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sdl3-dos-port-pr

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This is the combined work of @icculus @madebr @glebm @jayschwa @ccawley2011 and me rounding it off with stability fixes and missing features, thanks to everyone for pitching in.

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This is a fairly complete port to DOS with only minor features like audio recording missing. I have tested it extensively with DevilutionX in DOSBox. But no real hardware testing. The features I didn't add is mostly because I didn't have a good way to test that they worked correctly.

For threading I took some conceptual inspiration from the PS2 port.

What's supported

  • Video: VGA and VESA 1.2+ framebuffer, RGB, and 8-bit indexed color with VGA DAC palette programming, hardware page-flipping with vsync, VBE state save/restore on exit
  • Audio: Sound Blaster 16 (16-bit stereo, up to 44.1 kHz), Sound Blaster Pro (8-bit stereo, up to 22 kHz), Sound Blaster 2.0/1.x (8-bit mono), all via IRQ-driven DMA with double-buffered auto-init
  • Input: PS/2 keyboard with extended scancodes (0xE0 prefix), INT 33h mouse with queried sensitivity, gameport joystick via BIOS INT 15h with auto-calibration
  • Threading: Cooperative scheduler using setjmp/longjmp with stack patching. Real mutexes, semaphores, TLS, and condition variables (generic fallback). Yield points in the event pump and delay functions keep audio and other threads responsive.
  • Timer: Native PIT-based timer using DJGPP's uclock() at ~1.19 MHz resolution
  • Filesystem: GetBasePath / GetPrefPath via DJGPP's searchpath(), POSIX filesystem ops fallback
  • Build: CMake cross-compilation toolchain file, DJGPP CI job, preseed cache for faster configure

What's NOT included

  • Audio recording playback only
  • SDL_TIME native implementation reuses Unix gettimeofday via DJGPP's POSIX layer (works fine)
  • Shared library loading support (no SDL_LoadObject).

How to build

cmake -S. -Bbuild-dos \
  -DCMAKE_TOOLCHAIN_FILE=build-scripts/i586-pc-msdosdjgpp.cmake \
  -DCMAKE_BUILD_TYPE=Release
cmake --build build-dos -j$(nproc)