shadow_sampling.wgsl

Do the lookup, using HW 2x2 PCF and comparison

Does a single sample of the blocker search, a part of the PCSS algorithm. This is the variant used for directional lights.

https://web.archive.org/web/20230210095515/http://the-witness.net/news/2013/09/shadow-mapping-summary-part-1

See: https://www.iryoku.com/next-generation-post-processing-in-call-of-duty-advanced-warfare/

Calculates the distance between spiral samples for the given texel size and penumbra size. This is used for the Jimenez ‘14 (i.e. temporal) variant of shadow sampling.

search_size is the size of the search region in texels.

A good overview of the technique: https://medium.com/@varunm100/soft-shadows-for-mobile-ar-9e8da2e6f4ba

NOTE: Due to the non-uniform control flow in shadows::fetch_point_shadow, we must use the Level variant of textureSampleCompare to avoid undefined behavior due to some of the fragments in a quad (2x2 fragments) being processed not being sampled, and this messing with mip-mapping functionality. The shadow maps have no mipmaps so Level just samples from LOD 0.

Performs one sample of the blocker search. This variation of the blocker search function is for point and spot lights.

x_basis, y_basis, and light_local form an orthonormal basis over which the blocker search happens.

This more or less does what Castano13 does, but in 3D space. Castano13 is essentially an optimized 2D Gaussian filter that takes advantage of the bilinear filtering hardware to reduce the number of samples needed. This trick doesn’t apply to cubemaps, so we manually apply a Gaussian filter over the standard 8xMSAA pattern instead.

This is a port of the Jimenez14 filter above to the 3D space. It jitters the points in the spiral pattern after first creating a 2D orthonormal basis along the principal light direction.

The scale parameter represents the size of the light.

A good overview of the technique: https://medium.com/@varunm100/soft-shadows-for-mobile-ar-9e8da2e6f4ba