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.

Creates a random rotation matrix using interleaved gradient noise. 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.

Performs the blocker search portion of percentage-closer soft shadows (PCSS). This is the variation used for directional lights. We can't use Castano '13 here because that has a hard-wired fixed size, while the PCSS algorithm requires a search size that varies based on the size of the light. So we instead use the D3D sample point positions, spaced according to the search size, to provide a sample pattern in a similar manner to the cubemap sampling approach we use for PCF. search_size is the size of the search region in texels.

Samples the shadow map for a directional light when percentage-closer soft shadows are being used. We first search for a *blocker*, which is the average depth value of any shadow map samples that are adjacent to the sample we're considering. That allows us to determine the penumbra size; a larger gap between the blocker and the depth of this sample results in a wider penumbra. Finally, we sample the shadow map the same way we do in PCF, using that penumbra width. 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.

Computes the search position and 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.

Searches for PCSS blockers in a cubemap. This is the variant of the blocker search used for point and spot lights. This follows the logic in sample_shadow_cubemap_gaussian, but uses linear sampling instead of percentage-closer filtering. The scale parameter represents the size of the light.

Samples the shadow map for a point or spot light when percentage-closer soft shadows are being used. A good overview of the technique: <https://medium.com/@varunm100/soft-shadows-for-mobile-ar-9e8da2e6f4ba>