Alembic import: fixed bug where local matrix from Alembic was used as object matrix

Also renamed AbcObjectReader::readObjectMatrix to
setupObjectTransform, as it does more than just reading the object
matrix; it also sets up an object constraint if the Alembic Xform is
animated.

3 files changed, 19 insertions, 3 deletions

diff --git a/source/blender/alembic/intern/abc_object.cc b/source/blender/alembic/intern/abc_object.cc
index 0b2c8cb6b8a..62042d25501 100644
--- a/source/blender/alembic/intern/abc_object.cc
+++ b/source/blender/alembic/intern/abc_object.cc
@@ -214,7 +214,7 @@ Imath::M44d get_matrix(const IXformSchema &schema, const float time)
 	return s0.getMatrix();
 }
 
-void AbcObjectReader::readObjectMatrix(const float time)
+void AbcObjectReader::setupObjectTransform(const float time)
 {
 	bool is_constant = false;
 
@@ -292,6 +292,16 @@ void AbcObjectReader::read_matrix(float mat[4][4], const float time, const float
 	const Imath::M44d matrix = get_matrix(schema, time);
 	convert_matrix(matrix, m_object, mat, scale, has_alembic_parent);
 
+	if (has_alembic_parent) {
+		/* In this case, the matrix in Alembic is in local coordinates, so
+		 * convert to world matrix. To prevent us from reading and accumulating
+		 * all parent matrices in the Alembic file, we assume that the Blender
+		 * parent object is already updated for the current timekey, and use its
+		 * world matrix. */
+		BLI_assert(m_object->parent);
+		mul_m4_m4m4(mat, m_object->parent->obmat, mat);
+	}
+
 	is_constant = schema.isConstant();
 }
 
diff --git a/source/blender/alembic/intern/abc_object.h b/source/blender/alembic/intern/abc_object.h
index 6d97c0359b7..5b7663943c2 100644
--- a/source/blender/alembic/intern/abc_object.h
+++ b/source/blender/alembic/intern/abc_object.h
@@ -183,7 +183,8 @@ public:
 		return dm;
 	}
 
-	void readObjectMatrix(const float time);
+	/** Reads the object matrix and sets up an object transform if animated. */
+	void setupObjectTransform(const float time);
 
 	void addCacheModifier();
 
diff --git a/source/blender/alembic/intern/alembic_capi.cc b/source/blender/alembic/intern/alembic_capi.cc
index 44d902907c3..44f49542828 100644
--- a/source/blender/alembic/intern/alembic_capi.cc
+++ b/source/blender/alembic/intern/alembic_capi.cc
@@ -639,7 +639,6 @@ static void import_startjob(void *user_data, short *stop, short *do_update, floa
 
 		if (reader->valid()) {
 			reader->readObjectData(data->bmain, 0.0f);
-			reader->readObjectMatrix(0.0f);
 
 			min_time = std::min(min_time, reader->minTime());
 			max_time = std::max(max_time, reader->maxTime());
@@ -712,6 +711,12 @@ static void import_startjob(void *user_data, short *stop, short *do_update, floa
 			return;
 		}
 	}
+
+	/* Setup transformations and constraints. */
+	for (iter = data->readers.begin(); iter != data->readers.end(); ++iter) {
+		AbcObjectReader *reader = *iter;
+		reader->setupObjectTransform(0.0f);
+	}
 }
 
 static void import_endjob(void *user_data)