Hi!

I have some problems in blending when I blit an ARGB surface with 8 bit
alpha channel used (eg. from png file) onto another ARGB surface (for
eg. solid, full opaque rectangle drawn).

I use only DSBLIT_BLEND_ALPHACHANNEL flag on both surfaces, no SrcBlend
Function neither
DstBlend or PorterDuff.

The problem is that after blitting the source image surface to the
destination surface with the rectangle, the final image looks following:

if src_alpha==0 : final_alpha=dest_alpha / no problem
if src_alpha>0  : final_alpha is (seems to be) src_alpha

The effect is that when I blit alphachanneled source to full opaque
destination, final composition is not opaque in spaces, where source
alpha was greater than 0 (So the background I have below the destination
surface, is unfortunately visible)

I thought that in blitting operation, final_alpha should be dest_alpha,
so source surface is drawn onto dest_surface, and gets destination alpha
channel, not source!

I tested various Blitting& blending flags, and I still don't know where
the problem lies.

What flags should I use or maybe the cause of problem is different ?

Thanks in advance!

Michal Lebik
mailto:[EMAIL PROTECTED]
http://www.adescom.pl

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