vo_opengl: refactor into vo_gpu

This is done in several steps:

1. refactor MPGLContext -> struct ra_ctx
2. move GL-specific stuff in vo_opengl into opengl/context.c
3. generalize context creation to support other APIs, and add --gpu-api
4. rename all of the --opengl- options that are no longer opengl-specific
5. move all of the stuff from opengl/* that isn't GL-specific into gpu/
   (note: opengl/gl_utils.h became opengl/utils.h)
6. rename vo_opengl to vo_gpu
7. to handle window screenshots, the short-term approach was to just add
   it to ra_swchain_fns. Long term (and for vulkan) this has to be moved to
   ra itself (and vo_gpu altered to compensate), but this was a stop-gap
   measure to prevent this commit from getting too big
8. move ra->fns->flush to ra_gl_ctx instead
9. some other minor changes that I've probably already forgotten

Note: This is one half of a major refactor, the other half of which is
provided by rossy's following commit. This commit enables support for
all linux platforms, while his version enables support for all non-linux
platforms.

Note 2: vo_opengl_cb.c also re-uses ra_gl_ctx so it benefits from the
--opengl- options like --opengl-early-flush, --opengl-finish etc. Should
be a strict superset of the old functionality.

Disclaimer: Since I have no way of compiling mpv on all platforms, some
of these ports were done blindly. Specifically, the blind ports included
context_mali_fbdev.c and context_rpi.c. Since they're both based on
egl_helpers, the port should have gone smoothly without any major
changes required. But if somebody complains about a compile error on
those platforms (assuming anybody actually uses them), you know where to
complain.

1 files changed, 9 insertions, 4 deletions

diff --git a/wscript b/wscript
index 9c4c823a08..a50dcfed69 100644
--- a/wscript
+++ b/wscript
@@ -783,15 +783,20 @@ video_output_features = [
         ),
     }, {
         'name': '--gl',
-        'desc': 'OpenGL video outputs',
+        'desc': 'OpenGL context support',
         'deps': 'gl-cocoa || gl-x11 || egl-x11 || egl-drm || '
                  + 'gl-win32 || gl-wayland || rpi || mali-fbdev || '
                  + 'plain-gl',
         'func': check_true,
+    }, {
+        'name': '--gpu',
+        'desc': 'GPU-accelerated video output support',
+        'deps': 'gl',
+        'func': check_true,
         'req': True,
-        'fmsg': "No OpenGL video output found or enabled. " +
-                "Aborting. If you really mean to compile without OpenGL " +
-                "video outputs use --disable-gl."
+        'fmsg': "No GPU context found or enabled. Aborting. " +
+                "If you really mean to compile without support for " +
+                "`--vo=gpu`, then use --disable-gpu."
     }, {
         'name': 'egl-helpers',
         'desc': 'EGL helper functions',