Porting patch over from Phabricator.

@@ -1 +1 @@
-Subproject commit 4331c8e76c2f42b9fd903716c333d6cdeaa5cebd
+Subproject commit 8d04896a130c12eb440b7b9ac33bf9dc152506b5

@@ -0,0 +1,256 @@
+

@@ -0,0 +8,4 @@
+#include "DNA_mesh_types.h"
+#include "DNA_meshdata_types.h"
+#include "DNA_object_types.h"
+#include "DNA_space_types.h" /* for FILE_MAX */

@@ -0,0 +37,4 @@
+
+void USDShapeReader::create_object(Main *bmain, double motionSampleTime)
+{
+  UNUSED_VARS(motionSampleTime);

@@ -0,0 +52,4 @@
+
+  if (read_mesh != mesh) {
+    /* FIXME: after 2.80; `mesh->flag` isn't copied by #BKE_mesh_nomain_to_mesh() */
+    /* read_mesh can be freed by BKE_mesh_nomain_to_mesh(), so get the flag before that happens. */

@@ -0,0 +88,4 @@
+}
+
+bool USDShapeReader::read_mesh_values(double motionSampleTime,
+          pxr::VtVec3fArray &positions,

@@ -0,0 +93,4 @@
+          pxr::VtIntArray &face_counts) const
+{
+  const bool is_capsule = prim_.IsA<pxr::UsdGeomCapsule>();
+  const bool is_cylinder = prim_.IsA<pxr::UsdGeomCylinder>();

@@ -0,0 +130,4 @@
+  return false;
+}
+
+struct Mesh *USDShapeReader::read_mesh(struct Mesh *existing_mesh,

@@ -0,0 +142,4 @@
+    return existing_mesh;
+  }
+
+  UNUSED_VARS(read_flag);

@@ -0,0 +171,4 @@
+    }
+  }
+
+  BKE_mesh_calc_edges(active_mesh, false, false);

@@ -0,0 +172,4 @@
+  }
+
+  BKE_mesh_calc_edges(active_mesh, false, false);
+  BKE_mesh_normals_tag_dirty(active_mesh);

@@ -0,0 +178,4 @@
+}
+
+
+Mesh *USDShapeReader::mesh_from_prim(Mesh *existing_mesh, double motionSampleTime,

@@ -0,0 +196,4 @@
+        existing_mesh, positions.size(), 0, 0, face_indices.size(), face_counts.size());
+  }
+
+  MutableSpan<float3> verts = active_mesh->vert_positions_for_write();

@@ -0,0 +212,4 @@
+  const bool is_capsule = prim_.IsA<pxr::UsdGeomCapsule>();
+  const bool is_cylinder = prim_.IsA<pxr::UsdGeomCylinder>();
+  const bool is_cone = prim_.IsA<pxr::UsdGeomCone>();
+  const bool is_cube = prim_.IsA<pxr::UsdGeomCube>();

@@ -0,0 +1,58 @@
+

@@ -0,0 +33,4 @@
+
+  /* Read the pxr:UsdGeomMesh values and convert them to a Blender Mesh,
+   * also returning face_indices and counts for further loop processing. */
+  Mesh *mesh_from_prim(Mesh *existing_mesh, double motionSampleTime,

@@ -0,0 +43,4 @@
+
+  void create_object(Main *bmain, double motionSampleTime) override;
+  void read_object_data(Main *bmain, double motionSampleTime) override;
+  struct Mesh *read_mesh(struct Mesh *existing_mesh,

@@ -0,0 +49,4 @@
+                         const char **err_str) override;
+  bool is_time_varying();
+
+  virtual bool topology_changed(const Mesh * /* existing_mesh */, double /* motionSampleTime */)

@@ -0,0 +141,4 @@
+  MutableSpan<MPoly> polys = active_mesh->polys_for_write();
+  MutableSpan<MLoop> loops = active_mesh->loops_for_write();
+
+  int loop_index = 0;

@@ -0,0 +123,4 @@
+  return false;
+}
+
+Mesh *USDShapeReader::read_mesh(struct Mesh *existing_mesh,

@@ -0,0 +138,4 @@
+  /* Should have a good set of data by this point-- copy over. */
+  Mesh *active_mesh = mesh_from_prim(existing_mesh, motionSampleTime, face_indices, face_counts);
+
+  MutableSpan<MPoly> polys = active_mesh->polys_for_write();

@@ -0,0 +47,4 @@
+
+  void create_object(Main *bmain, double /*motionSampleTime*/) override;
+  void read_object_data(Main *bmain, double motionSampleTime) override;
+  Mesh *read_mesh(struct Mesh *existing_mesh,