GTK progressbar call on XRenderComposite

[Huang, FrankR]

You know I want to know the use of alpha value for ARGB32 format picture? For example,
	RGB: 255,0,0
	ARGB: 100,255,0,0

What's the use of 100?

-----Original Message-----
From: xorg-devel-bounces+frankr.huang=amd.com at lists.x.org [mailto:xorg-devel-bounces+frankr.huang=amd.com at lists.x.org] On Behalf Of Huang, FrankR
Sent: 2010年5月29日 16:10
To: Jonathan Morton
Cc: xorg-devel at lists.x.org; gtk-list at gnome.org
Subject: RE: GTK progressbar call on XRenderComposite

Thanks.
Is there any difference in RGB24 and ARGB32 to display them on the screen without mask(mask=0)? The same? I gave a test, seems that for ARGB32 picture, I change the alpha value of it, no difference.

If CA is used for text rendering, I don't care that.




-----Original Message-----
From: Jonathan Morton [mailto:jonathan.morton at movial.com] 
Sent: 2010年5月28日 22:18
To: Huang, FrankR
Cc: xorg-devel at lists.x.org; gtk-list at gnome.org
Subject: RE: GTK progressbar call on XRenderComposite

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.

-- 
------
From: Jonathan Morton
      jonathan.morton at movial.com




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