OpenJPEG cross-compiled for JavaScript

This is based on the openjpeg+js work in cornerstone, except upgraded for new openjpeg builds.

Prerequisites

Software required:

• emscripten (installed via emsdk)

Build Instructions

Ensure that you have activated an emscripten SDK. Afterwards, source the emsdk environment.

/emsdk/emsdk activate latest
source /emsdk/emsdk_env.sh

Once the environment is set up, clone the OpenJPEG official repo and checkout the desired version.

git clone https://github.com/uclouvain/openjpeg.git

Apply the patch file openjpeg-js.patch.

cd openjpeg/
git apply ../openjpeg-js.patch

After applying the patch, we will now build openjpeg into LLVM bitcode. The second cmake invocation is to skip the error related to TestEndian from cmake. Make sure you have sourced the emsdk_env.sh as shown above.

mkdir openjpeg/build
cd openjpeg/build

cmake \
  -DCMAKE_TOOLCHAIN_FILE=/path/to/emsdk/fastcomp/emscripten/cmake/Modules/Platform/Emscripten.cmake \
  -DBUILD_CODEC=OFF \
  -DBUILD_SHARED_LIBS=OFF \
  -G'Unix Makefiles' \
  -DCMAKE_BUILD_TYPE=Release \
  ..

cmake .

make

The output will be in openjpeg/build/bin/libopenjp2.a.

Once openjpeg has been compiled, it’s time to compile the wrapping. Edit emcc-compile.sh and update the OPENJPEG_ROOT to the path of the openjpeg repo from above. You may also adjust the emcc flags as you see fit.

Once edited, just compile! Be sure to have the emsdk_env.sh sourced from above.

./emcc-compile.sh

The resulting cross-compiled OpenJPEG will be found in out/.