Implement gradual falloff and blending for light probes. #22610
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Currently, if a fragment overlaps multiple reflection probes and/or irradiance volumes, Bevy arbitrarily chooses one to provide diffuse and/or specular light. This is unsightly. The standard approach is to accumulate radiance and irradiance as a weighted sum. In most engines, light probes have an artist-controllable *falloff* range, which causes the weight of each probe to diminish gradually from the center of the probe. This PR implements both falloff and blending for light probes. Reflection probes and irradiance volumes are blended using a weighted sum. In the case of reflection probes, if the weights sum to less than 1.0, and an environment map is present on the camera, than the environment map receives the remaining weight necessary to bring the total weight up to 1.0. This is useful for reflection probes that correspond to building interiors, to allow smooth transitions between the indoor building and an exterior environment map when exiting the building. Falloff is specified as a fraction of the *interior* of each light probe that applies gradual falloff, instead of specifying a distance *outside* the light probe over which the influence diminishes. (See the documentation comments in `LightProbe` for more detail.) The reason why I chose to do it this way is that the voxel contents of an irradiance volume would be ill-defined within the falloff range otherwise. Clamping to the edge of the 3D voxel cube inside the falloff region (i.e. extending the edge voxels out) is likely to be incorrect, and extending the voxel region to encompass the falloff range plus the interior range would complicate the calculations in the performance-critical PBR shader. TODO: talk about the new example.
alice-i-cecile
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A-Rendering
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Currently, if a fragment overlaps multiple reflection probes and/or irradiance volumes, Bevy arbitrarily chooses one to provide diffuse and/or specular light. This is unsightly. The standard approach is to accumulate radiance and irradiance as a weighted sum. In most engines, light probes have an artist-controllable falloff range, which causes the weight of each probe to diminish gradually from the center of the probe.
This PR implements both falloff and blending for light probes. Reflection probes and irradiance volumes are blended using a weighted sum. In the case of reflection probes, if the weights sum to less than 1.0, and an environment map is present on the camera, than the environment map receives the remaining weight necessary to bring the total weight up to 1.0. This is useful for reflection probes that correspond to building interiors, to allow smooth transitions between the indoor building and an exterior environment map when exiting the building.
Falloff is specified as a fraction of the interior of each light probe that applies gradual falloff, instead of specifying a distance outside the light probe over which the influence diminishes. (See the documentation comments in
LightProbefor more detail.) The reason why I chose to do it this way is that the voxel contents of an irradiance volume would be ill-defined within the falloff range otherwise. Clamping to the edge of the 3D voxel cube inside the falloff region (i.e. extending the edge voxels out) is likely to be incorrect, and extending the voxel region to encompass the falloff range plus the interior range would complicate the calculations in the performance-critical PBR shader.This needs an example, so it's a draft for now.