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, 12 insertions, 0 deletions

diff --git a/source/blender/compositor/intern/COM_NodeOperationBuilder.h b/source/blender/compositor/intern/COM_NodeOperationBuilder.h
index ab890282bab..633ddc9152a 100644
--- a/source/blender/compositor/intern/COM_NodeOperationBuilder.h
+++ b/source/blender/compositor/intern/COM_NodeOperationBuilder.h
@@ -44,6 +44,7 @@ class NodeOperationOutput;
 
 class PreviewOperation;
 class WriteBufferOperation;
+class ViewerOperation;
 
 class NodeOperationBuilder {
 public:
@@ -87,6 +88,12 @@ private:
 	
 	Node *m_current_node;
 	
+	/** Operation that will be writing to the viewer image
+	 *  Only one operation can occupy this place at a time,
+	 *  to avoid race conditions
+	 */
+	ViewerOperation *m_active_viewer;
+	
 public:
 	NodeOperationBuilder(const CompositorContext *context, bNodeTree *b_nodetree);
 	~NodeOperationBuilder();
@@ -110,6 +117,11 @@ public:
 	/** Add a preview operation for a node input */
 	void addNodeInputPreview(NodeInput *input);
 	
+	/** Define a viewer operation as the active output, if possible */
+	void registerViewer(ViewerOperation *viewer);
+	/** The currently active viewer output operation */
+	ViewerOperation *active_viewer() const { return m_active_viewer; }
+	
 protected:
 	static NodeInput *find_node_input(const InputSocketMap &map, NodeOperationInput *op_input);
 	static const OpInputs &find_operation_inputs(const OpInputInverseMap &map, NodeInput *node_input);