Warping and Partitioning for Low Error Shadow Maps


When we compute the storage factor in the paper for the light behind the viewer, we ignore the near plane. This makes little difference when the depth ratio (f/n) is large. But after repeated z-partitioning, the depth ratio becomes much smaller and the near plane becomes significant. Figure 12 in the paper should actually look like this:

Storage factor vs. number of shadow maps

Note that for the light behind the viewer, the storage factor for z-partitioning with and without warping (ZP and ZP+W) initially decreases, but then begins to slowly grow. This is due to the fact that from this light direction there is significant overlap between the shadow maps.

There is a point at which face partitioning (FP+ZP+W) actually becomes better than z-partitioning. This figure shows where that crossover occurs for varying parameters:

f/n vs. number of shadow maps

Each region is labelled with the lowest error algorithm. Since we are looking for an algorithm that performs well at high depth ranges with just a few shadow maps, our recommendation to use z-partitioning with warping (ZP+W) does not change.

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