To compile CanvasKit, you will first need to install
emscripten. This will set the environment
EMSDK (among others) which is required for compilation. Which version should you use?
/infra/wasm-common/docker/emsdk-base/Dockerfile shows the version we build and test with. We try to keep this up-to-date.
This document also assumes you have followed the instructions to download Skia and its deps https://skia.org/user/download.
Make sure you have Python3 installed, otherwise the downloading emscripten toolchain can fail with errors about SSL certificates. https://github.com/emscripten-core/emsdk/pull/273
See also https://github.com/emscripten-core/emscripten/issues/9036#issuecomment-532092743 for a solution to Python3 using the wrong certificates.
make release # make debug is much faster and has better error messages make local-example
This will print a local endpoint for viewing the example. You can experiment with the CanvasKit API by modifying
./canvaskit/example.html and refreshing the page. For some more experimental APIs, there's also
For other available build targets, see
compile.sh. For example, building a stripped-down version of CanvasKit with no text support or any of the “extras”, one might run:
./compile.sh no_skottie no_particles no_font
Such a stripped-down version is about half the size of the default release build.
To run unit tests and compute test coverage on a debug gpu build
make debug make test-continuous
This reads karma.conf.js, and opens a chrome browser and begins running all the test in
test/ it will detect changes to the tests in that directory and automatically run again, however it will automatically rebuild and reload canvaskit. Closing the chrome window will just cause it to re-opened. Kill the karma process to stop continuous monitoring for changes.
The tests are run with whichever build of canvaskit you last made. be sure to also test with
release_cpu. testing with release builds will expose problems in closure compilation and usually forgotten externs.
Coverage will be automatically computed when running test-continuous locally. Note that the results will only be useful when testing a debug build. Open
coverage/<browser version>/index.html For a summary and detailed line-by-line result.
To measure the runtime of all benchmarks in
make release make perf
Performacnce benchmarks also use karma, with a different config
karma.bench.conf.js. It will run once and print results.
Typically, you'd want to run these at head, and with your CL to observe the effect of some optimization.
The tests in
perf/ are grouped into files by topic. Within each file there are
describe blocks further organizing the tests, and within those
it() functions which test particular behaviors.
it are jasmine methods which can both be temporarily renamed
fit. Which causes jasmine to only those.
We have also defined
gm which is a method for defining a test which draws something to a canvas that is shapshotted and reported to gold.skia.org, where you can compare it with the snapshot at head.
When submitting a CL in gerrit, click “choose tryjobs” and type canvaskit to filter them. select all of them, which at the time of this writing is four jobs, for each combination of perf/test gpu/cpu.
The performance results are reported to perf.skia.org gold results are reported to gold.skia.org
Coverage is not measured while running tests this way.
wasm2wat tool from the WebAssembly Binary Toolkit can be used to produce a human-readable text version of a
The output of
wasm2wat --version should be
1.0.13 (1.0.17). This version has been checked to work with the tools in
wasm_tools/SIMD/. These tools programmatically inspect the
.wasm output of a CanvasKit build to detect the presence of wasm SIMD operations.
When dealing with CanvasKit (or PathKit) on our bots, we use Docker. Check out $SKIA_ROOT/infra/wasm-common/docker/README.md for more on building/editing the images used for building and testing.
This presumes you have updated emscripten locally to a newer version of the sdk and verified/fixed any build issues that have arisen.
$SKIA_ROOT/infra/wasm-common/docker/emsdk-base/Dockerfileto install and activate the desired version of Emscripten.
EMSDK_VERSIONbe set to that desired version. If there is a suffix that is not
_v1, reset it to be
_v1. If testing the image later does not work and edits are made to the emsdk-base Dockerfile to correct that, increment to
_v3, etc to force the bots to pick up the new image.
$SKIA_ROOT/infra/canvaskit/docker/canvaskit-emsdk/Dockerfileto be based off the new version from step 2. CanvasKit has its own docker image because it needs a few extra dependencies to build with font support.
$SKIA_ROOT/infra/canvaskit/docker/Makefileto have the same version from step 2. It's easiest to keep the
canvaskit-emsdkversions be in lock-step.
DOCKER_IMAGEpoint to the desired tagged Docker containers from steps 2 and 5 (which should be the same).
$SKIA_ROOT/infra/bots/task_drivers/compile_wasm_gm_tests.go, update dockerImage to refer to the desired Docker containers from steps 2 and 5.
make trainto re-train the recipes.
git grep 1\\.38\\.in
$SKIA_ROOTto see if there are any other references that need updating.