RE: GTK progressbar call on XRenderComposite

[Jonathan Morton <jonathan morton movial com>]

On Fri, 2010-05-28 at 15:34 +0800, Huang, FrankR wrote:
> I know if the source pict format is RGB24, the mask will do multiply
> each color. For example Red*alpha, Green*alpha, Blue*alpha. 
> If the source pict format is ARGB32, how the calculate comes on?

The same - the alpha channel and each colour channel are all multiplied
by the mask value.  (Remembering of course that 255 == 1.0, so the
values always go down or stay the same.)

In fact this is also what should happen in the RGB24 case, since in the
XRender pipeline, RGB24 is treated the same as ARGB32, with the alpha
channel implied to be 255.

> And what's the difference between Composite and CompositeCA?

CA stands for Component Alpha.  It's used for subpixel antialiasing,
which you might have heard described as "ClearType".

You should probably not try to accelerate Component Alpha directly until
you deeply understand the formulae involved.  EXA can convert common use
cases of Component Alpha into pairs of simpler operations.

-- 
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From: Jonathan Morton
      jonathan morton movial com