2.x series change log

This page summarizes the major functional and performance changes in each release of the 2.x series.

All performance data on this page is measured on an Intel Core i5-9600K clocked at 4.2 GHz, running astcenc using 6 threads.

2.5

Status: Released, March 2021

The 2.5 release is the last major release in the 2.x series. After this release a 2.x branch will provide stable long-term support, and the main branch will switch to focusing on more radical changes for the 3.x series.

Reminder for users of the library interface - the API is not designed to be stable across versions, and this release is not compatible with earlier 2.x releases. Please update and rebuild your client-side code using the updated astcenc.h header.

General:

• Feature: The ISA_INVARIANCE build option is no longer supported, as there is no longer any performance benefit from the variant paths. All builds are now using the equivalent of the ISA_INVARIANCE=ON setting, and all builds (except Armv7) are now believed to be invariant across operating systems, compilers, CPU architectures, and SIMD instruction sets.
• Feature: Armv8 32-bit builds with NEON are now supported, with out-of-the-box support for Arm Linux soft-float and hard-float ABIs. There are no pre-built binaries for these targets; support is included for library users targeting older 32-bit Android and iOS devices.
• Feature: A compressor mode for encoding HDR textures that have been encoded into LDR RGBM wrapper format is now supported. Note that this encoding has some strong recommendations for how the RGBM encoding is implemented to avoid block artifacts in the compressed image.
• Core API:
  • API Change: The core API has been changed to be a pure C API, making it easier to wrap the codec in a stable shared library ABI. Some entry points that used to accept references now expect pointers.
  • API Change: The decompression functionality in the core API has been changed to allow use of multiple threads. The design pattern matches the compression functionality, requiring the caller to create the threads, synchronize them between images, and to call the new astcenc_decompress_reset() function between images.
• API Feature: Defines to support exporting public API entry point symbols from a shared object are provided, but not exposed off-the-shelf by the CMake provided by the project.
  • API Feature: New astcenc_get_block_info() function added to the core API to allow users to perform high level analysis of compressed data. This API is not implemented in decompressor-only builds.
  • API Feature: Codec configuration structure has been extended to expose the new RGBM compression mode. See the API header for details.

2.4

Status: Released, February 2021

The 2.4 release is the fifth release in the 2.x series. It is primarily a bug fix release for HDR image handling, which impacts all earlier 2.x series releases.

General:

• Feature: When using the -a option, or the equivalent config option for the API, any 2D blocks that are entirely zero alpha after the alpha filter radius is taken into account are replaced by transparent black constant color blocks. This is an RDO-like technique to improve compression ratios of any additional application packaging compression that is applied. Command Line:
• Bug fix: The command line wrapper now correctly loads HDR images that have a non-square aspect ratio.

2.3

Status: Released, January 2021

The 2.3 release is the fourth release in the 2.x series. It includes a number of performance improvements and new features.

Reminder for users of the library interface - the API is not designed to be stable across versions, and this release is not compatible with 2.2. Please recompile your client-side code using the updated astcenc.h header.

• General:
  • Feature: Decompressor-only builds of the codec are supported again. While this is primarily a feature for library users who want to shrink binary size, a variant command line tool astcdec can be built by specifying DECOMPRESSOR=ON on the CMake configure command line.
  • Feature: Diagnostic builds of the codec can now be built. These builds generate a JSON file containing a trace of the compressor execution. Diagnostic builds are only suitable for codec development; they are slower and JSON generation cannot be disabled. Build by setting DIAGNOSTICS=ON on the CMake configure command line.
  • Feature: Code compatibility improved with older versions of GCC, earliest compiler now tested is GCC 7.5 (was GCC 9.3).
  • Feature: Code compatibility improved with newer versions of LLVM, latest compiler now tested is Clang 12.0 (was Clang 9.0).
  • Feature: Code compatibility improved with the Visual Studio 2019 LLVM toolset (clang-cl). Using the LLVM toolset gives 25% performance improvements and is recommended.
• Command Line:
  • Feature: Quality level now accepts either a preset (-fast, etc) or a float value between 0 and 100, allowing more control over the compression quality vs performance trade-off. The presets are not evenly spaced in the float range; they have been spaced to give the best distribution of points between the fast and thorough presets.
    • -fastest: 0.0
    • -fast: 10.0
    • -medium: 60.0
    • -thorough: 98.0
    • -exhaustive: 100.0
• Core API:
  • API Change: Quality level preset enum replaced with a float value between 0 (-fastest) and 100 (-exhaustive). See above for more info.

Performance

This release includes a number of optimizations to improve performance.

• New compressor algorithm for handling encoding candidates and refinement.
• Vectorized implementation of compute_error_of_weight_set().
• Unrolled implementation of encode_ise().
• Many other small improvements!

The most significant change is the change to the compressor path, which now uses an adaptive approach to candidate trials and block refinement.

In earlier releases the quality level will determine the number of encoding candidates and the number of iterative refinement passes that are used for each major encoding trial. This is a fixed behavior; it will always try the full N candidates and M refinement iterations specified by the quality level for each encoding trial.

The new approach implements two optimizations for this:

• Compression will complete when a block candidate hits the specified target quality, after its M refinement iterations have been applied. Later block candidates are simply abandoned.
• Block candidates will predict how much refinement can improve them, and abandon refinement if they are unlikely to improve upon the best known encoding already in-hand.

This pair of optimizations provides significant performance improvement to the high quality modes which use the most block candidates and refinement iterations. A minor loss of image quality is expected, as the blocks we no longer test or refine may have been better coding choices.

Absolute performance vs 2.2 release:

Relative performance vs 2.2 release:

2.2

Status: Released, January 2021

The 2.2 release is the third release in the 2.x series. It includes a number of performance improvements and new features.

Reminder for users of the library interface - the API is not designed to be stable across versions, and this release is not compatible with 2.1. Please recompile your client-side code using the updated astcenc.h header.

• General:
  • Feature: New Arm aarch64 NEON accelerated vector library support.
  • Improvement: New CMake build system for all platforms.
  • Improvement: SSE4.2 feature profile changed to SSE4.1, which more accurately reflects the feature set used.
• Binary releases:
  • Improvement: Linux binaries changed to use Clang 9.0, which gives up to 15% performance improvement.
  • Improvement: Windows binaries are now code signed.
  • Improvement: macOS binaries for Apple silicon platforms now provided.
  • Improvement: macOS binaries are now code signed and notarized.
• Command Line:
  • Feature: New image preprocess -pp-normalize option added. This forces normal vectors to be unit length, which is useful when compressing source textures that use normal length to encode an NDF, which is incompatible with ASTC's two channel encoding.
  • Feature: New image preprocess -pp-premultiply option added. This scales RGB values by the alpha value. This can be useful to minimize cross-channel color bleed caused by GPU post-multiply filtering/blending.
  • Improvements: Command line tool cleanly traps and reports errors for corrupt input images rather than relying on standard library assert() calls in release builds.
• Core API:
  • API Change: Images using region-based metrics no longer need to include padding; all input images should be tightly packed and dim_pad is removed from the astcenc_image structure. This makes it easier to directly use images loaded from other libraries.
  • API Change: Image data is no longer a 3D array accessed using data[z][y][x] indexing, it's an array of 2D slices. This makes it easier to directly use images loaded from other libraries.
  • API Change: New ASTCENC_FLG_SELF_DECOMPRESS_ONLY flag added to the codec config. Using this flag enables additional optimizations that aggressively exploit implementation- and configuration-specific, behavior to gain performance. When using this flag the codec can only reliably decompress images that were compressed in the same context session. Images produced via other means may fail to decompress correctly, even if they are otherwise valid ASTC files.

Performance

There is one major set of optimizations in this release, related to the new ASTCENC_FLG_SELF_DECOMPRESS_ONLY mode. These allow the compressor to only create data tables it knows that it is going to use, based on its current set of heuristics, rather than needing the full set the format allows.

The first benefit of these changes is a reduced context creation time, which can be reduced by up to 250ms on our test machine. This is a significant percentage of the command line utility runtime for a small image when using a quick search preset. Compressing the whole Kodak test suite using the command line utility and the -fastest preset is ~30% faster with this release, which is mostly due to faster startup.

The reduction in the data table size in this mode also improve the core codec speed. Our test sets show an average of 12% improvement in the codec for -fastest mode, and an average of 3% for -medium mode.

Key for performance charts:

• Color = block size (see legend).
• Letter = image format (N = normal map, G = greyscale, L = LDR, H = HDR).

Absolute performance vs 2.1 release:

Relative performance vs 2.1 release:

2.1

Status: Released, November 2020

The 2.1 release is the second release in the 2.x series. It includes a number of performance optimizations and new features.

Reminder for users of the library interface - the API is not designed to be stable across versions, and this release is not compatible with 2.0. Please recompile your client-side code using the updated astcenc.h header.

Features:

• Command line:
  • Bug fix: The meaning of the -tH\cH\dH and -th\ch\dh compression modes was inverted. They now match the documentation; use -*H for HDR RGBA, and -*h for HDR RGB with LDR alpha.
  • Feature: A new -fastest quality preset is now available. This is designed for fast “roughing out” of new content, and sacrifices significant image quality compared to -fast. We do not recommend its use for production builds.
  • Feature: A new -candidatelimit compression tuning option is now available. This is a power-user control to determine how many candidates are returned for each block mode encoding trial. This feature is used automatically by the search presets; see -help for details.
  • Improvement: The compression test modes (-tl\ts\th\tH) now emit a MTex/s performance metric, in addition to coding time.
• Core API:
  • Feature: A new quality preset ASTCENC_PRE_FASTEST is available. See -fastest above for details.
  • Feature: A new tuning option tune_candidate_limit is available in the config structure. See -candidatelimit above for details.
  • Feature: Image input/output can now use ASTCENC_TYPE_F32 data types.
• Stability:
  • Feature: The SSE2, SSE4.2, and AVX2 variants now produce identical compressed output when run on the same CPU when compiled with the preprocessor define ASTCENC_ISA_INVARIANCE=1. For Make builds this can be set on the command line by setting ISA_INV=1. ISA invariance is off by default; it reduces performance by 1-3%.

Performance

Key for performance charts:

• Color = block size (see legend).
• Letter = image format (N = normal map, G = greyscale, L = LDR, H = HDR).

Absolute performance vs 2.0 release:

Relative performance vs 2.0 release:

2.0

Status: Released, August 2020

The 2.0 release is first release in the 2.x series. It includes a number of major changes over the earlier 1.7 series, and is not command-line compatible.

Features:

• The core codec can be built as a library, exposed via a new codec API.
• The core codec supports accelerated SIMD paths for SSE2, SSE4.2, and AVX2.
• The command line syntax has a clearer mapping to Khronos feature profiles.

Performance:

Key for performance charts

• Color = block size (see legend).
• Letter = image format (N = normal map, G = greyscale, L = LDR, H = HDR).

Absolute performance vs 1.7 release:

Relative performance vs 1.7 release: