Fix Cycles viewport render not updating when tweaking displacement shader.

This was disabled to avoid updating the geometry every time when the
material includes displacement, because there was no way to distinguish
between surface shader and displacement updates.

As a solution, we now compute an MD5 hash of the nodes linked to the
displacement socket, and only update the mesh if that changes.

Differential Revision: https://developer.blender.org/D3018

1 files changed, 19 insertions, 4 deletions

diff --git a/intern/cycles/render/shader.cpp b/intern/cycles/render/shader.cpp
index abb9e19a074..51b7f76b9d5 100644
--- a/intern/cycles/render/shader.cpp
+++ b/intern/cycles/render/shader.cpp
@@ -200,7 +200,7 @@ Shader::Shader()
 	used = false;
 
 	need_update = true;
-	need_update_attributes = true;
+	need_update_mesh = true;
 }
 
 Shader::~Shader()
@@ -235,9 +235,24 @@ void Shader::set_graph(ShaderGraph *graph_)
 	/* do this here already so that we can detect if mesh or object attributes
 	 * are needed, since the node attribute callbacks check if their sockets
 	 * are connected but proxy nodes should not count */
-	if(graph_)
+	if(graph_) {
 		graph_->remove_proxy_nodes();
 
+		if(displacement_method != DISPLACE_BUMP) {
+			graph_->compute_displacement_hash();
+		}
+	}
+
+	/* update geometry if displacement changed */
+	if(displacement_method != DISPLACE_BUMP) {
+		const char *old_hash = (graph)? graph->displacement_hash.c_str() : "";
+		const char *new_hash = (graph_)? graph_->displacement_hash.c_str() : "";
+
+		if(strcmp(old_hash, new_hash) != 0) {
+			need_update_mesh = true;
+		}
+	}
+
 	/* assign graph */
 	delete graph;
 	graph = graph_;
@@ -294,9 +309,9 @@ void Shader::tag_update(Scene *scene)
 	}
 	
 	/* compare if the attributes changed, mesh manager will check
-	 * need_update_attributes, update the relevant meshes and clear it. */
+	 * need_update_mesh, update the relevant meshes and clear it. */
 	if(attributes.modified(prev_attributes)) {
-		need_update_attributes = true;
+		need_update_mesh = true;
 		scene->mesh_manager->need_update = true;
 	}