blending in three dimensions

All the 3 dim. examples that do blending use
the following for the glBlendFunc:
Why do they use the GL_ONE instead of

We just had a discussion touching that topic here:


If you examine the blending arithmetic you get using those blending factors, you see that the blend is nothing more than a simple sum. And since addition is commutative, meaning things can be added in any order, no sorting is necessary. If you wish to use complete alpha blending, this blending is not commutative, again check the math to prove it to yourself, you must draw the blended polygons from farthest to nearest to ensure things are drawn correctly. Unless you have a Geforce 3 or better, which does allow you to perform order independent alpha blending. NVIDIA has a article about this in their developer section.