Michael Smith
3ba7b31148
Replace mouse input with cursor-based navigation (arrow keys / d-pad + Enter / A button) and add app-level volume control with a persistent vertical slider, enabling use on a handheld gaming device without mouse or system mixer access. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
62 lines
5.2 KiB
Markdown
62 lines
5.2 KiB
Markdown
# SDLamp2 - Functional Specification Document
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## Document Information
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| Field | Value |
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| :------ | :--------- |
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| Version | 1.0 |
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| Status | Draft |
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| Created | 2026-02-10 |
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| Updated | 2026-02-10 |
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## 1. Purpose
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This document specifies the functional requirements for an SDL2 based media player application written in C, aimed at being used by a pre-teen child. The name is a reference to the Winamp media player, popular in the 90's and inspiration can be drawn from that.
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## 2. Goals
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- Play large m4a audio files, approximately 3 hours each, created from original cassette tapes that contain collections of fairy tales for children
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- Present a super simple interface, easy to use by a child less than 10 years old, reminiscent of a cassette player: rewind, stop, play / pause, fast forward, load another tape
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- The playback of the audio files must emulate that of cassette tapes, meaning the position of each file should be stored and remembered and playback should resume from that position even if other files have been played in the mean time
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- The interface should show the embedded album cover if present in the file
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## 3. Software architecture
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- The program should be written in modern C using GCC or Clang
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- It should use the SDL2 library for screen rendering, audio playback and input handling
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- It should use the libav (ffmpeg) suite of libraries to decode m4a files and potentially other formats (e.g. mp3)
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- It should not call out to an ffmpeg binary, but instead use the libav C API library functions
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## 4. Design principles
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- Version control (git) must be used
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- Compilation should be performed by a simple shell script or batch file, not a complicated build system like make or cmake
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- C source code files should be formatted using "Google" style with an additional change of `ColumnLimit` set to 100
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- Less is more, minimize dependencies, avoid pulling in extra libraries, always talk through with owner first
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- Keep it simple, apply Casey Muratori's `semantic compression` principles, don't refactor too soon or write code that's too clever for its own good
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- Keep a changelog in this functional specification document
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## 5. Changelog
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### 2026-02-10 — Volume control and d-pad/keyboard navigation
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- **Cursor-based navigation**: Replaced mouse input with a focus-highlight model. Arrow keys (Left/Right) and d-pad move a visible blue highlight between UI elements; Enter/A button activates the focused button. Designed for use on a handheld gaming device with no mouse.
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- **App-level volume control**: Float samples are scaled by a volume factor (0–100%) before being queued to the audio device. Volume slider rendered as a vertical bar to the left of the transport buttons, using the same gray palette as the progress bar.
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- **Volume persistence**: Volume level saved to `volume.txt` in the audio directory. Defaults to 50% on first run. Loaded on startup, saved on quit and on every adjustment.
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- **SDL_GameController support**: Uses `SDL_INIT_GAMECONTROLLER` and the `SDL_GameController` API to normalize d-pad input across hardware. Hot-plug support via `SDL_CONTROLLERDEVICEADDED/REMOVED`. Keyboard (arrow keys + Enter) works identically for desktop testing.
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- **Removed mouse input**: `SDL_MOUSEBUTTONDOWN` handler removed entirely; all interaction is now via keyboard or gamepad.
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### 2026-02-10 — Full implementation of audio player features
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- **Streaming decoder**: Replaced fire-and-forget `decode_audio()` with a persistent `Decoder` struct that streams audio on demand via `decoder_pump()`. Uses `libswresample` (`swr_alloc_set_opts2`) to convert from the decoder's native format (e.g. planar float) to interleaved float stereo 48kHz. Fixes the sped-up/distorted audio bug and eliminates the multi-GB memory spike for long files.
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- **Seeking**: Rewind (10s back) and fast-forward (10s ahead) via `av_seek_frame()` with codec buffer flush and audio pipeline clear. Clamped to file bounds.
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- **Play/Stop separation**: Removed play/pause toggle. Play always resumes, stop always pauses in place and saves position. No icon toggling.
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- **Position persistence**: Saves/loads playback position per file in `positions.txt` (tab-separated) in the audio directory. Position saved on stop, quit, and file switch. Restored on file open.
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- **File selection**: Scans audio directory for `.m4a`, `.mp3`, `.wav`, `.ogg` files. Sorted alphabetically. 5th button ("next tape") cycles through files. Window title shows current filename.
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- **Album art**: Extracts embedded cover art (`AV_DISPOSITION_ATTACHED_PIC`) and displays it scaled with preserved aspect ratio in the upper portion of the window.
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- **Progress bar**: Gray bar between album art and controls showing playback position relative to duration.
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- **Command-line argument**: First argument sets audio directory (defaults to current working directory).
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- **Error handling**: Non-fatal errors (stream ops, corrupt files) use `fprintf(stderr)` and continue. Corrupt files are skipped when switching. Fatal errors (SDL init, window, audio device) still abort. Proper cleanup order on exit.
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- **EOF handling**: When a file plays to the end, playback auto-pauses and resets to the start.
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- **Removed dead code**: `load_audio_file()`, `wavbuf`/`wavlen`/`wavspec` globals.
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