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P2-R1: ALSA + JACK2 low-latency config (scripts, quirks, tuning) P2-R2: Carla integration (build scripts, 8ch rack config, NAM LV2 support) P2-R3: Plugin manager, categories, blacklist, NAM model support P3-R1: Mixer DSP engine (channel strip, routing matrix, bus mgr, automation) P4-R1: MIDI engine (learn mode, clock sync, HID discovery, mapping store) P4-R2: Network API (OSC server, FastAPI REST, WebSocket, auth, rate limiter) P5-R1: Touchscreen UI evaluation + main entry point docs: Audio stack, Carla integration, MIDI support, UI evaluation tests: Full test suite (292 passing)
90 lines
4.4 KiB
Markdown
90 lines
4.4 KiB
Markdown
# Touchscreen UI Toolkit Evaluation
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Raspberry Pi 4B, official 7" (800×480) or Waveshare 5" (720×720) DSI/HDMI
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touch displays. Requirements: faders, meters, mute/solo, routing matrix,
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plugin chain, touch gestures, DPI-aware layout.
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## Candidates
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### LVGL (Light and Versatile Graphics Library)
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- **Type**: C library, embedded-first, Python bindings via `lvgl` package
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- **RPi support**: Native framebuffer + SDL2/KMS backends, no X11 required
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- **Touch**: Native input device support (libinput/evdev), multi-touch, gestures
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- **DPI**: Pixel-based (px), no automatic scaling — manual math required
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- **Widgets**: Sliders, buttons, labels, charts, tables — good but basic
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- **Performance**: ⭐⭐⭐⭐⭐ — C rendering, 30-60 FPS on RPi 4
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- **Python ergonomics**: ⭐⭐ — Python bindings are auto-generated, not idiomatic;
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callbacks are C-style, error messages opaque; limited docs for Python usage
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- **Verdict**: Best performance, but Python API is friction-heavy. Good for C
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projects. Too much pain for a Python codebase.
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### GTK 3/4
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- **Type**: C library, GObject introspection for Python (`PyGObject`)
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- **RPi support**: Requires X11 or Wayland compositor — adds RAM overhead
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- **Touch**: Mouse-emulated touch; not natively touch-optimized
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- **DPI**: CSS-based theming, but DPI scaling is complex on small screens
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- **Widgets**: Very rich (sliders, buttons, tree views, notebooks)
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- **Performance**: ⭐⭐ — X11/Wayland overhead, not optimized for embedded
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- **Python ergonomics**: ⭐⭐⭐ — GObject patterns leak through; verbose
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- **Verdict**: Desktop toolkit forced onto embedded. Heavy, poor touch UX.
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Best for desktop companion apps, not the primary mixer UI.
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### SDL2
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- **Type**: C library, Python via `PySDL2`
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- **RPi support**: Framebuffer/KMSDRM backends, no X11 required
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- **Touch**: Raw input events only — no gesture recognition built in
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- **DPI**: None — raw pixels, manual scaling required
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- **Widgets**: None — you build every widget from primitives (rects, lines, text)
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- **Performance**: ⭐⭐⭐⭐ — low-level, fast rendering
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- **Python ergonomics**: ⭐ — no widgets, no layout engine, no theme system.
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Building a mixer UI in raw SDL2 means writing a UI toolkit from scratch.
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- **Verdict**: Great for games, terrible for complex UIs. Too much boilerplate.
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### Kivy (selected)
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- **Type**: Python-native UI framework, OpenGL ES 2.0 backend
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- **RPi support**: Native RPi support via `kivy-rpi`; framebuffer or X11 backends;
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works with official 7" and Waveshare displays out of the box
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- **Touch**: First-class multi-touch, gesture recognition (swipe, pinch, long-press),
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mouse fallback for development
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- **DPI**: `dp()` and `sp()` (density-independent pixels/scaled pixels) —
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automatic scaling across 5" / 7" / desktop displays
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- **Widgets**: Sliders, buttons, toggles, labels, layouts, screens, tabbed panels
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- **Performance**: ⭐⭐⭐ — OpenGL-accelerated; 30-60 FPS on RPi 4 for
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typical mixer UI complexity; GPU handles rendering, CPU free for DSP
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- **Python ergonomics**: ⭐⭐⭐⭐⭐ — Pure Python, declarative KV language or
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programmatic widget construction; natural fit for the existing Python codebase
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- **Verdict**: Best balance of performance, touch UX, and Python ergonomics.
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Purpose-built for multi-touch interfaces. DPI-aware by default. Rich widget
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set plus easy custom widget creation for faders/meters.
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## Decision: Kivy
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| Criterion | LVGL | GTK | SDL2 | Kivy |
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|-----------|------|-----|------|------|
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| Touch UX | ★★★★ | ★★ | ★ | ★★★★★ |
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| Performance | ★★★★★ | ★★ | ★★★★ | ★★★ |
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| Python API | ★★ | ★★★ | ★ | ★★★★★ |
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| DPI scaling | ★ | ★★★ | ★ | ★★★★★ |
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| Widget richness | ★★★ | ★★★★★ | ★ | ★★★★ |
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| RPi setup | ★★★★ | ★★ | ★★★ | ★★★★ |
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Kivy is the clear winner for a Python-project building a touch-optimized mixer
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UI on Raspberry Pi. The DPI-aware layout system means the same code works on
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5" and 7" displays without manual scaling math. Multi-touch and gestures
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come free. Custom widgets (faders, meters, knobs) are straightforward to
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build on Kivy's Canvas primitives.
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### Installation (RPi)
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```bash
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sudo apt install python3-kivy # system package, includes RPi deps
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# or
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pip3 install kivy # + manual SDL2/OpenGL deps
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```
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### Development (desktop)
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```bash
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pip3 install kivy
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# Run with: python3 main_touch.py
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# Mouse works as touch fallback
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```
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