godot/thirdparty/astcenc/astcenc_partition_tables.cpp

// SPDX-License-Identifier: Apache-2.0
// ----------------------------------------------------------------------------
// Copyright 2011-2023 Arm Limited
//
// 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
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/**
 * @brief Functions for generating partition tables on demand.
 */

#include "astcenc_internal.h"

/** @brief The number of 64-bit words needed to represent a canonical partition bit pattern. */
#define BIT_PATTERN_WORDS …

/**
 * @brief Generate a canonical representation of a partition pattern.
 *
 * The returned value stores two bits per texel, for up to 6x6x6 texels, where the two bits store
 * the remapped texel index. Remapping ensures that we only match on the partition pattern,
 * independent of the partition order generated by the hash.
 *
 * @param      texel_count          The number of texels in the block.
 * @param      partition_of_texel   The partition assignments, in hash order.
 * @param[out] bit_pattern          The output bit pattern representation.
 */
static void generate_canonical_partitioning(
	unsigned int texel_count,
	const uint8_t* partition_of_texel,
	uint64_t bit_pattern[BIT_PATTERN_WORDS]
) { … }

/**
 * @brief Compare two canonical patterns to see if they are the same.
 *
 * @param part1   The first canonical bit pattern to check.
 * @param part2   The second canonical bit pattern to check.
 *
 * @return @c true if the patterns are the same, @c false otherwise.
 */
static bool compare_canonical_partitionings(
	const uint64_t part1[BIT_PATTERN_WORDS],
	const uint64_t part2[BIT_PATTERN_WORDS]
) { … }

/**
 * @brief Hash function used for procedural partition assignment.
 *
 * @param inp   The hash seed.
 *
 * @return The hashed value.
 */
static uint32_t hash52(
	uint32_t inp
) { … }

/**
 * @brief Select texel assignment for a single coordinate.
 *
 * @param seed              The seed - the partition index from the block.
 * @param x                 The texel X coordinate in the block.
 * @param y                 The texel Y coordinate in the block.
 * @param z                 The texel Z coordinate in the block.
 * @param partition_count   The total partition count of this encoding.
 * @param small_block       @c true if the block has fewer than 32 texels.
 *
 * @return The assigned partition index for this texel.
 */
static uint8_t select_partition(
	int seed,
	int x,
	int y,
	int z,
	int partition_count,
	bool small_block
) { … }

/**
 * @brief Generate a single partition info structure.
 *
 * @param[out] bsd                     The block size information.
 * @param      partition_count         The partition count of this partitioning.
 * @param      partition_index         The partition index / seed of this partitioning.
 * @param      partition_remap_index   The remapped partition index of this partitioning.
 * @param[out] pi                      The partition info structure to populate.
 *
 * @return True if this is a useful partition index, False if we can skip it.
 */
static bool generate_one_partition_info_entry(
	block_size_descriptor& bsd,
	unsigned int partition_count,
	unsigned int partition_index,
	unsigned int partition_remap_index,
	partition_info& pi
) { … }

static void build_partition_table_for_one_partition_count(
	block_size_descriptor& bsd,
	bool can_omit_partitionings,
	unsigned int partition_count_cutoff,
	unsigned int partition_count,
	partition_info* ptab,
	uint64_t* canonical_patterns
) { … }

/* See header for documentation. */
void init_partition_tables(
	block_size_descriptor& bsd,
	bool can_omit_partitionings,
	unsigned int partition_count_cutoff
) { … }