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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 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.

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

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

# This should set the $EMSDK variable.
# If your node version is <16.4.0, you might need to update to a newer version or override
# the node binary with a version which supports SIMD:
echo "NODE_JS='/path/to/node_binary'" >> $EMSDK/.emscripten

# Assuming you are in the root level of the cloned libjxl repo,
# 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

Example site

Once you have build the wasm binary, you can give it a try by building a site that decodes jxl images, see wasm_demo.

Building wasm with Docker

There is a docker devcontainer which can be used to build the wasm libraries available in the .devcontainer package. That can be run in an editor supporting devcontainers, or can be run manually with:

docker build . -f .devcontainer/Dockerfile -t libjxl
docker run --mount type=bind,src=.,dst=/workspaces/libjxl -i libjxl
source $OPT/emsdk/emsdk_env.sh
BUILD_TARGET=wasm32 ENABLE_WASM_SIMD=1 emconfigure ./ci.sh release