Perspective Shadow Maps Marc Stamminger REVES/INRIA, Sophia-Antipolis, France now at: Bauhaus-Universität, Weimar, Germany George Drettakis REVES/INRIA, Sophia-Antipolis, France

shadow maps n Williams, Siggraph ‘78 –render scene from light source –shadowing by depth comparison

shadow map aliasing n prone to aliasing when zooming into shadow boundaries single shadow map pixel

shadow map aliasing n perspective aliasing parallel light okayaliased okay

shadow map aliasing n perspective aliasing –smooth transition aliased oversampled

shadow map aliasing n projection aliasing parallel light

shadow map aliasing n projection aliasing –very local aliased oversampled

previous work n Reeves et al., Siggraph ’87: –“Percentage Closer Filtering” n Tadamura et al., Visual Computer ’01 –“Plural Sunlight Depth Buffers” n Fernando et al., Siggraph ’01: –“Adaptive Shadow Maps”

perspective transformation post-perspective world space

perspective shadow map n standard shadow map n perspective shadow map shadow map image

perspective shadow map n standard shadow map n perspective shadow map aliased oversampled

perspective shadow map n shadow map in post-perspective space n just another shadow map projection n reduces perspective aliasing n regeneration per frame necessary

light source transformation n parallel light becomes point light

parallel light transformation post-perspective world space

point light transformation post-perspective world space

discussion n best case: –parallel light in post-perspective space –no new perspective distortion post-perspective world space

discussion n non-optimal case: –point light close to frustum n worst case: –becomes uniform shadow map post-perspective world space

near plane selection n near plane as far as possible

near plane selection n automatic selection: reading back depth buffer

shadows from behind n virtually move camera backwards

shadow map window n geometric method to include all necessary objects –details in the paper

results

n first implementation on an Xbox game developer kit courtesy of Thatcher Ulrich

conclusion n perspective shadow maps –shadow map in post-perspective space –just another shadow map matrix –non-uniform shadow map resolution –needs recomputation per frame –minimal overhead for dynamic scenes

acknowledgements n Marie Curie Post-Doctoral Fellowship of the European Union n Bauhaus-Universität Weimar n Lutz Kettner ( n Frédo Durand

thank you