[PATCH] OpenGL: Speed up transfer of packed images to texture buffer

[Lawrence Rust <lvr@…>]

I have observed that OpenGL TV playback can consume large amounts of CPU time making it unrealistic for some systems.

Profiling playback shows that, for interlaced content, the main overhead is the function pack_yv12interlaced which takes around 23mS using MMX instructions on an Intel i5 661 @ 3.33GHz using onboard graphics with Linux 3.4 KMS. With other processing overheads the VideoLoop? exceeds 40mS causing frames to be dropped.

Further profiling shows that the main overhead is in writing to the texture buffer which is situated in graphics memory. This patch coalesces all writes to the texture buffer into one burst and reduces the time taken by pack_yv12interlaced to 12mS using MMX and 15mS without - a reduction of ~300%

Using this patch, playback of interlaced content is smooth and no frames are dropped.

[Lawrence Rust <lvr@…>]

In 10d5820665ca01ed04e520651bdad4eae80da34f/mythtv:

OpenGL: Optimize writing packed images to pixel buffer objects (PBO)

pack_yv12interlaced() packs pixels and writes them to an OpenGL
pixel buffer object. This buffer may reside on the graphics card
so writes may be slower than to RAM. Combining writes to the buffer
can improve performance by 200-300%.

This patch also provides optimized non-mmx code and also tightens
const correctness.

Fixes #10922

Signed-off-by: Lawrence Rust <lvr@…>
Signed-off-by: Jean-Yves Avenard <jyavenard@…>

[JYA]

I should add that I believe this could be optimised (mainly for DXVA and VAAPI) using the same USWC methods implemented in MythUSWCCopy class