Add KHR_materials_scatter for discussion#2579
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…nisotropy semantics - Add scatterFactor (default 0) and scatterTexture (alpha channel) properties to control scattering weight; default-off follows glTF extension convention - scatterTexture uses the alpha channel so it can share a texture with multiscatterColorTexture - In thin-walled mode, scatterFactor lerps between specular BTDF and scatter BSDF, and lerps the scattered color between baseColor and multiscatterColor - In volumetric mode, scatterFactor scales the effective multi-scatter albedo - Correct scatterAnisotropy thin-walled semantics: the parameter controls the hemisphere split (forward fraction = (1+g)/2, backward = (1-g)/2), not a bias on a pure BTDF; rename scatter_btdf -> scatter_bsdf throughout Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Based on some discussions in the glTF PBR group this morning, I've had Claude throw together this proposed extension.
The purpose is to simplify our current approach to supporting diffuse transmission and scattering and to bring it more into line with material models like OpenPBR and Standard Surface which don't support both volumetric materials and diffusely-transmitting surfaces at the same time.
This is one extension that replaces both
KHR_materials_volume_scatterandKHR_materials_diffuse_transmission:KHR_materials_volume_scatter.scatterStrengthproperty is used to scale the affect of the extension and defaults to 0.0 (i.e. "off").Some notes:
KHR_materials_transmissionextension. That's probably okay because the OpenPBR slabs both implement the volume coefficients (including scattering) leading to somewhat redundant behaviour. In our glTF proposal, there is a single way to define coefficients, surface transmission, etc.