61 lines
1.7 KiB
C++
61 lines
1.7 KiB
C++
/* SPDX-License-Identifier: Apache-2.0
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* Copyright 2011-2022 Blender Foundation */
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#include "util/math_cdf.h"
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#include "util/algorithm.h"
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#include "util/math.h"
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CCL_NAMESPACE_BEGIN
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/* Invert pre-calculated CDF function. */
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void util_cdf_invert(const int resolution,
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const float from,
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const float to,
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const vector<float> &cdf,
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const bool make_symmetric,
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vector<float> &inv_cdf)
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{
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const int cdf_size = cdf.size();
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assert(cdf[0] == 0.0f && cdf[cdf_size - 1] == 1.0f);
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const float inv_resolution = 1.0f / (float)resolution;
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const float range = to - from;
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inv_cdf.resize(resolution);
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if (make_symmetric) {
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const int half_size = (resolution - 1) / 2;
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for (int i = 0; i <= half_size; i++) {
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float x = i / (float)half_size;
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int index = upper_bound(cdf.begin(), cdf.end(), x) - cdf.begin();
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float t;
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if (index < cdf_size - 1) {
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t = (x - cdf[index]) / (cdf[index + 1] - cdf[index]);
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}
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else {
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t = 0.0f;
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index = cdf_size - 1;
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}
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float y = ((index + t) / (resolution - 1)) * (2.0f * range);
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inv_cdf[half_size + i] = 0.5f * (1.0f + y);
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inv_cdf[half_size - i] = 0.5f * (1.0f - y);
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}
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}
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else {
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for (int i = 0; i < resolution; i++) {
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float x = (i + 0.5f) * inv_resolution;
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int index = upper_bound(cdf.begin(), cdf.end(), x) - cdf.begin() - 1;
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float t;
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if (index < cdf_size - 1) {
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t = (x - cdf[index]) / (cdf[index + 1] - cdf[index]);
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}
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else {
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t = 0.0f;
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index = resolution;
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}
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inv_cdf[i] = from + range * (index + t) * inv_resolution;
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}
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}
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}
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CCL_NAMESPACE_END
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