View Full Version : Cracks in shadow volume

03-30-2003, 09:43 AM
I'm working on implementing depth pass shadow volumes and I have come across a problem. I find the silhouette edges, of the shadow caster, seen from a given point in space and then extrude each edge as a quad to form the shadow volume. I use GL_QUADS to draw the quads but it results in visible cracks between adjacent quads. I do not understand this, since two quads which share an edge (in the shadow volume) have the same vertices, so how can the crack between them exist?

I was thinking that maybe it is necessary to draw the quads using GL_QUAD_STRIP to avoid the cracks, is this true? If so, I have to find "silhouette edge loops" and draw each loop as a quad strip. How can this be done efficiently, without doing several brute force passes on the silhouette edge list?

03-30-2003, 11:48 AM
There shouldn't be any cracks if the card obeys GL rules, but I think you do get cracks if polygon orientation is not the same for the 2 polygons sharing an edge.

I'm not sure about that part. Better check the spec.

I have also noticed some perculiar things on certain cards depending on the GL state