UnrealEngine/Engine/Source/ThirdParty/astcenc/4.2.0/Docs/ChangeLog-4x.md

4.x series change log

This page summarizes the major functional and performance changes in each release of the 4.x series.

All performance data on this page is measured on an Intel Core i5-9600K clocked at 4.2 GHz, running astcenc using AVX2 and 6 threads.

4.2.0

Status: November 2022

The 4.2.0 release is an optimization release. There are significant performance improvements, minor image quality improvements, and library interface changes in this release.

Reminder - the codec library API is not designed to be binary compatible across versions. We always recommend rebuilding your client-side code using the updated astcenc.h header.

• General:
  • Bug-fix: Compression for RGB and RGBA base+offset encodings no longer generate endpoints with the incorrect blue-contract behavior.
  • Bug-fix: Lowest channel correlation calculation now correctly ignores constant color channels for the purposes of filtering 2 plane encodings. On average this improves both performance and image quality.
  • Bug-fix: ISA compatibility now checked in config_init() as well as in context_alloc().
  • Change: Removed the low-weight count optimization, as more recent changes had significantly reduced its performance benefit. Option removed from both command line and configuration structure.
  • Feature: The -exhaustive mode now runs full trials on more partitioning candidates and block candidates. This improves image quality by 0.1 to 0.25 dB, but slows down compression by 3x. The -verythorough and -thorough modes also test more candidates.
  • Feature: A new preset, -verythorough, has been introduced to provide a standard performance point between -thorough and the re-tuned -exhaustive mode. This new mode is faster and higher quality than the -exhaustive preset in the 4.1 release.
  • Feature: The compressor can now independently vary the number of partitionings considered for error estimation for 2/3/4 partitions. This allows heuristics to put more effort into 2 partitions, and less in to 3/4 partitions.
  • Feature: The compressor can now run trials on a variable number of candidate partitionings, allowing high quality modes to explore more of the search space at the expense of slower compression. The number of trials is independently configurable for 2/3/4 partition cases.
  • Optimization: Introduce early-out threshold for 2/3/4 partition searches based on the results after 1 of 2 trials. This significantly improves performance for -medium and -thorough searches, for a minor loss in image quality.
  • Optimization: Reduce early-out threshold for 3/4 partition searches based on 2/3 partition results. This significantly improves performance, especially for -thorough searches, for a minor loss in image quality.
  • Optimization: Use direct vector compare to create a SIMD mask instead of a scalar compare that is broadcast to a vector mask.
  • Optimization: Remove obsolete partition validity masks from the partition selection algorithm.
  • Optimization: Removed obsolete channel scaling from partition avgs_and_dirs() calculation.

Performance:

Key for charts:

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

Relative performance vs 4.0 and 4.1 release:

4.1.0

Status: August 2022

The 4.1.0 release is a maintenance release. There is no performance or image quality change in this release.

• General:
  • Change: Command line decompressor no longer uses the legacy GL_LUMINANCE or GL_LUMINANCE_ALPHA format enums when writing KTX output files. Luminance textures now use the GL_RED format and luminance_alpha textures now use the GL_RG format.
  • Change: Command line tool gains a new -dimage option to generate diagnostic images showing aspects of the compression encoding. The output file name with its extension stripped is used as the stem of the diagnostic image file names.
  • Bug-fix: Library decompressor builds for SSE no longer use masked store maskmovdqu instructions, as they can generate faults on masked lanes.
  • Bug-fix: Command line decompressor now correctly uses sized type enums for the internal format when writing output KTX files.
  • Bug-fix: Command line compressor now correctly loads 16 and 32-bit per component input KTX files.
  • Bug-fix: Fixed GCC9 compiler warnings on Arm aarch64.

4.0.0

Status: July 2022

The 4.0.0 release introduces some major performance enhancement, and a number of larger changes to the heuristics used in the codec to find a more effective cost:quality trade off.

• General:
  • Change: The -array option for specifying the number of image planes for ASTC 3D volumetric block compression been renamed to -zdim.
  • Change: The build root package directory is now bin instead of astcenc, allowing the CMake install step to write binaries into /usr/local/bin if the user wishes to do so.
  • Feature: A new -ssw option for specifying the shader sampling swizzle has been added as convenience alternative to the -cw option. This is needed to correct error weighting during compression if not all components are read in the shader. For example, to extract and compress two components from an RGBA input image, weighting the two components equally when sampling through .ra in the shader, use -esw ggga -ssw ra. In this example -ssw ra is equivalent to the alternative -cw 1 0 0 1 encoding.
  • Feature: The -a alpha weighting option has been re-enabled in the backend, and now again applies alpha scaling to the RGB error metrics when encoding. This is based on the maximum alpha in each block, not the individual texel alpha values used in the earlier implementation.
  • Feature: The command line tool now has -repeats <count> for testing, which will iterate around compression and decompression count times. Reported performance metrics also now separate compression and decompression scores.
  • Feature: The core codec is now warning clean up to /W4 for both MSVC cl.exe and clangcl.exe compilers.
  • Feature: The core codec now supports arm64 for both MSVC cl.exe and clangcl.exe compilers.
  • Feature: NO_INVARIANCE builds will enable the -ffp-contract=fast option for all targets when using Clang or GCC. In addition AVX2 targets will also set the -mfma option. This reduces image quality by up to 0.2dB (normally much less), but improves performance by up to 5-20%.
  • Optimization: Angular endpoint min/max weight selection is restricted to weight QUANT_11 or lower. Higher quantization levels assume default 0-1 range, which is less accurate but much faster.
  • Optimization: Maximum weight quantization for later trials is selected based on the weight quantization of the best encoding from the 1 plane 1 partition trial. This significantly reduces the search space for the later trials with more planes or partitions.
  • Optimization: Small data tables now use in-register SIMD permutes rather than gathers (AVX2) or unrolled scalar lookups (SSE/NEON). This can be a significant optimization for paths that are load unit limited.
  • Optimization: Decompressed image block writes in the decompressor now use a vectorized approach to writing each row of texels in the block, including to ability to exploit masked stores if the target supports them.
  • Optimization: Weight scrambling has been moved into the physical layer; the rest of the codec now uses linear order weights.
  • Optimization: Weight packing has been moved into the physical layer; the rest of the codec now uses unpacked weights in the 0-64 range.
  • Optimization: Consistently vectorize the creation of unquantized weight grids when they are needed.
  • Optimization: Remove redundant per-decimation mode copies of endpoint and weight structures, which were really read-only duplicates.
  • Optimization: Early-out the same endpoint mode color calculation if it cannot be applied.
  • Optimization: Numerous type size reductions applied to arrays to reduce both context working buffer size usage and stack usage.

Performance:

Key for charts:

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

Relative performance vs 3.7 release:

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