How to build Skia

Make sure you have first followed the instructions to download Skia.

Skia uses GN to configure its builds.

is_official_build and Third-party Dependencies

Most 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.

Quickstart

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

Android

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

Mac users may want to pass --ide=xcode to bin/gn gen to generate an Xcode project.

iOS

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.

Windows

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.

Visual Studio Solutions

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.

CMake

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