Sort meshes by texture index to avoid unnecessary texture binds

- This reduces the texture bind count form 103 to 25 in the Sponza scene.

src/common/gltf_model.cpp

@@ -351,6 +351,10 @@ GltfModel::GltfModel(const fs::path gltfPath)
     }
 
     cgltf_free(data);
+
+    std::sort(meshes.begin(), meshes.end(), [](const GltfMesh& a, const GltfMesh& b) -> bool {
+        return a.baseColorTextureIndex < b.baseColorTextureIndex;
+    });
 }
 
 GltfModel::GltfModel(std::vector<GltfMesh> meshes, std::vector<Texture> baseColorTextures)

src/common/gltf_model.hpp

@@ -27,6 +27,12 @@ struct GltfMesh
     {
     }
 
+    GltfMesh(const GltfMesh&) = delete;
+    GltfMesh& operator=(const GltfMesh&) = delete;
+
+    GltfMesh(GltfMesh&&) noexcept = default;
+    GltfMesh& operator=(GltfMesh&&) noexcept = default;
+
     std::vector<glm::vec3>     positions;
     std::vector<glm::vec3>     normals;
     std::vector<glm::vec2>     texCoords;

src/pt/deferred_renderer.cpp

@@ -798,6 +798,7 @@ void DeferredRenderer::GbufferPass::render(
     wgpuRenderPassEncoderSetBindGroup(renderPassEncoder, 0, mUniformBindGroup.ptr(), 0, nullptr);
     wgpuRenderPassEncoderSetBindGroup(renderPassEncoder, 1, mSamplerBindGroup.ptr(), 0, nullptr);
 
+    std::size_t currentTextureIdx = ~static_cast<std::size_t>(0);
     for (std::size_t idx = 0; idx < mPositionBuffers.size(); ++idx)
     {
         const GpuBuffer& positionBuffer = mPositionBuffers[idx];
@@ -818,10 +819,14 @@ void DeferredRenderer::GbufferPass::render(
             0,
             indexBuffer.buffer.byteSize());
 
-        const std::size_t   textureIdx = mBaseColorTextureIndices[idx];
-        const GpuBindGroup& baseColorBindGroup = mBaseColorTextureBindGroups[textureIdx];
-        wgpuRenderPassEncoderSetBindGroup(
-            renderPassEncoder, 2, baseColorBindGroup.ptr(), 0, nullptr);
+        const std::size_t textureIdx = mBaseColorTextureIndices[idx];
+        if (textureIdx != currentTextureIdx)
+        {
+            currentTextureIdx = textureIdx;
+            const GpuBindGroup& baseColorBindGroup = mBaseColorTextureBindGroups[textureIdx];
+            wgpuRenderPassEncoderSetBindGroup(
+                renderPassEncoder, 2, baseColorBindGroup.ptr(), 0, nullptr);
+        }
 
         wgpuRenderPassEncoderDrawIndexed(renderPassEncoder, indexBuffer.count, 1, 0, 0, 0);
     }