Martin Fiedler
To be precise, this is about *desktop OpenGL* on X11. For OpenGL ES, EGL is already used (as it's the only way to get an OpenGL ES context), as Sylvain noted above.
To shine some light on why this is needed:
In 99% of all cases, using GLX on X11 is fine, even though it's effectively deprecated in favor of EGL [1]. However, there's at least one use case that *requires* the OpenGL context being created with EGL instead of GLX, and that's DRM_PRIME interoperability: The function glEGLImageTargetTexture2DOES simply doesn't work with GLX. (Currently, Mesa actually crashes when trying that.)
Some example code:
https://gist.github.com/kajott/d1b29c613be30893c855621edd1f212e
Runs on Intel and open-source AMD drivers just fine (others unconfirmed), but with #define USE_EGL 0 (i.e. forcing it to GLX), it crashes. The same happens when using SDL for window and context creation.
The good news is that most of the pieces for EGL support on X11 are already in place: SDL_egl.c is pretty complete (and used for desktop OpenGL on Wayland, for example), and SDL_x11opengl.c has the aforementioned OpenGL-ES-on-EGL support. However, when it comes to desktop OpenGL, it's hardcoded to fall back to GLX.
I'm not advocating to make EGL the default for desktop OpenGL on X11; don't fix what ain't broken. But something like an SDL_HINT_VIDEO_X11_FORCE_EGL would be very appreciated to make use cases like the above work with SDL.
[1] source: Eric Anholt, major Linux graphics stack developer, 7 years ago already - see last paragraph of https://www.phoronix.com/scan.php?page=news_item&px=MTE3MTI
Luis Caceres
The current handling of Wayland mouse pointer events only handles wl_pointer.axis events, which, according to the Wayland documentation, deal with mouse wheel scroll events on a continuous scale. While this is reasonable for some input sources (e.g. touchpad two-finger scrolling), it is not for mouse wheel clicks which generate wl_pointer.axis events with large deltas.
This patch adds handling for wl_pointer.axis_discrete and wl_pointer.frame events and prefers to report SDL_MouseWheelEvent in discrete units if they are available. This means that for mouse wheel scrolling we count in clicks, but for touchpad two-finger scrolling we still use whatever units Wayland uses. This behaviour is closer to that of the X11 backend.
Since these events are only available since version 5 of the wl_seat interface, this patch also checks for this and falls back to the previous behaviour if its not available. I also had to add definitions for some of the pointer and keyboard events specified in versions 2-5 but these are just stubs and do nothing.
Sam Lantinga
Ryan C. Gordon
Sylvain Becker