forked from bartvdbraak/blender
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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