Differential D12367 Diff 41308 intern/cycles/integrator/tile.cpp

Changeset View

Standalone View

intern/cycles/integrator/tile.cpp

This file was added.

				/*
				* Copyright 2011-2021 Blender Foundation
				*
				* Licensed under the Apache License, Version 2.0 (the "License");
				* you may not use this file except in compliance with the License.
				* You may obtain a copy of the License at
				*
				* http://www.apache.org/licenses/LICENSE-2.0
				*
				* Unless required by applicable law or agreed to in writing, software
				* distributed under the License is distributed on an "AS IS" BASIS,
				* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
				* See the License for the specific language governing permissions and
				* limitations under the License.
				*/

				#include "integrator/tile.h"

				#include "util/util_logging.h"
				#include "util/util_math.h"

				CCL_NAMESPACE_BEGIN

				std::ostream &operator<<(std::ostream &os, const TileSize &tile_size)
				{
				os << "size: (" << tile_size.width << ", " << tile_size.height << ")";
				os << ", num_samples: " << tile_size.num_samples;
				return os;
				}

				ccl_device_inline uint round_down_to_power_of_two(uint x)
				{
				if (is_power_of_two(x)) {
				return x;
				}

				return prev_power_of_two(x);
				}

				ccl_device_inline uint round_up_to_power_of_two(uint x)
				{
				if (is_power_of_two(x)) {
				return x;
				}

				return next_power_of_two(x);
				}

				TileSize tile_calculate_best_size(const int2 &image_size,
				const int num_samples,
				const int max_num_path_states)
				{
				if (max_num_path_states == 1) {
				/* Simple case: avoid any calculation, which could cause rounding issues. */
				return TileSize(1, 1, 1);
				}

				const int64_t num_pixels = image_size.x * image_size.y;
				const int64_t num_pixel_samples = num_pixels * num_samples;

				if (max_num_path_states >= num_pixel_samples) {
				/* Image fully fits into the state (could be border render, for example). */
				return TileSize(image_size.x, image_size.y, num_samples);
				}

				/* The idea here is to keep number of samples per tile as much as possible to improve coherency
				* across threads.
				*
				* Some general ideas:
				* - Prefer smaller tiles with more samples, which improves spatial coherency of paths.
				* - Keep values a power of two, for more integer fit into the maximum number of paths. */

				TileSize tile_size;

				/* Calculate tile size as if it is the most possible one to fit an entire range of samples.
				* The idea here is to keep tiles as small as possible, and keep device occupied by scheduling
				* multiple tiles with the same coordinates rendering different samples. */
				const int num_path_states_per_sample = max_num_path_states / num_samples;
				if (num_path_states_per_sample != 0) {
				tile_size.width = round_down_to_power_of_two(lround(sqrt(num_path_states_per_sample)));
				tile_size.height = tile_size.width;
				}
				else {
				tile_size.width = tile_size.height = 1;
				}

				if (num_samples == 1) {
				tile_size.num_samples = 1;
				}
				else {
				/* Heuristic here is to have more uniform division of the sample range: for example prefer
				* [32 <38 times>, 8] over [1024, 200]. This allows to greedily add more tiles early on. */
				tile_size.num_samples = min(round_up_to_power_of_two(lround(sqrt(num_samples / 2))),
				static_cast<uint>(num_samples));

				const int tile_area = tile_size.width / tile_size.height;
				tile_size.num_samples = min(tile_size.num_samples, max_num_path_states / tile_area);
				}

				DCHECK_GE(tile_size.width, 1);
				DCHECK_GE(tile_size.height, 1);
				DCHECK_GE(tile_size.num_samples, 1);
				DCHECK_LE(tile_size.width * tile_size.height * tile_size.num_samples, max_num_path_states);

				return tile_size;
				}

				CCL_NAMESPACE_END