Make sure you have first followed the instructions to download Skia.
Skia uses GN to configure its builds.
is_official_build and Third-party DependenciesMost users of Skia should set is_official_build=true, and most developers should leave it to its false default.
This mode configures Skia in a way that's suitable to ship: an optimized build with no debug symbols, dynamically linked against its third-party dependencies using the ordinary library search path.
In contrast, the developer-oriented default is an unoptimized build with full debug symbols and all third-party dependencies built from source and embedded into libskia. This is how do all our manual and automated testing.
Skia offers several features that make use of third-party libraries, like libpng, libwebp, or libjpeg-turbo to decode images, or ICU and sftnly to subset fonts. All these third-party dependencies are optional and can be controlled by a GN argument that looks something like skia_use_foo for appropriate foo.
If skia_use_foo is enabled, enabling skia_use_system_foo will build and link Skia against the headers and libaries found on the system paths. is_official_build=true enables all skia_use_system_foo by default. You can use extra_cflags and extra_ldflags to add include or library paths if needed.
Run GN to generate your build files.
bin/gn gen out/Static --args='is_official_build=true' bin/gn gen out/Shared --args='is_official_build=true is_component_build=true'
If you find you don‘t have bin/gn, make sure you’ve run
python tools/git-sync-deps
GN allows fine-grained settings for developers and special situations.
bin/gn gen out/Debug bin/gn gen out/Release --args='is_debug=false' bin/gn gen out/Clang --args='cc="clang" cxx="clang++"' bin/gn gen out/Cached --args='cc_wrapper="ccache"' bin/gn gen out/RTTI --args='extra_cflags_cc=["-frtti"]'
To see all the arguments available, you can run
bin/gn args out/Debug --list
Having generated your build files, run Ninja to compile and link Skia.
ninja -C out/Static ninja -C out/Shared ninja -C out/Debug ninja -C out/Release ninja -C out/Clang ninja -C out/Cached ninja -C out/RTTI
To build Skia for Android you need an Android NDK.
If you do not have an NDK and have access to CIPD, you can use one of these commands to fetch the NDK our bots use:
python infra/bots/assets/android_ndk_linux/download.py -t /tmp/ndk python infra/bots/assets/android_ndk_darwin/download.py -t /tmp/ndk python infra/bots/assets/android_ndk_windows/download.py -t C:/ndk
When generating your GN build files, pass the path to your ndk and your desired target_cpu:
bin/gn gen out/arm --args='ndk="/tmp/ndk" target_cpu="arm"' bin/gn gen out/arm64 --args='ndk="/tmp/ndk" target_cpu="arm64"' bin/gn gen out/mips64el --args='ndk="/tmp/ndk" target_cpu="mips64el"' bin/gn gen out/mipsel --args='ndk="/tmp/ndk" target_cpu="mipsel"' bin/gn gen out/x64 --args='ndk="/tmp/ndk" target_cpu="x64"' bin/gn gen out/x86 --args='ndk="/tmp/ndk" target_cpu="x86"'
Other arguments like is_debug and is_component_build continue to work. Tweaking ndk_api gives you access to newer Android features like Vulkan.
To test on an Android device, push the binary and resources over, and run it as normal. You may find bin/droid convenient.
ninja -C out/arm64 adb push out/arm64/dm /data/local/tmp adb push resources /data/local/tmp adb shell "cd /data/local/tmp; ./dm --src gm --config gl"
Mac users may want to pass --ide=xcode to bin/gn gen to generate an Xcode project.
Run GN to generate your build files. Set target_os="ios" to build for iOS. This defaults to target_cpu="arm64". Choosing x64 targets the iOS simulator.
bin/gn gen out/ios64 --args='target_os="ios"' bin/gn gen out/ios32 --args='target_os="ios" target_cpu="arm"' bin/gn gen out/iossim --args='target_os="ios" target_cpu="x64"'
Googlers who want to sign and run iOS test binaries can do so by running something like
python gn/package_ios.py out/Debug/dm python gn/package_ios.py out/Release/nanobench
These commands will create and sign dm.app or nanobench.app packages you can push to iOS devices registered for Google development. ios-deploy makes installing and running these packages easy:
ios-deploy -b out/Debug/dm.app -d --args "--match foo"
If you find yourself missing a Google signing identity or provisioning profile, you'll want to have a read through go/appledev.
Skia can build on Windows with Visual Studio 2015 Update 3, or Visual Studio 2017 by setting msvc = 2017 in GN. No older versions are supported. The bots use a packaged 2015 toolchain, which Googlers can download like this:
python infra/bots/assets/win_toolchain/download.py -t C:/toolchain
If you pass that downloaded path to GN via windk, you can build using that toolchain instead of your own from Visual Studio. This toolchain is the only way we support 32-bit builds with 2015, by also setting target_cpu="x86". 32-bit builds should work with the default 2017 install if you follow the directions GN prints to set up your environment.
If you use Visual Studio, you may want to pass --ide=vs to bin/gn gen to generate all.sln. That solution will exist within the GN directory for the specific configuration, and will only build/run that configuration.
If you want a Visual Studio Solution that supports multiple GN configurations, there is a helper script. It requires that all of your GN directories be inside the out directory. First, create all of your GN configurations as usual. Pass --ide=vs when running bin/gn gen for each one. Then:
python gn/gn_meta_sln.py
This creates a new dedicated output directory and solution file out/sln/skia.sln. It has one solution configuration for each GN configuration, and supports building and running any of them. It also adjusts syntax highlighting of inactive code blocks based on preprocessor definitions from the selected solution configuration.
We have added a GN-to-CMake translator mainly for use with IDEs that like CMake project descriptions. This is not meant for any purpose beyond development.
bin/gn gen out/config --ide=json --json-ide-script=../../gn/gn_to_cmake.py