Re: [pygame] Setting alpha with a blit?

[Pete Shinners <pete@shinners.org>]

Jasper Phillips wrote:
> I have a surface to which I want to add hex shaped transparent holes, with
> the aim of creating a "frame" that I can blit onto a hex map to mask
> anything outside the hexes.
>
> Is there some api or trick for doing this?
The only tricky way to do this is with colorkeys. If you have a two 
color image, you set the colorkey to the 'interior' color and blit that 
on top of the image to mask. Then on that image you set the colorkey to 
the remaining color.

This works pretty well actually, as long as you don't need antialiasing 
 or semitransparent pixels. If you want to control true alpha 
transparency, you'll probably want to use the surfarray to manually 
control the pixel values. Of course, loading the alpha on from a file is 
a good idea too.

For examples of the colorkey masking, see some of the old Font Contest 
entries, where Font.render() is used to create masks on some sort of 
pattern.

http://www.pygame.org/pcr/progress_text/index.php
http://www.pygame.org/pcr/static_text/index.php