[Pixman] sRGB scaling without alpha channel?

Claude Heiland-Allen claude at mathr.co.uk
Fri Mar 5 16:00:19 UTC 2021

Hi Søren,

On 04/03/2021 19:55, Søren Sandmann wrote:
> You are right that pixman doesn't have support for sRGB formats
> without an alpha channel. It would make sense to add such support (and
> it should be straightforward to do so).
Is there a guide for this kind of work?  For example a patch series 
wherein a similar format was added?  I could try to implement it, but 
I'm not familiar with pixman code.
> You might consider biting the bullet and just use an alpha channel.
> Usually a8r8g8b8 images are faster to work with than r8g8b8 anyway
> since they are aligned at 32 bits and tend to have more optimized fast
> paths available for them.
That is something to think about longer term for my project, but for the 
short term the only thing I'd need an alpha channel for would be this 
sRGB gamma-correct downscaling.  I'd rather spend my development time to 
try to contribute sRGB-without-alpha to pixman as I'm sure others would 
find it useful too.


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