Merge of the PyNodes branch (aka "custom nodes") into trunk.

PyNodes opens up the node system in Blender to scripters and adds a number of UI-level improvements.

=== Dynamic node type registration ===
Node types can now be added at runtime, using the RNA registration mechanism from python. This enables addons such as render engines to create a complete user interface with nodes.

Examples of how such nodes can be defined can be found in my personal wiki docs atm [1] and as a script template in release/scripts/templates_py/custom_nodes.py [2].

=== Node group improvements ===
Each node editor now has a tree history of edited node groups, which allows opening and editing nested node groups. The node editor also supports pinning now, so that different spaces can be used to edit different node groups simultaneously. For more ramblings and rationale see (really old) blog post on code.blender.org [3].

The interface of node groups has been overhauled. Sockets of a node group are no longer displayed in columns on either side, but instead special input/output nodes are used to mirror group sockets inside a node tree. This solves the problem of long node lines in groups and allows more adaptable node layout. Internal sockets can be exposed from a group by either connecting to the extension sockets in input/output nodes (shown as empty circle) or by adding sockets from the node property bar in the "Interface" panel. Further details such as the socket name can also be changed there.

[1] http://wiki.blender.org/index.php/User:Phonybone/Python_Nodes
[2] http://projects.blender.org/scm/viewvc.php/trunk/blender/release/scripts/templates_py/custom_nodes.py?view=markup&root=bf-blender
[3] http://code.blender.org/index.php/2012/01/improving-node-group-interface-editing/

14 files changed, 125 insertions, 102 deletions

diff --git a/source/blender/compositor/intern/COM_CompositorContext.cpp b/source/blender/compositor/intern/COM_CompositorContext.cpp
index e1cc25d028a..6008a889205 100644
--- a/source/blender/compositor/intern/COM_CompositorContext.cpp
+++ b/source/blender/compositor/intern/COM_CompositorContext.cpp
@@ -29,7 +29,6 @@ CompositorContext::CompositorContext()
 	this->m_rd = NULL;
 	this->m_quality = COM_QUALITY_HIGH;
 	this->m_hasActiveOpenCLDevices = false;
-	this->m_activegNode = NULL;
 	this->m_fastCalculation = false;
 	this->m_viewSettings = NULL;
 	this->m_displaySettings = NULL;
diff --git a/source/blender/compositor/intern/COM_CompositorContext.h b/source/blender/compositor/intern/COM_CompositorContext.h
index 840a9e59584..3c7db703bf9 100644
--- a/source/blender/compositor/intern/COM_CompositorContext.h
+++ b/source/blender/compositor/intern/COM_CompositorContext.h
@@ -64,11 +64,12 @@ private:
 	 * @see ExecutionSystem
 	 */
 	bNodeTree *m_bnodetree;
-	
+
 	/**
-	 * @brief activegNode the group node that is currently being edited.
+	 * @brief Preview image hash table
+	 * This field is initialized in ExecutionSystem and must only be read from that point on.
 	 */
-	bNode *m_activegNode;
+	bNodeInstanceHash *m_previews;
 
 	/**
 	 * @brief does this system have active opencl devices?
@@ -115,19 +116,19 @@ public:
 	const bNodeTree *getbNodeTree() const { return this->m_bnodetree; }
 
 	/**
-	 * @brief set the active groupnode of the context
+	 * @brief get the scene of the context
 	 */
-	void setActivegNode(bNode *gnode) { this->m_activegNode = gnode; }
+	const RenderData *getRenderData() const { return this->m_rd; }
 
 	/**
-	 * @brief get the active groupnode of the context
+	 * @brief set the preview image hash table
 	 */
-	const bNode *getActivegNode() const { return this->m_activegNode; }
+	void setPreviewHash(bNodeInstanceHash *previews) { this->m_previews = previews; }
 
 	/**
-	 * @brief get the scene of the context
+	 * @brief get the preview image hash table
 	 */
-	const RenderData *getRenderData() const { return this->m_rd; }
+	bNodeInstanceHash *getPreviewHash() const { return this->m_previews; }
 
 	/**
 	 * @brief set view settings of color color management
diff --git a/source/blender/compositor/intern/COM_Converter.cpp b/source/blender/compositor/intern/COM_Converter.cpp
index 9c4a32f20c9..80f5b4fc149 100644
--- a/source/blender/compositor/intern/COM_Converter.cpp
+++ b/source/blender/compositor/intern/COM_Converter.cpp
@@ -124,7 +124,7 @@
 
 Node *Converter::convert(bNode *b_node, bool fast)
 {
-	Node *node;
+	Node *node = NULL;
 
 	if (b_node->flag & NODE_MUTED) {
 		node = new MuteNode(b_node);
@@ -226,6 +226,10 @@ Node *Converter::convert(bNode *b_node, bool fast)
 		case NODE_GROUP:
 			node = new GroupNode(b_node);
 			break;
+		case NODE_GROUP_INPUT:
+		case NODE_GROUP_OUTPUT:
+			/* handled in GroupNode::ungroup */
+			break;
 		case CMP_NODE_NORMAL:
 			node = new NormalNode(b_node);
 			break;
@@ -399,7 +403,6 @@ Node *Converter::convert(bNode *b_node, bool fast)
 			node = new PixelateNode(b_node);
 			break;
 		default:
-			node = new MuteNode(b_node);
 			break;
 	}
 	return node;
diff --git a/source/blender/compositor/intern/COM_ExecutionSystem.cpp b/source/blender/compositor/intern/COM_ExecutionSystem.cpp
index 2b2af73d0c8..2da1c34ab44 100644
--- a/source/blender/compositor/intern/COM_ExecutionSystem.cpp
+++ b/source/blender/compositor/intern/COM_ExecutionSystem.cpp
@@ -49,7 +49,9 @@ ExecutionSystem::ExecutionSystem(RenderData *rd, bNodeTree *editingtree, bool re
                                  const ColorManagedViewSettings *viewSettings, const ColorManagedDisplaySettings *displaySettings)
 {
 	this->m_context.setbNodeTree(editingtree);
+	this->m_context.setPreviewHash(editingtree->previews);
 	this->m_context.setFastCalculation(fastcalculation);
+#if 0	/* XXX TODO find a better way to define visible output nodes from all editors */
 	bNode *gnode;
 	for (gnode = (bNode *)editingtree->nodes.first; gnode; gnode = gnode->next) {
 		if (gnode->type == NODE_GROUP && gnode->typeinfo->group_edit_get(gnode)) {
@@ -57,6 +59,7 @@ ExecutionSystem::ExecutionSystem(RenderData *rd, bNodeTree *editingtree, bool re
 			break;
 		}
 	}
+#endif
 
 	/* initialize the CompositorContext */
 	if (rendering) {
@@ -68,7 +71,7 @@ ExecutionSystem::ExecutionSystem(RenderData *rd, bNodeTree *editingtree, bool re
 	this->m_context.setRendering(rendering);
 	this->m_context.setHasActiveOpenCLDevices(WorkScheduler::hasGPUDevices() && (editingtree->flag & NTREE_COM_OPENCL));
 
-	ExecutionSystemHelper::addbNodeTree(*this, 0, editingtree, NULL);
+	ExecutionSystemHelper::addbNodeTree(*this, 0, editingtree, NODE_INSTANCE_KEY_BASE);
 
 	this->m_context.setRenderData(rd);
 	this->m_context.setViewSettings(viewSettings);
diff --git a/source/blender/compositor/intern/COM_ExecutionSystemHelper.cpp b/source/blender/compositor/intern/COM_ExecutionSystemHelper.cpp
index 506bd42ace3..ad396e053f2 100644
--- a/source/blender/compositor/intern/COM_ExecutionSystemHelper.cpp
+++ b/source/blender/compositor/intern/COM_ExecutionSystemHelper.cpp
@@ -26,7 +26,6 @@
 #include <stdio.h>
 
 #include "PIL_time.h"
-#include "BKE_node.h"
 
 #include "COM_Converter.h"
 #include "COM_NodeOperation.h"
@@ -39,18 +38,25 @@
 #include "COM_ReadBufferOperation.h"
 #include "COM_ViewerBaseOperation.h"
 
-void ExecutionSystemHelper::addbNodeTree(ExecutionSystem &system, int nodes_start, bNodeTree *tree, bNode *groupnode)
+extern "C" {
+#include "BKE_node.h"
+}
+
+void ExecutionSystemHelper::addbNodeTree(ExecutionSystem &system, int nodes_start, bNodeTree *tree, bNodeInstanceKey parent_key)
 {
 	vector<Node *>& nodes = system.getNodes();
 	vector<SocketConnection *>& links = system.getConnections();
-	const bNode *activeGroupNode = system.getContext().getActivegNode();
-	bool isActiveGroup = activeGroupNode == groupnode;
 	
 	/* add all nodes of the tree to the node list */
 	bNode *node = (bNode *)tree->nodes.first;
 	while (node != NULL) {
+		/* XXX TODO replace isActiveGroup by a more accurate check, all visible editors should do this! */
+		bool isActiveGroup = true;
 		Node *nnode = addNode(nodes, node, isActiveGroup, system.getContext().isFastCalculation());
-		nnode->setbNodeGroup(groupnode);
+		if (nnode) {
+			nnode->setbNodeTree(tree);
+			nnode->setInstanceKey(BKE_node_instance_key(parent_key, tree, node));
+		}
 		node = node->next;
 	}
 
@@ -81,8 +87,10 @@ void ExecutionSystemHelper::addNode(vector<Node *>& nodes, Node *node)
 Node *ExecutionSystemHelper::addNode(vector<Node *>& nodes, bNode *b_node, bool inActiveGroup, bool fast)
 {
 	Node *node = Converter::convert(b_node, fast);
-	node->setIsInActiveGroup(inActiveGroup);
-	addNode(nodes, node);
+	if (node) {
+		node->setIsInActiveGroup(inActiveGroup);
+		addNode(nodes, node);
+	}
 	return node;
 }
 void ExecutionSystemHelper::addOperation(vector<NodeOperation *>& operations, NodeOperation *operation)
@@ -109,43 +117,21 @@ void ExecutionSystemHelper::findOutputNodeOperations(vector<NodeOperation *> *re
 
 static InputSocket *find_input(NodeRange &node_range, bNode *bnode, bNodeSocket *bsocket)
 {
-	if (bnode != NULL) {
-		for (NodeIterator it = node_range.first; it != node_range.second; ++it) {
-			Node *node = *it;
-			if (node->getbNode() == bnode)
-				return node->findInputSocketBybNodeSocket(bsocket);
-		}
-	}
-	else {
-		for (NodeIterator it = node_range.first; it != node_range.second; ++it) {
-			Node *node = *it;
-			if (node->isProxyNode()) {
-				InputSocket *proxySocket = node->getInputSocket(0);
-				if (proxySocket->getbNodeSocket() == bsocket)
-					return proxySocket;
-			}
-		}
+	for (NodeIterator it = node_range.first; it != node_range.second; ++it) {
+		Node *node = *it;
+		InputSocket *input = node->findInputSocketBybNodeSocket(bsocket);
+		if (input)
+			return input;
 	}
 	return NULL;
 }
 static OutputSocket *find_output(NodeRange &node_range, bNode *bnode, bNodeSocket *bsocket)
 {
-	if (bnode != NULL) {
-		for (NodeIterator it = node_range.first; it != node_range.second; ++it) {
-			Node *node = *it;
-			if (node->getbNode() == bnode)
-				return node->findOutputSocketBybNodeSocket(bsocket);
-		}
-	}
-	else {
-		for (NodeIterator it = node_range.first; it != node_range.second; ++it) {
-			Node *node = *it;
-			if (node->isProxyNode()) {
-				OutputSocket *proxySocket = node->getOutputSocket(0);
-				if (proxySocket->getbNodeSocket() == bsocket)
-					return proxySocket;
-			}
-		}
+	for (NodeIterator it = node_range.first; it != node_range.second; ++it) {
+		Node *node = *it;
+		OutputSocket *output = node->findOutputSocketBybNodeSocket(bsocket);
+		if (output)
+			return output;
 	}
 	return NULL;
 }
@@ -190,7 +176,7 @@ void ExecutionSystemHelper::debugDump(ExecutionSystem *system)
 	tot = system->getNodes().size();
 	for (int i = 0; i < tot; i++) {
 		node = system->getNodes()[i];
-		printf("// NODE: %s\r\n", node->getbNode()->typeinfo->name);
+		printf("// NODE: %s\r\n", node->getbNode()->typeinfo->ui_name);
 	}
 	tot = system->getOperations().size();
 	for (int i = 0; i < tot; i++) {
diff --git a/source/blender/compositor/intern/COM_ExecutionSystemHelper.h b/source/blender/compositor/intern/COM_ExecutionSystemHelper.h
index 307e082ea80..e05796b9127 100644
--- a/source/blender/compositor/intern/COM_ExecutionSystemHelper.h
+++ b/source/blender/compositor/intern/COM_ExecutionSystemHelper.h
@@ -48,7 +48,7 @@ public:
 	 * @param tree bNodeTree to add
 	 * @return Node representing the "Compositor node" of the maintree. or NULL when a subtree is added
 	 */
-	static void addbNodeTree(ExecutionSystem &system, int nodes_start, bNodeTree *tree, bNode *groupnode);
+	static void addbNodeTree(ExecutionSystem &system, int nodes_start, bNodeTree *tree, bNodeInstanceKey parent_key);
 
 	/**
 	 * @brief add an editor node to the system.
diff --git a/source/blender/compositor/intern/COM_InputSocket.cpp b/source/blender/compositor/intern/COM_InputSocket.cpp
index 2493d4e5a27..6868745d631 100644
--- a/source/blender/compositor/intern/COM_InputSocket.cpp
+++ b/source/blender/compositor/intern/COM_InputSocket.cpp
@@ -157,24 +157,3 @@ NodeOperation *InputSocket::getOperation() const
 		return NULL;
 	}
 }
-
-float *InputSocket::getStaticValues()
-{
-	/* XXX only works for socket types with actual float input values.
-	 * currently all compositor socket types (value, rgba, vector) support this.
-	 */
-	bNodeSocket *b_socket = this->getbNodeSocket();
-	static float default_null = 0.0f;
-	
-	switch (this->getDataType()) {
-		case COM_DT_VALUE:
-			return &((bNodeSocketValueFloat *)b_socket->default_value)->value;
-		case COM_DT_COLOR:
-			return ((bNodeSocketValueRGBA *)b_socket->default_value)->value;
-		case COM_DT_VECTOR:
-			return ((bNodeSocketValueVector *)b_socket->default_value)->value;
-		default:
-			/* XXX this should never happen, just added to please the compiler */
-			return &default_null;
-	}
-}
diff --git a/source/blender/compositor/intern/COM_InputSocket.h b/source/blender/compositor/intern/COM_InputSocket.h
index 5cd4cf3beb7..5a36fe3f33b 100644
--- a/source/blender/compositor/intern/COM_InputSocket.h
+++ b/source/blender/compositor/intern/COM_InputSocket.h
@@ -143,7 +143,6 @@ public:
 	
 	bool isStatic();
 	
-	float *getStaticValues();
 	SocketReader *getReader();
 	NodeOperation *getOperation() const;
 };
diff --git a/source/blender/compositor/intern/COM_Node.cpp b/source/blender/compositor/intern/COM_Node.cpp
index d49bb5f96fb..f59580acb50 100644
--- a/source/blender/compositor/intern/COM_Node.cpp
+++ b/source/blender/compositor/intern/COM_Node.cpp
@@ -67,10 +67,9 @@ Node::Node(bNode *editorNode, bool create_sockets): NodeBase()
 
 void Node::addSetValueOperation(ExecutionSystem *graph, InputSocket *inputsocket, int editorNodeInputSocketIndex)
 {
-	bNodeSocket *bSock = this->getEditorInputSocket(editorNodeInputSocketIndex);
+	InputSocket *input = getInputSocket(editorNodeInputSocketIndex);
 	SetValueOperation *operation = new SetValueOperation();
-	bNodeSocketValueFloat *val = (bNodeSocketValueFloat *)bSock->default_value;
-	operation->setValue(val->value);
+	operation->setValue(input->getEditorValueFloat());
 	this->addLink(graph, operation->getOutputSocket(), inputsocket);
 	graph->addOperation(operation);
 }
@@ -79,11 +78,13 @@ void Node::addPreviewOperation(ExecutionSystem *system, CompositorContext *conte
 {
 	if (this->isInActiveGroup()) {
 		if (!(this->getbNode()->flag & NODE_HIDDEN)) { // do not calculate previews of hidden nodes.
-			if (this->getbNode()->flag & NODE_PREVIEW) {
+			bNodeInstanceHash *previews = context->getPreviewHash();
+			if (previews && (this->getbNode()->flag & NODE_PREVIEW)) {
 				PreviewOperation *operation = new PreviewOperation(context->getViewSettings(), context->getDisplaySettings());
 				system->addOperation(operation);
 				operation->setbNode(this->getbNode());
 				operation->setbNodeTree(system->getContext().getbNodeTree());
+				operation->verifyPreview(previews, this->getInstanceKey());
 				this->addLink(system, outputSocket, operation->getInputSocket(0));
 			}
 		}
@@ -114,25 +115,27 @@ SocketConnection *Node::addLink(ExecutionSystem *graph, OutputSocket *outputSock
 
 void Node::addSetColorOperation(ExecutionSystem *graph, InputSocket *inputsocket, int editorNodeInputSocketIndex)
 {
-	bNodeSocket *bSock = this->getEditorInputSocket(editorNodeInputSocketIndex);
+	InputSocket *input = getInputSocket(editorNodeInputSocketIndex);
 	SetColorOperation *operation = new SetColorOperation();
-	bNodeSocketValueRGBA *val = (bNodeSocketValueRGBA *)bSock->default_value;
-	operation->setChannel1(val->value[0]);
-	operation->setChannel2(val->value[1]);
-	operation->setChannel3(val->value[2]);
-	operation->setChannel4(val->value[3]);
+	float col[4];
+	input->getEditorValueColor(col);
+	operation->setChannel1(col[0]);
+	operation->setChannel2(col[1]);
+	operation->setChannel3(col[2]);
+	operation->setChannel4(col[3]);
 	this->addLink(graph, operation->getOutputSocket(), inputsocket);
 	graph->addOperation(operation);
 }
 
 void Node::addSetVectorOperation(ExecutionSystem *graph, InputSocket *inputsocket, int editorNodeInputSocketIndex)
 {
-	bNodeSocket *bSock = this->getEditorInputSocket(editorNodeInputSocketIndex);
-	bNodeSocketValueVector *val = (bNodeSocketValueVector *)bSock->default_value;
+	InputSocket *input = getInputSocket(editorNodeInputSocketIndex);
 	SetVectorOperation *operation = new SetVectorOperation();
-	operation->setX(val->value[0]);
-	operation->setY(val->value[1]);
-	operation->setZ(val->value[2]);
+	float vec[3];
+	input->getEditorValueVector(vec);
+	operation->setX(vec[0]);
+	operation->setY(vec[1]);
+	operation->setZ(vec[2]);
 	this->addLink(graph, operation->getOutputSocket(), inputsocket);
 	graph->addOperation(operation);
 }
diff --git a/source/blender/compositor/intern/COM_Node.h b/source/blender/compositor/intern/COM_Node.h
index 5b0381f6443..fb5dfe2e9b7 100644
--- a/source/blender/compositor/intern/COM_Node.h
+++ b/source/blender/compositor/intern/COM_Node.h
@@ -53,12 +53,11 @@ private:
 	 * @brief Is this node part of the active group
 	 */
 	bool m_inActiveGroup;
-	
+
 	/**
-	 * @brief The group node this node belongs to.
-	 * @note: used to find the links in the current subtree for muting nodes
+	 * @brief Instance key to identify the node in an instance hash table
 	 */
-	bNode *m_bNodeGroup;
+	bNodeInstanceKey m_instanceKey;
 
 public:
 	Node(bNode *editorNode, bool create_sockets = true);
@@ -145,8 +144,9 @@ public:
 	 */
 	OutputSocket *findOutputSocketBybNodeSocket(bNodeSocket *socket);
 	
-	inline void setbNodeGroup(bNode *group) {this->m_bNodeGroup = group;}
-	inline bNode *getbNodeGroup() {return this->m_bNodeGroup;}
+	void setInstanceKey(bNodeInstanceKey instance_key) { m_instanceKey = instance_key; }
+	bNodeInstanceKey getInstanceKey() const { return m_instanceKey; }
+	
 protected:
 	void addPreviewOperation(ExecutionSystem *system, CompositorContext *context, InputSocket *inputSocket);
 	void addPreviewOperation(ExecutionSystem *system, CompositorContext *context, OutputSocket *outputSocket);
diff --git a/source/blender/compositor/intern/COM_NodeBase.h b/source/blender/compositor/intern/COM_NodeBase.h
index e386b5e08a0..41b6ab70bf9 100644
--- a/source/blender/compositor/intern/COM_NodeBase.h
+++ b/source/blender/compositor/intern/COM_NodeBase.h
@@ -59,6 +59,11 @@ private:
 	 */
 	bNode *m_editorNode;
 
+	/**
+	 * @brief stores the reference to the SDNA bNode struct
+	 */
+	bNodeTree *m_editorNodeTree;
+
 protected:
 	/**
 	 * @brief get access to the vector of input sockets
@@ -82,14 +87,25 @@ public:
 	/**
 	 * @brief get the reference to the SDNA bNode struct
 	 */
-	bNode *getbNode() {return m_editorNode;}
+	bNode *getbNode() const {return m_editorNode;}
+
+	/**
+	 * @brief get the reference to the SDNA bNodeTree struct
+	 */
+	bNodeTree *getbNodeTree() const {return m_editorNodeTree;}
 	
 	/**
 	 * @brief set the reference to the bNode
 	 * @note used in Node instances to receive the storage/settings and complex node for highlight during execution
 	 * @param bNode
 	 */
-	void setbNode(bNode *bNode) {this->m_editorNode = bNode;}
+	void setbNode(bNode *node) {this->m_editorNode = node;}
+	
+	/**
+	 * @brief set the reference to the bNodeTree
+	 * @param bNodeTree
+	 */
+	void setbNodeTree(bNodeTree *nodetree) {this->m_editorNodeTree = nodetree;}
 	
 	/**
 	 * @brief is this node an operation?
diff --git a/source/blender/compositor/intern/COM_Socket.cpp b/source/blender/compositor/intern/COM_Socket.cpp
index 30f28f9dddb..3465fa6f56d 100644
--- a/source/blender/compositor/intern/COM_Socket.cpp
+++ b/source/blender/compositor/intern/COM_Socket.cpp
@@ -24,6 +24,10 @@
 #include "COM_Node.h"
 #include "COM_SocketConnection.h"
 
+extern "C" {
+#include "RNA_access.h"
+}
+
 Socket::Socket(DataType datatype)
 {
 	this->m_datatype = datatype;
@@ -41,3 +45,24 @@ int Socket::isOutputSocket() const { return false; }
 const int Socket::isConnected() const { return false; }
 void Socket::setNode(NodeBase *node) { this->m_node = node; }
 NodeBase *Socket::getNode() const { return this->m_node; }
+
+float Socket::getEditorValueFloat()
+{
+	PointerRNA ptr;
+	RNA_pointer_create((ID *)getNode()->getbNodeTree(), &RNA_NodeSocket, getbNodeSocket(), &ptr);
+	return RNA_float_get(&ptr, "default_value");
+}
+
+void Socket::getEditorValueColor(float *value)
+{
+	PointerRNA ptr;
+	RNA_pointer_create((ID *)getNode()->getbNodeTree(), &RNA_NodeSocket, getbNodeSocket(), &ptr);
+	return RNA_float_get_array(&ptr, "default_value", value);
+}
+
+void Socket::getEditorValueVector(float *value)
+{
+	PointerRNA ptr;
+	RNA_pointer_create((ID *)getNode()->getbNodeTree(), &RNA_NodeSocket, getbNodeSocket(), &ptr);
+	return RNA_float_get_array(&ptr, "default_value", value);
+}
diff --git a/source/blender/compositor/intern/COM_Socket.h b/source/blender/compositor/intern/COM_Socket.h
index bad112d20c7..6532864a4d9 100644
--- a/source/blender/compositor/intern/COM_Socket.h
+++ b/source/blender/compositor/intern/COM_Socket.h
@@ -36,6 +36,7 @@
 using namespace std;
 class SocketConnection;
 class NodeBase;
+struct PointerRNA;
 
 /**
  * @brief Base class for InputSocket and OutputSocket.
@@ -86,6 +87,10 @@ public:
 	void setEditorSocket(bNodeSocket *editorSocket) { this->m_editorSocket = editorSocket; }
 	bNodeSocket *getbNodeSocket() const { return this->m_editorSocket; }
 	
+	float getEditorValueFloat();
+	void getEditorValueColor(float *value);
+	void getEditorValueVector(float *value);
+
 #ifdef WITH_CXX_GUARDEDALLOC
 	MEM_CXX_CLASS_ALLOC_FUNCS("COM:Socket")
 #endif
diff --git a/source/blender/compositor/intern/COM_compositor.cpp b/source/blender/compositor/intern/COM_compositor.cpp
index 49ab9db5dd8..94a27e17b68 100644
--- a/source/blender/compositor/intern/COM_compositor.cpp
+++ b/source/blender/compositor/intern/COM_compositor.cpp
@@ -21,9 +21,9 @@
  */
 
 
-#include "BKE_node.h"
 extern "C" {
-	#include "BLI_threads.h"
+#include "BKE_node.h"
+#include "BLI_threads.h"
 }
 #include "BKE_main.h"
 #include "BKE_global.h"
@@ -63,6 +63,11 @@ void COM_execute(RenderData *rd, bNodeTree *editingtree, int rendering,
 		return;
 	}
 
+	/* Make sure node tree has previews.
+	 * Don't create previews in advance, this is done when adding preview operations.
+	 */
+	BKE_node_preview_init_tree(editingtree, COM_PREVIEW_SIZE, COM_PREVIEW_SIZE, FALSE);
+
 	/* initialize workscheduler, will check if already done. TODO deinitialize somewhere */
 	bool use_opencl = (editingtree->flag & NTREE_COM_OPENCL);
 	WorkScheduler::initialize(use_opencl);
@@ -85,7 +90,6 @@ void COM_execute(RenderData *rd, bNodeTree *editingtree, int rendering,
 		}
 	}
 
-	
 	ExecutionSystem *system = new ExecutionSystem(rd, editingtree, rendering, false, viewSettings, displaySettings);
 	system->execute();
 	delete system;