KTX纹理压缩KTX-Software-main 源码

# basis_universal Basis Universal Supercompressed GPU Texture Codec _{(This software is available under a free and permissive license (Apache 2.0), but like many other large open source projects it needs financial support to sustain its continued security, bug fixes and improvements. In addition to maintenance and stability there are many desirable features and new interchange formats we would like to add. If your company is using Basis Universal in a product, please consider reaching out.)} Businesses: support continued development and maintenance via invoiced technical support, maintenance, or sponsoring contracts: <br>&nbsp;&nbsp;_E-mail: info @ binomial dot info_ or contact us on [Twitter](https://twitter.com/_binomial) Also see the [Sponsors](https://github.com/BinomialLLC/basis_universal/wiki/Sponsors-and-Supporters) wiki page. ---- [](https://ci.appveyor.com/project/BinomialLLC/basis-universal) Basis Universal is a ["supercompressed"](http://gamma.cs.unc.edu/GST/gst.pdf) GPU texture data interchange system that supports two highly compressed intermediate file formats (.basis or the [.KTX2 open standard from the Khronos Group](https://github.khronos.org/KTX-Specification/)) that can be quickly transcoded to a [very wide variety](https://github.com/BinomialLLC/basis_universal/wiki/OpenGL-texture-format-enums-table) of GPU compressed and uncompressed pixel formats: ASTC 4x4 L/LA/RGB/RGBA, PVRTC1 4bpp RGB/RGBA, PVRTC2 RGB/RGBA, BC7 mode 6 RGB, BC7 mode 5 RGB/RGBA, BC1-5 RGB/RGBA/X/XY, ETC1 RGB, ETC2 RGBA, ATC RGB/RGBA, ETC2 EAC R11 and RG11, FXT1 RGB, and uncompressed raster image formats 8888/565/4444. The system now supports two modes: a high quality mode which is internally based off the [UASTC compressed texture format](https://richg42.blogspot.com/2020/01/uastc-block-format-encoding.html), and the original lower quality mode which is based off a subset of ETC1 called "ETC1S". UASTC is for extremely high quality (similar to BC7 quality) textures, and ETC1S is for very small files. The ETC1S system includes built-in data compression, while the UASTC system includes an optional Rate Distortion Optimization (RDO) post-process stage that conditions the encoded UASTC texture data in the .basis file so it can be more effectively LZ compressed by the end user. More technical details about UASTC integration are [here](https://github.com/BinomialLLC/basis_universal/wiki/UASTC-implementation-details). Basis files support non-uniform texture arrays, so cubemaps, volume textures, texture arrays, mipmap levels, video sequences, or arbitrary texture "tiles" can be stored in a single file. The compressor is able to exploit color and pattern correlations across the entire file, so multiple images with mipmaps can be stored very efficiently in a single file. The system's bitrate depends on the quality setting and image content, but common usable ETC1S bitrates are .3-1.25 bits/texel. ETC1S .basis files are typically 10-25% smaller than using RDO texture compression of the internal texture data stored in the .basis file followed by LZMA. For UASTC files, the bitrate is fixed at 8bpp, but with RDO post-processing and user-provided LZ compression on the .basis file the effective bitrate can be as low as 2bpp for video or for individual textures approximately 4-6bpp. The .basis and .KTX2 transcoders have been fuzz tested using [zzuf](https://www.linux.com/news/fuzz-testing-zzuf). So far, we've compiled the code using MSVC 2019, under Ubuntu 18.04 and 20 x64 using cmake with either clang 3.8 or gcc 5.4, and emscripten 1.35 to asm.js. (Be sure to use this version or later of emcc, as earlier versions fail with internal errors/exceptions during compilation.) Basis Universal supports "skip blocks" in ETC1S compressed texture arrays, which makes it useful for basic [compressed texture video](http://gamma.cs.unc.edu/MPTC/) applications. Note that Basis Universal is still at heart a GPU texture compression system, not a dedicated video codec, so bitrates will be larger than even MPEG1. 1/10/21 release notes: For v1.13, we've added numerous ETC1S encoder optimizations designed to greatly speed up single threaded encoding time, as well as greatly reducing overall CPU utilization when multithreading is enabled. For benchmarking, we're using "-q 128 -no_multithreading -mip_fast". The encoder now uses approximately 1/3rd as much total CPU time for the same PSNR. The encoder can now optionally utilize SSE 4.1 - see the "-no_sse" command line option. [Release Notes](https://github.com/BinomialLLC/basis_universal/wiki/Release-Notes) ### The first texture (and possibly image/video) compression codec developed without "Lena" We retired Lena years ago. No testing is done with this image: https://www.losinglena.com/ ### Quick Introduction Probably the most important concept to understand about Basis Universal before using it: The system supports **two** very different universal texture modes: The original "ETC1S" mode is low/medium quality, but the resulting file sizes are very small because the system has built-in compression for ETC1S texture format files. This is the command line encoding tool's default mode. ETC1S textures work best on images, photos, map data, or albedo/specular/etc. textures, but don't work as well on normal maps. There's the second "UASTC" mode, which is significantly higher quality (comparable to BC7 and highest quality LDR ASTC 4x4), and is usable on all texture types including complex normal maps. UASTC mode purposely does not have built-in file compression like ETC1S mode does, so the resulting files are quite large (8-bits/texel - same as BC7) compared to ETC1S mode. The UASTC encoder has an optional Rate Distortion Optimization (RDO) encoding mode (implemented as a post-process over the encoded UASTC texture data), which conditions the output texture data in a way that results in better lossless compression when UASTC .basis files are compressed with Deflate/Zstd, etc. In UASTC mode, you must losslessly compress .basis files yourself. .KTX2 files have built-in lossless compression support using [Zstandard](https://facebook.github.io/zstd/), which is used by default on UASTC textures. Basis Universal is not an image compression codec, but a GPU texture compression codec. It can be used just like an image compression codec, but that's not the only use case. Here's a [good intro](http://renderingpipeline.com/2012/07/texture-compression/) to GPU texture compression. If you're looking to primarily use the system as an image compression codec on sRGB photographic content, use the default ETC1S mode, because it has built-in compression. **The "-q X" option controls the output quality in ETC1S mode.** The default is quality level 128. "-q 255" will increase quality quite a bit. If you want even higher quality, try "-max_selectors 16128 -max_endpoints 16128" instead of -q. -q internally tries to set the codebook sizes (or the # of quantization intervals for endpoints/selectors) for you. You need to experiment with the quality level on your content. For tangent space normal maps, you should separate X into RGB and Y into Alpha, and provide the compressor with 32-bit/pixel input images. Or use the "-separate_rg_to_color_alpha" command line option which does this for you. The internal texture format that Basis Universal uses (ETC1S) doesn't handle tangent space normal maps encoded into RGB well. You need to separate the channels and recover Z in the pixel shader using z=sqrt(1-x^2-y^2). ### License and 3rd party code dependencies Detailed legal, license, and IP information is [here](https://github.com/BinomialLLC/basis_universal/wiki/Legal-IP-License-Information). Basis Universal itself uses the Apache 2.0 licenses, but it also utilizes some optional BSD code (Zstandard). The supported texture formats are [open Khronos Group standards](https:/