Add BCn encoders/decoders with RDO support

.github/workflows/linux.yml

@@ -294,11 +294,21 @@ jobs:
             -Source "${{ env.NUGET_FEED_URL }}"
 
       - name: script
+        id: buildstep
         env:
           VCPKG_BINARY_SOURCES: clear;nuget,${{ env.NUGET_FEED_URL }},readwrite
         run: |
           ./scripts/build_linux.sh
 
+    # Currently this runs if build_linux fails for any reason whatsoever (because detecting
+    # that the CTS tests have failed requires some changes to build_linux)
+#    - name: Upload generated CTS output files if CTS tests fail
+#      if: failure() && matrix.options.tools_cts == 'ON'  && steps.buildstep.outcome == 'failure'
+#      uses: actions/upload-artifact@v7
+#      with:
+#        name: cts_failure_artifacts_${{ github.sha }}
+#        path: tests/cts/clitests/output
+
       - name: Sanitize release notes
         if: matrix.options.package == 'YES' && github.event_name == 'push' && github.ref_type == 'tag'
         run: |

.github/workflows/macos.yml

@@ -272,6 +272,7 @@ jobs:
           scripts/smudge_date.sh
 
       - name: script
+        id: buildstep
         env:
           VCPKG_BINARY_SOURCES: clear;nuget,${{ env.NUGET_FEED_URL }},readwrite
         run: |
@@ -284,6 +285,15 @@ jobs:
           fi
           set +e
 
+    # Currently this runs if build_macos fails for any reason whatsoever (because detecting
+    # that the CTS tests have failed requires some changes to build_macos)
+#    - name: Upload generated CTS output files if CTS tests fail
+#      if: failure() && matrix.options.tools_cts == 'ON'  && steps.buildstep.outcome == 'failure'
+#      uses: actions/upload-artifact@v7
+#      with:
+#        name: cts_failure_artifacts_${{ github.sha }}
+#        path: tests/cts/clitests/output
+
       # Re. packaging, note that the build script only creates packages for
       # the Release configuration. If this is changed work will be needed
       # here to prevent failures from uploading same-named artifacts from both

.github/workflows/mingw.yml

@@ -84,7 +84,15 @@ jobs:
     - name: Build Mingw x64 Release
       run: cmake --build build --config Release
     - name: Test Mingw build
+      id: teststep
       run: ctest --output-on-failure --test-dir build -C Release
+#    - name: Upload generated CTS output files if CTS tests fail
+#      if: failure() && matrix.options.tools_cts == 'ON'  && steps.teststep.outcome == 'failure'
+#      uses: actions/upload-artifact@v7
+#      with:
+#        name: cts_failure_artifacts_${{ github.sha }}
+#        path: tests/cts/clitests/output
+
 #    - name: Upload test log
 #      shell: pwsh
 #      if: ${{ failure() }}

.github/workflows/windows.yml

@@ -331,10 +331,18 @@ jobs:
       run: scripts/check_mkvk.ps1
 
     - name: Test Windows build
+      id: teststep
       # Tests built for arm64 can't be run as the CI runners are all x64.
       if: matrix.options.tests == 'ON'
       run: ctest --output-on-failure --test-dir $env:BUILD_DIR -C Release
 
+#    - name: Upload generated CTS output files if CTS tests fail
+#      if: failure() && matrix.options.tools_cts == 'ON'  && steps.teststep.outcome == 'failure'
+#      uses: actions/upload-artifact@v7
+#      with:
+#        name: cts_failure_artifacts_${{ github.sha }}
+#        path: tests/cts/clitests/output
+
 #    - name: Upload test log
 #      if: ${{ failure() }}
 #      run: scripts/on_failure.ps1

.gitignore

@@ -58,3 +58,6 @@ the_khronos_group_inc.p12
 
 # Place for random developer test files.
 /testground/
+
+# clangd compile commands (used by LSPs)
+compile_commands.json

.gitmodules

@@ -4,5 +4,5 @@
 
 [submodule "tests/cts"]
 	path = tests/cts
-	url = https://github.com/KhronosGroup/KTX-Software-CTS.git
+	url = https://github.com/walcht/KTX-Software-CTS.git
 	branch = main

REUSE.toml

@@ -17,6 +17,12 @@ precedence = "aggregate"
 SPDX-FileCopyrightText = "Copyright (c) 2004, Industrial Light & Magic, a division of Lucasfilm Entertainment Company Ltd."
 SPDX-License-Identifier = "BSD-3-Clause"
 
+[[annotations]]
+path = "tests/resources/input/exr/rgb16_sfloat_bc6hu.exr"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2026 The Khronos Group Inc."
+SPDX-License-Identifier = "Apache-2.0"
+
 [[annotations]]
 path = "tests/resources/ktx2/Desk_uastc_hdr4x4_zstd_15.ktx2"
 precedence = "aggregate"

external/bc7enc_rdo/CMakeLists.txt

@@ -0,0 +1,22 @@
+# Copyright 2019-2020 The Khronos Group Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+add_library(bc7enc_rdo)
+target_compile_features(bc7enc_rdo PUBLIC cxx_std_17)
+
+# original bc7enc_rdo disables strict aliasing (see https://github.com/richgel999/bc7enc_rdo/blob/master/CMakeLists.txt)
+# basisu also emphasises on compiling with '-fno-strict-aliasing'
+if (NOT MSVC)
+  target_compile_options(bc7enc_rdo PRIVATE -fno-strict-aliasing)
+endif()
+
+target_sources(bc7enc_rdo
+  PRIVATE
+    ${CMAKE_CURRENT_LIST_DIR}/rgbcx.cpp     # BC1, BC3, BC4 and BC5 encoders/decoders
+    ${CMAKE_CURRENT_LIST_DIR}/ert.cpp       # RDO post processing step and some utils
+)
+
+target_include_directories(bc7enc_rdo
+  PUBLIC
+    ${CMAKE_CURRENT_LIST_DIR}/
+)

external/bc7enc_rdo/LICENSES/MIT.txt

@@ -0,0 +1,19 @@
+MIT License Copyright (c) <year> <copyright holders>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is furnished
+to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice (including the next
+paragraph) shall be included in all copies or substantial portions of the
+Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
+OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
+OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

external/bc7enc_rdo/README.md

@@ -0,0 +1,88 @@
+# About
+
+This branch of bc7enc_rdo forked from [bc7enc_rdo][bc7enc_rdo] contains two
+components used by KTX-Software with some changes:
+
+  - rgbcx: BC1, BC3, BC4, and BC5 encoders/decoders (+ added BC2 decoder).
+  - ert: rate distortion optimization (RDO) (agnostic to encoders/decoders).
+
+Changes:
+
+  - added [[maybe_unused]] to silence compiler warnings about unused variables
+
+Essentially: only what is absolutely necessary and not already provided by Basis
+Universal is left. The following components have been removed:
+
+  - bc7 encoder/decoder. See [Notes][#Notes] below.
+  - CLI components.
+  - utils.h/cpp because it relies on some heavy classes.
+
+Currently, the remaining two components are compiled together under a single
+STATIC library bc7enc_rdo (if the need arises where only the RDO component is needed,
+this will be separated into multiple libraries).
+
+## Building
+
+This is intended to be built as a static library dependency (see minimal
+CMakeLists.txt).
+
+Somewhere in your project's CMakeLists:
+
+```bash
+# Make sure bc7enc_rdo is built as a STATIC library
+set(BUILD_SHARED_LIBS OFF)
+add_subdirectory(path-to-bc7enc_rdo)
+set(BUILD_SHARED_LIBS ${BUILD_SHARED_LIBS_RESET})
+
+# Then append it to your target's link dependencies
+target_link_libraries(your_target PRIVATE bc7enc_rdo)
+```
+
+## Notes
+
+BC2 encoder is currently not implemented because practically it is very rarely
+used (if at all) and can almost always be replaced with the more capable BC3
+format (which offers same color RGB block encoding as BC1 but with added alpha
+support that is usually better than the one implemented by BC2).
+
+BC6HU/BC6HS HDR formats are already originally not supported by this repo.
+Basis Universal provides bc6hu (emphasis on the **u**) encoder and bc6hu/bc6hs decoders.
+
+BC7 encoder/decoder is not included because Basis Universal already provides a
+much more capable encoder (bc7f).
+
+Notes about choice with BC1 vs. BC3 vs. BC7 (from Basisu wiki):
+
+> bc7f encodes so rapidly (on average), that apart from lower VRAM consumption
+> (4bpp vs. 8bpp) and better GPU texture cache efficiency, there's little need
+> to use BC1 now. BC3 still has an advantage vs. BC7, because it very strongly
+> separates how RGB is encoded from the alpha channel, in a predictable way.
+
+## Compilation Notes
+
+**Makes sure to compile with `-fno-strict-aliasing`** since the original
+bc7enc_rdo repo was mainly developed and tested on MSVC (which doesn't do
+excessive optimizations including strict aliasing).
+
+There are pointer conversions all over the place and if strict aliasing is
+enabled, these conversions are most likely UB (see strict aliasing rule or type
+punning).
+
+This can be re-written a way that complies with strict aliasing but a lot of
+`memcpy`s have to be added which will result in the code being significantly
+less readable (also questionable if there is any benefit to this whatsoever).
+
+## TODOs
+
+There are some features that I'd like to add (from most important to least):
+
+1. [] HDR RDO (this is possible but need to be extremely careful when changing
+ert.cpp/h code to handle uint16_t instead of chars/uint8_t)
+1. [] BC2 encoder (even though it is seldom used)
+1. [] BC6HS encoder
+
+## License
+
+MIT License Rich Geldreich.
+
+[bc7enc_rdo]: https://github.com/richgel999/bc7enc_rdo.git)

external/bc7enc_rdo/REUSE.toml

@@ -0,0 +1,9 @@
+version = 1
+SPDX-PackageName = "bc7enc_rdo"
+SPDX-PackageDownloadLocation = "https://github.com/richgel999/bc7enc_rdo"
+
+[[annotations]]
+path = "**"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "2020-2021 Richard Geldreich, Jr. <richgel99@gmail.com>"
+SPDX-License-Identifier = "MIT"