[Wayland-bugs] [Bug 103063] YUV I420 SHM broken with GStreamer/Weston

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103063

--- Comment #2 from Daniel Stone <daniel at fooishbar.org> ---
First, it would be interesting to validate how GStreamer is rendering the
buffer. It should be laid out, in order:
Y plane: offset == 0, stride == (width * 1), i.e. 1bpp, size == (stride *
height), i.e. full height
U plane: offset == size[Y], stride == (width/2 * 1), i.e. 1bpp but half width,
size == (stride * height/2), i.e. half height
V plane: offset == offset[U] + size[U], stride == (width/2 * 1), size ==
(stride * height/2), i.e. half width/height

If GStreamer is rendering correctly, this comes in to Weston at
libweston/gl-renderer.c's gl_renderer_attach_shm(). In the YUV420 case (aka
GStreamer's I420), this sets up the textures as described above. It then
uploads the content in gl_renderer_flush_damage(), where it uploads according
to the parameters set in attach_shm.

It looks from a quick inspection of the code that this is done correctly (i.e.
dividing by hsub/vsub to halve the dimensions of the U/V planes), but it would
be good to validate the parameters passed to glTex(Sub)Image2D() for the
upload, after validating GStreamer's buffer layout.

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