Depth Map Shadows

[newyorkjihen]

Another noob question. A depth map shadow is creating light where it shouldn't (at least where I don't want it). This is a simple test case:

Create a poly cube, width 3, height 6, depth 3. Delete the top face.
Create an identical poly cube (but don't delete the top face). Move it up in the y-axis 3.
Now scale the top face in x & z, so the second cube looks like a pyramid (or a ziggurat shape because the top is still flat).
Add lambert material to both.
Create a spotlight. Move it away an arbitrary distance in the z-axis, so it is pointing at the objects.
Turn on depth map shadows for the spotlight.
Render from top view.

A shadow appears on the pyramid exactly as I would expect, except the very base of the pyramid is lit! There is a thin band of light at the very bottom, where I don't think it should be. I've tested for various settings of resolution, filter size, and bias. I've also tried shrinking the pyramid a bit. Why is there light poking though ?!

[joojaa]

yes its the mid distanc e map style thats doing you a trick here. (by the way mid distance shadow is also known as woo trick), what hapens is tha far corner comes very close to the next sample casusing the linitted sample amount to see the opposite corner.

Adjust the dmap bias. Or turn the object one sided.

[newyorkjihen]

Thank you for replying, Joojaa. I can't get it to work! But at least I have a better understanding of what is going on.

If by make it single sided you mean uncheck "double sided" in the shadow caster's render stats, then that didn't help. And unfortunately, the shadow caster has a double sided texture that I want to render, so I can't go that route anyway.

And the dmap bias, I've nudged it both ways with no success. I've tried negative dmap values. I've tried unchecking "use mid distance". Nothing works.

Now I'm trying raytraced shadows. I've gotten it to work (sort of) in my simple test case only. But it introduces new problems that I don't understand yet. And for some reason I can't get it to work in the real version.

This page helped me out earlier, with some depth map issues:
http://www.halbstein.com/tutorials.htm

Does anyone know of any tutorials that cover this issue?

[newyorkjihen]

I know I'm the king of replying to my own posts, but I just found this:

http://www.highend3d.com/maya/tutorials/re...haders/175.html

I hope it helps.

[joojaa]

Well truthfully speaking if your using double sided materials for stuff yoru cheating and deserve all the pains in th world anyways

Its just that to get realworld effects you need real world geometry NAd a twosided polygon surface would be something you cant do in reality because it would simulate a unlimittedly thin film and light dont react with unlimitedly thin things.

[newyorkjihen]

You're right. I've given up on the double sided material.

I couldn't get the depth map to work. For some reason, the filtering of the shadows would blur up from the bottom of the object, exposing light no matter what I set for the bias.

And I don't know enough about raytracing to get the shadows to look nice.

So I'm instead I'm going to just use cubes with useBackground as the material, and boolean subtract holes for the computer keys to fit into. I still might "cheat" and have an infinitely thin material for the inside of the holes. Ideally I'd like to figure out how to apply different materials to different sections of the same polygon, but even if that's possible it's too advanced for me now.

I keep starting over from scratch as I'm learning. Like, before I was actually creating real duplicates, but now I want to make instances instead so it will be easier to make changes throughout.

And I still have a huge task of figuring out how to handle anti-aliasing. But that is for another day.

I really appreciate all of your comments, Joojaa. I'm grateful that someone who knows what they're doing is willing to waste their time... err... I mean impart their knowledge... helping out new users. Thanks again.

[newyorkjihen]

Assign material to selection ?!

What ?!

That solved all my problems. Seriously. No more double sided texture. No more shadow problems.