Cycles / Shader Graph optimization:

* Unnecessary shader inputs inside the Mix Shader are now ignored, in case the factor is 0.0 / 1.0 and not connected. 
This way we save some render time for complex node graphs. 

Example: http://www.pasteall.org/pic/show.php?id=48226
Check the Mix Shader at the end: In this case, Cycles will now avoid the complete huge shader tree, and only calculate the Diffuse Shader.
Rendertime decreased from 1:50 min to 1:20 min on CPU. GPU rendering benefits as well from this. 

This only affects SVM, OSL was already doing these optimizations. 

1 files changed, 39 insertions, 0 deletions

diff --git a/intern/cycles/render/graph.cpp b/intern/cycles/render/graph.cpp
index af27b46771c..50fee15c231 100644
--- a/intern/cycles/render/graph.cpp
+++ b/intern/cycles/render/graph.cpp
@@ -365,6 +365,45 @@ void ShaderGraph::remove_proxy_nodes(vector<bool>& removed)
 				}
 			}
 		}
+		
+		/* remove unused mix closure input when factor is 0.0 or 1.0 */
+		if(node->special_type == SHADER_SPECIAL_TYPE_MIX_CLOSURE) {
+			MixClosureNode *mix = static_cast<MixClosureNode*>(node);
+			/* Check for closure links and make sure factor link is disconnected */
+			if(mix->outputs[0]->links.size() && mix->inputs[1]->link && mix->inputs[2]->link && !mix->inputs[0]->link) {
+			
+				/* Factor 0.0 */
+				if(mix->inputs[0]->value.x == 0.0f) {
+					ShaderOutput *output = mix->inputs[1]->link;
+					vector<ShaderInput*> inputs = mix->outputs[0]->links;
+					
+					foreach(ShaderInput *sock, mix->inputs)
+					if(sock->link)
+						disconnect(sock);
+
+					foreach(ShaderInput *input, inputs) {
+						disconnect(input);
+						if (output)
+						connect(output, input);
+					}
+				}
+				/* Factor 1.0 */
+				else if (mix->inputs[0]->value.x == 1.0f) {
+					ShaderOutput *output = mix->inputs[2]->link;
+					vector<ShaderInput*> inputs = mix->outputs[0]->links;
+					
+					foreach(ShaderInput *sock, mix->inputs)
+					if(sock->link)
+						disconnect(sock);
+
+					foreach(ShaderInput *input, inputs) {
+						disconnect(input);
+						if (output)
+							connect(output, input);
+					}
+				}
+			}
+		}
 	}
 }