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View Full Version : Polygon Offset for Special use



Sheepie
04-21-2001, 03:08 PM
I thought I knew how to use glPolygonOffset properly, at least using it for outlining objects is easy, but now I am attempting something rather unusual.

I have a Model that has Glows. In D3D, the glows are zbiased towards the user before they are drawn the amount of the glows radius. In OpenGL, I have only been able to accomplish similar results by translating the glow. I tried using glPolygon Offset with my radius as the units and factor set to 0, but it doesn't come nearly as fas as a translate does. In fact, I usually need to multiply the radius by 1000 or so, before it looks equivalent.

I had read in some other posts that polygon offset and zbias do the same thing. If that is the case could someone please explain why it is that I need to use a vastly larger number? I have the redbook, and some other tutorials, but they don't talk about anything other than using it for outlining objects.

I hope someone has some suggestions. http://www.opengl.org/discussion_boards/ubb/smile.gif

ehart
04-21-2001, 05:02 PM
PolygonOffset is a slippery slope. The parameters you are adjusting can vary quite a bit between implementations. (and even on a single implementation based on depth buffer format)

I profess to be ignorant of the exact behavior of the depth offset in D3D, though you are correct that it does something similar.

You're best bet to provide repeatable behavior is to use tha app-based methods.