Cycles: constant folding for RGB/Vector Curves and Color Ramp.

These are complex nodes, and it's conceivable they may end up constant
in some circumstances within node groups, so folding support is useful.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D2084

intern/cycles/kernel/svm/svm_ramp_util.h

@@ -0,0 +1,97 @@
+/*
+ * 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.
+ */
+
+#ifndef __SVM_RAMP_UTIL_H__
+#define __SVM_RAMP_UTIL_H__
+
+CCL_NAMESPACE_BEGIN
+
+/* NOTE: svm_ramp.h, svm_ramp_util.h and node_ramp_util.h must stay consistent */
+
+ccl_device float3 rgb_ramp_lookup(const float3 *ramp,
+                                  float f,
+                                  bool interpolate,
+                                  bool extrapolate,
+                                  int table_size)
+{
+	if ((f < 0.0f || f > 1.0f) && extrapolate) {
+		float3 t0, dy;
+		if (f < 0.0f) {
+			t0 = ramp[0];
+			dy = t0 - ramp[1],
+			f = -f;
+		}
+		else {
+			t0 = ramp[table_size - 1];
+			dy = t0 - ramp[table_size - 2];
+			f = f - 1.0f;
+		}
+		return t0 + dy * f * (table_size - 1);
+	}
+
+	f = clamp(f, 0.0f, 1.0f) * (table_size - 1);
+
+	/* clamp int as well in case of NaN */
+	int i = clamp(float_to_int(f), 0, table_size-1);
+	float t = f - (float)i;
+
+	float3 result = ramp[i];
+
+	if (interpolate && t > 0.0f)
+		result = (1.0f - t) * result + t * ramp[i + 1];
+
+	return result;
+}
+
+ccl_device float float_ramp_lookup(const float *ramp,
+                                   float f,
+                                   bool interpolate,
+                                   bool extrapolate,
+                                   int table_size)
+{
+	if ((f < 0.0f || f > 1.0f) && extrapolate) {
+		float t0, dy;
+		if (f < 0.0f) {
+			t0 = ramp[0];
+			dy = t0 - ramp[1],
+			f = -f;
+		}
+		else {
+			t0 = ramp[table_size - 1];
+			dy = t0 - ramp[table_size - 2];
+			f = f - 1.0f;
+		}
+		return t0 + dy * f * (table_size - 1);
+	}
+
+	f = clamp(f, 0.0f, 1.0f) * (table_size - 1);
+
+	/* clamp int as well in case of NaN */
+	int i = clamp(float_to_int(f), 0, table_size-1);
+	float t = f - (float)i;
+
+	float result = ramp[i];
+
+	if (interpolate && t > 0.0f)
+		result = (1.0f - t) * result + t * ramp[i + 1];
+
+	return result;
+}
+
+CCL_NAMESPACE_END
+
+#endif /* __SVM_RAMP_UTIL_H__ */
+