Transparent Color in blitting with X11

[Peter Harris]

On 2010-07-28 05:44, Rashid wrote:
> but xlib doesnt support an alpha channel (and the freerunner has only 16
> bits per pixel). is there an easy way to do transparency (one
> transparent color is enough) with xlib or a toolkit which builds on it?

If you can easily extract that color into a 1-bit bitmap, you can use
XSetClipMask.

Many GPUs accelerate the RENDER extension, so you can use XRenderCompose
instead of XCopyArea to gain an alpha channel. (I'm not familiar with
your particular GPU).

If you want something higher level than Xlib, I hear good things about
Cairo - http://cairographics.org/ - but I haven't used it myself.

> Btw. im doing the double buffering in a very stupid way.
> 
> I write everything to a buffer and then copy the buffer to a window. Is
> there a faster and more clever way?

No. You just have to be careful; if your toolkit already does double
buffering, you'll wind up triple buffering.

Peter Harris
-- 
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