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/* SPDX-License-Identifier: Apache-2.0
* Copyright 2019-2022 Blender Foundation */
/* This file is based on "Progressive Multi-Jittered Sample Sequences"
* by Christensen, Kensler, and Kilpatrick, but with a much simpler and
* faster implementation based on "Stochastic Generation of (t, s)
* Sample Sequences" by Helmer, Christensen, and Kensler.
*/
#include "scene/jitter.h"
#include "util/hash.h"
#include <math.h>
#include <vector>
CCL_NAMESPACE_BEGIN
void progressive_multi_jitter_02_generate_2D(float2 points[], int size, int rng_seed)
{
/* Xor values for generating the PMJ02 sequence. These permute the
* order we visit the strata in, which is what makes the code below
* produce the PMJ02 sequence. Other choices are also possible, but
* result in different sequences. */
static uint xors[2][32] = {
{0x00000000, 0x00000000, 0x00000002, 0x00000006, 0x00000006, 0x0000000e, 0x00000036,
0x0000004e, 0x00000016, 0x0000002e, 0x00000276, 0x000006ce, 0x00000716, 0x00000c2e,
0x00003076, 0x000040ce, 0x00000116, 0x0000022e, 0x00020676, 0x00060ece, 0x00061716,
0x000e2c2e, 0x00367076, 0x004ec0ce, 0x00170116, 0x002c022e, 0x02700676, 0x06c00ece,
0x07001716, 0x0c002c2e, 0x30007076, 0x4000c0ce},
{0x00000000, 0x00000001, 0x00000003, 0x00000003, 0x00000007, 0x0000001b, 0x00000027,
0x0000000b, 0x00000017, 0x0000013b, 0x00000367, 0x0000038b, 0x00000617, 0x0000183b,
0x00002067, 0x0000008b, 0x00000117, 0x0001033b, 0x00030767, 0x00030b8b, 0x00071617,
0x001b383b, 0x00276067, 0x000b808b, 0x00160117, 0x0138033b, 0x03600767, 0x03800b8b,
0x06001617, 0x1800383b, 0x20006067, 0x0000808b}};
uint rng_i = rng_seed;
points[0].x = hash_hp_float(rng_i++);
points[0].y = hash_hp_float(rng_i++);
/* Subdivide the domain into smaller and smaller strata, filling in new
* points as we go. */
for (int log_N = 0, N = 1; N < size; log_N++, N *= 2) {
float strata_count = (float)(N * 2);
for (int i = 0; i < N && (N + i) < size; i++) {
/* Find the strata that are already occupied in this cell. */
uint occupied_x_stratum = (uint)(points[i ^ xors[0][log_N]].x * strata_count);
uint occupied_y_stratum = (uint)(points[i ^ xors[1][log_N]].y * strata_count);
/* Generate a new point in the unoccupied strata. */
points[N + i].x = ((float)(occupied_x_stratum ^ 1) + hash_hp_float(rng_i++)) / strata_count;
points[N + i].y = ((float)(occupied_y_stratum ^ 1) + hash_hp_float(rng_i++)) / strata_count;
}
}
}
CCL_NAMESPACE_END
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