Alexander Suvorov
bec4114bea
This change makes it possible to use Crunch algorithms for ETC textures with Alpha channel.
Explanation:
For simplicity, Crunch algorithms currently do not use ETC2 specific modes (T, H or P). For this reason, the currently used ETC2A compression format is technically equivalent to ETC1 + Alpha. Note that ETC2 encoding is a superset of ETC1, so any texture, which consists of ETC1 color blocks and ETC2 Alpha blocks, can be correctly decoded by an ETC2A (ETC2_RGBA8) decoder.
Compression scheme for ETC2 Alpha blocks is equivalent to the compression scheme for DXT5 Alpha blocks. ETC2 Alpha endpoint clusterization is performed based on the very same output of the Alpha palettizer which is used for DXT5 Alpha. The only part which is actually different is the Alpha endpoint optimization step.
In order to perform ETC2 Alpha encoding, we can first run the already existing algorithm for DXT5 Alpha endpoint optimization, in order to obtain the initial approximate solution. Then the approximate solution is refined based on the ETC2 Alpha modifier table. When performing raw ETC2A encoding, all the 16 ETC2 Alpha modifiers are used during optimization. However, when performing ETC2A quantization, for performance reasons, only 2 Alpha modifiers are currently used (modifier 13, which allows to perform precise approximation on short Alpha intervals, and modifier 11, which has more or less regularly distributed values, and is used for large Alpha intervals).
For compatibility reasons, ETC2 color compression wrappers have also been added to the code, though, as has been mentioned before, at the current moment ETC2 specific modes are not used, so ETC2 color compression is currently equivalent to ETC1 compression.
The ETC decoder functionality has been significantly extended, Crunch is now capable to decode ETC2 and ETC2A textures (input ETC2 textures can have T, H or P blocks).
In order to use ETC2A compression, use the -ETC2A command line option (i.e. "crunch_x64.exe -ETC2A input.png"). By default, compressed ETC2A textures will be decompressed into KTX file format.
DXT Testing:
The modified algorithm has been tested on the Kodak test set using 64-bit build with default settings (running on Windows 10, i7-4790, 3.6GHz). All the decompressed test images are identical to the images being compressed and decompressed using original version of Crunch (revision ea9b8d8).
[Compressing Kodak set without mipmaps using DXT1 encoding]
Original: 1582222 bytes / 28.880 sec
Modified: 1468204 bytes / 13.288 sec
Improvement: 7.21% (compression ratio) / 53.99% (compression time)
[Compressing Kodak set with mipmaps using DXT1 encoding]
Original: 2065243 bytes / 36.936 sec
Modified: 1914805 bytes / 18.044 sec
Improvement: 7.28% (compression ratio) / 51.15% (compression time)
ETC Testing:
The modified algorithm has been tested on the Kodak test set using 64-bit build with default settings (running on Windows 10, i7-4790, 3.6GHz). The ETC1 quantization parameters have been selected in such a way, so that ETC1 compression gives approximately the same average Luma PSNR as the corresponding DXT1 compression (which is equal to 34.044 dB for the Kodak test set compressed without mipmaps using DXT1 encoding and default quality settings).
[Compressing Kodak set without mipmaps using ETC1 encoding]
Total size: 1607858 bytes
Total time: 17.361 sec
Average bitrate: 1.363 bpp
Average Luma PSNR: 34.050 dB
93 lines
3.6 KiB
C++
93 lines
3.6 KiB
C++
// File: rg_etc1.h - Fast, high quality ETC1 block packer/unpacker - Rich Geldreich <richgel99@gmail.com>
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// Please see ZLIB license at the end of this file.
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#pragma once
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namespace crnlib {
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namespace rg_etc1 {
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// Unpacks an 8-byte ETC1 compressed block to a block of 4x4 32bpp RGBA pixels.
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// Returns false if the block is invalid. Invalid blocks will still be unpacked with clamping.
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// This function is thread safe, and does not dynamically allocate any memory.
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// If preserve_alpha is true, the alpha channel of the destination pixels will not be overwritten. Otherwise, alpha will be set to 255.
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bool unpack_etc1_block(const void* pETC1_block, unsigned int* pDst_pixels_rgba, bool preserve_alpha = false);
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bool unpack_etc2_color(const void* pBlock, unsigned int* pDst_pixels_rgba, bool preserve_alpha = false);
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bool unpack_etc2_alpha(const void* pBlock, unsigned int* pDst_pixels_rgba, int comp_index = 3);
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// Quality setting = the higher the quality, the slower.
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// To pack large textures, it is highly recommended to call pack_etc1_block() in parallel, on different blocks, from multiple threads (particularly when using cHighQuality).
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enum etc1_quality {
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cLowQuality,
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cMediumQuality,
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cHighQuality,
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};
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struct etc1_pack_params {
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etc1_quality m_quality;
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bool m_dithering;
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inline etc1_pack_params() {
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clear();
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}
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void clear() {
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m_quality = cHighQuality;
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m_dithering = false;
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}
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};
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struct etc2a_pack_params {
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etc1_quality m_quality;
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int comp_index;
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inline etc2a_pack_params() {
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clear();
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}
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void clear() {
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m_quality = cHighQuality;
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comp_index = 3;
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}
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};
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// Important: pack_etc1_block_init() must be called before calling pack_etc1_block().
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void pack_etc1_block_init();
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// Packs a 4x4 block of 32bpp RGBA pixels to an 8-byte ETC1 block.
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// 32-bit RGBA pixels must always be arranged as (R,G,B,A) (R first, A last) in memory, independent of platform endianness. A should always be 255.
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// Returns squared error of result.
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// This function is thread safe, and does not dynamically allocate any memory.
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// pack_etc1_block() does not currently support "perceptual" colorspace metrics - it primarily optimizes for RGB RMSE.
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unsigned int pack_etc1_block(void* pETC1_block, const unsigned int* pSrc_pixels_rgba, etc1_pack_params& pack_params);
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unsigned int pack_etc2_alpha(void* pBlock, const unsigned int* pSrc_pixels_rgba, etc2a_pack_params& pack_params);
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} // namespace rg_etc1
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} // namespace crnlib
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//------------------------------------------------------------------------------
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//
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// rg_etc1 uses the ZLIB license:
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// http://opensource.org/licenses/Zlib
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//
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// Copyright (c) 2012 Rich Geldreich
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//
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// This software is provided 'as-is', without any express or implied
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// warranty. In no event will the authors be held liable for any damages
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// arising from the use of this software.
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//
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// Permission is granted to anyone to use this software for any purpose,
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// including commercial applications, and to alter it and redistribute it
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// freely, subject to the following restrictions:
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//
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// 1. The origin of this software must not be misrepresented; you must not
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// claim that you wrote the original software. If you use this software
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// in a product, an acknowledgment in the product documentation would be
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// appreciated but is not required.
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//
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// 2. Altered source versions must be plainly marked as such, and must not be
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// misrepresented as being the original software.
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//
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// 3. This notice may not be removed or altered from any source distribution.
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//
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//------------------------------------------------------------------------------
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