Hello, I have a question about using alpha values. I have drawn many many triangles with varying alpha values and varying depths. To get the transparency effect I draw them in depth-sorted order. Now if I use glRotate to spin them around then I lose my transparency effect because I’m not drawing in depth-sorted order anymore. Is there a way to solve this, i.e. a way to rotate my object while maintaining transparencies?
Thanks in advance.
You’ll need to transform your polygons from model space to camera (or projection) space and sort them there. And yes, this is all done on the CPU. And yes, it’s not a great solution, but that’s pretty much all there is unless you’re willing to take a whole bunch of rendering passes (if you are, then Google for “depth peeling”, I think there’s a paper on nVidia’s dev website somewhere). The standard (and fast) solution is to transform and sort. Note: this only applies to alpha blended triangles, if your triangles are additive ( glBlend(GL_ONE,GL_ONE) ) then you can render them in any order.
Many thanks for your reply.
I’m using glBlendFunc(GL_SRC_ALPHA, GL_ONE) because it’s the one that’s giving me the kind of effect I’m looking for. I found that simply disabling depth testing altogether solved my problem. I think this works because ALL my triangles need to be translucent, and they’re also all the same color.