Paper

Abstract:
Soft shadow mapping is an attractive solution to the problem of real-time soft shadows because it works with any kind of rasterizable geometry (in particular alpha-transparent textures and hair), it does not require any precomputation, and it is simple to implement on the GPU. However, state-of-the-art approaches have several limitations that prevent them from being practical for all scenes. First, parameter tuning is required to avoid surface acne. Second, gaps between shadow map pixels are either ignored which results in light bleeding, or handled using gap filling which results in overshadowing. We present a more robust soft shadow mapping algorithm based on depth peeling that addresses the problems of surfaces acne and light bleeding. Our algorithm uses a multi-layer shadow map to handle light bleeding, and midpoint shadow maps to handle self-shadowing without parameters. It provides high-quality soft shadowing for complex scenes while still maintaining interactive rendering rates. Source code is available online.

"Robust Soft Shadow Mapping with Backprojection and Depth Peeling", Louis Bavoil, Steven P. Callahan, Claudio T. Silva, Journal of Graphics Tools; 13(1), 2008. (pdf) (webpage)

Demo

Here is a demo for GeForce 6 and above. The demo includes a simple test scene with three quads. The Cg code of the shaders is available in the shaders subdirectory. The number of layers used by the shadowing shader can be changed in shaders/config.h.

• Drag the mouse left/middle/right buttons to move the camera
• "+/-" to increase/decrease the maximum number of samples per pixel
• "r" reload the shadow shader

Related Projects

Real-Time, All-Frequency Shadows in Dynamic Scenes, Real-Time, All-Frequency Shadows in Dynamic Scenes, Annen et al., SIGGRAPH 2008
Soft Shadows by Ray Tracing Multilayer Transparent Shadow Maps, Xie, Tabellion, Pearce, EGSR 2007
Bitmask Soft Shadows, Schwarz, Stamminger, Eurographics 2007
High-Quality Adaptive Soft Shadow Mapping, Guennebaud, Barthe, Paulin, Eurographics 2007
Real-time Soft Shadow Mapping by Backprojection, Guennebaud, Barthe, Paulin, EGSR 2006
Soft Shadow Maps: Efficient Sampling of Light Source Visibility, Atty et al., Computer Graphics Forum 2006
Plausible Image Based Soft Shadows Using Occlusion Textures, Eisemann, Decoret, SIBGRAPI 2006
A Method to Generate Soft Shadows Using a Layered Depth Image and Warping, Im, Han, Kim, TVCG 2005
Percentage Closer Soft Shadows (PCSS), Randy Fernando, SIGGRAPH 2005