82cf25dfbf
Adds scrambling distance to the PMJ sampler. This is based on the work by Mathieu Menuet in D12318 who created the original implementation for the Sobol sampler. Reviewed By: brecht Maniphest Tasks: T92181 Differential Revision: https://developer.blender.org/D12854
117 lines
3.9 KiB
C++
117 lines
3.9 KiB
C++
/*
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* Copyright 2011-2021 Blender Foundation
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "integrator/tile.h"
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#include "util/log.h"
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#include "util/math.h"
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CCL_NAMESPACE_BEGIN
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std::ostream &operator<<(std::ostream &os, const TileSize &tile_size)
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{
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os << "size: (" << tile_size.width << ", " << tile_size.height << ")";
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os << ", num_samples: " << tile_size.num_samples;
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return os;
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}
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ccl_device_inline uint round_down_to_power_of_two(uint x)
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{
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if (is_power_of_two(x)) {
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return x;
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}
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return prev_power_of_two(x);
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}
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ccl_device_inline uint round_up_to_power_of_two(uint x)
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{
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if (is_power_of_two(x)) {
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return x;
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}
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return next_power_of_two(x);
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}
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TileSize tile_calculate_best_size(const int2 &image_size,
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const int num_samples,
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const int max_num_path_states,
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const float scrambling_distance)
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{
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if (max_num_path_states == 1) {
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/* Simple case: avoid any calculation, which could cause rounding issues. */
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return TileSize(1, 1, 1);
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}
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const int64_t num_pixels = image_size.x * image_size.y;
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const int64_t num_pixel_samples = num_pixels * num_samples;
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if (max_num_path_states >= num_pixel_samples) {
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/* Image fully fits into the state (could be border render, for example). */
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return TileSize(image_size.x, image_size.y, num_samples);
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}
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/* The idea here is to keep number of samples per tile as much as possible to improve coherency
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* across threads.
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*
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* Some general ideas:
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* - Prefer smaller tiles with more samples, which improves spatial coherency of paths.
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* - Keep values a power of two, for more integer fit into the maximum number of paths. */
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TileSize tile_size;
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const int num_path_states_per_sample = max_num_path_states / num_samples;
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if (scrambling_distance < 0.9f) {
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/* Prefer large tiles for scrambling distance, bounded by max num path states. */
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tile_size.width = min(image_size.x, max_num_path_states);
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tile_size.height = min(image_size.y, max(max_num_path_states / tile_size.width, 1));
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}
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else {
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/* Calculate tile size as if it is the most possible one to fit an entire range of samples.
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* The idea here is to keep tiles as small as possible, and keep device occupied by scheduling
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* multiple tiles with the same coordinates rendering different samples. */
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if (num_path_states_per_sample != 0) {
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tile_size.width = round_down_to_power_of_two(lround(sqrt(num_path_states_per_sample)));
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tile_size.height = tile_size.width;
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}
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else {
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tile_size.width = tile_size.height = 1;
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}
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}
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if (num_samples == 1) {
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tile_size.num_samples = 1;
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}
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else {
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/* Heuristic here is to have more uniform division of the sample range: for example prefer
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* [32 <38 times>, 8] over [1024, 200]. This allows to greedily add more tiles early on. */
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tile_size.num_samples = min(round_up_to_power_of_two(lround(sqrt(num_samples / 2))),
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static_cast<uint>(num_samples));
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const int tile_area = tile_size.width * tile_size.height;
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tile_size.num_samples = min(tile_size.num_samples, max_num_path_states / tile_area);
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}
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DCHECK_GE(tile_size.width, 1);
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DCHECK_GE(tile_size.height, 1);
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DCHECK_GE(tile_size.num_samples, 1);
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DCHECK_LE(tile_size.width * tile_size.height * tile_size.num_samples, max_num_path_states);
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return tile_size;
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}
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CCL_NAMESPACE_END
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