USD: add USD importer

This is an initial implementation of a USD importer.

This work is comprised of Tangent Animation's open source USD importer,
combined with features @makowalski had implemented.

The design is very similar to the approach taken in the Alembic
importer. The core functionality resides in a collection of "reader"
classes, each of which is responsible for converting an instance of a
USD prim to the corresponding Blender Object representation.

The flow of control for the conversion can be followed in the
`import_startjob()` and `import_endjob()` functions in `usd_capi.cc`.
The `USDStageReader` class is responsible for traversing the USD stage
and instantiating the appropriate readers.

Reviewed By: sybren, HooglyBoogly

Differential Revision: https://developer.blender.org/D10700

2 files changed, 63 insertions, 10 deletions

diff --git a/source/blender/modifiers/CMakeLists.txt b/source/blender/modifiers/CMakeLists.txt
index 0138dd0c3ad..d9b9fa96d04 100644
--- a/source/blender/modifiers/CMakeLists.txt
+++ b/source/blender/modifiers/CMakeLists.txt
@@ -141,6 +141,16 @@ if(WITH_ALEMBIC)
   )
 endif()
 
+if(WITH_USD)
+  add_definitions(-DWITH_USD)
+  list(APPEND INC
+    ../io/usd
+  )
+  list(APPEND LIB
+    bf_usd
+  )
+endif()
+
 if(WITH_MOD_REMESH)
   list(APPEND INC
     ../../../intern/dualcon
diff --git a/source/blender/modifiers/intern/MOD_meshsequencecache.c b/source/blender/modifiers/intern/MOD_meshsequencecache.c
index c2f9cd8c867..3e6081e0a18 100644
--- a/source/blender/modifiers/intern/MOD_meshsequencecache.c
+++ b/source/blender/modifiers/intern/MOD_meshsequencecache.c
@@ -55,18 +55,29 @@
 #include "MOD_modifiertypes.h"
 #include "MOD_ui_common.h"
 
-#ifdef WITH_ALEMBIC
-#  include "ABC_alembic.h"
+#if defined(WITH_USD) || defined(WITH_ALEMBIC)
 #  include "BKE_global.h"
 #  include "BKE_lib_id.h"
 #endif
 
+#ifdef WITH_ALEMBIC
+#  include "ABC_alembic.h"
+#endif
+
+#ifdef WITH_USD
+#  include "usd.h"
+#endif
+
 static void initData(ModifierData *md)
 {
   MeshSeqCacheModifierData *mcmd = (MeshSeqCacheModifierData *)md;
 
   BLI_assert(MEMCMP_STRUCT_AFTER_IS_ZERO(mcmd, modifier));
 
+  mcmd->cache_file = NULL;
+  mcmd->object_path[0] = '\0';
+  mcmd->read_flag = MOD_MESHSEQ_READ_ALL;
+
   MEMCPY_STRUCT_AFTER(mcmd, DNA_struct_default_get(MeshSeqCacheModifierData), modifier);
 }
 
@@ -109,7 +120,7 @@ static bool isDisabled(const struct Scene *UNUSED(scene),
 
 static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *ctx, Mesh *mesh)
 {
-#ifdef WITH_ALEMBIC
+#if defined(WITH_USD) || defined(WITH_ALEMBIC)
   MeshSeqCacheModifierData *mcmd = (MeshSeqCacheModifierData *)md;
 
   /* Only used to check whether we are operating on org data or not... */
@@ -127,16 +138,32 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *ctx, Mesh *
     BKE_cachefile_reader_open(cache_file, &mcmd->reader, ctx->object, mcmd->object_path);
     if (!mcmd->reader) {
       BKE_modifier_set_error(
-          ctx->object, md, "Could not create Alembic reader for file %s", cache_file->filepath);
+          ctx->object, md, "Could not create reader for file %s", cache_file->filepath);
       return mesh;
     }
   }
 
-  /* If this invocation is for the ORCO mesh, and the mesh in Alembic hasn't changed topology, we
+  /* If this invocation is for the ORCO mesh, and the mesh hasn't changed topology, we
    * must return the mesh as-is instead of deforming it. */
-  if (ctx->flag & MOD_APPLY_ORCO &&
-      !ABC_mesh_topology_changed(mcmd->reader, ctx->object, mesh, time, &err_str)) {
-    return mesh;
+  if (ctx->flag & MOD_APPLY_ORCO) {
+    switch (cache_file->type) {
+      case CACHEFILE_TYPE_ALEMBIC:
+#  ifdef WITH_ALEMBIC
+        if (!ABC_mesh_topology_changed(mcmd->reader, ctx->object, mesh, time, &err_str)) {
+          return mesh;
+        }
+#  endif
+        break;
+      case CACHEFILE_TYPE_USD:
+#  ifdef WITH_USD
+        if (!USD_mesh_topology_changed(mcmd->reader, ctx->object, mesh, time, &err_str)) {
+          return mesh;
+        }
+#  endif
+        break;
+      case CACHE_FILE_TYPE_INVALID:
+        break;
+    }
   }
 
   if (me != NULL) {
@@ -156,7 +183,23 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *ctx, Mesh *
     }
   }
 
-  Mesh *result = ABC_read_mesh(mcmd->reader, ctx->object, mesh, time, &err_str, mcmd->read_flag);
+  Mesh *result = NULL;
+
+  switch (cache_file->type) {
+    case CACHEFILE_TYPE_ALEMBIC:
+#  ifdef WITH_ALEMBIC
+      result = ABC_read_mesh(mcmd->reader, ctx->object, mesh, time, &err_str, mcmd->read_flag);
+#  endif
+      break;
+    case CACHEFILE_TYPE_USD:
+#  ifdef WITH_USD
+      result = USD_read_mesh(
+          mcmd->reader, ctx->object, mesh, time * FPS, &err_str, mcmd->read_flag);
+#  endif
+      break;
+    case CACHE_FILE_TYPE_INVALID:
+      break;
+  }
 
   mcmd->velocity_delta = 1.0f;
   if (mcmd->cache_file->velocity_unit == CACHEFILE_VELOCITY_UNIT_SECOND) {
@@ -187,7 +230,7 @@ static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *ctx, Mesh *
 
 static bool dependsOnTime(ModifierData *md)
 {
-#ifdef WITH_ALEMBIC
+#if defined(WITH_USD) || defined(WITH_ALEMBIC)
   MeshSeqCacheModifierData *mcmd = (MeshSeqCacheModifierData *)md;
   return (mcmd->cache_file != NULL);
 #else