docs: record the FFmpeg/SDL pixel-format naming trap in memory

2026-09-07 11:27:59 +02:00
parent 64ab9c5f74
commit dcbcde6410
1 changed files with 5 additions and 0 deletions
@@ -75,6 +75,11 @@ loopback validation pending. See bottom for the run commands.
  signaling/discovery). IPv4 only at the transport level for now.
 - Rendering: **SDL3** (`sdl3` pkg-config, 3.4 installed); plain texture
  upload, no GPU pipeline yet.
+- **Pixel-format convention trap**: FFmpeg names packed formats in memory
+  byte order (AV_PIX_FMT_RGBA = R,G,B,A in memory), but SDL names 32-bit
+  formats MSB-first (SDL_PIXELFORMAT_RGBA8888 = A,B,G,R in memory).
+  FFmpeg RGBA data therefore needs SDL_PIXELFORMAT_ABGR8888 — using
+  RGBA8888 paints the alpha byte as red (red-tinted image).
 - Discovery: mDNS/Avahi.
 - Namespace: `sc`.
 - Module error results use per-module `std::variant<T, XError>` types