So I need an alpha channel. My question is, how exactly do I convert the black areas of the picture to an alpha of 0? What should the blending mode be? Is it better to use a sprite than a billboard?
If it's a static image, you'd be best off editing it to have an alpha channel, and then setting the alpha appropriately. That's beyond the scope of this reply, of course :)
Next best, you're gonna have to filter the image -- you want blend mode to be Over (so that alpha is honoured), and you need to generate the alpha data.
To generate the alpha data, you'll want to whip up a core image filter, like this:
kernel vec4 darkToTransparent(sampler image)
{
vec4 color = sample(image, samplerCoord(image));
color.a = (color.r+color.g+color.b) > 0.005 ? 1.0:0.;
return color;
}
the 0.005 is the cutoff -- depending on your hardware, image, and
color depth, you may need to set this higher to properly cut out the
black parts.
Hope that helps -- there's probably a better way out there, but this should get you started at least.
-- [ christopher wright ] [EMAIL PROTECTED] http://kineme.net/
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