This is a build2 package for the ARM astc-encoder C library. It provides Adaptive Scalable Texture Compression (ASTC) encoding and decoding via the public C API in <astcenc.h>.

Usage

To start using libastcenc in your project, add the following depends value to your manifest, adjusting the version constraint as appropriate:

depends: libastcenc ^5.7.0

Then import the library in your buildfile:

import libs = libastcenc%lib{astcenc}

Include the public header as:

#include <astcenc.h>

Importable targets

5.x series change log

This page summarizes the major functional and performance changes in each release of the 5.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.

5.7.0

Status: Released August 2026.

The 5.7.0 release is a minor maintenance release.

• Command line tool updates:
  • Bug fix: Avoid pixel count overflow when loading input PNG file.
  • Bug fix: Error if payload is undersized for stated image dimensions when loading compressed input KTX file.
  • Improvement: Top-level -help text as been rewritten to improve clarity and consistency.
  • Change: Removed -repeats benchmarking option, because we prefer to repeat by invoking the command line multiple times. This gives performance results closer to what a real user sees.
  • Change: Removed -dimage diagnostic images generation option from normal builds. Now only available for builds configured with ASTCENC_DIAGNOSTICS=ON.

5.6.0

Status: Released July 2026

The 5.6.0 release is a minor maintenance release.

• Codec library updates:
  • Bug fix: Avoid undefined behavior caused by passing floating point values outside of the [0.0, 1.0] range as input data for a UNORM color channel.
  • Bug fix: Avoid undefined behavior caused by unaligned access in SSE, AVX2, and NEON SIMD library implementations.
• Command line tool updates:
  • Bug fix: Fixed incorrect plane stride when writing an uncompressed 3D LDR image to a DDS container.
  • Bug fix: Fixed potential integer overflow when storing very large uncompressed images to a dds or .ktx output image format.
  • Bug fix: Fixed missing initialization of the reserved2 field in the DDS file header when writing uncompressed .dds output images.
  • Bug fix: Fixed typos and grammar issues in the command line -help text.

5.5.0

Status: Released June 2026

The 5.5.0 release is a minor maintenance release, fixing minor functional issues and improving robustness when processing invalid images.

• Codec library updates:
  • Bug fix: Correct vfloat8 NaN inequality comparisons for AVX2 builds, so that decompressing an invalid encoding returns the correct max magenta error color for UNORM output formats instead of black.
  • Bug fix: Add overflow detection so that the API returns errors for cases when input image size would result in integer overflow in calculations of total texel count, total block count, or compressed image byte size.
  • Bug fix: Fix bad offset calculation in compute_averages() when using 3D block sizes.
  • Bug fix: Add missing low-clamp when storing decompressed HDR data into a UNORM8 image. Prior to this fix, output colors would be incorrect if a HDR void-extent block contained a negative FP16 constant color component.
  • Improvement: Return standard error color when decompression requires an unavailable partitioning when using an ASTCENC_FLG_SELF_DECOMPRESS_ONLY context. Note that this is still not allowed API usage and may trigger asserts in a debug build.
• Command line tool updates:
  • Update: Update stb_image to v2.30.
  • Update: Update Wuffs to v0.3.4.
  • Update: Update TinyEXR to v1.0.13.
  • Bug fix: Use C++ RAII to manage resource lifetime, removing resource leaks when an error condition is encountered.
  • Bug fix: Report errors for .astc, .dds, and .ktx input image sizes that would result in integer overflow in calculations of total block count or data size.
  • Bug fix: Avoid undefined behavior on NaN to int conversion triggered by atan2() calls when both inputs are zero.
  • Bug fix: Avoid undefined behavior on left shift of negative integer, that is triggered for some HDR encodings in hdr_alpha_unpack().
  • Bug fix: Redirect error logging for failed .dds and .ktx input image loading to stderr, and improve message consistency.

5.4.0

Status: Released May 2026

The 5.4.0 release is a minor feature release.

This release includes changes to the public interface in the astcenc.h header. We always recommend rebuilding your client-side code using the header from the same release to avoid compatibility issues.

• General:
  • Improvement: The interface header astcenc.h is now C compliant to make it usable from C programs.
  • Improvement: Contexts using the same configuration can now share read-only data tables. This can significantly reduce the amount of memory needed for applications that parallelize by processing multiple images in parallel instead of slicing a single image in parallel.
  • Improvement: Decompressor (astcdec) builds, which lack compression support, now use a smaller block_size_descriptor by omitting fields that are only needed for compression. This reduces the size of a decompressor context by more than 10MB!
  • Optimization: A SIMD backend for the RISC-V Vector extensions has been added, and is auto-selected when configured with ASTCENC_ISA_NONE and a core with a 256-bit vector width. See Building.md for details.
  • Bug fix: Avoid using an undefined quant_weight value if all one partition trials return an error block.
  • Bug fix: Remove remaining instances of type aliasing through unions.
  • Bug fix: Avoid compiler double definition warning for NOMINMAX when compiling with MinGW.
  • Bug fix: Avoid compiler floating point model override warning when compiling with Clang 20.