Fix T40986: crash on using the viewer node inside of group nodes.

Viewers were activated both inside the active group as well as the top
level tree (the latter being a quick fix for getting a fallback viewer).
This caused a race condition on the shared viewer image.

Now the active viewer is defined at node conversion time in the converter
so that only one can be active at a time without each node having to
follow complicated rules for exclusion.

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/compositor/intern/COM_NodeConverter.h b/source/blender/compositor/intern/COM_NodeConverter.h
index cad8408a2bf..e5e7629f39a 100644
--- a/source/blender/compositor/intern/COM_NodeConverter.h
+++ b/source/blender/compositor/intern/COM_NodeConverter.h
@@ -34,6 +34,8 @@ class NodeOperationInput;
 class NodeOperationOutput;
 class NodeOperationBuilder;
 
+class ViewerOperation;
+
 /** Interface type for converting a \a Node into \a NodeOperation.
  *  This is passed to \a Node::convertToOperation methods and allows them
  *  to register any number of operations, create links between them,
@@ -102,6 +104,11 @@ public:
 	 */
 	NodeOperation *setInvalidOutput(NodeOutput *output);
 	
+	/** Define a viewer operation as the active output, if possible */
+	void registerViewer(ViewerOperation *viewer);
+	/** The currently active viewer output operation */
+	ViewerOperation *active_viewer() const;
+	
 private:
 	/** The internal builder for storing the results of the graph construction. */
 	NodeOperationBuilder *m_builder;