[cairo] transparency with alpha channel RGBA

M Joonas Pihlaja jpihlaja at cc.helsinki.fi
Thu Oct 29 03:28:58 PDT 2009

On Thu, 29 Oct 2009, uray meiviar wrote:

> currently I solved it by un-multiply the RGB value (divide RGB 
> values by A) on fragment shader, which is no significant penalty 
> since it was done on GPU, 

Ah, sounds good!

> but now my concern is the wasted CPU cycle 
> for RGB*A multiplication by Cairo (since CPU is far too slow 
> compared to GPU), is there any switch to turn off premultiplied RGB 
> process?

No, sorry.  I wouldn't worry about it though.



More information about the cairo mailing list