feat(3d): Implement basic OBJ mesh asset pipeline

Added support for loading and rendering OBJ meshes.
- Updated asset_packer to parse .obj files into a binary format.
- Added MeshAsset and GetMeshAsset helper to asset_manager.
- Extended Object3D with mesh_asset_id and ObjectType::MESH.
- Implemented mesh rasterization pipeline in Renderer3D.
- Added a sample cube mesh and verified in test_3d_render.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/util/asset_manager.cc b/src/util/asset_manager.cc
index d4dd5c7..c12331c 100644
--- a/src/util/asset_manager.cc
+++ b/src/util/asset_manager.cc
@@ -153,6 +153,25 @@ TextureAsset GetTextureAsset(AssetId asset_id) {
   return {(int)header[0], (int)header[1], data + 8};
 }
 
+MeshAsset GetMeshAsset(AssetId asset_id) {
+  size_t size = 0;
+  const uint8_t* data = GetAsset(asset_id, &size);
+  if (!data || size < 8) {
+    return {0, nullptr, 0, nullptr};
+  }
+
+  const uint8_t* ptr = data;
+  uint32_t num_vertices = *reinterpret_cast<const uint32_t*>(ptr);
+  ptr += sizeof(uint32_t);
+  const MeshVertex* vertices = reinterpret_cast<const MeshVertex*>(ptr);
+  ptr += num_vertices * sizeof(MeshVertex);
+  uint32_t num_indices = *reinterpret_cast<const uint32_t*>(ptr);
+  ptr += sizeof(uint32_t);
+  const uint32_t* indices = reinterpret_cast<const uint32_t*>(ptr);
+
+  return {num_vertices, vertices, num_indices, indices};
+}
+
 void DropAsset(AssetId asset_id, const uint8_t* asset) {
   uint16_t index = (uint16_t)asset_id;
   if (index >= (uint16_t)AssetId::ASSET_LAST_ID) {