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

1 files changed, 18 insertions, 8 deletions

diff --git a/source/blender/makesdna/DNA_cachefile_types.h b/source/blender/makesdna/DNA_cachefile_types.h
index 04c99c6c4b1..b38c7827ea5 100644
--- a/source/blender/makesdna/DNA_cachefile_types.h
+++ b/source/blender/makesdna/DNA_cachefile_types.h
@@ -31,6 +31,13 @@ extern "C" {
 
 struct GSet;
 
+/* CacheFile::type */
+typedef enum {
+  CACHEFILE_TYPE_ALEMBIC = 1,
+  CACHEFILE_TYPE_USD = 2,
+  CACHE_FILE_TYPE_INVALID = 0,
+} eCacheFileType;
+
 /* CacheFile::flag */
 enum {
   CACHEFILE_DS_EXPAND = (1 << 0),
@@ -44,13 +51,13 @@ enum {
 };
 #endif
 
-/* Representation of an object's path inside the Alembic file.
+/* Representation of an object's path inside the archive.
  * Note that this is not a file path. */
-typedef struct AlembicObjectPath {
-  struct AlembicObjectPath *next, *prev;
+typedef struct CacheObjectPath {
+  struct CacheObjectPath *next, *prev;
 
   char path[4096];
-} AlembicObjectPath;
+} CacheObjectPath;
 
 /* CacheFile::velocity_unit
  * Determines what temporal unit is used to interpret velocity vectors for motion blur effects. */
@@ -63,7 +70,7 @@ typedef struct CacheFile {
   ID id;
   struct AnimData *adt;
 
-  /** Paths of the objects inside of the Alembic archive referenced by this CacheFile. */
+  /** Paths of the objects inside of the archive referenced by this CacheFile. */
   ListBase object_paths;
 
   /** 1024 = FILE_MAX. */
@@ -84,14 +91,17 @@ typedef struct CacheFile {
   short flag;
   short draw_flag; /* UNUSED */
 
-  char _pad[3];
+  /* eCacheFileType enum. */
+  char type;
+
+  char _pad[2];
 
   char velocity_unit;
-  /* Name of the velocity property in the Alembic file. */
+  /* Name of the velocity property in the archive. */
   char velocity_name[64];
 
   /* Runtime */
-  struct AbcArchiveHandle *handle;
+  struct CacheArchiveHandle *handle;
   char handle_filepath[1024];
   struct GSet *handle_readers;
 } CacheFile;