This reverts commit 0b5302d96a.
# Objective
- Fixes#18158
- #17482 introduced rendering changes and was merged a bit too fast
## Solution
- Revert #17482 so that it can be redone and rendering changes discussed
before being merged. This will make it easier to compare changes with
main in the known "valid" state
This is not an issue with the work done in #17482 that is still
interesting
# Objective
Transparently uses simple `EnvironmentMapLight`s to mimic
`AmbientLight`s. Implements the first part of #17468, but I can
implement hemispherical lights in this PR too if needed.
## Solution
- A function `EnvironmentMapLight::solid_color(&mut Assets<Image>,
Color)` is provided to make an environment light with a solid color.
- A new system is added to `SimulationLightSystems` that maps
`AmbientLight`s on views or the world to a corresponding
`EnvironmentMapLight`.
I have never worked with (or on) Bevy before, so nitpicky comments on
how I did things are appreciated :).
## Testing
Testing was done on a modified version of the `3d/lighting` example,
where I removed all lights except the ambient light. I have not included
the example, but can if required.
## Migration
`bevy_pbr::AmbientLight` has been deprecated, so all usages of it should
be replaced by a `bevy_pbr::EnvironmentMapLight` created with
`EnvironmentMapLight::solid_color` placed on the camera. There is no
alternative to ambient lights as resources.
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.
