I've implemented several volume rendering algorithms and am currently trying to implement Kruger and Westermanns multiple pass approach on the GPU.
I'm having trouble getting the early z test to work on GeForce 6 series.
Is it possible to use the easrly z test with EXT_framebuffer_object with a shared depth buffer amonst several textures?
Render front face of bounding box into a 2D texture (depth test Greater, clear 0)
// second pass
Render back face of bounding box into a 2D texture (depth test less, clear 1)
(this pass calculates ray direction and length using the first rendering target)
The result of rendering pass two is used in the rest of the algorithm which i have working apart from the early Z test. There is a main pass and an intermediate pass applied several times (to compute ray steps) the depth function is set before these passes to be Greater and 0
This i have to work, however im wandering if rendering the same geometry and altering the depth test is somehow disabling early Z ?
In the paper it suggests that depth function is always set to Greater.
If this does disable the depth test, how can I alter the bounding box geometry to render the back faces instead of the front faces?
Any help would be greatly appreciated!