diff options
author | Nathan Vegdahl <cessen> | 2022-08-23 21:48:48 +0300 |
---|---|---|
committer | Brecht Van Lommel <brecht@blender.org> | 2022-09-01 15:57:39 +0300 |
commit | 50df9caef01a4225db216d9c4c0515134f7a37bf (patch) | |
tree | e6632fc669d7d5a9d084b2ad33764810b286e156 /intern/cycles/scene | |
parent | ba1bf87bd8f13fa2c67c435eb4a31a0c898d65ac (diff) |
Cycles: improve Progressive Multi-Jittered sampling
Fix two issues in the previous implementation:
* Only power-of-two prefixes were progressively stratified, not suffixes.
This resulted in unnecessarily increased noise when using non-power-of-two
sample counts.
* In order to try to get away with just a single sample pattern, the code
used a combination of sample index shuffling and Cranley-Patterson rotation.
Index shuffling is normally fine, but due to the sample patterns themselves
not being quite right (as described above) this actually resulted in
additional increased noise. Cranley-Patterson, on the other hand, always
increases noise with randomized (t,s) nets like PMJ02, and should be avoided
with these kinds of sequences.
Addressed with the following changes:
* Replace the sample pattern generation code with a much simpler algorithm
recently published in the paper "Stochastic Generation of (t, s) Sample
Sequences". This new implementation is easier to verify, produces fully
progressively stratified PMJ02, and is *far* faster than the previous code,
being O(N) in the number of samples generated.
* It keeps the sample index shuffling, which works correctly now due to the
improved sample patterns. But it now uses a newer high-quality hash instead
of the original Laine-Karras hash.
* The scrambling distance feature cannot (to my knowledge) be implemented with
any decorrelation strategy other than Cranley-Patterson, so Cranley-Patterson
is still used when that feature is enabled. But it is now disabled otherwise,
since it increases noise.
* In place of Cranley-Patterson, multiple independent patterns are generated
and randomly chosen for different pixels and dimensions as described in the
original PMJ paper. In this patch, the pattern selection is done via
hash-based shuffling to ensure there are no repeats within a single pixel
until all patterns have been used.
The combination of these fixes brings the quality of Cycles' PMJ sampler in
line with the previously submitted Sobol-Burley sampler in D15679. They are
essentially indistinguishable in terms of quality/noise, which is expected
since they are both randomized (0,2) sequences.
Differential Revision: https://developer.blender.org/D15746
Diffstat (limited to 'intern/cycles/scene')
-rw-r--r-- | intern/cycles/scene/jitter.cpp | 287 | ||||
-rw-r--r-- | intern/cycles/scene/jitter.h | 1 |
2 files changed, 38 insertions, 250 deletions
diff --git a/intern/cycles/scene/jitter.cpp b/intern/cycles/scene/jitter.cpp index 4f9c4fb9418..8287a029752 100644 --- a/intern/cycles/scene/jitter.cpp +++ b/intern/cycles/scene/jitter.cpp @@ -2,267 +2,56 @@ * Copyright 2019-2022 Blender Foundation */ /* This file is based on "Progressive Multi-Jittered Sample Sequences" - * by Per Christensen, Andrew Kensler and Charlie Kilpatrick. - * http://graphics.pixar.com/library/ProgressiveMultiJitteredSampling/paper.pdf - * - * Performance can be improved in the future by implementing the new - * algorithm from Matt Pharr in http://jcgt.org/published/0008/01/04/ - * "Efficient Generation of Points that Satisfy Two-Dimensional Elementary Intervals" + * 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 -static uint cmj_hash(uint i, uint p) -{ - i ^= p; - i ^= i >> 17; - i ^= i >> 10; - i *= 0xb36534e5; - i ^= i >> 12; - i ^= i >> 21; - i *= 0x93fc4795; - i ^= 0xdf6e307f; - i ^= i >> 17; - i *= 1 | p >> 18; - - return i; -} - -static float cmj_randfloat(uint i, uint p) -{ - return cmj_hash(i, p) * (1.0f / 4294967808.0f); -} - -class PMJ_Generator { - public: - static void generate_2D(float2 points[], int size, int rng_seed_in) - { - PMJ_Generator g(rng_seed_in); - points[0].x = g.rnd(); - points[0].y = g.rnd(); - int N = 1; - while (N < size) { - g.extend_sequence_even(points, N); - g.extend_sequence_odd(points, 2 * N); - N = 4 * N; - } - } - - protected: - PMJ_Generator(int rnd_seed_in) : num_samples(1), rnd_index(2), rnd_seed(rnd_seed_in) - { - } - - float rnd() - { - return cmj_randfloat(++rnd_index, rnd_seed); - } - - virtual void mark_occupied_strata(float2 points[], int N) - { - int NN = 2 * N; - for (int s = 0; s < NN; ++s) { - occupied1Dx[s] = occupied1Dy[s] = false; - } - for (int s = 0; s < N; ++s) { - int xstratum = (int)(NN * points[s].x); - int ystratum = (int)(NN * points[s].y); - occupied1Dx[xstratum] = true; - occupied1Dy[ystratum] = true; - } - } - - virtual void generate_sample_point( - float2 points[], float i, float j, float xhalf, float yhalf, int n, int N) - { - int NN = 2 * N; - float2 pt; - int xstratum, ystratum; - do { - pt.x = (i + 0.5f * (xhalf + rnd())) / n; - xstratum = (int)(NN * pt.x); - } while (occupied1Dx[xstratum]); - do { - pt.y = (j + 0.5f * (yhalf + rnd())) / n; - ystratum = (int)(NN * pt.y); - } while (occupied1Dy[ystratum]); - occupied1Dx[xstratum] = true; - occupied1Dy[ystratum] = true; - points[num_samples] = pt; - ++num_samples; - } - - void extend_sequence_even(float2 points[], int N) - { - int n = (int)sqrtf(N); - occupied1Dx.resize(2 * N); - occupied1Dy.resize(2 * N); - mark_occupied_strata(points, N); - for (int s = 0; s < N; ++s) { - float2 oldpt = points[s]; - float i = floorf(n * oldpt.x); - float j = floorf(n * oldpt.y); - float xhalf = floorf(2.0f * (n * oldpt.x - i)); - float yhalf = floorf(2.0f * (n * oldpt.y - j)); - xhalf = 1.0f - xhalf; - yhalf = 1.0f - yhalf; - generate_sample_point(points, i, j, xhalf, yhalf, n, N); - } - } - - void extend_sequence_odd(float2 points[], int N) - { - int n = (int)sqrtf(N / 2); - occupied1Dx.resize(2 * N); - occupied1Dy.resize(2 * N); - mark_occupied_strata(points, N); - std::vector<float> xhalves(N / 2); - std::vector<float> yhalves(N / 2); - for (int s = 0; s < N / 2; ++s) { - float2 oldpt = points[s]; - float i = floorf(n * oldpt.x); - float j = floorf(n * oldpt.y); - float xhalf = floorf(2.0f * (n * oldpt.x - i)); - float yhalf = floorf(2.0f * (n * oldpt.y - j)); - if (rnd() > 0.5f) { - xhalf = 1.0f - xhalf; - } - else { - yhalf = 1.0f - yhalf; - } - xhalves[s] = xhalf; - yhalves[s] = yhalf; - generate_sample_point(points, i, j, xhalf, yhalf, n, N); - } - for (int s = 0; s < N / 2; ++s) { - float2 oldpt = points[s]; - float i = floorf(n * oldpt.x); - float j = floorf(n * oldpt.y); - float xhalf = 1.0f - xhalves[s]; - float yhalf = 1.0f - yhalves[s]; - generate_sample_point(points, i, j, xhalf, yhalf, n, N); - } - } - - std::vector<bool> occupied1Dx, occupied1Dy; - int num_samples; - int rnd_index, rnd_seed; -}; - -class PMJ02_Generator : public PMJ_Generator { - protected: - void generate_sample_point( - float2 points[], float i, float j, float xhalf, float yhalf, int n, int N) override - { - int NN = 2 * N; - float2 pt; - do { - pt.x = (i + 0.5f * (xhalf + rnd())) / n; - pt.y = (j + 0.5f * (yhalf + rnd())) / n; - } while (is_occupied(pt, NN)); - mark_occupied_strata1(pt, NN); - points[num_samples] = pt; - ++num_samples; - } - - void mark_occupied_strata(float2 points[], int N) override - { - int NN = 2 * N; - int num_shapes = (int)log2f(NN) + 1; - occupiedStrata.resize(num_shapes); - for (int shape = 0; shape < num_shapes; ++shape) { - occupiedStrata[shape].resize(NN); - for (int n = 0; n < NN; ++n) { - occupiedStrata[shape][n] = false; - } - } - for (int s = 0; s < N; ++s) { - mark_occupied_strata1(points[s], NN); - } - } - - void mark_occupied_strata1(float2 pt, int NN) - { - int shape = 0; - int xdivs = NN; - int ydivs = 1; - do { - int xstratum = (int)(xdivs * pt.x); - int ystratum = (int)(ydivs * pt.y); - size_t index = ystratum * xdivs + xstratum; - assert(index < NN); - occupiedStrata[shape][index] = true; - shape = shape + 1; - xdivs = xdivs / 2; - ydivs = ydivs * 2; - } while (xdivs > 0); - } - - bool is_occupied(float2 pt, int NN) - { - int shape = 0; - int xdivs = NN; - int ydivs = 1; - do { - int xstratum = (int)(xdivs * pt.x); - int ystratum = (int)(ydivs * pt.y); - size_t index = ystratum * xdivs + xstratum; - assert(index < NN); - if (occupiedStrata[shape][index]) { - return true; - } - shape = shape + 1; - xdivs = xdivs / 2; - ydivs = ydivs * 2; - } while (xdivs > 0); - return false; - } - - private: - std::vector<std::vector<bool>> occupiedStrata; -}; - -static void shuffle(float2 points[], int size, int rng_seed) +void progressive_multi_jitter_02_generate_2D(float2 points[], int size, int rng_seed) { - if (rng_seed == 0) { - return; - } - - constexpr int odd[8] = {0, 1, 4, 5, 10, 11, 14, 15}; - constexpr int even[8] = {2, 3, 6, 7, 8, 9, 12, 13}; - - int rng_index = 0; - for (int yy = 0; yy < size / 16; ++yy) { - for (int xx = 0; xx < 8; ++xx) { - int other = (int)(cmj_randfloat(++rng_index, rng_seed) * (8.0f - xx) + xx); - float2 tmp = points[odd[other] + yy * 16]; - points[odd[other] + yy * 16] = points[odd[xx] + yy * 16]; - points[odd[xx] + yy * 16] = tmp; - } - for (int xx = 0; xx < 8; ++xx) { - int other = (int)(cmj_randfloat(++rng_index, rng_seed) * (8.0f - xx) + xx); - float2 tmp = points[even[other] + yy * 16]; - points[even[other] + yy * 16] = points[even[xx] + yy * 16]; - points[even[xx] + yy * 16] = tmp; + /* 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; } } } -void progressive_multi_jitter_generate_2D(float2 points[], int size, int rng_seed) -{ - PMJ_Generator::generate_2D(points, size, rng_seed); - shuffle(points, size, rng_seed); -} - -void progressive_multi_jitter_02_generate_2D(float2 points[], int size, int rng_seed) -{ - PMJ02_Generator::generate_2D(points, size, rng_seed); - shuffle(points, size, rng_seed); -} - CCL_NAMESPACE_END diff --git a/intern/cycles/scene/jitter.h b/intern/cycles/scene/jitter.h index 2fda0e556c0..8d497d5e9f5 100644 --- a/intern/cycles/scene/jitter.h +++ b/intern/cycles/scene/jitter.h @@ -8,7 +8,6 @@ CCL_NAMESPACE_BEGIN -void progressive_multi_jitter_generate_2D(float2 points[], int size, int rng_seed); void progressive_multi_jitter_02_generate_2D(float2 points[], int size, int rng_seed); CCL_NAMESPACE_END |