[SDL] blitting and alpha blending

Kylotan kylotan at kylotan.eidosnet.co.uk
Sun Sep 22 15:44:00 PDT 2002

Mike Mullen wrote:
> I am probably way off on all this and would appreciate any thoughts
> the more knowledgable may have. Do I have to implement the pixel
> copies myself in order to blend the alpha channels from source and
> destination together? It's not a problem, I guess I just assumed that
> SDL would handle this kind of thing.

I think that, since most people only use the source alpha and not the
destination alpha, it makes sense to just copy the pixels across and
leave the destination alpha as it is. To do otherwise would incur a
performance penalty for the majority that don't care about destination
alpha. Perhaps there is some sort of SDL add-on library that will do
what you want though? Or use OpenGL directly - I assume it is much more
configurable with regards to alpha settings.


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