USD Import: Scale option fixes.

Updated the code to apply the global scale option, which
was previously ignored.  Fixed application of global scale
in the xform reader matrix calculation to only apply the
scale to root objects.  Also fixed bug in setting the
is_constant flag and simplified some of the code.

2 files changed, 68 insertions, 17 deletions

diff --git a/source/blender/io/usd/intern/usd_reader_xform.cc b/source/blender/io/usd/intern/usd_reader_xform.cc
index fbefa2a50bf..9a7f5c73503 100644
--- a/source/blender/io/usd/intern/usd_reader_xform.cc
+++ b/source/blender/io/usd/intern/usd_reader_xform.cc
@@ -39,6 +39,7 @@ extern "C" {
 }
 
 #include <pxr/base/gf/math.h>
+#include <pxr/base/gf/matrix4f.h>
 #include <pxr/pxr.h>
 #include <pxr/usd/usd/prim.h>
 #include <pxr/usd/usd/primRange.h>
@@ -62,7 +63,7 @@ void USDXformReader::readObjectData(Main *bmain, double motionSampleTime)
   bool is_constant;
   float transform_from_usd[4][4];
 
-  read_matrix(transform_from_usd, motionSampleTime, 1.0f, is_constant);
+  read_matrix(transform_from_usd, motionSampleTime, m_import_params.scale, is_constant);
 
   if (!is_constant) {
     bConstraint *con = BKE_constraint_add_for_object(
@@ -85,36 +86,82 @@ void USDXformReader::read_matrix(float r_mat[4][4] /* local matrix */,
                                  bool &is_constant)
 {
   is_constant = true;
-  pxr::UsdGeomXformable xformable = pxr::UsdGeomXformable(
-      m_prim);  // pxr::UsdGeomXformable::Get(m_stage, m_prim.GetPath());
+  unit_m4(r_mat);
+
+  pxr::UsdGeomXformable xformable(m_prim);
+
+  if (!xformable) {
+    // This might happen if the prim is a Scope.
+    return;
+  }
 
   bool resetsXformStack = false;
   std::vector<pxr::UsdGeomXformOp> orderedXformOps = xformable.GetOrderedXformOps(
       &resetsXformStack);
 
-  unit_m4(r_mat);
-
-  if (orderedXformOps.size() <= 0)
-    return;
-
-  int opCount = 0;
   for (std::vector<pxr::UsdGeomXformOp>::iterator I = orderedXformOps.begin();
        I != orderedXformOps.end();
        ++I) {
 
     pxr::UsdGeomXformOp &xformOp = (*I);
 
-    is_constant = !xformOp.MightBeTimeVarying();
+    if (xformOp.MightBeTimeVarying()) {
+      is_constant = false;
+    }
+
+    // Note, we don't apply the scale here because the XformOps may
+    // be empty, in which case this code won't be reached.
+    pxr::GfMatrix4d mat = xformOp.GetOpTransform(time);
 
-    pxr::GfMatrix4d mat = xformOp.GetOpTransform(time) * pxr::GfMatrix4d(1.0f).SetScale(scale);
+    // Convert the result to a float matrix.
+    pxr::GfMatrix4f mat4f(mat);
 
     float t_mat[4][4];
-    for (int i = 0; i < 4; ++i) {
-      for (int j = 0; j < 4; ++j) {
-        t_mat[j][i] = mat[j][i];
+    mat4f.Get(t_mat);
+
+    mul_m4_m4m4(r_mat, r_mat, t_mat);
+  }
+
+  /* Apply scaling only to root objects, parenting will propagate it. */
+  if (scale != 1.0 && is_root_xform_object()) {
+    float scale_mat[4][4];
+    scale_m4_fl(scale_mat, scale);
+    mul_m4_m4m4(r_mat, scale_mat, r_mat);
+  }
+}
+
+bool USDXformReader::is_root_xform_object() const
+{
+  // It's not sufficient to check for a null parent to determine
+  // if the current object is the root, because the parent could
+  // represent a scope, which is not xformable.  E.g., an Xform
+  // parented to a single Scope would be considered the root.
+
+  if (m_prim.IsInMaster()) {
+    // We don't consider prototypes to be root prims,
+    // because we never want to apply global scaling
+    // or rotations to the ptototypes themselves.
+    return false;
+  }
+
+  if (m_prim.IsA<pxr::UsdGeomXformable>()) {
+    // If we don't have an ancestor that also wraps
+    // UsdGeomXformable, then we are the root.
+    const USDPrimReader *cur_parent = m_parent_reader;
+
+    while (cur_parent) {
+      if (cur_parent->prim().IsA<pxr::UsdGeomXformable>()) {
+        return false;
       }
+      cur_parent = cur_parent->parent();
+    }
+
+    if (!cur_parent) {
+      // No ancestor prim was an xformable, so we
+      // are the root.
+      return true;
     }
-    mul_m4_m4m4(r_mat, r_mat, t_mat);
-    opCount++;
   }
-}
\ No newline at end of file
+
+  return false;
+}
diff --git a/source/blender/io/usd/intern/usd_reader_xform.h b/source/blender/io/usd/intern/usd_reader_xform.h
index 7c8bf397c5f..6899722ee4a 100644
--- a/source/blender/io/usd/intern/usd_reader_xform.h
+++ b/source/blender/io/usd/intern/usd_reader_xform.h
@@ -39,6 +39,10 @@ class USDXformReader : public USDPrimReader {
   void readObjectData(Main *bmain, double motionSampleTime) override;
 
   void read_matrix(float r_mat[4][4], const float time, const float scale, bool &is_constant);
+
+  // Returns true if this reader represents an object that is the root of the
+  // transform hierarchy.
+  bool is_root_xform_object() const;
 };
 
 #endif /* __USD_READER_XFORM_H__ */