Shadow Volumes Revisited
We present a method to utilize the Shadow Volume Algorithm
by Crow and Williams without using a stencil buffer. We show that the
shadow mask can be generated in the alpha channel or even in the
screen buffer, if a hardware accelerated stencil buffer is not
available. In comparison to the original stencil buffer method, a
small speed up can be achieved, if the shadow mask is computed in the
alpha buffer. The method using the screen buffer requires the scene to
be rendered a second time after the shadow mask has been
computed. Both methods are less restrictive with respect to hardware
requirements, since we use only standard color blending and depth
testing. In general, rasterization bandwidth is the main bottle neck
when generating the shadow mask at high screen resolutions. In order
to overcome this bottle neck we propose a way to compute the shadow
mask at a resolution that is lower than the resolution of the screen
buffer. Then the shadow mask is applied to the scene by utilizing
texture mapping. The latter method might be reasonable especially in
interactive entertainment, where rendering speed is traded in favour
of image quality.