axmol/thirdparty/astc/astcenc_partition_tables.cpp

// SPDX-License-Identifier: Apache-2.0
// ----------------------------------------------------------------------------
// Copyright 2011-2021 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
// License for the specific language governing permissions and limitations
// under the License.
// ----------------------------------------------------------------------------

/**
 * @brief Functions for generating partition tables on demand.
 */

#include "astcenc_internal.h"

/**
 * @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(
	int texel_count,
	const uint8_t* partition_of_texel,
	uint64_t bit_pattern[7]
) {
	// Clear the pattern
	for (int i = 0; i < 7; i++)
	{
		bit_pattern[i] = 0;
	}

	// Store a mapping to reorder the raw partitions so that the the partitions are ordered such
	// that the lowest texel index in partition N is smaller than the lowest texel index in
	// partition N + 1.
	int mapped_index[BLOCK_MAX_PARTITIONS];
	int map_weight_count = 0;

	for (unsigned int i = 0; i < BLOCK_MAX_PARTITIONS; i++)
	{
		mapped_index[i] = -1;
	}

	for (int i = 0; i < texel_count; i++)
	{
		int index = partition_of_texel[i];

		if (mapped_index[index] == -1)
		{
			mapped_index[index] = map_weight_count++;
		}

		uint64_t xlat_index = mapped_index[index];
		bit_pattern[i >> 5] |= xlat_index << (2 * (i & 0x1F));
	}
}

/**
 * @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[7],
	const uint64_t part2[7]
) {
	return (part1[0] == part2[0]) && (part1[1] == part2[1]) &&
	       (part1[2] == part2[2]) && (part1[3] == part2[3]) &&
	       (part1[4] == part2[4]) && (part1[5] == part2[5]) &&
	       (part1[6] == part2[6]);
}

/**
 * @brief Compare all partition patterns and remove duplicates.
 *
 * The partitioning algorithm uses a hash function for texel assignment that can produce partitions
 * which have the same texel assignment groupings. It is only useful for the compressor to test one
 * of each, so we mark duplicates as invalid.
 *
 * @param         texel_count   The first canonical bit pattern to check.
 * @param[in,out] pt            The table of partitioning information entries.
 */
static void remove_duplicate_partitionings(
	int texel_count,
	partition_info pt[BLOCK_MAX_PARTITIONINGS]
) {
	uint64_t bit_patterns[BLOCK_MAX_PARTITIONINGS * 7];

	for (unsigned int i = 0; i < BLOCK_MAX_PARTITIONINGS; i++)
	{
		generate_canonical_partitioning(texel_count, pt[i].partition_of_texel, bit_patterns + i * 7);

		for (unsigned int j = 0; j < i; j++)
		{
			if (compare_canonical_partitionings(bit_patterns + 7 * i, bit_patterns + 7 * j))
			{
				pt[i].partition_count = 0;
				break;
			}
		}
	}
}

/**
 * @brief Hash function used for procedural partition assignment.
 *
 * @param inp The hash seed.
 *
 * @return The hashed value.
 */
static uint32_t hash52(
	uint32_t inp
) {
	inp ^= inp >> 15;

	// (2^4 + 1) * (2^7 + 1) * (2^17 - 1)
	inp *= 0xEEDE0891;
	inp ^= inp >> 5;
	inp += inp << 16;
	inp ^= inp >> 7;
	inp ^= inp >> 3;
	inp ^= inp << 6;
	inp ^= inp >> 17;
	return 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 blockhas 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
) {
	// For small blocks bias the coordinates to get better distribution
	if (small_block)
	{
		x <<= 1;
		y <<= 1;
		z <<= 1;
	}

	seed += (partition_count - 1) * 1024;

	uint32_t rnum = hash52(seed);

	uint8_t seed1 = rnum & 0xF;
	uint8_t seed2 = (rnum >> 4) & 0xF;
	uint8_t seed3 = (rnum >> 8) & 0xF;
	uint8_t seed4 = (rnum >> 12) & 0xF;
	uint8_t seed5 = (rnum >> 16) & 0xF;
	uint8_t seed6 = (rnum >> 20) & 0xF;
	uint8_t seed7 = (rnum >> 24) & 0xF;
	uint8_t seed8 = (rnum >> 28) & 0xF;
	uint8_t seed9 = (rnum >> 18) & 0xF;
	uint8_t seed10 = (rnum >> 22) & 0xF;
	uint8_t seed11 = (rnum >> 26) & 0xF;
	uint8_t seed12 = ((rnum >> 30) | (rnum << 2)) & 0xF;

	// Squaring all the seeds in order to bias their distribution towards lower values.
	seed1 *= seed1;
	seed2 *= seed2;
	seed3 *= seed3;
	seed4 *= seed4;
	seed5 *= seed5;
	seed6 *= seed6;
	seed7 *= seed7;
	seed8 *= seed8;
	seed9 *= seed9;
	seed10 *= seed10;
	seed11 *= seed11;
	seed12 *= seed12;

	int sh1, sh2;
	if (seed & 1)
	{
		sh1 = (seed & 2 ? 4 : 5);
		sh2 = (partition_count == 3 ? 6 : 5);
	}
	else
	{
		sh1 = (partition_count == 3 ? 6 : 5);
		sh2 = (seed & 2 ? 4 : 5);
	}

	int sh3 = (seed & 0x10) ? sh1 : sh2;

	seed1 >>= sh1;
	seed2 >>= sh2;
	seed3 >>= sh1;
	seed4 >>= sh2;
	seed5 >>= sh1;
	seed6 >>= sh2;
	seed7 >>= sh1;
	seed8 >>= sh2;

	seed9 >>= sh3;
	seed10 >>= sh3;
	seed11 >>= sh3;
	seed12 >>= sh3;

	int a = seed1 * x + seed2 * y + seed11 * z + (rnum >> 14);
	int b = seed3 * x + seed4 * y + seed12 * z + (rnum >> 10);
	int c = seed5 * x + seed6 * y + seed9 * z + (rnum >> 6);
	int d = seed7 * x + seed8 * y + seed10 * z + (rnum >> 2);

	// Apply the saw
	a &= 0x3F;
	b &= 0x3F;
	c &= 0x3F;
	d &= 0x3F;

	// Remove some of the components if we are to output < 4 partitions.
	if (partition_count <= 3)
	{
		d = 0;
	}

	if (partition_count <= 2)
	{
		c = 0;
	}

	if (partition_count <= 1)
	{
		b = 0;
	}

	uint8_t partition;
	if (a >= b && a >= c && a >= d)
	{
		partition = 0;
	}
	else if (b >= c && b >= d)
	{
		partition = 1;
	}
	else if (c >= d)
	{
		partition = 2;
	}
	else
	{
		partition = 3;
	}

	return partition;
}

/**
 * @brief Generate a single partition info structure.
 *
 * @param      bsd               The block size information.
 * @param      partition_count   The partition count of this partitioning.
 * @param      partition_index   The partition index / see of this partitioning.
 * @param[out] pi                The partition info structure to populate.
 */
static void generate_one_partition_info_entry(
	const block_size_descriptor& bsd,
	int partition_count,
	int partition_index,
	partition_info& pi
) {
	int texels_per_block = bsd.texel_count;
	bool small_block = texels_per_block < 32;

	uint8_t *partition_of_texel = pi.partition_of_texel;

	// Assign texels to partitions
	int texel_idx = 0;
	int counts[BLOCK_MAX_PARTITIONS] { 0 };
	for (unsigned int z = 0; z < bsd.zdim; z++)
	{
		for (unsigned int y = 0; y <  bsd.ydim; y++)
		{
			for (unsigned int x = 0; x <  bsd.xdim; x++)
			{
				uint8_t part = select_partition(partition_index, x, y, z, partition_count, small_block);
				pi.texels_of_partition[part][counts[part]++] = static_cast<uint8_t>(texel_idx++);
				*partition_of_texel++ = part;
			}
		}
	}

	// Fill loop tail so we can overfetch later
	for (int i = 0; i < partition_count; i++)
	{
		int ptex_count = counts[i];
		int ptex_count_simd = round_up_to_simd_multiple_vla(ptex_count);
		for (int j = ptex_count; j < ptex_count_simd; j++)
		{
			pi.texels_of_partition[i][j] = pi.texels_of_partition[i][ptex_count - 1];
		}
	}

	if (counts[0] == 0)
	{
		pi.partition_count = 0;
	}
	else if (counts[1] == 0)
	{
		pi.partition_count = 1;
	}
	else if (counts[2] == 0)
	{
		pi.partition_count = 2;
	}
	else if (counts[3] == 0)
	{
		pi.partition_count = 3;
	}
	else
	{
		pi.partition_count = 4;
	}

	for (unsigned int i = 0; i < BLOCK_MAX_PARTITIONS; i++)
	{
		pi.partition_texel_count[i] = static_cast<uint8_t>(counts[i]);
		pi.coverage_bitmaps[i] = 0ULL;
	}

	unsigned int texels_to_process = astc::min(bsd.texel_count, BLOCK_MAX_KMEANS_TEXELS);
	for (unsigned int i = 0; i < texels_to_process; i++)
	{
		unsigned int idx = bsd.kmeans_texels[i];
		pi.coverage_bitmaps[pi.partition_of_texel[idx]] |= 1ULL << i;
	}
}

/* See header for documentation. */
void init_partition_tables(
	block_size_descriptor& bsd
) {
	partition_info *par_tab2 = bsd.partitions;
	partition_info *par_tab3 = par_tab2 + BLOCK_MAX_PARTITIONINGS;
	partition_info *par_tab4 = par_tab3 + BLOCK_MAX_PARTITIONINGS;
	partition_info *par_tab1 = par_tab4 + BLOCK_MAX_PARTITIONINGS;

	generate_one_partition_info_entry(bsd, 1, 0, *par_tab1);
	for (int i = 0; i < 1024; i++)
	{
		generate_one_partition_info_entry(bsd, 2, i, par_tab2[i]);
		generate_one_partition_info_entry(bsd, 3, i, par_tab3[i]);
		generate_one_partition_info_entry(bsd, 4, i, par_tab4[i]);
	}

	remove_duplicate_partitionings(bsd.texel_count, par_tab2);
	remove_duplicate_partitionings(bsd.texel_count, par_tab3);
	remove_duplicate_partitionings(bsd.texel_count, par_tab4);
}