As defined in the ARB_multisample OpenGL extension (available at
http://oss.sgi.com/projects/ogl-sample/registry/ARB/multisample.txt), in
order to turn on multisampling (aka full screen anti-aliasing) on X11
you must pass in GLX_SAMPLE_BUFFERS_ARB and GL_SAMPLES_ARB to
glXChooseVisual(). This patch adds some new SDL_GLattr tokens for those
two OpenGL constants so you can call SDL_SetAttribute
(SDL_GL_SAMPLE_BUFFERS_SIZE, value) and
SDL_SetAttribute(SDL_GL_SAMPLES_SIZE, value) to turn on support for
multisampling on the requested glx visual. As it is in the current SDL
code, you cannot turn on anti-aliasing from within the application.
Notes:
- SDL_GL_SAMPLE_BUFFERS_SIZE and SDL_GL_SAMPLES_SIZE might be poor
names. Feel free to rename them. - The multisampling extension was added to OpenGL 1.4. It seems they
renamed the constants to drop the _ARB naming scheme, but it also seems
that the _ARB names were kept for backward compatibility. Since the
_ARB version also works with OpenGL versions prior to 1.4, I choose to
use those. - Since SDL tries to make things as easy as possible, you might want to
consider only exposing the SDL_GL_SAMPLES_SIZE constant for this, and
toggling GLX_SAMPLE_BUFFERS_ARB to 1 if GLX_SAMPLES_ARB is set to be
higher than 1. - This does not add support for multisampling to any other
implementation other than the glX drivers. My apologies for this.
Jon
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