surface buffer cardinality and outputs

[Daniel Stone]

Hi,

On 18 March 2013 02:55, Sylvain BERTRAND <sylware at legeek.net> wrote:

> Another though which targets sub-surface interfaces: are the
> hardware overlays for YUV buffers that more energy efficient than
> GPU scaling/color space conversion since most the energy would be
> burned into the video decoding anyway?


Yes, much.  In a real-life usetime test on a mobile product I worked on, we
were able to see a 20% difference between GPU and overlay usage.  Also, the
overlays have much better colourspace conversion, and _much_ better
filtering, especially for scaling.  Often you can only import YUV textures
as TEXTURE_EXTERNAL in GL, which only gives you linear or nearest filters.
 The difference in final image quality is huge.

The other benefit is that the overlay scales as scanout occurs.  By
contrast, using the GPU implies writing out the post-scaled texture every
frame.  For higher resolutions, this can push you over your memory
bandwidth and make you start to drop frames.

There was a brief fad amongst desktop GPU manufacturers several years ago
where they tried to drop overlays in favour of shaders - they all brought
them back by the next generation.

Cheers,
Daniel
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