
This commit allows specular highlights to be tinted with a color and for the reflectance and color tint values to vary across a model via a pair of maps. The implementation follows the [`KHR_materials_specular`] glTF extension. In order to reduce the number of samplers and textures in the default `StandardMaterial` configuration, the maps are gated behind the `pbr_specular_textures` Cargo feature. Specular tinting is currently unsupported in the deferred renderer, because I didn't want to bloat the deferred G-buffers. A possible fix for this in the future would be to make the G-buffer layout more configurable, so that specular tints could be supported on an opt-in basis. As an alternative, Bevy could force meshes with specular tints to render in forward mode. Both of these solutions require some more design, so I consider them out of scope for now. Note that the map is a *specular* map, not a *reflectance* map. In Bevy and Filament terms, the reflectance values in the specular map range from [0.0, 0.5], rather than [0.0, 1.0]. This is an unfortunate [`KHR_materials_specular`] specification requirement that stems from the fact that glTF is specified in terms of a specular strength model, not the reflectance model that Filament and Bevy use. A workaround, which is noted in the `StandardMaterial` documentation, is to set the `reflectance` value to 2.0, which spreads the specular map range from [0.0, 1.0] as normal. The glTF loader has been updated to parse the [`KHR_materials_specular`] extension. Note that, unless the non-default `pbr_specular_textures` is supplied, the maps are ignored. The `specularFactor` value is applied as usual. Note that, as with the specular map, the glTF `specularFactor` is twice Bevy's `reflectance` value. This PR adds a new example, `specular_tint`, which demonstrates the specular tint and map features. Note that this example requires the [`KHR_materials_specular`] Cargo feature. [`KHR_materials_specular`]: https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_specular ## Changelog ### Added * Specular highlights can now be tinted with the `specular_tint` field in `StandardMaterial`. * Specular maps are now available in `StandardMaterial`, gated behind the `pbr_specular_textures` Cargo feature. * The `KHR_materials_specular` glTF extension is now supported, allowing for customization of specular reflectance and specular maps. Note that the latter are gated behind the `pbr_specular_textures` Cargo feature.
180 KiB
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180 KiB
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