Cycles microdisplacement: Support for Catmull-Clark subdivision via OpenSubdiv

Enables Catmull-Clark subdivision meshes with support for creases and attribute
subdivision. Still waiting on OpenSubdiv to fully support face varying
interpolation for subdividing uv coordinates tho. Also there may be some
inconsistencies with Blender's subdivision which will be resolved at a
later time.

Code for reading patch tables and creating patch maps is borrowed
from OpenSubdiv.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D2111

intern/cycles/render/attribute.cpp

@@ -44,6 +44,7 @@ void Attribute::set(ustring name_, TypeDesc type_, AttributeElement element_)
 	type = type_;
 	element = element_;
 	std = ATTR_STD_NONE;
+	flags = 0;
 
 	/* string and matrix not supported! */
 	assert(type == TypeDesc::TypeFloat || type == TypeDesc::TypeColor ||
@@ -61,6 +62,11 @@ void Attribute::resize(Mesh *mesh, AttributePrimitive prim, bool reserve_only)
 	}
 }
 
+void Attribute::resize(size_t num_elements)
+{
+	buffer.resize(num_elements * data_sizeof(), 0);
+}
+
 void Attribute::add(const float& f)
 {
 	char *data = (char*)&f;
@@ -130,6 +136,10 @@ size_t Attribute::data_sizeof() const
 
 size_t Attribute::element_size(Mesh *mesh, AttributePrimitive prim) const
 {
+	if(flags & ATTR_FINAL_SIZE) {
+		return buffer.size() / data_sizeof();
+	}
+
 	size_t size;
 
 	switch(element) {