a8ecd677ed
* dos: Some initial work. * dos: Turn off buffer on stdio SDL_IOStreams. Seeking breaks otherwise. We might be able to just fflush() before or seeking instead? * dos: Audio implementation using the Sound Blaster 16. * dos: remove audio Pump interface. Turns out DosBox-X was having trouble with the Sound Blaster or something; standard DosBox works correctly directly from the interrupt handler, and without doubling the buffer size. * dos: just dump and restore the stdio buffer when seeking. This is MUCH faster than just leaving buffering disabled, and also works around getting bogus reads after an fseek. SDL_LoadWAV on test/sample.wav no longer takes several seconds to finish, and comes up with the correct data. I wonder if we're triggering this in LoadWAV because we're malloc'ing data between seeks/reads, and it's causing the djgpp transfer buffer to change. Or maybe the Fat DS trick is confusing it? I don't know, I haven't had time to debug it, it might just be a legit libc bug in djgpp too, for all I know. * dos: Protect audio device "thread" iterations when streams are locked. This uses an old trick we used in SDL 1.2 for MacOS Classic, which did its audio callback in a hardware interrupt. If the audio is locked when the interrupt fires, make a note of it and return immediately. When the lock is released, if the interrupt has been fired, run the audio device iteration right then. Since there isn't a big device lock in SDL3 (available to the app, at least), this keeps a counter of when any SDL_AudioStream is locked, which is probably good enough. * dos: Implemented initial video subsystem. This uses VESA interfaces to manage the display and works with the software renderer. Events aren't hooked up yet, so prepare to close DosBox on each run. :) * dos: Whoops, forgot to add these to revision control. Core and Main support. * dos: Wired up basic filesystem support. This gets most of the rendering examples, which use SDL_GetBasePath() to find textures to load, working. * dos: Fixed compiler warning. * dos: Initial mouse support! * dos: Move interrupt hooking code into core/dos. * dos: Initial keyboard support! * dos: Use a simple ring buffer for keyboard events. Of course Quake 1 solved this better, haha. It's smart: less memory, dirt simple, and you don't even have to worry about synchronizing with the interrupt handler, because it's safe for both sides no matter when an interrupt fires. * ci: add djgpp job [sdl-ci-filter djgpp] [sdl-ci-artifacts] * dos: Fix build issues after rebase onto current main - SDL_runapp.c: Add SDL_PLATFORM_DOS to the exclusion list so the generic SDL_RunApp() is disabled when the DOS-specific one is compiled. - SDL.c: Exclude SDL_Gtk_Quit() on DOS. DJGPP defines __unix__ which sets SDL_PLATFORM_UNIX, but DOS has no GTK/display server. The GTK source is not compiled (CMake UNIX is false for DOS) so this was a link error. - sdlplatform.cmake: Add DOS case to SDL_DetectCMakePlatform so the platform is properly detected from CMAKE_SYSTEM_NAME=DOS. - i586-pc-msdosdjgpp.cmake: Add i386-pc-msdosdjgpp-gcc as a fallback compiler name, since some DJGPP toolchain builds use the i386 prefix. * Add 8-bit palette support to DOS VESA driver * Add VBE page-flipping, state restore, and robust keyboard handling - Implement double-buffered page-flipping for VBE modes with >1 image page - Save and restore full VBE state on video init/quit for clean mode switching - Improve DOS keyboard handling: support extended scancodes and Pause key - Lock ISR code/data to prevent page faults during interrupts - Always vsync when blitting in single-buffered modes to reduce tearing * Refactor Sound Blaster audio mixing to main loop Move audio mixing out of IRQ handler to main loop for improved stability and to avoid reentrancy issues. Add SDL_DOS_PumpAudio function, update DMA buffer handling, and adjust sample rate to 22050 Hz. Silence stale DMA buffer halves to prevent stutter during load. * Add DOS timer support and update build config * Add support for pre-SB16 8-bit mono Sound Blaster audio Detect SB version and select 8-bit mono or 16-bit stereo mode. Handle DMA and DSP setup for both SB16 and pre-SB16 hardware. Add FORCE_SB_8BIT option for testing in DOSBox. * Add SB Pro stereo support and simplify IRQ handler * Add DOS joystick driver support * Improve DOS hardware handling and clarify memory allocation - Poll Sound Blaster DSP status instead of fixed delay after speaker-on - Clarify DPMI conventional memory is always locked; update comments - Document and justify DMA memory allocation strategy - Free IRET wrapper after restoring interrupt vector to avoid leaks - Throttle joystick axis polling to ~60 Hz to reduce BIOS timing loop cost - Always poll joystick buttons directly for responsiveness * Query and use mouse sensitivity from INT 33h function 0x1B * Add support for VESA banked framebuffer modes Implement banked framebuffer access for VBE 1.2+ modes without LFB. Detect and initialize banked modes, copy framebuffer data using bank switching, and blank the framebuffer on mode set. Page-flipping is disabled in banked mode. * Add optional vsync to page flipping in DOS VESA driver * Add cooperative threading support for DOS platform * Move SoundBlaster audio mixing to SDL audio thread * Fix DOS platform comments and workarounds for DJGPP support * Fix SoundBlaster IRQ handling and DMA setup for DOS - Pass IRQ number to DOS_EndOfInterrupt and handle slave PIC EOI - Validate DMA channel from BLASTER variable - Correct DMA page register selection for SB16 - Improve BLASTER variable parsing and error messages - Unmask/mask IRQs on correct PIC in DOS_HookInterrupt - Rename SDL_dosjoystick.c to SDL_sysjoystick.c - Include SDL_main_callbacks.h in SDL_sysmain_runapp.c - Add include guard to SDL_systhread_c.h * Add DOS platform options and preseed cache for DJGPP Disable unsupported SDL features when building for DOS. Add PreseedDOSCache.cmake to pre-populate CMake cache variables for DJGPP. * cmake: use a 8.3 naming scheme for tests on DOS * Apply code style * Update include/SDL3/SDL_platform_defines.h Co-authored-by: Anonymous Maarten <madebr@users.noreply.github.com> * Code review clean up - Split DOS VESA mode-setting into its own file - Replace magic numbers with named constants - Update copyright dates to 2026 - Substract time taken by other threads form delays * Fix DOS bugs and improve compatibility - Disable fseeko64 for DJGPP due to broken implementation - Refactor DOS timer delay to always yield and avoid busy-waiting - Fix animated cursor rendering in DOS VESA backend - Always set display mode when creating DOS VESA window - Work around DJGPP allowing invalid file access in testfile.c - Bump max threads to 16 - Apply workarounds for threading tests * Add DOS platform documentation and fix a few issues - Fix fullscreen default resolution - Improve best mode matching - Fix builds on GCC older than 7.0 - Fix text input events * Fix keyboard mapping of "*" * Fix running, and existing, under PCem * Apply suggestions from code review Co-authored-by: Cameron Cawley <ccawley2011@gmail.com> * Pre-mix audio in ring buffer and copy to DMA via IRQ thread * Video fixes and optimizations * DOS: Fix Intel 740 and VGA compatability * DOS: Update readme * DOS: Fix thread ID, get GPU name * DOS: Cap mouse range * DOS: Map test resources to 8.3 names * DOS: Skip unsupported WM color modes * Fix "windowed" resolution selection * DOS: Hide INDEX8 modes behind SDL_DOS_ALLOW_INDEX8_MODES * Remove SDL_HINT_DOS_ALLOW_INDEX8_MODES and order modes logically * Don't convert cursor if dest is not INDEX8 --------- Co-authored-by: Ryan C. Gordon <icculus@icculus.org> Co-authored-by: Anonymous Maarten <anonymous.maarten@gmail.com> Co-authored-by: Cameron Cawley <ccawley2011@gmail.com> Co-authored-by: Gleb Mazovetskiy <glex.spb@gmail.com> Co-authored-by: Jay Petacat <jay@jayschwa.net> Tested-by: Cameron Cawley <ccawley2011@gmail.com>
4.9 KiB
DOS
SDL port for MS-DOS using the DJGPP GCC cross-compiler.
Building
To build for DOS, make sure you have a DJGPP cross-compiler in your PATH and run:
cmake -S. -Bbuild -DCMAKE_TOOLCHAIN_FILE=build-scripts/i586-pc-msdosdjgpp.cmake -DCMAKE_BUILD_TYPE=Release
cmake --build build
The toolchain file looks for i586-pc-msdosdjgpp-gcc or i386-pc-msdosdjgpp-gcc in PATH.
Running
DOS executables require a DPMI host. Place CWSDPMI.EXE next to your executable.
To run in DOSBox:
dosbox myapp.exe
System Requirements
| Component | Minimum |
|---|---|
| CPU | i386 or higher |
| RAM | 4 MB |
| Video | VGA (256-color mode 13h) |
| Audio | Sound Blaster |
| DPMI | CWSDPMI.exe or compatible host |
Higher resolutions (640×480 and above) require a VESA VBE 1.2+ compatible video card.
Notes
Memory Model
The DOS port produces 32-bit protected-mode DPMI executables. It uses the "fat DS" nearptr trick (__djgpp_nearptr_enable()) to convert physical addresses to usable C pointers. This allows direct access to the VESA linear framebuffer and DMA buffers from C code without segment descriptor manipulation.
SDL on DOS requires the fat DS trick. SDL_RunApp() enables it automatically via SDL_main.h. If you define SDL_MAIN_HANDLED, you must call __djgpp_nearptr_enable() yourself before initializing SDL, or video initialization will fail with a clear error message.
Threading
DOS has no OS-level threads. SDL on DOS implements cooperative threading via a mini-scheduler that uses setjmp/longjmp for context switching. Threads are never preempted mid-instruction. Context switches occur only at explicit yield points such as SDL_Delay and the event pump, so make sure your main loop calls SDL_PumpEvents or SDL_Delay regularly. SDL_Delay(0) yields to other threads without sleeping and is safe to call in tight loops. In some cases, like a load screen, a longer delay (e.g. SDL_Delay(16)) may be needed to give background threads enough CPU time.
Video
The video driver supports VGA mode 13h (320×200×256) on any VGA card, and higher resolutions via VESA BIOS Extensions (VBE 1.2+). Both linear framebuffer (VBE 2.0+) and banked framebuffer modes are supported. Hardware page-flipping is used for tear-free rendering when available.
Only software rendering is supported. There is no GPU renderer.
All video modes are effectively fullscreen. When creating a window, the driver selects the closest available video mode to the requested size.
8-bit indexed color (INDEX8) modes with programmable VGA DAC palettes are supported but will only be used when explicitly requested via the SDL_PIXELFORMAT window creation property.
EGA and CGA cards are not supported. The driver detects VGA hardware at initialization and will fail with a clear error message if VGA is not present.
Direct Framebuffer Hint
Setting SDL_HINT_DOS_ALLOW_DIRECT_FRAMEBUFFER to "1" before calling SDL_GetWindowSurface() enables a fast path that skips the normal surface copy. SDL_UpdateWindowSurface() copies the system-RAM surface directly to VRAM via dosmemput and only programs the VGA DAC palette when it changes. Page flipping is done without waiting for vblank. No software cursor compositing is performed.
This mode is designed for applications like Quake that manage their own rendering and want maximum frame throughput. The trade-offs are:
- No vsync. Tearing is expected.
- No software cursor. The application must draw its own cursor if needed.
- Reading back the surface may be slow on real hardware (uncached VRAM).
The hint must be set before the first call to SDL_GetWindowSurface(). Changing it after that has no effect.
Audio
Sound Blaster support is available for SB16 (16-bit stereo), SB Pro (8-bit stereo), and SB 2.0/1.x (8-bit mono). Configured automatically from the BLASTER environment variable.
A ring buffer sits between the SDL audio pipeline and the DMA hardware. The audio thread fills the ring buffer cooperatively, and the Sound Blaster IRQ handler copies data from the ring buffer to the DMA buffer directly. This gives roughly 45 ms of cushion before audio would stutter. If your game runs at 22 fps or above, audio will be glitch-free with no extra effort. Below 20 fps, adding a SDL_Delay(0) in the middle of your game loop should be enough to keep the ring buffer fed.
Audio recording is not implemented.
Input
- Keyboard: IRQ1-driven with full extended scancode (0xE0 prefix) support.
- Mouse: INT 33h mouse driver with relative motion via mickeys.
- Joystick: gameport joystick via BIOS INT 15h (axes) and direct port 0x201 reads (buttons) with software calibration.
Limitations
- No shared library / dynamic loading support (no
SDL_LoadObject). DXE support may be added in the future.