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, 3 insertions, 3 deletions

diff --git a/DOCS/mplayer-changes.rst b/DOCS/mplayer-changes.rst
index 7c8ec50a90..66cacb3205 100644
--- a/DOCS/mplayer-changes.rst
+++ b/DOCS/mplayer-changes.rst
@@ -76,8 +76,8 @@ Video
 
 * Wayland support.
 * Native support for VAAPI and VDA. Improved VDPAU video output.
-* Improved OpenGL output (see the ``opengl-hq`` video output).
-* Make hardware decoding work with the ``opengl`` video output.
+* Improved GPU-accelerated video output (see the ``gpu-hq`` preset).
+* Make hardware decoding work with the ``gpu`` video output.
 * Support for libavfilter (for video->video and audio->audio). This allows
   using most of FFmpeg's filters, which improve greatly on the old MPlayer
   filters in features, performance, and correctness.
@@ -85,7 +85,7 @@ Video
   for BT.2020 (Ultra HD). linear XYZ (Digital Cinema) and SMPTE ST2084 (HDR)
   inputs.
 * Support for color managed displays, via ICC profiles.
-* High-quality image resamplers (see the ``opengl`` ``scale`` suboption).
+* High-quality image resamplers (see the ``--scale`` suboption).
 * Support for scaling in (sigmoidized) linear light.
 * Better subtitle rendering using libass by default.
 * Improvements when playing multiple files (``-fixed-vo`` is default, do not