Import the second UV map if present in glTF files.

Conventionally, the second UV map (`TEXCOORD1`, `UV1`) is used for
lightmap UVs. This commit allows Bevy to import them, so that a custom
shader that applies lightmaps can use those UVs if desired.

Note that this doesn't actually apply lightmaps to Bevy meshes; that
will be a followup. It does, however, open the door to future Bevy
plugins that implement baked global illumination.

crates/bevy_gltf/src/vertex_attributes.rs

@@ -263,6 +263,7 @@ pub(crate) fn convert_attribute(
  gltf::Semantic::Tangents => Some((Mesh::ATTRIBUTE_TANGENT, ConversionMode::Any)),
  gltf::Semantic::Colors(0) => Some((Mesh::ATTRIBUTE_COLOR, ConversionMode::Rgba)),
  gltf::Semantic::TexCoords(0) => Some((Mesh::ATTRIBUTE_UV_0, ConversionMode::TexCoord)),
+ gltf::Semantic::TexCoords(1) => Some((Mesh::ATTRIBUTE_UV_1, ConversionMode::TexCoord)),
  gltf::Semantic::Joints(0) => {
  Some((Mesh::ATTRIBUTE_JOINT_INDEX, ConversionMode::JointIndex))
  }

crates/bevy_pbr/src/render/mesh.rs

@@ -779,14 +779,19 @@ impl SpecializedMeshPipeline for MeshPipeline {
  vertex_attributes.push(Mesh::ATTRIBUTE_UV_0.at_shader_location(2));
  }
 
+ if layout.contains(Mesh::ATTRIBUTE_UV_1) {
+ shader_defs.push("VERTEX_UVS_1".into());
+ vertex_attributes.push(Mesh::ATTRIBUTE_UV_1.at_shader_location(3));
+ }
+
  if layout.contains(Mesh::ATTRIBUTE_TANGENT) {
  shader_defs.push("VERTEX_TANGENTS".into());
- vertex_attributes.push(Mesh::ATTRIBUTE_TANGENT.at_shader_location(3));
+ vertex_attributes.push(Mesh::ATTRIBUTE_TANGENT.at_shader_location(4));
  }
 
  if layout.contains(Mesh::ATTRIBUTE_COLOR) {
  shader_defs.push("VERTEX_COLORS".into());
- vertex_attributes.push(Mesh::ATTRIBUTE_COLOR.at_shader_location(4));
+ vertex_attributes.push(Mesh::ATTRIBUTE_COLOR.at_shader_location(5));
  }
 
  let mut bind_group_layout = match key.msaa_samples() {

crates/bevy_pbr/src/render/mesh.wgsl

@@ -16,15 +16,16 @@ struct Vertex {
 #ifdef VERTEX_UVS
  @location(2) uv: vec2<f32>,
 #endif
+// (Alternate UVs are at location 3, but they're currently unused here.)
 #ifdef VERTEX_TANGENTS
- @location(3) tangent: vec4<f32>,
+ @location(4) tangent: vec4<f32>,
 #endif
 #ifdef VERTEX_COLORS
- @location(4) color: vec4<f32>,
+ @location(5) color: vec4<f32>,
 #endif
 #ifdef SKINNED
- @location(5) joint_indices: vec4<u32>,
- @location(6) joint_weights: vec4<f32>,
+ @location(6) joint_indices: vec4<u32>,
+ @location(7) joint_weights: vec4<f32>,
 #endif
 #ifdef MORPH_TARGETS
  @builtin(vertex_index) index: u32,

crates/bevy_render/src/mesh/mesh/mod.rs

@@ -146,6 +146,14 @@ impl Mesh {
  pub const ATTRIBUTE_UV_0: MeshVertexAttribute =
  MeshVertexAttribute::new("Vertex_Uv", 2, VertexFormat::Float32x2);
 
+ /// Alternate texture coordinates for the vertex. Use in conjuction with
+ /// [`Mesh::insert_attribute`].
+ ///
+ /// Typically, these are used for lightmaps, textures that provide
+ /// precomputed illumination.
+ pub const ATTRIBUTE_UV_1: MeshVertexAttribute =
+ MeshVertexAttribute::new("Vertex_Uv_1", 2, VertexFormat::Float32x2);
+
  /// The direction of the vertex tangent. Used for normal mapping.
  /// Usually generated with [`generate_tangents`](Mesh::generate_tangents).
  pub const ATTRIBUTE_TANGENT: MeshVertexAttribute =