Implement PBR anisotropy per `KHR_materials_anisotropy`. #13450

pcwalton · 2024-05-21T06:40:07Z

This commit implements support for physically-based anisotropy in Bevy's StandardMaterial, following the specification for the KHR_materials_anisotropy glTF extension.

Anisotropy (not to be confused with anisotropic filtering) is a PBR feature that allows roughness to vary along the tangent and bitangent directions of a mesh. In effect, this causes the specular light to stretch out into lines instead of a round lobe. This is useful for modeling brushed metal, hair, and similar surfaces. Support for anisotropy is a common feature in major game and graphics engines; Unity, Unreal, Godot, three.js, and Blender all support it to varying degrees.

Two new parameters have been added to StandardMaterial: anisotropy_strength and anisotropy_rotation. Anisotropy strength, which ranges from 0 to 1, represents how much the roughness differs between the tangent and the bitangent of the mesh. In effect, it controls how stretched the specular highlight is. Anisotropy rotation allows the roughness direction to differ from the tangent of the model.

In addition to these two fixed parameters, an anisotropy texture can be supplied. Such a texture should be a 3-channel RGB texture, where the red and green values specify a direction vector using the same conventions as a normal map ([0, 1] color values map to [-1, 1] vector values), and the the blue value represents the strength. This matches the format that the KHR_materials_anisotropy specification requires. Such textures should be loaded as linear and not sRGB. Note that this texture does consume one additional texture binding in the standard material shader.

The glTF loader has been updated to properly parse the KHR_materials_anisotropy extension.

A new example, anisotropy, has been added. This example loads and displays the barn lamp example from the glTF-Sample-Assets repository. Note that the textures were rather large, so I shrunk them down and converted them to a mixture of JPEG and KTX2 format, in the interests of saving space in the Bevy repository.

Changelog

Added

Physically-based anisotropy is now available for materials, which enhances the look of surfaces such as brushed metal or hair. glTF scenes can use the new feature with the KHR_materials_anisotropy extension.

Screenshots

With anisotropy:

Without anisotropy:

This commit implements support for physically-based anisotropy in Bevy's `StandardMaterial`, following the specification for the [`KHR_materials_anisotropy`] glTF extension. [*Anisotropy*] (not to be confused with [anisotropic filtering]) is a PBR feature that allows roughness to vary along the tangent and bitangent directions of a mesh. In effect, this causes the specular light to stretch out into lines instead of a round lobe. This is useful for modeling brushed metal, hair, and similar surfaces. Support for anisotropy is a common feature in major game and graphics engines; Unity, Unreal, Godot, three.js, and Blender all support it to varying degrees. Two new parameters have been added to `StandardMaterial`: `anisotropy_strength` and `anisotropy_rotation`. Anisotropy strength, which ranges from 0 to 1, represents how much the roughness differs between the tangent and the bitangent of the mesh. In effect, it controls how stretched the specular highlight is. Anisotropy rotation allows the roughness direction to differ from the tangent of the model. In addition to these two fixed parameters, an *anisotropy texture* can be supplied. Such a texture should be a 3-channel RGB texture, where the red and green values specify a direction vector using the same conventions as a normal map ([0, 1] color values map to [-1, 1] vector values), and the the blue value represents the strength. This matches the format that the [`KHR_materials_anisotropy`] specification requires. Such textures should be loaded as linear and not sRGB. Note that this texture does consume one additional texture binding in the standard material shader. The glTF loader has been updated to properly parse the `KHR_materials_anisotropy` extension. A new example, `anisotropy`, has been added. This example loads and displays the barn lamp example from the [`glTF-Sample-Assets`] repository. Note that the textures were rather large, so I shrunk them down and converted them to a mixture of JPEG and KTX2 format, in the interests of saving space in the Bevy repository. [*Anisotropy*]: https://google.github.io/filament/Filament.md.html#materialsystem/anisotropicmodel [anisotropic filtering]: https://en.wikipedia.org/wiki/Anisotropic_filtering [`KHR_materials_anisotropy`]: https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_materials_anisotropy/README.md [`glTF-Sample-Assets`]: https://github.com/KhronosGroup/glTF-Sample-Assets/

github-actions · 2024-05-21T06:52:11Z

The generated examples/README.md is out of sync with the example metadata in Cargo.toml or the example readme template. Please run cargo run -p build-templated-pages -- update examples to update it, and commit the file change.

Cargo.toml

torsteingrindvik · 2024-05-21T07:54:16Z

assets/models/AnisotropyBarnLamp/AnisotropyBarnLamp_basecolor.jpeg

Any particular reason to keep this as jpeg?

You likely know but: basisu -ktx2 -uastc -mipmap foo.jpeg has worked nicely for me to get mipmaps.

I think JPEG results in the smallest possible file size, and there's been a lot of discussion about keeping example files small in the repo. The original size was several MB. Mipmaps would increase size, which I didn't think was worth it as the textures look pretty good and the performance is fine.

crates/bevy_pbr/src/render/pbr_fragment.wgsl

atlv24

love the specular normal mixing trick, and the example is very good too. sweet beans

atlv24 · 2024-05-21T14:44:53Z

crates/bevy_gltf/src/loader.rs

 /// Returns the index (within the `textures` array) of the texture with the
 /// given field name in the data for the material extension with the given name,
 /// if there is one.
-#[cfg(feature = "pbr_multi_layer_material_textures")]


why was this removed?

Anisotropy needs to use this function. Unlike clearcoat (the previous user of this function), anisotropy's textures aren't gated behind the pbr_multi_layer_material_textures feature, as it's not technically a separate layer. So the feature gate needs to be removed.

crates/bevy_pbr/src/pbr_material.rs

IceSentry · 2024-06-02T06:00:42Z

The volumetric_fog example crashes with this PR.

wgpu error: Validation Error

Caused by:
    In a RenderPass
      note: encoder = `<CommandBuffer-(4, 75, Vulkan)>`
    In a set_bind_group command
      note: bind group = `mesh_view_bind_group`
    Bind group 0 expects 5 dynamic offsets. However 4 dynamic offsets were provided.

crates/bevy_pbr/src/render/pbr_lighting.wgsl

IceSentry · 2024-06-02T06:22:36Z

crates/bevy_pbr/src/render/pbr_lighting.wgsl

+    let F_ab = (*input).F_ab;
+
+    var Fr = (specular_intensity * D * V) * F;
+    Fr *= 1.0 + F0 * (1.0 / F_ab.x - 1.0);


The linked Filament doc uses dfg.y instead F_ab.x. I assume F_ab is the same as dfg, but is the .x vs .y correct?

Ah, I see you just copied that from somewhere else. I guess we shouldn't touch this in this PR then.

Yeah, we might want to check this later but I just copy and pasted this one.

crates/bevy_pbr/src/render/pbr_lighting.wgsl

examples/3d/anisotropy.rs

pcwalton · 2024-06-02T17:43:43Z

@IceSentry volumetric_fog runs fine for me now that I've updated this PR to main. Pretty sure this was the unrelated problem with SSR from earlier.

IceSentry

I ran a bunch of examples again and found no new regressions

LGTM

alice-i-cecile · 2024-06-04T15:57:05Z

Thank you to everyone involved with the authoring or reviewing of this PR! This work is relatively important and needs release notes! Head over to bevyengine/bevy-website#1346 if you'd like to help out.

pcwalton requested review from JMS55, IceSentry and superdump May 21, 2024 06:40

pcwalton added this to the 0.15 milestone May 21, 2024

pcwalton added A-Rendering Drawing game state to the screen C-Enhancement A new feature S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels May 21, 2024

IceSentry added the X-Uncontroversial This work is generally agreed upon label May 21, 2024

torsteingrindvik reviewed May 21, 2024

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pcwalton requested a review from torsteingrindvik May 21, 2024 12:47

atlv24 approved these changes May 21, 2024

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Fix typo

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alice-i-cecile added the D-Modest A "normal" level of difficulty; suitable for simple features or challenging fixes label May 22, 2024

pcwalton added 2 commits May 25, 2024 01:04

Merge remote-tracking branch 'origin/main' into anisotropy

bd901ea

Merge remote-tracking branch 'origin/main' into anisotropy

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IceSentry reviewed Jun 2, 2024

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Merge remote-tracking branch 'origin/main' into anisotropy

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Address review comments

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pcwalton requested a review from IceSentry June 2, 2024 17:47

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alice-i-cecile modified the milestones: 0.15, 0.14 Jun 3, 2024

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Merged via the queue into bevyengine:main with commit df8ccb8 Jun 4, 2024
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alice-i-cecile mentioned this pull request Jun 4, 2024

Write release notes for PR #13450: Implement PBR anisotropy per KHR_materials_anisotropy. bevyengine/bevy-website#1346

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Implement PBR anisotropy per `KHR_materials_anisotropy`. #13450

Implement PBR anisotropy per `KHR_materials_anisotropy`. #13450

pcwalton commented May 21, 2024

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alice-i-cecile commented Jun 4, 2024

Implement PBR anisotropy per KHR_materials_anisotropy. #13450

Implement PBR anisotropy per KHR_materials_anisotropy. #13450

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pcwalton commented May 21, 2024

Changelog

Added

Screenshots

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alice-i-cecile commented Jun 4, 2024

Implement PBR anisotropy per `KHR_materials_anisotropy`. #13450

Implement PBR anisotropy per `KHR_materials_anisotropy`. #13450

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