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TinyEXR texcomp — Licensing and Third-Party Notices

third_party/tinyexr/tools/texcomp/NOTICE.md

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TinyEXR texcomp — Licensing and Third-Party Notices

License of this component

The TinyEXR texcomp texture-compression suite (everything under tools/texcomp/) is original work licensed under the Apache License, Version 2.0.

Copyright 2014-2026 Syoyo Fujita and TinyEXR authors
SPDX-License-Identifier: Apache-2.0

The full license text is in LICENSE in this directory, and every source file carries an SPDX-License-Identifier: Apache-2.0 tag.

Note: this is a licensing choice for the texcomp subcomponent specifically. The rest of the TinyEXR project is BSD-3-Clause; Apache-2.0 is compatible with it for combined/redistributed works.

The pure-C11 library (make texcomp) has no third-party runtime dependencies. The pieces below are either (a) vendored elsewhere in the repo and only used by optional CLI/test targets, or (b) small ports / spec-data transcriptions whose provenance is credited here and in the relevant file headers.

Third-party components

Arm astcenc — Apache-2.0

  • Copyright 2011-2024 Arm Limited. Vendored at deps/astcenc; license in deps/astcenc/LICENSE.txt.
  • Optional C++ backend. make texcomp-arm builds astcenc as an alternate encoder selectable with --encoder arm. The default make texcomp build is pure C11 with no C++ parts.
  • HDR endpoint codec port. The ASTC HDR CEM 7 (base+scale) and CEM 11 (RGB direct) endpoint pack/unpack in src/texcomp_astc_hdr.c (tc_astc_cem7_pack/unpack, tc_astc_cem11_pack/unpack) are ports of astcenc's quantize_hdr_rgbo, hdr_rgbo_unpack and hdr_rgb_unpack.
  • Conformance oracle. The texcomp-astc-arm-gate and texcomp-astc-hdr-gate tests decode texcomp output with astcenc's conformant decoder to verify correctness.

bcdec.h — MIT (dual-licensed MIT / Unlicense)

  • Copyright (c) 2022 Sergii Kudlai. https://github.com/iOrange/bcdec
  • The corrected BPTC (BC7) partition + anchor tables in test/bc7_ref_decode.h, and the BC6H two-region (mode 9) partition table and block bit layout in src/texcomp_bc6h.c, are transcribed / mirrored from bcdec (the tables published in the Khronos spec contain known errors).
  • The BC6H reference decoder test/bc6h_ref_decode.h (all 14 modes) is a C port of bcdec's bcdec_bc6h_half, used test-only as the conformance oracle for the texcomp-bc6h-gate. It is not linked into the shipped library.

Khronos ASTC / BPTC specifications

  • The ISE codec, 2D block-mode tables, partition-pattern hashing, and unquantization tables in src/texcomp_astc.c, and the BC6H/BC7 block bit layouts, follow the Khronos Data Format Specification (ASTC) and the BPTC spec. Specification data (constants, bit layouts) is not copyrightable.

Basis Universal — Apache-2.0

  • Copyright (c) 2019-2024 Binomial LLC. https://github.com/BinomialLLC/basis_universal
  • The UASTC LDR / UASTC HDR 4x4 mode subsets implemented by texcomp's --format uastc_ldr / astc_hdr follow the Basis UASTC specifications (all output is standard ASTC). The xbc7 format is a texcomp-native take on the XBC7 idea (windowed RDO + entropy coding of BC7) — it is not bitstream-compatible with Basis XBC7.
  • The uni universal-transcodable intermediate (--format uni, src/texcomp_uni.c: encode once, transcode at load to BC7/BC1/ASTC/ETC2) follows the concept pioneered by Basis Universal / UASTC — a canonical single-subset block re-packed cheaply to the device's GPU format. It is a texcomp-native intermediate and is not the Basis .basis/UASTC bitstream. Its optional codebook supercompression (--basis) is a BasisLZ-style endpoint/selector deduplication with RDO; it is not the Basis ETC1S codec and does not emit KTX2 supercompressionScheme=1 (BasisLZ) — the KTX2 output uses Zstd (scheme 2) with the codebook as an inner pre-transform.

QuickBC7 / etcpak

  • BC7 quick-mode heuristics and API naming derive from a pure-C11 port of the QuickBC7-enabled etcpak fork.
    • Paper: QuickBC7: Fast BC7 Texture Compression Heuristics, Hyeon-ki Lee and Jae-Ho Nah, Computers & Graphics 2026.
    • Reference source: https://github.com/gusrlLee/etcpak (commit b88c8f4).

Zstandard (zstd) — BSD-3-Clause (dual BSD / GPLv2)

  • Copyright (c) Meta Platforms, Inc. Used via TinyEXR's vendored deps/zstd (tinyexr_zstd). The xbc7 container entropy-codes the BC7 stream with zstd, and the uni KTX2 writer uses zstd for per-level supercompression (supercompressionScheme=2). Only the CLI links zstd; the pure-C11 texcomp library does not depend on it.

stb_image — public domain / MIT

  • Sean Barrett. examples/common/stb_image.h, used by the CLI (texcomp_cli.c) only, for PNG loading.

Feature status (informational)

  • BC1/BC3/BC5/BC7 direct encoders; BC7 covers all 8 modes with a quick-mode heuristic path and an exhaustive search, plus optional windowed RDO (--rdo).
  • BC6H (unsigned + signed): one-region mode 11 and two-region mode 9, both with least-squares endpoint refinement; the mode-11 selector search has SSE4.1/AVX2/NEON kernels that are bit-identical to scalar (cross-backend parity tested). The higher-base delta-encoded 2-region modes remain future work.
  • ETC2 / EAC encoders.
  • ASTC LDR: all fourteen 2D footprints, 1-4 partitions, dual-plane, CEM 0/4/6/8/10/12; integer least-squares endpoint refinement; SSE2/SSE4.1/AVX2/ NEON kernels bit-identical to scalar. Includes the constrained UASTC LDR 19-mode subset (--format uastc_ldr).
  • ASTC HDR (UASTC HDR 4x4): void-extent + CEM 7 (base+scale) and CEM 11 (RGB direct: single / dual-plane / 2-subset), LSQ-refined.
  • xbc7: texcomp-native supercompressed BC7 (windowed RDO + zstd), transcodes to standard BC7.
  • uni: universal transcodable intermediate — encode once, transcode at load to BC7/BC1/ASTC/ETC2; optional codebook (--basis) + Zstd KTX2 mip chain.

Conformance is verified by in-tree reference decoders (test/astc_ref_decode.h, test/bc7_ref_decode.h, test/astc_hdr_ref_decode.h) and by cross-checks against astcenc; quality is tracked by make texcomp-astc-psnr.