etc2native — DDS → KTX1(ETC2) via BCnEncoder.NET + etc2comp

C#  : parse DDS, decode BCn -> RGBA8 (BCnEncoder.NET, managed), optional 50% resize, write KTX1
C++ : RGBA8 -> ETC2 blocks (etc2comp fork + a tiny C ABI)

Mapping (forceRgba8 == false): DXT1 no-alpha→ETC2_RGB, DXT1 alpha→ETC2_RGBA1, DXT3/DXT5/BC7→ETC2_RGBA8, uncompressed→ETC2_RGBA8 (only with forceTranscodeUncompressed). forceRgba8 forces ETC2_RGBA8; forceResize halves W/H (regenerating mips); quality is etc2comp effort 0..100; jobs is encoder threads.

Repo layout

etc2native/                      
  CMakeLists.txt
  EtcCApi.cpp  EtcCApi.h 
build_etc2native_windows.cmd     <- Windows  x64 / x86 / arm64
build_etc2native_linux.sh        <- Linux    x64 / arm64 / riscv64
build_etc2native_android.sh      <- Android  arm64-v8a / armeabi-v7a / x86 / x86_64
Dockerfile.etc2native-linux
Dockerfile.etc2native-android
compose.etc2native.yaml
csharp/   
  Etc2Transcoder.cs 

The build scripts clone the etc2comp fork (https://github.com/Shivansps/etc2comp) fresh on every run and build it together with EtcCApi.cpp. Override the source with ETC2_FORK=<url> ETC2_REF=<tag>.

Output is **loose .so / .dll per arch **

Windows

build_etc2native_windows.cmd
:: -> build-win-x64\Release\etc2native.dll
:: -> build-win-x86\Release\etc2native.dll
:: -> build-win-arm64\Release\etc2native.dll

Needs VS 2022 Desktop C++ plus the ARM64 build tools (Individual Components → "MSVC v143 ARM64 build tools") for the arm64 target.

Linux (Docker)

docker compose -f compose.etc2native.yaml run --rm etc2native-linux
# -> prebuilt_linux_etc2native/{x64,arm64,riscv64}/libetc2native.so

Android (Docker)

docker compose -f compose.etc2native.yaml run --rm etc2native-android
# -> prebuilt_android_etc2native/{arm64-v8a,armeabi-v7a,x86,x86_64}/libetc2native.so

The image bakes NDK r29 (android-24).

using Etc2;
var status = Etc2Transcoder.TranscodeFile("tex.dds", "tex.ktx",
    forceRgba8: false, forceResize: true, forceTranscodeUncompressed: false,
    quality: 20, jobs: 8);