Cycles: Add utility functions to evaluate CDF of a given functor

intern/cycles/util/CMakeLists.txt

@@ -12,6 +12,7 @@ set(SRC
 	util_aligned_malloc.cpp
 	util_cache.cpp
 	util_logging.cpp
+	util_math_cdf.cpp
 	util_md5.cpp
 	util_path.cpp
 	util_string.cpp
@@ -49,6 +50,7 @@ set(SRC_HEADERS
 	util_logging.h
 	util_map.h
 	util_math.h
+	util_math_cdf.h
 	util_math_fast.h
 	util_md5.h
 	util_opengl.h

intern/cycles/util/util_math_cdf.cpp

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2011-2015 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 "util_math_cdf.h"
+
+#include "util_algorithm.h"
+#include "util_math.h"
+
+CCL_NAMESPACE_BEGIN
+
+/* Invert pre-calculated CDF function. */
+void util_cdf_invert(const int resolution,
+                     const float from,
+                     const float to,
+                     const vector<float> &cdf,
+                     const bool make_symmetric,
+                     vector<float> &inv_cdf) {
+	const float inv_resolution = 1.0f / (float)resolution;
+	const float range = to - from;
+	inv_cdf.resize(resolution);
+	if(make_symmetric) {
+		const int half_size = (resolution - 1) / 2;
+		for(int i = 0; i <= half_size; i++) {
+			float x = i / (float)half_size;
+			int index = upper_bound(cdf.begin(), cdf.end(), x) - cdf.begin();
+			float t;
+			if(index < cdf.size()) {
+				t = (x - cdf[index])/(cdf[index+1] - cdf[index]);
+			} else {
+				t = 0.0f;
+				index = cdf.size() - 1;
+			}
+			float y = ((index + t) / (resolution - 1)) * (2.0f * range);
+			inv_cdf[half_size+i] = 0.5f*(1.0f + y);
+			inv_cdf[half_size-i] = 0.5f*(1.0f - y);
+		}
+	}
+	else {
+		for(int i = 0; i <= resolution; i++) {
+			float x = from + range * (float)i * inv_resolution;
+			int index = upper_bound(cdf.begin(), cdf.end(), x) - cdf.begin();
+			float t;
+			if(index < cdf.size()) {
+				t = (x - cdf[index])/(cdf[index+1] - cdf[index]);
+			} else {
+				t = 0.0f;
+				index = resolution;
+			}
+			inv_cdf[i] = (index + t) * inv_resolution;
+		}
+	}
+}
+
+CCL_NAMESPACE_END

intern/cycles/util/util_math_cdf.h

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2011-2015 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 __UTIL_MATH_CDF_H__
+#define __UTIL_MATH_CDF_H__
+
+#include "util_algorithm.h"
+#include "util_math.h"
+#include "util_vector.h"
+
+CCL_NAMESPACE_BEGIN
+
+/* Evaluate CDF of a given functor with given range and resolution. */
+template <typename Functor>
+void util_cdf_evaluate(const int resolution,
+                       const float from,
+                       const float to,
+                       const Functor functor,
+                       vector<float> &cdf)
+{
+	const int cdf_count = resolution + 1;
+	const float range = to - from;
+	cdf.resize(cdf_count);
+	cdf[0] = 0.0f;
+	/* Actual CDF evaluation. */
+	for(int i = 0; i < resolution; ++i) {
+		float x = from + range * (float)i / (resolution - 1);
+		float y = functor(x);
+		cdf[i + 1] = cdf[i] + fabsf(y);
+	}
+	/* Normalize the CDF. */
+	for(int i = 0; i <= resolution; i++) {
+		cdf[i] /= cdf[resolution];
+	}
+}
+
+/* Invert pre-calculated CDF function. */
+void util_cdf_invert(const int resolution,
+                     const float from,
+                     const float to,
+                     const vector<float> &cdf,
+                     const bool make_symmetric,
+                     vector<float> &inv_cdf);
+
+/* Evaluate inverted CDF of a given functor with given range and resolution. */
+template <typename Functor>
+void util_cdf_inverted(const int resolution,
+                       const float from,
+                       const float to,
+                       const Functor functor,
+                       const bool make_symmetric,
+                       vector<float> &inv_cdf)
+{
+	vector<float> cdf;
+	/* There is no much smartness going around lower resolution for the CDF table,
+	 * this just to match the old code from pixel filter so it all stays exactly
+	 * the same and no regression tests are failed.
+	 */
+	util_cdf_evaluate(resolution - 1, from, to, functor, cdf);
+	util_cdf_invert(resolution, from, to, cdf, make_symmetric, inv_cdf);
+}
+
+CCL_NAMESPACE_END
+
+#endif /* __UTIL_MATH_H_CDF__ */