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Simple DirectMedia Layer (SDL) sdl12-compat

https://www.libsdl.org/

This is the Simple DirectMedia Layer, a general API that provides low level access to audio, keyboard, mouse, joystick, 3D hardware via OpenGL, and 2D framebuffer across multiple platforms.

This code is a compatibility layer; it provides a binary and source compatible API for programs written against SDL 1.2, but it uses SDL 2.0 behind the scenes. If you are writing new code, please target SDL 2.0 directly and do not use this layer.

If you absolutely must have the real SDL 1.2 ("SDL 1.2 Classic"), please use the source tree at https://github.com/libsdl-org/SDL-1.2, which occasionally gets bug fixes but no formal release. But we strongly encourage you not to do that.

How to use:

  • Build the library. This will need access to SDL2's headers (v2.0.7 or newer), CMake and the build tools of your choice. Once built, you will have a drop-in replacement that can be used with any existing binary that relies on SDL 1.2. You can copy this library over the existing 1.2 build, or force it to take priority over a system copy with LD_LIBRARY_PATH, etc. At runtime, sdl12-compat needs to be able to find a copy of SDL2 (v2.0.7 or newer -- v2.0.12 or newer for Windows), so plan to include it with the library if necessary.

  • If you want to build an SDL 1.2 program from source code, we have included compatibility headers, so that sdl12-compat can completely replace SDL 1.2 at all points. These headers are just the bare minimum needed for source-level compatibility and don't have a lot of documentation or fanciness at all. The new headers are also under the zlib license. Note that sdl12-compat itself does not use these headers, so if you just want the library, you don't need them.

Building the library:

These are quick-start instructions; there isn't anything out of the ordinary here if you're used to using CMake.

You'll need to use CMake to build sdl12-compat. Download at cmake.org or install from your package manager (sudo apt-get install cmake on Ubuntu, etc).

Please refer to the CMake documentation for complete details, as platform and build tool details vary.

You'll need a copy of SDL 2.0.x to build sdl12-compat, because we need the SDL2 headers. You can build this from source or install from a package manager. Windows and Mac users can download prebuilt binaries from SDL's download page; make sure you get the "development libraries" and not "runtime binaries" there.

Linux users might need some packages from their Linux distribution. On Ubuntu, you might need to do:

sudo apt-get install build-essential cmake libsdl2-2.0-0 libsdl2-dev libgl-dev

Now just point CMake at sdl12-compat's directory. Here's a command-line example:

cd sdl12-compat
cmake -Bbuild -DCMAKE_BUILD_TYPE=Release .
cmake --build build

On Windows or macOS, you might prefer to use CMake's GUI, but it's the same idea: give it the directory where sdl12-compat is located, click "Configure," choose your favorite compiler, then click "Generate." Now you have project files! Click "Open Project" to launch your development environment. Then you can build however you like with Visual Studio, Xcode, etc.

If necessary, you might have to fill in the location of the SDL2 headers when using CMake. sdl12-compat does not need SDL2's library to build, just its headers (although it may complain about the missing library, you can ignore that). From the command line, add -DSDL2_INCLUDE_DIR=/path/to/SDL2/include, or find this in the CMake GUI and set it appropriately, click "Configure" again, and then "Generate."

When the build is complete, you'll have a shared library you can drop in as a replacement for an existing SDL 1.2 build. This will also build the original SDL 1.2 test apps, so you can verify the library is working.

Building for older CPU architectures on Linux:

There are a lot of binaries from many years ago that used SDL 1.2, which is to say they are for CPU architectures that are likely not your current system's.

If you want to build a 32-bit x86 library on an x86-64 Linux machine, for compatibility with older games, you should install some basic 32-bit development libraries for your distribution. On Ubuntu, this would be:

sudo apt-get install gcc-multilib libsdl2-dev:i386

...and then add -m32 to your build options:

cd sdl12-compat
cmake -Bbuild32 -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_FLAGS=-m32
cmake --build build32

Building for older CPU architectures on macOS:

macOS users can try adding -DCMAKE_OSX_ARCHITECTURES='arm64;x86_64' instead of -DCMAKE_C_FLAGS=-m32 to make a Universal Binary for both 64-bit Intel and Apple Silicon machines. If you have an older (or much older!) version of Xcode, you can try to build with "i386" or maybe even "powerpc" for 32-bit Intel or PowerPC systems, but Xcode (and macOS itself) has not supported either of these for quite some time, and you will likely struggle to get SDL2 to compile here in small ways, as well...but with some effort, it's maybe possible to run SDL2 and sdl12-compat on Apple's abandoned architectures.

Building for older CPU architectures on Windows:

Windows users just select a 32-bit version of Visual Studio when running CMake, when it asks you what compiler to target in the CMake GUI.

Configuration options:

sdl12-compat has a number of configuration options which can be used to work around issues with individual applications, or to better fit your system or preferences.

These options are all specified as environment variables, and can be set by running your application with them set on the command-line, for example:

SDL12COMPAT_HIGHDPI=1 SDL12COMPAT_OPENGL_SCALING=0 %command%

will run %command% with high-dpi monitor support enabled, but OpenGL scaling support disabled.

(While these environment variables are checked at various times throughout the lifetime of the app, sdl12-compat expects these to be set before the process starts and not change during the life of the process, and any places where changing it later might affect operation is purely accidental and might change. That is to say: don't write an SDL 1.2-based app with plans to tweak these values on the fly!)

The available options are:

  • SDL12COMPAT_DEBUG_LOGGING: (checked at startup) If enabled, print debugging messages to stderr. These messages are mostly useful to developers, or when trying to track down a specific bug.

  • SDL12COMPAT_FAKE_CDROM_PATH: (checked during SDL_Init) A path to a directory containing MP3 files (named trackXX.mp3, where XX is a two-digit track number) to be used by applications which play CD audio. Using an absolute path is recommended: relative paths are not guaranteed to work correctly.

  • SDL12COMPAT_OPENGL_SCALING: (checked during SDL_Init) Enables scaling of OpenGL applications to the current desktop resolution. If disabled, applications can change the real screen resolution. This option is enabled by default, but not all applications are compatible with it: try changing this if you can only see a black screen.

  • SDL12COMPAT_FIX_BORDERLESS_FS_WIN: (checked during SDL_SetVideoMode) Enables turning borderless windows at the desktop resolution into actual fullscreen windows (so they'll go into a separate space on macOS and properly hide dock windows on other desktop environments, etc). If disabled, applications may not get the full display to theirselves as they expect. This option is enabled by default, but this option is here so it can be manually disabled, in case this causes some negative result we haven't anticipated.

  • SDL12COMPAT_SCALE_METHOD: (checked during SDL_Init) Choose the scaling method used when applications render at a non-native resolution. The options are nearest, for nearest-neighbour sampling (more pixelated) and linear for bilinear sampling (blurrier).

  • SDL12COMPAT_HIGHDPI: (checked during SDL_SetVideoMode) Advertise the application as supporting high-DPI displays. Enabling this will usually result in sharper graphics, but on some applications text and other elements may become very small.

  • SDL12COMPAT_SYNC_TO_VBLANK: (checked during SDL_SetVideoMode) Force the application to sync (or not sync) to the vertical blanking interval (VSync). When enabled, this will cap the application's framerate to the screen's refresh rate (and may resolve issues with screen tearing).

  • SDL12COMPAT_USE_KEYBOARD_LAYOUT: (checked during SDL_Init) Make all keyboard input take the current keyboard layout into account. This may need to be disabled for applications which provide their own keyboard layout support, or if the position of the keys on the keyboard is more important than the character they produce. Note that text input (in most applications) will take the keyboard layout into account regardless of this option.

  • SDL12COMPAT_USE_GAME_CONTROLLERS: (checked during SDL_Init) Use SDL2's higher-level Game Controller API to expose joysticks instead of its lower-level joystick API. The benefit of this is that you can exert more control over arbitrary hardware (deadzones, button mapping, device name, etc), and button and axes layouts are consistent (what is physically located where an Xbox360's "A" button is will always be SDL 1.2 joystick button 0, "B" will be 1, etc). The downside is it might not expose all of a given piece of hardware's functionality, or simply not make sense in general...if you need to use a flight stick, for example, you should not use this hint. If there is no known game controller mapping for a joystick, and this hint is in use, it will not be listed as an availble device.

  • SDL12COMPAT_WINDOW_SCALING: (checked during SDL_SetVideoMode) When creating non-fullscreen, non-resizable windows, use this variable to size the window differently. If, for example, you have a 4K monitor and the game is running in a window the size of a postage stamp, you might set this to 2 to double the size of the window. Fractional values work, so "1.5" might be a more-pleasing value on your hardware. You can even shrink the window with values less than 1.0! When scaling a window like this, sdl12-compat will use all the usual scaling options (SDL12COMPAT_OPENGL_SCALING, SDL12COMPAT_SCALE_METHOD, etc). If sdl12-compat can't scale the contents of the window for various technical reasons, it will create the window at the originally-requested size. If this variable isn't specified, it defaults to 1.0 (no scaling).

  • SDL12COMPAT_MAX_VIDMODE: (checked during SDL_Init) This is a string in the form of WxH, where W is the maximum width and H is the maximum height (for example: 640x480). The list of valid resolutions that will be reported by SDL_ListModes and SDL_VideoModeOK will not include any dimensions that are wider or taller than these sizes. A size of zero will be ignored, so for 0x480 a resolution of 1920x480 would be accepted). If not specified, or set to 0x0, no resolution clamping is done. This is for old software-rendered games that might always choose the largest resolution offered, but never conceived of 4K displays. In these cases, it might be better for them to use a smaller resolution and let sdl12-compat scale their output up with the GPU.

  • SDL_MOUSE_RELATIVE_SCALING: (checked during SDL_SetVideoMode) If enabled, relative mouse motion is scaled when the application is running at a non-native resolution. This may be required with some applications which use their own mouse cursors. See also: https://wiki.libsdl.org/SDL_HINT_MOUSE_RELATIVE_SCALING

  • SDL12COMPAT_ALLOW_THREADED_DRAWS: (checked during SDL_Init) Enabled by default. If disabled, calls to SDL_UpdateRects() from non-main threads are converted into requests for the main thread to carry out the update later. The thread that called SDL_SetVideoMode() is treated as the main thread.

  • SDL12COMPAT_ALLOW_THREADED_PUMPS: (checked during SDL_Init) Enabled by default. If disabled, calls to SDL_PumpEvents() from non-main threads are completely ignored. The thread that called SDL_SetVideoMode() is treated as the main thread.

  • SDL12COMPAT_ALLOW_SYSWM: (checked during SDL_Init) Enabled by default. If disabled, SDL_SYSWMEVENT events will not be delivered to the app, and SDL_GetWMInfo() will fail; this is useful if you have a program that tries to access X11 directly through SDL's interfaces, but can survive without it, becoming compatible with, for example, Wayland, or perhaps just avoiding a bug in target-specific code. Note that sdl12-compat already disallows SysWM things unless SDL2 is using its "windows" or "x11" video backends, because SDL 1.2 didn't have wide support for its SysWM APIs outside of Windows and X11 anyhow.

  • SDL12COMPAT_NO_QUIT_VIDEO: (checked during SDL_QuitSubsystem) If enabled, SDL_Quit() and SDL_QuitSubsystem() will never shut down the video subsystem. This works around buggy applications which try to use the video subsystem after shutting it down.

Compatibility issues with OpenGL scaling

The OpenGL scaling feature of sdl12-compat allows applications which wish to run at a non-native screen resolution to do so without changing the system resolution. It does this by redirecting OpenGL rendering calls to a "fake" backbuffer which is scaled when rendering.

This works well for simple applications, but for more complicated applications which use Frame Buffer Objects, sdl12-compat needs to intercept and redirect some OpenGL calls. Applications which access these functions without going though SDL (even if via a library) may not successfully render anything, or may render incorrectly if OpenGL scaling is enabled.

In these cases, you can disable OpenGL scaling by setting the environment variable:

SDL12COMPAT_OPENGL_SCALING=0

Compatibility issues with applications directly accessing underlying APIs

Some applications combine the use of SDL with direct access to the underlying OS or window system. When running these applications on the same OS and SDL video driver (e.g. a program written for X11 on Linux is run on X11 on Linux), sdl12-compat is usually compatible.

However, if you wish to run an application on a different video driver, the application will be unable to access the underlying API it is expecting, and may fail. This often occurs trying to run applications written for X11 under Wayland, and particularly affects a number of popular OpenGL extension loaders.

In this case, the best workaround is to run under a compatibility layer like XWayland, and set the SDL_VIDEODRIVER environment variable to the driver the program is expecting:

SDL_VIDEODRIVER=x11