// 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 // License for the specific language governing permissions and limitations // under the License. // ---------------------------------------------------------------------------- #if !defined(ASTCENC_DECOMPRESS_ONLY) /** * @brief Functions for finding best partition for a block. * * The partition search operates in two stages. The first pass uses kmeans clustering to group * texels into an ideal partitioning for the requested partition count, and then compares that * against the 1024 partitionings generated by the ASTC partition hash function. The generated * partitions are then ranked by the number of texels in the wrong partition, compared to the ideal * clustering. All 1024 partitions are tested for similarity and ranked, apart from duplicates and * partitionings that actually generate fewer than the requested partition count, but only the top * N candidates are actually put through a more detailed search. N is determined by the compressor * quality preset. * * For the detailed search, each candidate is checked against two possible encoding methods: * * - The best partitioning assuming different chroma colors (RGB + RGB or RGB + delta endpoints). * - The best partitioning assuming same chroma colors (RGB + scale endpoints). * * This is implemented by computing the compute mean color and dominant direction for each * partition. This defines two lines, both of which go through the mean color value. * * - One line has a direction defined by the dominant direction; this is used to assess the error * from using an uncorrelated color representation. * - The other line goes through (0,0,0,1) and is used to assess the error from using a same chroma * (RGB + scale) color representation. * * The best candidate is selected by computing the squared-errors that result from using these * lines for endpoint selection. */ #include <limits> #include "astcenc_internal.h" /** * @brief Pick some initial kmeans cluster centers. * * @param blk The image block color data to compress. * @param texel_count The number of texels in the block. * @param partition_count The number of partitions in the block. * @param[out] cluster_centers The initial partition cluster center colors. */ static void kmeans_init( const image_block& blk, unsigned int texel_count, unsigned int partition_count, vfloat4 cluster_centers[BLOCK_MAX_PARTITIONS] ) { … } /** * @brief Assign texels to clusters, based on a set of chosen center points. * * @param blk The image block color data to compress. * @param texel_count The number of texels in the block. * @param partition_count The number of partitions in the block. * @param cluster_centers The partition cluster center colors. * @param[out] partition_of_texel The partition assigned for each texel. */ static void kmeans_assign( const image_block& blk, unsigned int texel_count, unsigned int partition_count, const vfloat4 cluster_centers[BLOCK_MAX_PARTITIONS], uint8_t partition_of_texel[BLOCK_MAX_TEXELS] ) { … } /** * @brief Compute new cluster centers based on their center of gravity. * * @param blk The image block color data to compress. * @param texel_count The number of texels in the block. * @param partition_count The number of partitions in the block. * @param[out] cluster_centers The new cluster center colors. * @param partition_of_texel The partition assigned for each texel. */ static void kmeans_update( const image_block& blk, unsigned int texel_count, unsigned int partition_count, vfloat4 cluster_centers[BLOCK_MAX_PARTITIONS], const uint8_t partition_of_texel[BLOCK_MAX_TEXELS] ) { … } /** * @brief Compute bit-mismatch for partitioning in 2-partition mode. * * @param a The texel assignment bitvector for the block. * @param b The texel assignment bitvector for the partition table. * * @return The number of bit mismatches. */ static inline uint8_t partition_mismatch2( const uint64_t a[2], const uint64_t b[2] ) { … } /** * @brief Compute bit-mismatch for partitioning in 3-partition mode. * * @param a The texel assignment bitvector for the block. * @param b The texel assignment bitvector for the partition table. * * @return The number of bit mismatches. */ static inline uint8_t partition_mismatch3( const uint64_t a[3], const uint64_t b[3] ) { … } /** * @brief Compute bit-mismatch for partitioning in 4-partition mode. * * @param a The texel assignment bitvector for the block. * @param b The texel assignment bitvector for the partition table. * * @return The number of bit mismatches. */ static inline uint8_t partition_mismatch4( const uint64_t a[4], const uint64_t b[4] ) { … } mismatch_dispatch; /** * @brief Count the partition table mismatches vs the data clustering. * * @param bsd The block size information. * @param partition_count The number of partitions in the block. * @param bitmaps The block texel partition assignment patterns. * @param[out] mismatch_counts The array storing per partitioning mismatch counts. */ static void count_partition_mismatch_bits( const block_size_descriptor& bsd, unsigned int partition_count, const uint64_t bitmaps[BLOCK_MAX_PARTITIONS], uint8_t mismatch_counts[BLOCK_MAX_PARTITIONINGS] ) { … } /** * @brief Use counting sort on the mismatch array to sort partition candidates. * * @param partitioning_count The number of packed partitionings. * @param mismatch_count Partitioning mismatch counts, in index order. * @param[out] partition_ordering Partition index values, in mismatch order. * * @return The number of active partitions in this selection. */ static unsigned int get_partition_ordering_by_mismatch_bits( unsigned int texel_count, unsigned int partitioning_count, const uint8_t mismatch_count[BLOCK_MAX_PARTITIONINGS], uint16_t partition_ordering[BLOCK_MAX_PARTITIONINGS] ) { … } /** * @brief Use k-means clustering to compute a partition ordering for a block.. * * @param bsd The block size information. * @param blk The image block color data to compress. * @param partition_count The desired number of partitions in the block. * @param[out] partition_ordering The list of recommended partition indices, in priority order. * * @return The number of active partitionings in this selection. */ static unsigned int compute_kmeans_partition_ordering( const block_size_descriptor& bsd, const image_block& blk, unsigned int partition_count, uint16_t partition_ordering[BLOCK_MAX_PARTITIONINGS] ) { … } /** * @brief Insert a partitioning into an order list of results, sorted by error. * * @param max_values The max number of entries in the best result arrays. * @param this_error The error of the new entry. * @param this_partition The partition ID of the new entry. * @param[out] best_errors The array of best error values. * @param[out] best_partitions The array of best partition values. */ static void insert_result( unsigned int max_values, float this_error, unsigned int this_partition, float* best_errors, unsigned int* best_partitions) { … } /* See header for documentation. */ unsigned int find_best_partition_candidates( const block_size_descriptor& bsd, const image_block& blk, unsigned int partition_count, unsigned int partition_search_limit, unsigned int best_partitions[TUNE_MAX_PARTITIONING_CANDIDATES], unsigned int requested_candidates ) { … } #endif
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