Re: texture alpha: premultiplied or not?

[James W. <ja...@fr...>]

In parallel to this thread, I have been reading up on alpha compositing 
and premultiplied alpha, and I can see that it is reasonable to prefer 
premultiplied alpha.  It's still not completely clear how QuickDraw 3D 
handled alpha, but it does appear that the Interactive Renderer in Quesa 
assumes premultiplied alpha, and probably has always done so.

Here's what I've done:

* Changed the OpenGL renderer back to assuming premultiplied alpha.

* Added documentation about premultiplied alpha to TQ3PixelType in Quesa.h.

* Defined a new object property, 
kQ3RendererPropertyConvertToPremultipliedAlpha, which can be applied to 
the renderer object.  This causes a conversion to premultiplied alpha 
when the texture is loaded into OpenGL, and works on both Interactive 
and OpenGL renderers.
-- 
   James W. Walker, Innoventive Software LLC
   <http://www.frameforge3d.com/>