blender/intern/cycles/util/util_math_cdf.h

/*
 * 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,
                       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,
                       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__ */