USD: more efficient mesh & curve writing

- The default value of USD attributes is now only set on the first sample.
  Previously this was done for every sample (so the final default was the
  last value, rather than the first value).
- More use of the sparse value writer, now also for UV coordinates, mesh
  normals, and curve points.

2 files changed, 43 insertions, 11 deletions

diff --git a/source/blender/usd/intern/usd_writer_hair.cc b/source/blender/usd/intern/usd_writer_hair.cc
index d09922be908..9251425c0b8 100644
--- a/source/blender/usd/intern/usd_writer_hair.cc
+++ b/source/blender/usd/intern/usd_writer_hair.cc
@@ -66,8 +66,14 @@ void USDHairWriter::do_write(HierarchyContext &context)
     }
   }
 
-  curves.CreatePointsAttr().Set(points, timecode);
-  curves.CreateCurveVertexCountsAttr().Set(curve_point_counts, timecode);
+  pxr::UsdAttribute attr_points = curves.CreatePointsAttr(pxr::VtValue(), true);
+  pxr::UsdAttribute attr_vertex_counts = curves.CreateCurveVertexCountsAttr(pxr::VtValue(), true);
+  if (!attr_points.HasValue()) {
+    attr_points.Set(points, pxr::UsdTimeCode::Default());
+    attr_vertex_counts.Set(curve_point_counts, pxr::UsdTimeCode::Default());
+  }
+  usd_value_writer_.SetAttribute(attr_points, pxr::VtValue(points), timecode);
+  usd_value_writer_.SetAttribute(attr_vertex_counts, pxr::VtValue(curve_point_counts), timecode);
 
   if (psys->totpart > 0) {
     pxr::VtArray<pxr::GfVec3f> colors;
diff --git a/source/blender/usd/intern/usd_writer_mesh.cc b/source/blender/usd/intern/usd_writer_mesh.cc
index ca0171fd60e..28e13013cfd 100644
--- a/source/blender/usd/intern/usd_writer_mesh.cc
+++ b/source/blender/usd/intern/usd_writer_mesh.cc
@@ -153,13 +153,19 @@ void USDGenericMeshWriter::write_uv_maps(const Mesh *mesh, pxr::UsdGeomMesh usd_
     for (int loop_idx = 0; loop_idx < mesh->totloop; loop_idx++) {
       uv_coords.push_back(pxr::GfVec2f(mloopuv[loop_idx].uv));
     }
-    uv_coords_primvar.Set(uv_coords, timecode);
+
+    if (!uv_coords_primvar.HasValue()) {
+      uv_coords_primvar.Set(uv_coords, pxr::UsdTimeCode::Default());
+    }
+    const pxr::UsdAttribute &uv_coords_attr = uv_coords_primvar.GetAttr();
+    usd_value_writer_.SetAttribute(uv_coords_attr, pxr::VtValue(uv_coords), timecode);
   }
 }
 
 void USDGenericMeshWriter::write_mesh(HierarchyContext &context, Mesh *mesh)
 {
   pxr::UsdTimeCode timecode = get_export_time_code();
+  pxr::UsdTimeCode defaultTime = pxr::UsdTimeCode::Default();
   pxr::UsdStageRefPtr stage = usd_export_context_.stage;
   const pxr::SdfPath &usd_path = usd_export_context_.usd_path;
 
@@ -194,9 +200,19 @@ void USDGenericMeshWriter::write_mesh(HierarchyContext &context, Mesh *mesh)
     return;
   }
 
-  pxr::UsdAttribute attr_points = usd_mesh.CreatePointsAttr();
-  pxr::UsdAttribute attr_face_vertex_counts = usd_mesh.CreateFaceVertexCountsAttr();
-  pxr::UsdAttribute attr_face_vertex_indices = usd_mesh.CreateFaceVertexIndicesAttr();
+  pxr::UsdAttribute attr_points = usd_mesh.CreatePointsAttr(pxr::VtValue(), true);
+  pxr::UsdAttribute attr_face_vertex_counts = usd_mesh.CreateFaceVertexCountsAttr(pxr::VtValue(),
+                                                                                  true);
+  pxr::UsdAttribute attr_face_vertex_indices = usd_mesh.CreateFaceVertexIndicesAttr(pxr::VtValue(),
+                                                                                    true);
+
+  if (!attr_points.HasValue()) {
+    // Provide the initial value as default. This makes USD write the value as constant if they
+    // don't change over time.
+    attr_points.Set(usd_mesh_data.points, defaultTime);
+    attr_face_vertex_counts.Set(usd_mesh_data.face_vertex_counts, defaultTime);
+    attr_face_vertex_indices.Set(usd_mesh_data.face_indices, defaultTime);
+  }
 
   usd_value_writer_.SetAttribute(attr_points, pxr::VtValue(usd_mesh_data.points), timecode);
   usd_value_writer_.SetAttribute(
@@ -205,9 +221,16 @@ void USDGenericMeshWriter::write_mesh(HierarchyContext &context, Mesh *mesh)
       attr_face_vertex_indices, pxr::VtValue(usd_mesh_data.face_indices), timecode);
 
   if (!usd_mesh_data.crease_lengths.empty()) {
-    pxr::UsdAttribute attr_crease_lengths = usd_mesh.CreateCreaseLengthsAttr();
-    pxr::UsdAttribute attr_crease_indices = usd_mesh.CreateCreaseIndicesAttr();
-    pxr::UsdAttribute attr_crease_sharpness = usd_mesh.CreateCreaseSharpnessesAttr();
+    pxr::UsdAttribute attr_crease_lengths = usd_mesh.CreateCreaseLengthsAttr(pxr::VtValue(), true);
+    pxr::UsdAttribute attr_crease_indices = usd_mesh.CreateCreaseIndicesAttr(pxr::VtValue(), true);
+    pxr::UsdAttribute attr_crease_sharpness = usd_mesh.CreateCreaseSharpnessesAttr(pxr::VtValue(),
+                                                                                   true);
+
+    if (!attr_crease_lengths.HasValue()) {
+      attr_crease_lengths.Set(usd_mesh_data.crease_lengths, defaultTime);
+      attr_crease_indices.Set(usd_mesh_data.crease_vertex_indices, defaultTime);
+      attr_crease_sharpness.Set(usd_mesh_data.crease_sharpnesses, defaultTime);
+    }
 
     usd_value_writer_.SetAttribute(
         attr_crease_lengths, pxr::VtValue(usd_mesh_data.crease_lengths), timecode);
@@ -404,8 +427,11 @@ void USDGenericMeshWriter::write_normals(const Mesh *mesh, pxr::UsdGeomMesh usd_
     }
   }
 
-  pxr::UsdAttribute attr_normals = usd_mesh.CreateNormalsAttr(pxr::VtValue(loop_normals), true);
-  attr_normals.Set(loop_normals, timecode);
+  pxr::UsdAttribute attr_normals = usd_mesh.CreateNormalsAttr(pxr::VtValue(), true);
+  if (!attr_normals.HasValue()) {
+    attr_normals.Set(loop_normals, pxr::UsdTimeCode::Default());
+  }
+  usd_value_writer_.SetAttribute(attr_normals, pxr::VtValue(loop_normals), timecode);
   usd_mesh.SetNormalsInterpolation(pxr::UsdGeomTokens->faceVarying);
 }