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Building WASM artifacts

This file describes the building and testing of JPEG XL Web Assembly bundles and wrappers.

These instructions assume an up-to-date Debian/Ubuntu system. For other platforms, or if you encounter any difficulties, please instead use the Docker container.

For the sake of simplicity, it is considered, that the following environment variables are set:

  • OPT - path to the directory containing additional software; the emsdk directory with the Emscripten SDK should reside there; in the Docker container (mentioned above) this should be /opt

Requirements

CMake is used as a build system. To install it, follow Debian build instructions.

Emscripten SDK is required for building WebAssembly artifacts. To install it, follow the Download and Install guide:

cd $OPT

# Get the emsdk repo.
git clone https://github.com/emscripten-core/emsdk.git

# Enter that directory.
cd emsdk

# Download and install the latest SDK tools.
./emsdk install latest

# Make the "latest" SDK "active" for the current user. (writes ~/.emscripten file)
./emsdk activate latest

v8 is a JavaScript engine used for running tests. v8 has better WASM SIMD support than NodeJS 14. To install it use JSVU:

# Fix some v8 version know to work well.
export v8_version="8.5.133"

# Install JSVU
npm install jsvu -g

# Trick JSVU to install to specific location instead of user "home".
# Note: "os" flag should match the host OS.
HOME=$OPT jsvu --os=linux64 "v8@${v8_version}"

# Link v8 binary to version-indepentent path.
ln -s "$OPT/.jsvu/v8-${v8_version}" "$OPT/.jsvu/v8"

In Docker container CMake, Emscripten SDK and V8 are pre-installed.

Building and testing the project

# Setup EMSDK and other environment variables. In practice EMSDK is set to be
# $OPT/emsdk.
source $OPT/emsdk/emsdk_env.sh

# Specify JS engine binary
export V8=$OPT/.jsvu/v8

# If building using the jpegxl-builder docker container prefix the following commands with:
# CMAKE_FLAGS=-I/usr/wasm32/include
# ex. CMAKE_FLAGS=-I/usr/wasm32/include BUILD_TARGET=wasm32 emconfigure ./ci.sh release

# Either build with regular WASM:
BUILD_TARGET=wasm32 emconfigure ./ci.sh release
# or with SIMD WASM:
BUILD_TARGET=wasm32 ENABLE_WASM_SIMD=1 emconfigure ./ci.sh release