis labels ──
+        ImU32 textCol = IM_COL32(180, 180, 200, 200);
+        double freqFullMin = freqMin(settings.sampleRate, settings.isIQ);
+        double freqFullMax = freqMax(settings.sampleRate, settings.isIQ);
+
+        auto viewFracToFreq = [&](float vf) -> double {
+            if (logMode) {
+                constexpr float kMinBinFrac = kMinLogBinFrac;
+                float logMin2 = std::log10(kMinBinFrac);
+                float logMax2 = 0.0f;
+                float binFrac = std::pow(10.0f, logMin2 + vf * (logMax2 - logMin2));
+                return freqFullMin + binFrac * (freqFullMax - freqFullMin);
+            }
+            return freqFullMin + vf * (freqFullMax - freqFullMin);
+        };
+
+        int numLabels = 8;
+        for (int i = 0; i <= numLabels; ++i) {
+            float frac = static_cast<float>(i) / numLabels;
+            float vf = ui.viewLo + frac * (ui.viewHi - ui.viewLo);
+            double freq = viewFracToFreq(vf);
+            float x = pos.x + frac * availW;
+
+            char label[32];
+            if (std::abs(freq) >= 1e6)
+                std::snprintf(label, sizeof(label), "%.2fM", freq / 1e6);
+            else if (std::abs(freq) >= 1e3)
+                std::snprintf(label, sizeof(label), "%.1fk", freq / 1e3);
+            else
+                std::snprintf(label, sizeof(label), "%.0f", freq);
+
+            dl->AddText({x + 2, pos.y + 2}, textCol, label);
+        }
+
+        wfPosX = pos.x; wfPosY = pos.y; wfSizeX = availW; wfSizeY = availH;
+
+        int hopSamples = std::max(1, static_cast<int>(settings.fftSize * (1.0f - settings.overlap)));
+        double secondsPerLine = static_cast<double>(hopSamples) / settings.sampleRate;
+
+        measurements.drawWaterfall(specDisplay, wfPosX, wfPosY, wfSizeX, wfSizeY,
+                                   settings.sampleRate, settings.isIQ, ui.freqScale,
+                                   ui.viewLo, ui.viewHi, screenRows, audio.spectrumSize());
+
+        // ── Timescale ruler ──
+        if (showRuler && rulerWidth_ > 0.0f) {
+            double totalTime = screenRows * secondsPerLine;
+
+            float rulerX = basePos.x;
+            float rulerY = basePos.y;
+
+            dl->AddRectFilled({rulerX, rulerY},
+                              {rulerX + rulerWidth_, rulerY + availH}, kRulerBg);
+            dl->AddLine({rulerX + rulerWidth_ - 1, rulerY},
+                        {rulerX + rulerWidth_ - 1, rulerY + availH},
+                        kRulerTickCol, 1.0f);
+
+            // Pick a nice major tick interval targeting ~80px spacing.
+            constexpr float kTargetTickSpacing = 80.0f;
+            static const double kNiceIntervals[] = {
+                0.001, 0.002, 0.005, 0.01, 0.02, 0.05,
+                0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10.0, 20.0, 30.0, 60.0, 120.0, 300.0
+            };
+            double majorInterval = pickNiceStep(kNiceIntervals,
+                                                totalTime * (kTargetTickSpacing / availH));
+            double minorInterval = majorInterval / 4.0;
+            bool useMs = (majorInterval < 1.0);
+            float charH = ImGui::CalcTextSize("0").y;
+
+            // Minor ticks
+            float minorTickLen = rulerWidth_ / 3.0f;
+            for (int idx = 1;; ++idx) {
+                double t = minorInterval * idx;
+                if (t >= totalTime) break;
+                if (idx % 4 == 0) continue;
+
+                float y = rulerY + availH - static_cast<float>(t / totalTime) * availH;
+                if (y < rulerY) break;
+
+                float tickLen = (idx % 2 == 0) ? minorTickLen * 1.5f : minorTickLen;
+                dl->AddLine({rulerX + rulerWidth_ - 1 - tickLen, y},
+                            {rulerX + rulerWidth_ - 1, y}, kRulerTickCol, 1.5f);
+            }
+
+            // Major ticks with vertically stacked digit labels
+            for (int idx = 1;; ++idx) {
+                double t = majorInterval * idx;
+                if (t >= totalTime) break;
+
+                float y = rulerY + availH - static_cast<float>(t / totalTime) * availH;
+                if (y < rulerY) break;
+
+                dl->AddLine({rulerX, y},
+                            {rulerX + rulerWidth_ - 1, y}, kRulerTickCol, 2.0f);
+
+                char numBuf[16];
+                int ival = static_cast<int>((useMs ? t * 1000.0 : t) + 0.5);
+                std::snprintf(numBuf, sizeof(numBuf), "%d", ival);
+
+                int nDigits = static_cast<int>(std::strlen(numBuf));
+                float digitX = rulerX + 2.0f;
+                float digitY = y + 3.0f;
+                for (int d = 0; d < nDigits; ++d) {
+                    if (digitY + charH > rulerY + availH - charH) break;
+                    char ch[2] = {numBuf[d], '\0'};
+                    dl->AddText({digitX, digitY}, kRulerLabelCol, ch);
+                    digitY += charH;
+                }
+            }
+
+            // Unit label at the very bottom
+            const char* unit = useMs ? "ms" : "s";
+            ImVec2 unitSz = ImGui::CalcTextSize(unit);
+            dl->AddText({rulerX + 2.0f, rulerY + availH - unitSz.y - 2.0f},
+                        kRulerUnitCol, unit);
+        }
+
+        // ── Mouse interaction: zoom, pan & hover on waterfall ──
+        ImGuiIO& io = ImGui::GetIO();
+        float mx = io.MousePos.x;
+        float my = io.MousePos.y;
+        bool inWaterfall = mx >= pos.x && mx <= pos.x + availW &&
+                           my >= pos.y && my <= pos.y + availH;
+
+        if (inWaterfall) {
+            hoverPanel = HoverPanel::Waterfall;
+            double freq = specDisplay.screenXToFreq(mx, pos.x, availW,
+                                                     settings.sampleRate,
+                                                     settings.isIQ, ui.freqScale,
+                                                     ui.viewLo, ui.viewHi);
+            int bins = audio.spectrumSize();
+            double fMin = freqMin(settings.sampleRate, settings.isIQ);
+            double fMax = freqMax(settings.sampleRate, settings.isIQ);
+            int bin = static_cast<int>((freq - fMin) / (fMax - fMin) * (bins - 1));
+            bin = std::clamp(bin, 0, bins - 1);
+
+            float yFrac = 1.0f - (my - pos.y) / availH;
+            hoverWfTimeOff = static_cast<float>(yFrac * screenRows * secondsPerLine);
+
+            int curCh = std::clamp(ui.waterfallChannel, 0, audio.totalNumSpectra() - 1);
+            const auto& spec = audio.getSpectrum(curCh);
+            if (!spec.empty()) {
+                cursors.hover = {true, freq, spec[bin], bin};
+            }
+
+            if (io.MouseWheel != 0)
+                zoomView(ui.viewLo, ui.viewHi, (mx - pos.x) / availW, io.MouseWheel);
+
+            if (ImGui::IsMouseDragging(ImGuiMouseButton_Middle, 1.0f))
+                panView(ui.viewLo, ui.viewHi, io.MouseDelta.x, availW);
+
+            if (ImGui::IsMouseDoubleClicked(ImGuiMouseButton_Middle)) {
+                ui.viewLo = 0.0f;
+                ui.viewHi = 1.0f;
+            }
+        }
+    }
+
+    ImGui::Dummy({fullW, availH});
+}
+
+void DisplayPanel::renderHoverOverlay(const AudioEngine& audio, const UIState& ui,
+                                       const Cursors& cursors, const SpectrumDisplay& specDisplay) {
+    if (!cursors.hover.active || specSizeX <= 0 || wfSizeX <= 0)
+        return;
+
+    const auto& settings = audio.settings();
+    ImDrawList* dl = ImGui::GetWindowDrawList();
+
+    float hx = specDisplay.freqToScreenX(cursors.hover.freq,
+                   specPosX, specSizeX, settings.sampleRate,
+                   settings.isIQ, ui.freqScale, ui.viewLo, ui.viewHi);
+    ImU32 hoverCol = IM_COL32(200, 200, 200, 80);
+
+    dl->AddLine({hx, specPosY}, {hx, specPosY + specSizeY}, hoverCol, 1.0f);
+
+    char freqLabel[48];
+    fmtFreq(freqLabel, sizeof(freqLabel), cursors.hover.freq);
+
+    ImVec2 tSz = ImGui::CalcTextSize(freqLabel);
+    float lx = std::min(hx + 4, wfPosX + wfSizeX - tSz.x - 4);
+    float ly = wfPosY + 2;
+    dl->AddRectFilled({lx - 2, ly - 1}, {lx + tSz.x + 2, ly + tSz.y + 1},
+                       IM_COL32(0, 0, 0, 180));
+    dl->AddText({lx, ly}, IM_COL32(220, 220, 240, 240), freqLabel);
+
+    // Hover info (right side)
+    {
+        int bins = audio.spectrumSize();
+        double fMin = freqMin(settings.sampleRate, settings.isIQ);
+        double fMax = freqMax(settings.sampleRate, settings.isIQ);
+        double binCenterFreq = fMin + (static_cast<double>(cursors.hover.bin) + 0.5)
+                               / bins * (fMax - fMin);
+
+        char hoverBuf[128];
+        if (hoverPanel == HoverPanel::Spectrum) {
+            fmtFreqDB(hoverBuf, sizeof(hoverBuf), "", binCenterFreq, cursors.hover.dB);
+        } else if (hoverPanel == HoverPanel::Waterfall) {
+            fmtFreqTime(hoverBuf, sizeof(hoverBuf), "", binCenterFreq, -hoverWfTimeOff);
+        } else {
+            fmtFreq(hoverBuf, sizeof(hoverBuf), binCenterFreq);
+        }
+
+        ImU32 hoverTextCol = IM_COL32(100, 230, 130, 240);
+        float rightEdge = specPosX + specSizeX - 8;
+        float hy2 = specPosY + 4;
+        ImVec2 hSz = ImGui::CalcTextSize(hoverBuf);
+        dl->AddText({rightEdge - hSz.x, hy2}, hoverTextCol, hoverBuf);
+    }
+}
+
+void DisplayPanel::handleSpectrumInput(AudioEngine& audio, UIState& ui,
+                                        SpectrumDisplay& specDisplay, Cursors& cursors,
+                                        float posX, float posY, float sizeX, float sizeY) {
+    const auto& settings = audio.settings();
+
+    ImGuiIO& io = ImGui::GetIO();
+    float mx = io.MousePos.x;
+    float my = io.MousePos.y;
+
+    bool inRegion = mx >= posX && mx <= posX + sizeX &&
+                    my >= posY && my <= posY + sizeY;
+
+    if (inRegion) {
+        hoverPanel = HoverPanel::Spectrum;
+        double freq = specDisplay.screenXToFreq(mx, posX, sizeX,
+                                                 settings.sampleRate,
+                                                 settings.isIQ, ui.freqScale,
+                                                 ui.viewLo, ui.viewHi);
+        float dB = specDisplay.screenYToDB(my, posY, sizeY, ui.minDB, ui.maxDB);
+
+        int bins = audio.spectrumSize();
+        double fMin = freqMin(settings.sampleRate, settings.isIQ);
+        double fMax = freqMax(settings.sampleRate, settings.isIQ);
+        int bin = static_cast<int>((freq - fMin) / (fMax - fMin) * (bins - 1));
+        bin = std::clamp(bin, 0, bins - 1);
+
+        int curCh = std::clamp(ui.waterfallChannel, 0, audio.totalNumSpectra() - 1);
+        const auto& spec = audio.getSpectrum(curCh);
+        if (!spec.empty()) {
+            dB = spec[bin];
+            cursors.hover = {true, freq, dB, bin};
+        }
+
+        if (ImGui::IsMouseDown(ImGuiMouseButton_Left)) {
+            int cBin = cursors.snapToPeaks ? cursors.findLocalPeak(spec, bin, 10) : bin;
+            double cFreq = audio.binToFreq(cBin);
+            cursors.setCursorA(cFreq, spec[cBin], cBin);
+        }
+        if (ImGui::IsMouseDown(ImGuiMouseButton_Right)) {
+            int cBin = cursors.snapToPeaks ? cursors.findLocalPeak(spec, bin, 10) : bin;
+            double cFreq = audio.binToFreq(cBin);
+            cursors.setCursorB(cFreq, spec[cBin], cBin);
+        }
+
+        {
+            if (io.MouseWheel != 0 && (io.KeyCtrl || io.KeyShift)) {
+                float zoom = io.MouseWheel * 5.0f;
+                ui.minDB += zoom;
+                ui.maxDB -= zoom;
+                if (ui.maxDB - ui.minDB < 10.0f) {
+                    float mid = (ui.minDB + ui.maxDB) / 2.0f;
+                    ui.minDB = mid - 5.0f;
+                    ui.maxDB = mid + 5.0f;
+                }
+            }
+            else if (io.MouseWheel != 0) {
+                zoomView(ui.viewLo, ui.viewHi, (mx - posX) / sizeX, io.MouseWheel);
+            }
+
+            if (ImGui::IsMouseDragging(ImGuiMouseButton_Middle, 1.0f))
+                panView(ui.viewLo, ui.viewHi, io.MouseDelta.x, sizeX);
+
+            if (ImGui::IsMouseDoubleClicked(ImGuiMouseButton_Middle)) {
+                ui.viewLo = 0.0f;
+                ui.viewHi = 1.0f;
+            }
+        }
+    } else {
+        if (hoverPanel != HoverPanel::Waterfall) {
+            hoverPanel = HoverPanel::None;
+            cursors.hover.active = false;
+        }
+    }
+}
+
+void DisplayPanel::handleTouch(const SDL_Event& event, UIState& ui, SDL_Window* window) {
+    if (event.type == SDL_FINGERDOWN) {
+        ++touch_.count;
+    } else if (event.type == SDL_FINGERUP) {
+        touch_.count = std::max(0, touch_.count - 1);
+    }
+
+    if (touch_.count == 2 && event.type == SDL_FINGERDOWN) {
+        int w, h;
+        SDL_GetWindowSize(window, &w, &h);
+        SDL_TouchID tid = event.tfinger.touchId;
+        int nf = SDL_GetNumTouchFingers(tid);
+        if (nf >= 2) {
+            SDL_Finger* f0 = SDL_GetTouchFinger(tid, 0);
+            SDL_Finger* f1 = SDL_GetTouchFinger(tid, 1);
+            if (!f0 || !f1) return;
+            float x0 = f0->x * w, x1 = f1->x * w;
+            float dx = x1 - x0, dy = (f1->y - f0->y) * h;
+            touch_.startDist = std::sqrt(dx * dx + dy * dy);
+            touch_.lastDist = touch_.startDist;
+            touch_.startCenterX = (x0 + x1) * 0.5f;
+            touch_.lastCenterX = touch_.startCenterX;
+            touch_.startLo = ui.viewLo;
+            touch_.startHi = ui.viewHi;
+        }
+    }
+
+    if (touch_.count == 2 && event.type == SDL_FINGERMOTION) {
+        int w, h;
+        SDL_GetWindowSize(window, &w, &h);
+        SDL_TouchID tid = event.tfinger.touchId;
+        int nf = SDL_GetNumTouchFingers(tid);
+        if (nf >= 2) {
+            SDL_Finger* f0 = SDL_GetTouchFinger(tid, 0);
+            SDL_Finger* f1 = SDL_GetTouchFinger(tid, 1);
+            if (!f0 || !f1) return;
+            float x0 = f0->x * w, x1 = f1->x * w;
+            float dx = x1 - x0, dy = (f1->y - f0->y) * h;
+            float dist = std::sqrt(dx * dx + dy * dy);
+            float centerX = (x0 + x1) * 0.5f;
+
+            if (touch_.startDist > 1.0f) {
+                float span0 = touch_.startHi - touch_.startLo;
+                float ratio = touch_.startDist / std::max(dist, 1.0f);
+                float newSpan = std::clamp(span0 * ratio, 0.001f, 1.0f);
+
+                float panelW = wfSizeX > 0 ? wfSizeX : static_cast<float>(w);
+                float panelX = wfPosX;
+                float midFrac = (touch_.startCenterX - panelX) / panelW;
+                float midView = touch_.startLo + midFrac * span0;
+
+                float panDelta = -(centerX - touch_.startCenterX) / panelW * newSpan;
+
+                float newLo = midView - midFrac * newSpan + panDelta;
+                float newHi = newLo + newSpan;
+
+                if (newLo < 0.0f) { newHi -= newLo; newLo = 0.0f; }
+                if (newHi > 1.0f) { newLo -= (newHi - 1.0f); newHi = 1.0f; }
+                ui.viewLo = std::clamp(newLo, 0.0f, 1.0f);
+                ui.viewHi = std::clamp(newHi, 0.0f, 1.0f);
+            }
+        }
+    }
+}
+
+} // namespace baudmine

src/ui/DisplayPanel.h

@@ -0,0 +1,69 @@
+#pragma once
+
+#include "core/Types.h"
+#include "ui/UIState.h"
+#include "ui/WaterfallDisplay.h"
+#include "ui/SpectrumDisplay.h"
+#include "ui/Cursors.h"
+#include "ui/Measurements.h"
+#include "ui/ColorMap.h"
+
+#include <SDL.h>
+#include <vector>
+
+namespace baudmine {
+
+class AudioEngine;
+
+class DisplayPanel {
+public:
+    void renderSpectrum(AudioEngine& audio, UIState& ui,
+                        SpectrumDisplay& specDisplay, Cursors& cursors,
+                        Measurements& measurements);
+
+    void renderWaterfall(AudioEngine& audio, UIState& ui,
+                         WaterfallDisplay& waterfall, SpectrumDisplay& specDisplay,
+                         Cursors& cursors, Measurements& measurements,
+                         ColorMap& colorMap);
+
+    void renderHoverOverlay(const AudioEngine& audio, const UIState& ui,
+                            const Cursors& cursors, const SpectrumDisplay& specDisplay);
+
+    void handleTouch(const SDL_Event& event, UIState& ui, SDL_Window* window);
+
+    // Panel geometry (read by Application for layout)
+    float specPosX = 0, specPosY = 0, specSizeX = 0, specSizeY = 0;
+    float wfPosX   = 0, wfPosY   = 0, wfSizeX   = 0, wfSizeY   = 0;
+
+    enum class HoverPanel { None, Spectrum, Waterfall };
+    HoverPanel hoverPanel      = HoverPanel::None;
+    float      hoverWfTimeOff  = 0.0f;
+
+    float spectrumFrac  = 0.35f;
+    bool  draggingSplit  = false;
+    bool  showRuler      = false;
+    float rulerWidth_    = 0.0f;   // current ruler width in pixels (0 when hidden)
+
+private:
+    void handleSpectrumInput(AudioEngine& audio, UIState& ui,
+                             SpectrumDisplay& specDisplay, Cursors& cursors,
+                             float posX, float posY, float sizeX, float sizeY);
+
+    struct TouchState {
+        int   count = 0;
+        float startDist = 0.0f;
+        float startLo = 0.0f;
+        float startHi = 0.0f;
+        float startCenterX = 0.0f;
+        float lastCenterX = 0.0f;
+        float lastDist = 0.0f;
+    } touch_;
+
+    // Scratch buffers
+    std::vector<std::vector<float>>   wfSpectraScratch_;
+    std::vector<WaterfallChannelInfo> wfChInfoScratch_;
+    std::vector<std::vector<float>>   allSpectraScratch_;
+    std::vector<ChannelStyle>         stylesScratch_;
+};
+
+} // namespace baudmine

src/ui/Measurements.cpp

@@ -61,24 +61,18 @@ void Measurements::findPeaks(const std::vector<float>& spectrumDB, int maxN,
     }
 }
 
-void Measurements::update(const std::vector<float>& spectrumDB,
+void Measurements::pushPeakTrace(const std::vector<float>& spectrumDB,
                                   double sampleRate, bool isIQ, int fftSize) {
-    lastSampleRate_ = sampleRate;
-    // Always track global peak (for the readout label).
-    if (!spectrumDB.empty()) {
-        auto it = std::max_element(spectrumDB.begin(), spectrumDB.end());
-        int bin = static_cast<int>(std::distance(spectrumDB.begin(), it));
-        globalPeak_.bin = bin;
-        globalPeak_.dB = *it;
-        globalPeak_.freq = binToFreq(bin, sampleRate, isIQ, fftSize);
+    if (spectrumDB.empty()) return;
 
-        // Push into peak history circular buffer (with optional freq range filter)
     constexpr int kMaxHistory = 4096;
     if (static_cast<int>(peakHistBins_.size()) < kMaxHistory)
         peakHistBins_.resize(kMaxHistory, -1);
 
-        // Find peak within the trace frequency range
-        int traceBin = bin;
+    auto it = std::max_element(spectrumDB.begin(), spectrumDB.end());
+    int traceBin = static_cast<int>(std::distance(spectrumDB.begin(), it));
+
+    // Optionally restrict to a frequency range.
     int bins = static_cast<int>(spectrumDB.size());
     if (traceMinFreq > 0.0f || traceMaxFreq > 0.0f) {
         double fMin = isIQ ? -sampleRate / 2.0 : 0.0;
@@ -97,6 +91,18 @@ void Measurements::update(const std::vector<float>& spectrumDB,
     peakHistIdx_ = (peakHistIdx_ + 1) % kMaxHistory;
     peakHistBins_[peakHistIdx_] = traceBin;
     if (peakHistLen_ < kMaxHistory) ++peakHistLen_;
+}
+
+void Measurements::update(const std::vector<float>& spectrumDB,
+                           double sampleRate, bool isIQ, int fftSize) {
+    lastSampleRate_ = sampleRate;
+    // Always track global peak (for the readout label).
+    if (!spectrumDB.empty()) {
+        auto it = std::max_element(spectrumDB.begin(), spectrumDB.end());
+        int bin = static_cast<int>(std::distance(spectrumDB.begin(), it));
+        globalPeak_.bin = bin;
+        globalPeak_.dB = *it;
+        globalPeak_.freq = binToFreq(bin, sampleRate, isIQ, fftSize);
     }
 
     if (!enabled) { peaks_.clear(); return; }

src/ui/Measurements.h

@@ -18,6 +18,10 @@ public:
     void update(const std::vector<float>& spectrumDB,
                 double sampleRate, bool isIQ, int fftSize);
 
+    // Push a single peak trace entry for this spectrum (call once per waterfall line).
+    void pushPeakTrace(const std::vector<float>& spectrumDB,
+                       double sampleRate, bool isIQ, int fftSize);
+
     // Draw markers on the spectrum display area.
     void draw(const SpectrumDisplay& specDisplay,
               float posX, float posY, float sizeX, float sizeY,

src/ui/SpectrumDisplay.cpp

@@ -2,8 +2,27 @@
 #include <cmath>
 #include <algorithm>
 
+#ifdef __EMSCRIPTEN__
+#include <GLES2/gl2.h>
+#elif defined(_WIN32)
+#define WIN32_LEAN_AND_MEAN
+#define NOMINMAX
+#include <windows.h>
+#include <GL/gl.h>
+#else
+#include <GL/gl.h>
+#endif
+
 namespace baudmine {
 
+// ImGui draw-list callbacks to switch GL blend mode for additive color mixing.
+static void setAdditiveBlend(const ImDrawList*, const ImDrawCmd*) {
+    glBlendFunc(GL_SRC_ALPHA, GL_ONE);
+}
+static void restoreDefaultBlend(const ImDrawList*, const ImDrawCmd*) {
+    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+}
+
 static float freqToLogFrac(double freq, double minFreq, double maxFreq) {
     if (freq <= 0 || minFreq <= 0) return 0.0f;
     double logMin = std::log10(minFreq);
@@ -41,9 +60,11 @@ static void buildPolyline(const std::vector<float>& spectrumDB,
                            bool isIQ, FreqScale freqScale,
                            float posX, float posY, float sizeX, float sizeY,
                            float viewLo, float viewHi,
-                           std::vector<ImVec2>& outPoints) {
+                           std::vector<ImVec2>& outPoints,
+                           int minPixPerBin = 1) {
     int bins = static_cast<int>(spectrumDB.size());
-    int displayPts = std::min(bins, static_cast<int>(sizeX));
+    int maxPts = std::max(1, static_cast<int>(sizeX) / std::max(1, minPixPerBin));
+    int displayPts = std::min(bins, maxPts);
     if (displayPts < 2) displayPts = 2;
 
     outPoints.resize(displayPts);
@@ -89,7 +110,8 @@ void SpectrumDisplay::draw(const std::vector<std::vector<float>>& spectra,
                            FreqScale freqScale,
                            float posX, float posY,
                            float sizeX, float sizeY,
-                           float viewLo, float viewHi) const {
+                           float viewLo, float viewHi,
+                           int minPixPerBin) const {
     if (spectra.empty() || spectra[0].empty() || sizeX <= 0 || sizeY <= 0) return;
 
     ImDrawList* dl = ImGui::GetWindowDrawList();
@@ -127,7 +149,7 @@ void SpectrumDisplay::draw(const std::vector<std::vector<float>>& spectra,
             dl->AddLine({posX, y}, {posX + sizeX, y}, gridCol);
             char label[16];
             std::snprintf(label, sizeof(label), "%.0f", db);
-            dl->AddText({posX + 2, y - ImGui::GetTextLineHeight()}, textCol, label);
+            dl->AddText({posX + 2 - dbLabelOffsetX, y - ImGui::GetTextLineHeight()}, textCol, label);
         }
 
         // ── Vertical (frequency) grid — adapt count to available width ──
@@ -152,52 +174,75 @@ void SpectrumDisplay::draw(const std::vector<std::vector<float>>& spectra,
         }
     }
 
-    // Draw each channel's spectrum.
-    std::vector<ImVec2> points;
+    // Build polylines for all channels.
     int nCh = static_cast<int>(spectra.size());
+    std::vector<std::vector<ImVec2>> allPoints(nCh);
     for (int ch = 0; ch < nCh; ++ch) {
         if (spectra[ch].empty()) continue;
-        const ChannelStyle& st = (ch < static_cast<int>(styles.size()))
-            ? styles[ch]
-            : styles.back();
-
         buildPolyline(spectra[ch], minDB, maxDB,
                       isIQ, freqScale, posX, posY, sizeX, sizeY,
-                      viewLo, viewHi, points);
+                      viewLo, viewHi, allPoints[ch], minPixPerBin);
+    }
 
-        // Fill
-        if (fillSpectrum && points.size() >= 2) {
-            for (size_t i = 0; i + 1 < points.size(); ++i) {
-                ImVec2 tl = points[i];
-                ImVec2 tr = points[i + 1];
-                ImVec2 bl = {tl.x, posY + sizeY};
-                ImVec2 br = {tr.x, posY + sizeY};
-                dl->AddQuadFilled(tl, tr, br, bl, st.fillColor);
+    // Draw spectra: all fills first, then all lines on top.
+    // Multi-channel uses additive GL blending so colors mix (green + purple = white).
+    {
+        bool additive = additiveBlend && nCh > 1;
+        // Use lower alpha under additive blend to avoid oversaturation.
+        constexpr ImU8 kLineAlpha = 180;
+        constexpr ImU8 kFillAlpha = 30;
+
+        if (additive)
+            dl->AddCallback(setAdditiveBlend, nullptr);
+
+        // Pass 1: fills (drawn first so lines sit on top of all fills).
+        if (fillSpectrum) {
+            for (int ch = 0; ch < nCh; ++ch) {
+                const auto& pts = allPoints[ch];
+                if (pts.size() < 2) continue;
+                const ChannelStyle& st = (ch < static_cast<int>(styles.size()))
+                    ? styles[ch] : styles.back();
+                ImU32 col = additive
+                    ? ((st.fillColor & 0x00FFFFFF) | (static_cast<ImU32>(kFillAlpha) << 24))
+                    : st.fillColor;
+                for (size_t i = 0; i + 1 < pts.size(); ++i) {
+                    dl->AddQuadFilled(pts[i], pts[i + 1],
+                                      {pts[i + 1].x, posY + sizeY},
+                                      {pts[i].x, posY + sizeY}, col);
+                }
             }
         }
 
-        // Line
-        if (points.size() >= 2)
-            dl->AddPolyline(points.data(), static_cast<int>(points.size()),
-                            st.lineColor, ImDrawFlags_None, 1.5f);
+        // Pass 2: lines.
+        for (int ch = 0; ch < nCh; ++ch) {
+            const auto& pts = allPoints[ch];
+            if (pts.size() < 2) continue;
+            const ChannelStyle& st = (ch < static_cast<int>(styles.size()))
+                ? styles[ch] : styles.back();
+            ImU32 col = additive
+                ? ((st.lineColor & 0x00FFFFFF) | (static_cast<ImU32>(kLineAlpha) << 24))
+                : st.lineColor;
+            dl->AddPolyline(pts.data(), static_cast<int>(pts.size()),
+                            col, ImDrawFlags_None, 1.5f);
         }
 
-    // Peak hold traces (drawn as dashed-style thin lines above the live spectrum).
+        if (additive)
+            dl->AddCallback(restoreDefaultBlend, nullptr);
+    }
+
+    // Peak hold traces.
     if (peakHoldEnable && !peakHold_.empty()) {
+        std::vector<ImVec2> phPoints;
         for (int ch = 0; ch < nCh && ch < static_cast<int>(peakHold_.size()); ++ch) {
             if (peakHold_[ch].empty()) continue;
             const ChannelStyle& st = (ch < static_cast<int>(styles.size()))
                 ? styles[ch] : styles.back();
-
-            // Use the same line color but dimmer.
             ImU32 col = (st.lineColor & 0x00FFFFFF) | 0x90000000;
-
             buildPolyline(peakHold_[ch], minDB, maxDB,
                           isIQ, freqScale, posX, posY, sizeX, sizeY,
-                          viewLo, viewHi, points);
-
-            if (points.size() >= 2)
-                dl->AddPolyline(points.data(), static_cast<int>(points.size()),
+                          viewLo, viewHi, phPoints, minPixPerBin);
+            if (phPoints.size() >= 2)
+                dl->AddPolyline(phPoints.data(), static_cast<int>(phPoints.size()),
                                 col, ImDrawFlags_None, 1.0f);
         }
     }

src/ui/SpectrumDisplay.h

@@ -22,7 +22,8 @@ public:
               double sampleRate, bool isIQ,
               FreqScale freqScale,
               float posX, float posY, float sizeX, float sizeY,
-              float viewLo = 0.0f, float viewHi = 1.0f) const;
+              float viewLo = 0.0f, float viewHi = 1.0f,
+              int minPixPerBin = 1) const;
 
     // Convenience: single-channel draw (backward compat).
     void draw(const std::vector<float>& spectrumDB,
@@ -46,8 +47,10 @@ public:
 
     bool  showGrid       = true;
     bool  fillSpectrum   = false;
+    bool  additiveBlend  = true;   // additive color mixing for multi-channel
     bool  peakHoldEnable = false;
     float peakHoldDecay  = 20.0f;  // dB/second decay rate
+    float dbLabelOffsetX = 0.0f;   // shift dB labels left (into ruler area)
 
 private:
     // One peak-hold trace per channel.

src/ui/UIState.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include "core/Types.h"
+#include <imgui.h>
+#include <array>
+
+namespace baudmine {
+
+// Shared display state accessed by both ControlPanel and DisplayPanel.
+struct UIState {
+    float     minDB       = -120.0f;
+    float     maxDB       = 0.0f;
+    FreqScale freqScale   = FreqScale::Linear;
+    float     viewLo      = 0.0f;
+    float     viewHi      = 0.5f;
+    bool      paused      = false;
+
+    int  waterfallChannel = 0;
+    bool waterfallMultiCh = true;
+    int  specMinPixPerBin = 1;   // min screen pixels per spectrum bin (1 = no decimation)
+    std::array<bool, kMaxChannels> channelEnabled = {true,true,true,true,true,true,true,true};
+    // Complementary pairs: colors at indices 0+1, 2+3, 4+5, 6+7 sum to white.
+    std::array<ImVec4, kMaxChannels> channelColors = {{
+        {0.20f, 0.90f, 0.20f, 1.0f},  // green
+        {0.80f, 0.10f, 0.80f, 1.0f},  // purple
+        {1.00f, 0.55f, 0.00f, 1.0f},  // orange
+        {0.00f, 0.45f, 1.00f, 1.0f},  // cyan
+        {1.00f, 0.25f, 0.25f, 1.0f},  // red
+        {0.00f, 0.75f, 0.75f, 1.0f},  // teal
+        {1.00f, 1.00f, 0.20f, 1.0f},  // yellow
+        {0.00f, 0.00f, 0.80f, 1.0f},  // blue
+    }};
+};
+
+} // namespace baudmine

src/ui/WaterfallDisplay.h

@@ -2,7 +2,15 @@
 
 #include "core/Types.h"
 #include "ui/ColorMap.h"
+#ifdef _WIN32
+#define WIN32_LEAN_AND_MEAN
+#define NOMINMAX
+#include <windows.h>
+#endif
 #include <GL/gl.h>
+#ifndef GL_CLAMP_TO_EDGE // for Windows
+#define GL_CLAMP_TO_EDGE 0x812F
+#endif
 #include <vector>
 #include <deque>