Hi there,

So I'm trying to implement the ATI method of Parallax Occlusion Mapping. It all makes sense except for one slick part which I cannot understand. I've drawn a diagram to help myself understand what the variables are. Here it is:



The ray coming in diagnally is the view ray. So we basically do a linear search to find the point at which the boundary supertends the height. The D3D10 sample has a variable called fParallaxAmount. I've done some simplifying and canceling out and it turns out:

fParallaxAmount = (currBound * deltaHeight + currHeight * stepSize) / (stepSize + deltaHeight)

This is all dandy, but I can't just copy and paste it without understanding the theory behind it. I am tempted to solve a parametric system of equations that assumes the slope of the height map stays the same, but the code above seems to be either similar triangles or Green's Theorem. I can't figure out what it is. Does anyone have any insight into what it does? Note that (as far as I can tell) all values are along the vertical axis. Let me know if you have any input.

Thanks,

Mike

Yeah, I'm trying to make sense of it, but I think it's a rough estimate of where the intersection point should be. The equation gives you a point between currBound and currHeight. I'm going to try it on my own using this shortcut and also by intersecting the ray with a psuedo-slope from the heightmap and see which gives better results. Obviously, the D3D10 sample works and looks great so I'm hoping I end up with a result similar to it.

But yeah, currBound starts at 1.0 and moves toward 0.0. At the same time, the height sampling moves to the right. So it looks like if you're moving to the right, prevHeight will be lower than currHeight on a counter-relief extruded surface. Am I wrong? Maybe I'm looking at it wrong?

Mike

Haha, I hear you. Right now I'm trying to write a custom Maya export for "boxy models" where the corner normals are not shared. Wish me luck!