libwebp/README.wasm

Description:
============

This file describes the compilation of libwebp using portable intrinsics /
WebAssembly (wasm) to native targets using clang and CMake.

Prerequisites:
==============

- cmake 2.8+

- clang 3.9+ for portable intrinsics support; as wasm progresses a tip of tree
  build may be necessary.

Building:
=========

 - configure the project with CMake using:

 $ mkdir -p build && \
   cd build && \
   cmake -DWEBP_BUILD_DWEBP=1 -DCMAKE_C_COMPILER=clang -DWEBP_ENABLE_WASM=1 ../

 - compile dwebp using 'make'.

 - Note this currently generates native executables only and is incompatible
   with -DWEBP_BUILD_WEBP_JS.

Build options:
==============

- platform specific multiply high (mulhi) implementation, disabled by default.
  arm: -DCMAKE_C_FLAGS='-DENABLE_NEON_BUILTIN_MULHI_INT16X8 ...'
  x86: -DCMAKE_C_FLAGS='-DENABLE_X86_BUILTIN_MULHI_INT16X8 ...'

Cross compilation:
==================

 - arm toolchains can be obtained from:
   http://www.linaro.org/downloads/

 - the android ndk can be obtained from:
   https://developer.android.com/ndk/downloads/index.html

armv7:
------

Android:
 $ ./android-ndk-r15b/build/tools/make_standalone_toolchain.py \
   --arch arm --api 24 --stl gnustl --install-dir /opt/android-arm-24
 $ mkdir -p build && cd build
 $ cmake ../libwebp \
   -DWEBP_BUILD_DWEBP=1 \
   -DCMAKE_C_COMPILER=/opt/android-arm-24/bin/clang \
   -DCMAKE_PREFIX_PATH=/opt/android-arm-24/sysroot/usr/lib \
   -DCMAKE_C_FLAGS=-fPIE \
   -DCMAKE_EXE_LINKER_FLAGS=-Wl,-pie \
   -DCMAKE_BUILD_TYPE=Release \
   -DWEBP_ENABLE_WASM=1

Linux:
 $ gcc_arm=/opt/gcc-arm; target=arm-linux-gnueabihf
 $ mkdir -p build && cd build
 $ cmake ../libwebp -DWEBP_BUILD_DWEBP=1 -DWEBP_ENABLE_WASM=1 \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_C_FLAGS="--target=$target --gcc-toolchain=$gcc_arm --sysroot=$gcc_arm/$target/libc -march=armv7-a -mfpu=neon" \
   -DCMAKE_PREFIX_PATH=$gcc_arm/$target/libc/usr

aarch64 / arm64:
----------------

Android:
 $ ./android-ndk-r15b/build/tools/make_standalone_toolchain.py \
   --arch arm64 --api 24 --stl gnustl --install-dir /opt/android-arm64-24
 $ mkdir -p build && cd build
 $ cmake ../libwebp \
   -DWEBP_BUILD_DWEBP=1 \
   -DCMAKE_C_COMPILER=/opt/android-arm64-24/bin/clang \
   -DCMAKE_PREFIX_PATH=/opt/android-arm64-24/sysroot/usr/lib \
   -DCMAKE_C_FLAGS=-fPIE \
   -DCMAKE_EXE_LINKER_FLAGS=-Wl,-pie \
   -DCMAKE_BUILD_TYPE=Release \
   -DWEBP_ENABLE_WASM=1

Linux:
 $ gcc_arm=/opt/gcc-aarch64; target=aarch64-linux-gnu
 $ mkdir -p build && cd build
 $ cmake ../libwebp -DWEBP_BUILD_DWEBP=1 -DWEBP_ENABLE_WASM=1 \
   -DCMAKE_C_COMPILER=clang \
   -DCMAKE_C_FLAGS="--target=$target --gcc-toolchain=$gcc_arm --sysroot=$gcc_arm/$target/libc" \
   -DCMAKE_PREFIX_PATH=$gcc_arm/$target/libc/usr