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

1 files changed, 31 insertions, 0 deletions

diff --git a/intern/cycles/kernel/shaders/node_bevel.osl b/intern/cycles/kernel/shaders/node_bevel.osl
new file mode 100644
index 00000000000..a5b185b6b4c
--- /dev/null
+++ b/intern/cycles/kernel/shaders/node_bevel.osl
@@ -0,0 +1,31 @@
+/*
+ * Copyright 2011-2013 Blender Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "stdosl.h"
+
+shader node_bevel(
+	int samples = 4,
+	float Radius = 0.05,
+	normal NormalIn = N,
+	output normal NormalOut = N)
+{
+	/* Abuse texture call with special @bevel token. */
+	NormalOut = (normal)(color)texture("@bevel", samples, Radius);
+
+	/* Preserve input normal. */
+	NormalOut = normalize(N + (NormalOut - NormalIn));
+}
+