Cycles: Add method to dump current shader graph to the graphiz file

This is rather useful to see how good optimization went and so.

Currently uses quite simple notation: shader nodes are nodes on the
graph, connects between graph nodes are named by the sockets names,
so i.e. connection between BSDF and Mix would be named bsdf:closure1.

Could be improved in the feature to draw fancier graph, but it's good
enough already.

Use in the following way:
- To create graphix file call graph->dump_graph("graph.dot")
- To visualize the grapf call: dot -Tpng graph.dot -o graph.png

intern/cycles/render/graph.cpp

@@ -835,5 +835,47 @@ void ShaderGraph::transform_multi_closure(ShaderNode *node, ShaderOutput *weight
 	}
 }
 
+void ShaderGraph::dump_graph(const char *filename)
+{
+	FILE *fd = fopen(filename, "w");
+
+	if(fd == NULL) {
+		printf("Error opening file for dumping the graph: %s\n", filename);
+		return;
+	}
+
+	fprintf(fd, "digraph dependencygraph {\n");
+	fprintf(fd, "ranksep=1.5\n");
+	fprintf(fd, "splines=false\n");
+
+	foreach(ShaderNode *node, nodes) {
+		fprintf(fd, "// NODE: %p\n", node);
+		fprintf(fd,
+		        "\"%p\" [shape=record,label=\"%s\"]\n",
+		        node,
+		        node->name.c_str());
+	}
+
+	foreach(ShaderNode *node, nodes) {
+		foreach(ShaderOutput *output, node->outputs) {
+			foreach(ShaderInput *input, output->links) {
+				fprintf(fd,
+				        "// CONNECTION: %p->%p (%s:%s)\n",
+				        output,
+				        input,
+				        output->name, input->name);
+				fprintf(fd,
+				        "\"%p\":s -> \"%p\":n [label=\"%s:%s\"]\n",
+				        output->parent,
+				        input->parent,
+				        output->name, input->name);
+			}
+		}
+	}
+
+	fprintf(fd, "}\n");
+	fclose(fd);
+}
+
 CCL_NAMESPACE_END
 

intern/cycles/render/graph.h

@@ -250,6 +250,8 @@ public:
 	void remove_unneeded_nodes();
 	void finalize(bool do_bump = false, bool do_osl = false);
 
+	void dump_graph(const char *filename);
+
 protected:
 	typedef pair<ShaderNode* const, ShaderNode*> NodePair;