Re: [pygame] Using Numeric & Surfarray with alpha values

[Jasper <jasper@xxxxxxxx>]

Mike Rotondo wrote:

> We are writing a 2D particle engine and we would like to render each 
> particle with gradually decreasing alpha values. However, our original 
> image for the particles has per-pixel alpha, so we can't use 
> set-alpha. So, we are going to have to modify each pixel's alpha value 
> ith Numeric, it seems. 


IMHO you are approaching this problem from the wrong angle.  Instead 
either render the particles as an animation w/ decreasing alpha values 
(# frames = fade-time/frames-per-second), or better yet render with OpenGL.

If you render with openGL, alpha fade is easily done by sticking the 
particle image into a Texture, pasting that on a Quad, and varrying the 
alpha part of the quad's color with 
glColor4ub(255,255,255,desiredAlpha).  Decreasing "desiredAlpha" will 
fade a particle -- even if you're using per pixel alpha for the texture.

At least, this is what works for me.
-Jasper