CC Shadow Volumes

Brandon Lloyd, Jeremy Wendt, Naga Govindaraju, Dinesh Manocha
University of North Carolina at Chapel Hill

These images demonstrate the benefits of CC shadow volumes on a scene with 96K polygons. Shadow volumes are shown in transparent yellow. Standard shadow volumes shown in the left image result in an enormous amount of useless overdraw. CC shadow volumes in the middle are rendered only in shadowed regions. The right image shows final rendered image. CC shadow volumes generate up to 7 times less fill than standard shadow volumes in this scene.


We present a technique that uses culling and clamping (CC) for accelerating the performance of stencil-based shadow volume computation. Our algorithm reduces the fill requirements and rasterization cost of shadow volumes by reducing unnecessary rendering. A culling step removes shadow volumes that are themselves in shadow or do not contribute to the final image. Our novel clamping algorithms restrict shadow volumes to those regions actually containing shadow receivers. In this way, we avoid rasterizing shadow volumes over large regions of empty space. We utilize temporal coherence between successive frames to speed up clamping computations. Even with fairly coarse clamping we obtain substantial reduction in fill requirements and shadow rendering time in dynamic environments composed of up to a 100K triangles.

Paper  (PDF).


Video 512x384 37 MB

Click on any of the following images to enlarge:

Scene 1

Standard shadow volumes

Continuous clamping

Discrete clamping

Scene 2

Standard shadow volumes

Culling only

Culling + clamping