Optimization for UsdMayaReferenceAssembly

Only activate a representation if it is not already the currently
activated representation. This fixes unnecessary reloading of models
that have their variant changed, especially noticeable in larger scenes
with many variants being applied.

Author: dj-mcg

plugin/pxr/maya/lib/usdMaya/referenceAssembly.cpp

@@ -375,6 +375,16 @@ bool UsdMayaReferenceAssembly::activateRep(const MString& repMStr)
     return true;
 }
 
+bool UsdMayaReferenceAssembly::activate(const MString& repMStr)
+{
+    // Early out if repMStr is already the active representation.
+    if (getActive() == repMStr) {
+        return true;
+    }
+
+    return MPxAssembly::activate(repMStr);
+}
+
 //
 // == Optional Function Overrides
 //

plugin/pxr/maya/lib/usdMaya/referenceAssembly.h

@@ -151,7 +151,9 @@ class UsdMayaReferenceAssembly
     MStatus setRepLabel(const MString& representation, const MString& label) override;
     PXRUSDMAYA_API
     bool activateRep(const MString& representation) override;
-
+    PXRUSDMAYA_API
+    bool activate(const MString& representation) override;
+    
     // Optional overrides
     PXRUSDMAYA_API
     bool supportsEdits() const override { return true; };