View Full Version : Question regarding shaders and shadow volumes

03-14-2007, 06:03 PM
Hey guys,

I have a question regarding shadowing and shaders.

I have an application which renders streetlamps and projects a spotlight into the scene onto my flat plane ground and onto the sides of houses.

To do this I first of all filter out which polygons are visible to each streetlamp in its spotlights' immediate area of influencem then I pass those polygons to my cg shader which does the spotlight calculations. Now, because i dont yet have shadowing the ground is also lit underneath the house which of course shouldn't be happening.

I want to implement shadows and have had some problem with shadow mapping already, and also because I already have sorted out the polygons visible to the light, I thought I should try shadow volumes as I can simply extrude out past the polygons visible to the light.

However one part of the problem is confusing me and I want to clarify it before i start coding it.

If i set up the shadow volume, how will my cg shader be able to perform the relevant stencil tests? i'm sorry if the question is a little vague but i'm really confused on how I'll do the actual testing against the stencil buffer in my shader.

Can anyone assist me please?


03-15-2007, 11:03 AM
The stencil test wouldn't be done in a shader. The stencil will be executed before the shader runs (early out)