HYDRA-1199 : Fix crash when switching to another render delegate (#185)

lib/mayaHydra/hydraExtensions/sceneIndex/registration.cpp

@@ -416,10 +416,19 @@ MayaHydraSceneIndexRegistry::~MayaHydraSceneIndexRegistry()
         MSceneMessage::removeCallback(_AfterOpenCBId);
     }
     _AfterOpenCBId = 0;
+    _RemoveAllSceneIndexNodes();
     _registrationsByObjectHandle.clear();
     _registrations.clear();
 }
 
+void MayaHydraSceneIndexRegistry::_RemoveAllSceneIndexNodes()
+{
+    //Always take the first element and remove it until it is empty
+    while (_registrationsByObjectHandle.begin() != _registrationsByObjectHandle.end()){
+        _RemoveSceneIndexForNode(_registrationsByObjectHandle.begin()->first.object());
+    }
+}
+
 bool MayaHydraSceneIndexRegistry::_RemoveSceneIndexForNode(const MObject& dagNode)
 {
     MObjectHandle dagNodeHandle(dagNode);

lib/mayaHydra/hydraExtensions/sceneIndex/registration.h

@@ -108,6 +108,7 @@ class MayaHydraSceneIndexRegistry
     void _AppendNodeToProcessAfterOpenScene(const MObject& node) {_nodesToProcessAfterOpenScene.append(node);}
     //We need to check if some nodes that need to be processed were added to our array during a file load
     void _ProcessNodesAfterOpen();
+    void _RemoveAllSceneIndexNodes();
 
     const std::shared_ptr<Fvp::RenderIndexProxy> _renderIndexProxy;
 

lib/mayaHydra/mayaPlugin/renderOverride.cpp

@@ -1122,7 +1122,7 @@ void MtohRenderOverride::_InitHydraResources(const MHWRender::MDrawContext& draw
     _initializationSucceeded = true;
 }
 
-//When fullReset is true, we remove the data producer scene indices that apply to all viewports and the scene index registry where the usd stages have been loaded.
+//When fullReset is true, we remove the data producer scene indices that apply to all viewports.
 //It means you are doing a full reset of hydra such as when doing "File New".
 //Use fullReset = false when you still want to see the previously registered data producer scene indices when using an hydra viewport.
 void MtohRenderOverride::ClearHydraResources(bool fullReset)
@@ -1140,10 +1140,11 @@ void MtohRenderOverride::ClearHydraResources(bool fullReset)
     if (fullReset){
         //Remove the data producer scene indices that apply to all viewports
         Fvp::DataProducerSceneIndexInterfaceImp::get().ClearDataProducerSceneIndicesThatApplyToAllViewports();
-        //Remove the scene index registry
-        _sceneIndexRegistry.reset();
     }
 
+    // Remove the scene index registry
+    _sceneIndexRegistry.reset();
+
     #ifdef CODE_COVERAGE_WORKAROUND
         // Leak the Maya scene index, as its base class HdRetainedSceneIndex
         // destructor crashes under Windows clang code coverage build.