Cycles: add bevel shader, for raytrace based rounded edges.

The algorithm averages normals from nearby surfaces. It uses the same
sampling strategy as BSSRDFs, casting rays along the normal and two
orthogonal axes, and combining the samples with MIS.

The main concern here is that we are introducing raytracing inside
shader evaluation, which could be quite bad for GPU performance and
stack memory usage. In practice it doesn't seem so bad though.

Note that using this feature can easily slow down renders 20%, and
that if you care about performance then it's better to use a bevel
modifier. Mainly this is useful for baking, and for cases where the
mesh topology makes it difficult for the bevel modifier to work well.

Differential Revision: https://developer.blender.org/D2803

2 files changed, 52 insertions, 0 deletions

diff --git a/intern/cycles/render/nodes.cpp b/intern/cycles/render/nodes.cpp
index 2b682756c6a..4452fadaf02 100644
--- a/intern/cycles/render/nodes.cpp
+++ b/intern/cycles/render/nodes.cpp
@@ -5604,4 +5604,44 @@ void TangentNode::compile(OSLCompiler& compiler)
 	compiler.add(this, "node_tangent"); 
 }
 
+/* Bevel */
+
+NODE_DEFINE(BevelNode)
+{
+	NodeType* type = NodeType::add("bevel", create, NodeType::SHADER);
+
+	SOCKET_INT(samples, "Samples", 4);
+
+	SOCKET_IN_FLOAT(radius, "Radius", 0.05f);
+	SOCKET_IN_NORMAL(normal, "Normal", make_float3(0.0f, 0.0f, 0.0f), SocketType::LINK_NORMAL);
+
+	SOCKET_OUT_NORMAL(bevel, "Normal");
+
+	return type;
+}
+
+BevelNode::BevelNode()
+: ShaderNode(node_type)
+{
+}
+
+void BevelNode::compile(SVMCompiler& compiler)
+{
+	ShaderInput *radius_in = input("Radius");
+	ShaderInput *normal_in = input("Normal");
+	ShaderOutput *normal_out = output("Normal");
+
+	compiler.add_node(NODE_BEVEL,
+		compiler.encode_uchar4(samples,
+		                       compiler.stack_assign(radius_in),
+		                       compiler.stack_assign_if_linked(normal_in),
+		                       compiler.stack_assign(normal_out)));
+}
+
+void BevelNode::compile(OSLCompiler& compiler)
+{
+	compiler.parameter(this, "samples");
+	compiler.add(this, "node_bevel");
+}
+
 CCL_NAMESPACE_END
diff --git a/intern/cycles/render/nodes.h b/intern/cycles/render/nodes.h
index 3b8a8bcd4b5..64d7522a23a 100644
--- a/intern/cycles/render/nodes.h
+++ b/intern/cycles/render/nodes.h
@@ -1015,6 +1015,18 @@ public:
 	float3 normal_osl;
 };
 
+class BevelNode : public ShaderNode {
+public:
+	SHADER_NODE_CLASS(BevelNode)
+	bool has_spatial_varying() { return true; }
+	virtual int get_group() { return NODE_GROUP_LEVEL_3; }
+	virtual bool has_raytrace() { return true; }
+
+	float radius;
+	float3 normal;
+	int samples;
+};
+
 CCL_NAMESPACE_END
 
 #endif /* __NODES_H__ */