Embed controls.png into binary so it can run from any directory

The spritesheet is compiled in as a C byte array. An external
controls.png in cwd still takes precedence for skinning. Includes
tools/embed_png.py to regenerate the header if the asset changes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -15,16 +15,16 @@ See `docs/sdlamp2-fsd.md` for the full functional specification and changelog.
 ```sh
 ./build.sh              # macOS — builds to build/sdlamp2
 ./build_aarch64.sh      # Linux aarch64 variant
-cd build && ./sdlamp2 [audio_directory]
+./build/sdlamp2 [audio_directory]
 ```
 
-The binary must be run from `build/` because it loads `controls.png` from the current working directory. Audio directory defaults to cwd if not specified.
+The controls spritesheet (`controls.png`) is embedded in the binary. If an external `controls.png` exists in the current working directory it takes precedence, allowing custom skins. Audio directory defaults to cwd if not specified.
 
 No test suite, no linter, no Makefile/CMake.
 
 ## Architecture
 
-Single-file C program: `src/sdlamp2.c` (~650 lines). No headers, no separate compilation units.
+Single-file C program: `src/sdlamp2.c` (~650 lines). One generated header: `src/controls_png.h` (embedded PNG byte array — regenerate with `./tools/embed_png.py build/controls.png src/controls_png.h` if the spritesheet changes).
 
 Key sections in order:
 - **Decoder struct** — holds all FFmpeg state (format/codec contexts, swr resampler, album art texture)

docs/sdlamp2-fsd.md

@@ -43,6 +43,11 @@ This document specifies the functional requirements for an SDL2 based media play
 
 ## 6. Changelog
 
+### 2026-02-13 — Embed controls spritesheet into binary
+
+- **Embedded asset**: `controls.png` is now compiled into the binary as a C byte array (`src/controls_png.h`), eliminating the requirement to run from the `build/` directory.
+- **External override**: If a `controls.png` file exists in the current working directory, it is loaded in preference to the embedded data, preserving the ability to use custom skins.
+
 ### 2026-02-11 — Debug flag for input diagnostics
 
 - **`--debug` flag**: New command-line option (`./sdlamp2 --debug [audio_dir]`) that enables verbose logging of all SDL input events to stdout. Designed to diagnose controller issues on retro handheld devices where non-standard controllers may not be recognized by SDL's GameController API.

src/sdlamp2.c

@@ -13,6 +13,8 @@
 #include "SDL.h"
 #include "SDL_image.h"
 
+#include "controls_png.h"
+
 #define MAX_FILES 64
 #define SEEK_SECONDS 10.0
 
@@ -626,6 +628,12 @@ int main(int argc, char** argv) {
   }
 
   SDL_Surface* controls_surface = IMG_Load("controls.png");
+  if (!controls_surface) {
+    SDL_RWops* rw = SDL_RWFromConstMem(controls_png_data, controls_png_size);
+    if (rw) {
+      controls_surface = IMG_Load_RW(rw, 1);
+    }
+  }
   if (!controls_surface) {
     panic_and_abort("Could not load controls asset!", SDL_GetError());
   }

tools/embed_png.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python3
+#
+# embed_png.py — Convert a PNG file into a C header with a byte array.
+#
+# Usage: ./tools/embed_png.py build/controls.png src/controls_png.h
+#
+
+import sys
+import os
+
+if len(sys.argv) != 3:
+    print(f"Usage: {sys.argv[0]} <input.png> <output.h>", file=sys.stderr)
+    sys.exit(1)
+
+input_path = sys.argv[1]
+output_path = sys.argv[2]
+
+data = open(input_path, "rb").read()
+
+with open(output_path, "w") as out:
+    out.write("/* Auto-generated from controls.png — do not edit */\n\n")
+    out.write("static const unsigned char controls_png_data[] = {\n")
+    for i in range(0, len(data), 16):
+        chunk = data[i : i + 16]
+        out.write("  " + ", ".join(f"0x{b:02x}" for b in chunk) + ",\n")
+    out.write("};\n\n")
+    out.write(f"static const unsigned int controls_png_size = {len(data)};\n")
+
+print(f"{input_path} -> {output_path} ({len(data)} bytes)")