Keep track of the vertex attributes in a Mesh.

PiperOrigin-RevId: 900583030
Change-Id: I5b1ff5ad7b698e3e68fd06f44f2c5d3399d08504

src/experimental/filament/filament/mesh.cc

@@ -18,6 +18,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
+#include <span>
 #include <utility>
 
 #include <filament/Box.h>
@@ -202,6 +203,7 @@ void Mesh::BuildVertexBuffer(const MeshData& data) {
         vb_builder.normalized(usage);
       }
       offset += VertexAttributeTypeSize(attrib);
+      attributes_[i] = usage;
     }
     vertex_buffer_ = vb_builder.build(*engine_);
     vertex_buffer_->setBufferAt(*engine_, 0, {bytes, nbytes, callback, this});
@@ -221,7 +223,9 @@ void Mesh::BuildVertexBuffer(const MeshData& data) {
       if (usage == filament::VertexAttribute::COLOR) {
         vb_builder.normalized(usage);
       }
+      attributes_[i] = usage;
     }
+    num_attributes_ = data.nattributes;
     vertex_buffer_ = vb_builder.build(*engine_);
 
     // Assign the individual data buffers.
@@ -334,6 +338,10 @@ filament::RenderableManager::PrimitiveType Mesh::GetPrimitiveType() const {
   return type_;
 }
 
+std::span<const filament::VertexAttribute> Mesh::GetVertexAttributes() const {
+  return {attributes_.data(), attributes_.data() + num_attributes_};
+}
+
 bool Mesh::HasBounds() const {
   return bounds_.has_value();
 }

src/experimental/filament/filament/mesh.h

@@ -15,10 +15,12 @@
 #ifndef MUJOCO_SRC_EXPERIMENTAL_FILAMENT_FILAMENT_MESH_H_
 #define MUJOCO_SRC_EXPERIMENTAL_FILAMENT_FILAMENT_MESH_H_
 
+#include <array>
 #include <cstddef>
 #include <functional>
 #include <memory>
 #include <optional>
+#include <span>
 #include <vector>
 
 #include <filament/Box.h>
@@ -31,6 +33,9 @@
 // Functions for creating filament vertex and index buffers.
 namespace mujoco {
 
+// Maximum number of vertex attributes that can be used by a mesh.
+static constexpr int kMaxVertexAttributes = 16;
+
 // The type of data stored in an index buffer.
 typedef enum mjtIndexType_ {
   mjINDEX_TYPE_USHORT = 0,
@@ -83,7 +88,7 @@ struct MeshData {
 
   // Information about each attribute of a vertex in the mesh. See `interleaved`
   // for more details.
-  VertexAttribute attributes[16];
+  VertexAttribute attributes[kMaxVertexAttributes];
 
   // Whether the vertex attributes are interleaved or not.
   //
@@ -147,6 +152,9 @@ class Mesh {
   // Returns the primitive type of the mesh.
   filament::RenderableManager::PrimitiveType GetPrimitiveType() const;
 
+  // Returns the vertex attribute usages for the mesh.
+  std::span<const filament::VertexAttribute> GetVertexAttributes() const;
+
   // Returns whether the mesh has bounds.
   bool HasBounds() const;
 
@@ -173,6 +181,8 @@ class Mesh {
       filament::RenderableManager::PrimitiveType::TRIANGLES;
   std::optional<filament::Box> bounds_;
   std::vector<std::function<void()>> release_callbacks_;
+  std::array<filament::VertexAttribute, kMaxVertexAttributes> attributes_;
+  int num_attributes_ = 0;
 };
 
 using MeshPtr = std::unique_ptr<Mesh>;