Hello, I'm trying to implement Lispsm for shadow mapping. It seems to solve perspective aliasing but, at certain angles of light and triangles, appears something strange that I don't understand. What kind of error could be? As you see on the face of the small parallelepiped there is a jagged edge of shadow. http://images3.fotoalbum.alice.it/v/www1-3//247/24783/261420/error-or.jpg Here we have a window of 1024*768 and a shadow map of 1024*1024 in 16 bit integer. If you need some more information please ask me, any idea is well accepted, please answer to this post. Thanks in advance Emanuele

This is a common issue with shadow maps. You need to use a bias value (ie mulitply one of the values in the shadow comparison by a like 1.001)... also use a higher precision render target... most shadow map implementations use floating point textures, not integers.

Dependent on which API and hardware you are using you could add the bias implicitly with render states.

Yes, I suppose you're right, my experiments demonstrate it clearly.
I will probably try to use cascaded shadow maps, but I did not understand exactly how they work, please correct me if I miss something:

first of all: do I have to divide the depth by the homogeneous coordinate? always? with lispsm too?

now about the cascaded shadow:

1. you divide the frustum in some slices ( e.g. 4 )
2. calculate the light space bounding box of each frustum;
3. calculate 4 view projection matrices for the 4 frusta; the projection is orthographic
4. now you should draw 4 shadow maps, correct? can't you draw a single shadow map writing the slice depth in the color channels? e.g. the first depth in red, the second slice in green etc... ?
5. reuse the 4 shadow maps to estimate the shadowing coefficient... but how? what is the depth to be compared with? here is my confusion...

Thanks
Emanuele