How to build Skia
Make sure you have first followed the instructions to download Skia.
Skia uses GN to configure its builds.
is_official_buildand Third-party Dependencies
- Supported and Preferred Compilers
- Windows ARM64
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
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 we 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
skia_use_foo is enabled, enabling
skia_use_system_foo will build and link
Skia against the headers and libraries found on the system paths.
is_official_build=true enables all
skia_use_system_foo by default. You can
extra_ldflags to add include or library paths if
Supported and Preferred Compilers
While Skia should compile with GCC, MSVC, and other compilers, a number of routines in Skia’s software backend have been written to run fastest when compiled with Clang. If you depend on software rasterization, image decoding, or color space conversion and compile Skia with a compiler other than Clang, you will see dramatically worse performance. This choice was only a matter of prioritization; there is nothing fundamentally wrong with non-Clang compilers. So if this is a serious issue for you, please let us know on the mailing list.
Skia makes use of C++17 language features (compiles with
-std=c++17 flag) and
thus requires a C++17 compatible compiler. Clang 5 and later implement all of
the features of the c++17 standard. Older compilers that lack C++17 support may
produce non-obvious compilation errors. You can configure your build to use
specific executables for
cxx invocations using e.g.
--args='cc="clang-6.0" cxx="clang++6.0"' GN build arguments, as illustrated in
Quickstart. This can be useful for building Skia without needing to
modify your machine’s default compiler toolchain.
gn gen to generate your build files. As arguments to
gn gen, pass a name
for your build directory, and optionally
--args= to configure the build type.
To build Skia as a static library in a build directory named
bin/gn gen out/Static --args='is_official_build=true'
To build Skia as a shared library (DLL) in a build directory named
bin/gn gen out/Shared --args='is_official_build=true is_component_build=true'
If you find that you don’t have
bin/gn, make sure you’ve run:
For a list of available build arguments, take a look at
gn/skia.gni, or run:
bin/gn args out/Debug --list
GN allows multiple build folders to coexist; each build can be configured separately as desired. For example:
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"]'
Once you have generated your build files, run Ninja to compile and link Skia:
ninja -C out/Static
If some header files are missing, install the corresponding dependencies:
To pull new changes and rebuild:
git pull python tools/git-sync-deps ninja -C out/Static
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:
python2 infra/bots/assets/android_ndk_linux/download.py -t /tmp/ndk python2 infra/bots/assets/android_ndk_darwin/download.py -t /tmp/ndk python2 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
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/x64 --args='ndk="/tmp/ndk" target_cpu="x64"' bin/gn gen out/x86 --args='ndk="/tmp/ndk" target_cpu="x86"'
Other arguments like
is_component_build continue to work.
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
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"
To cross-compile Skia for arm ChromeOS devices the following is needed:
- Clang 4 or newer
- An armhf sysroot
- The (E)GL lib files on the arm chromebook to link against.
To compile Skia for an x86 ChromeOS device, one only needs Clang and the lib files.
If you have access to CIPD, you can fetch all of these as follows:
python2 infra/bots/assets/clang_linux/download.py -t /opt/clang python2 infra/bots/assets/armhf_sysroot/download.py -t /opt/armhf_sysroot python2 infra/bots/assets/chromebook_arm_gles/download.py -t /opt/chromebook_arm_gles python2 infra/bots/assets/chromebook_x86_64_gles/download.py -t /opt/chromebook_x86_64_gles
Once those files are in place, generate the GN args that resemble the following:
#ARM cc= "/opt/clang/bin/clang" cxx = "/opt/clang/bin/clang++" extra_asmflags = [ "--target=armv7a-linux-gnueabihf", "--sysroot=/opt/armhf_sysroot/", "-march=armv7-a", "-mfpu=neon", "-mthumb", ] extra_cflags=[ "--target=armv7a-linux-gnueabihf", "--sysroot=/opt/armhf_sysroot", "-I/opt/chromebook_arm_gles/include", "-I/opt/armhf_sysroot/include/", "-I/opt/armhf_sysroot/include/c++/4.8.4/", "-I/opt/armhf_sysroot/include/c++/4.8.4/arm-linux-gnueabihf/", "-DMESA_EGL_NO_X11_HEADERS", "-funwind-tables", ] extra_ldflags=[ "--sysroot=/opt/armhf_sysroot", "-B/opt/armhf_sysroot/bin", "-B/opt/armhf_sysroot/gcc-cross", "-L/opt/armhf_sysroot/gcc-cross", "-L/opt/armhf_sysroot/lib", "-L/opt/chromebook_arm_gles/lib", "--target=armv7a-linux-gnueabihf", ] target_cpu="arm" skia_use_fontconfig = false skia_use_system_freetype2 = false skia_use_egl = true # x86_64 cc= "/opt/clang/bin/clang" cxx = "/opt/clang/bin/clang++" extra_cflags=[ "-I/opt/clang/include/c++/v1/", "-I/opt/chromebook_x86_64_gles/include", "-DMESA_EGL_NO_X11_HEADERS", "-DEGL_NO_IMAGE_EXTERNAL", ] extra_ldflags=[ "-stdlib=libc++", "-fuse-ld=lld", "-L/opt/chromebook_x86_64_gles/lib", ] target_cpu="x64" skia_use_fontconfig = false skia_use_system_freetype2 = false skia_use_egl = true
Compile dm (or another executable of your choice) with ninja, as per usual.
Push the binary to a chromebook via ssh and run dm as normal using the gles GPU config.
Most chromebooks by default have their home directory partition marked as noexec. To avoid “permission denied” errors, remember to run something like:
sudo mount -i -o remount,exec /home/chronos
Mac users may want to pass
bin/gn gen to generate an Xcode
Run GN to generate your build files. Set
target_os="ios" to build for iOS.
This defaults to
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"'
This will also package (and for devices, sign) iOS test binaries. This defaults
to a Google signing identity and provisioning profile. To use a different one
set the GN args
skia_ios_identity to match your code signing identity and
skia_ios_profile to the name of your provisioning profile, e.g.
skia_ios_identity=".*Jane Doe.*" skia_ios_profile="iPad Profile"`
A list of identities can be found by typing
security find-identity on the
command line. The name of the provisioning profile should be available on the
Apple Developer site. Alternatively,
skia_ios_profile can be the absolute path
to the mobileprovision file.
If you find yourself missing a Google signing identity or provisioning profile, you’ll want to have a read through go/appledev.
For signed packages
ios-deploy makes installing and running them on a device
ios-deploy -b out/Debug/dm.app -d --args "--match foo"
Alternatively you can generate an Xcode project by passing
bin/gn gen. If you are using Xcode version 10 or later, you may need to go to
Project Settings... and verify that
Build System: is set to
Legacy Build System.
Deploying to a device with an OS older than the current SDK can be done by
ios_min_target = "<major>.<minor>"
<major>.<minor> is the iOS version on the device, e.g., 12.0 or 11.4.
Skia can build on Windows with Visual Studio 2017 or 2019. If GN is unable to
locate either of those, it will print an error message. In that case, you can
VC path to GN via
Skia can be compiled with the free Build Tools for Visual Studio 2017 or 2019.
The bots use a packaged 2019 toolchain, which Googlers can download like this:
python2 infra/bots/assets/win_toolchain/download.py -t C:/toolchain
You can then pass the VC and SDK paths to GN by setting your GN args:
win_vc = "C:\toolchain\VC" win_sdk = "C:\toolchain\win_sdk"
This toolchain is the only way we support 32-bit builds, by also setting
The Skia build assumes that the PATHEXT environment variable contains “.EXE”.
Highly Recommended: Build with clang-cl
Skia uses generated code that is only optimized when Skia is built with clang. Other compilers get generic unoptimized code.
cxx gn args is not sufficient to build with clang-cl.
These variables are ignored on Windows. Instead set the variable
your LLVM installation directory. If you installed the prebuilt LLVM downloaded
from here in the
default location that would be:
clang_win = "C:\Program Files\LLVM"
Follow the standard Windows path specification and not MinGW convention (e.g.
C:\Program Files\LLVM not
Visual Studio Solutions
If you use Visual Studio, you may want to pass
bin/gn gen to
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
out directory. First, create all of your GN configurations as usual. Pass
--ide=vs when running
bin/gn gen for each one. Then:
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.
There is early, experimental support for
Windows 10 on ARM. This
currently requires (a recent version of) MSVC, and the
Visual C++ compilers and libraries for ARM64 individual component in the
Visual Studio Installer. For Googlers, the win_toolchain asset includes the
To use that toolchain, set the
target_cpu GN argument to
"arm64". Note that
OpenGL is not supported by Windows 10 on ARM, so Skia’s GL backends are stubbed
out, and will not work. ANGLE is supported:
bin/gn gen out/win-arm64 --args='target_cpu="arm64" skia_use_angle=true'
This will produce a build of Skia that can use the software or ANGLE backends,
in DM. Viewer only works when launched with
--backend angle, because the
software backend tries to use OpenGL to display the window contents.
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