HLSL Development Cookbook by unknow

Author:unknow
Language: eng
Format: epub
Publisher: Packt Publishing

During the lighting calculations for the pixel located at point P, we will need an estimate for the penumbra size. If you look at the right-hand side of the illustration, you will see a black triangle with the light source at its base and point P at its tip. By searching for blockers inside the triangle, we can decide how much of the light area is occluded from point P. In the illustration, the red line indicates the occluded portion and the green line indicates the lit portion. By dividing the size of the red line by the combined size of the green and red lines, we can get an estimate for how wide the penumbra is in that area. This step is called the blockers search.

Now that we have a way to decide how wide the penumbra is, we need a way to use this value when doing the actual shadow calculation. Fortunately, we already know that the penumbra size for PCF shadow mapping is defined by the amount and distance between the samples. We can now use the blocker's search step result to change the distance between the PCF samples, which will control the penumbra size. The more occluded area we find in the blockers search, the wider is the gap between the PCF samples.

As you can see from the implementation, PCSS works in three stages:

Search for blockers and early out if there are none

Find the penumbra size

Apply the PCF filter

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