Ozone is a platform abstraction layer beneath the Aura window system that is used for low level input and graphics. Once complete, the abstraction will support underlying systems ranging from embedded SoC targets to new X11-alternative window systems on Linux such as Wayland or Mir to bring up Aura Chromium by providing an implementation of the platform interface.
Note: There are 2 buildflags which target platforms who use OZONE. They are slightly different from each other:
- IS_OZONE: Targets Linux, ChromeOS, and Fuchsia.
- IS_OZONE_WAYLAND: Targets only Linux systems using the Wayland window manager. Does not include ChromeOS or Fuchsia.
Our goal is to enable chromium to be used in a wide variety of projects by making porting to new platforms easy. To support this goal, ozone follows the following principles:
--ozone-platform) if multiple are enabled. Each platform has a unique build define (e.g. ozone_platform_foo) that can be turned on or off independently.ozone_extra.gni file.Ozone moves platform-specific code behind the following interfaces:
PlatformWindow represents a window in the windowing system underlying chrome. Interaction with the windowing system (resize, maximize, close, etc) as well as dispatch of input events happens via this interface. Under aura, a PlatformWindow corresponds to a WindowTreeHost. Under mojo, it corresponds to a NativeViewport. On bare hardware, the underlying windowing system is very simple and a platform window corresponds to a physical display.SurfaceFactoryOzone is used to create surfaces for the Chrome compositor to paint on using EGL/GLES2 or Skia.GpuPlatformSupportHost provides the platform code access to IPC between the browser & GPU processes. Some platforms need this to provide additional services in the GPU process such as display configuration.OverlayManagerOzone is used to manage overlays.InputController allows to control input devices such as keyboard, mouse or touchpad.SystemInputInjector converts input into events and injects them to the Ozone platform.NativeDisplayDelegate is used to support display configuration & hotplug.PlatformScreen is used to fetch screen configuration.ClipboardDelegate provides an interface to exchange data with other applications on the host system using a system clipboard mechanism.Our implementation of Ozone required changes concentrated in these areas:
USE_X11 ifdef, and adding a new IS_OZONE path that works in a relatively platform-neutral way by delegating to the interfaces described above.WindowTreeHostOzone to send events into Aura and participate in display management on the host system, andGLSurfaceEGL which delegates allocation of accelerated surfaces and refresh syncing to the provided implementation of SurfaceFactoryOzone.Users of the Ozone abstraction need to do the following, at minimum:
PlatformWindow. This class (I'll call it PlatformWindowImpl) is responsible for window system integration. It can use MessagePumpLibevent to poll for events from file descriptors and then invoke PlatformWindowDelegate::DispatchEvent to dispatch each event.SurfaceFactoryOzone that handles allocating accelerated surfaces. I'll call this SurfaceFactoryOzoneImpl.CursorFactory to manage cursors, or use the BitmapCursorFactory implementation if only bitmap cursors need to be supported.OverlayManagerOzone or just use StubOverlayManager if your platform does not support overlays.NativeDisplayDelegate if necessary or just use FakeDisplayDelegate, and write a subclass of PlatformScreen, which is used by aura::ScreenOzone then.GpuPlatformSupportHost or just use StubGpuPlatformSupportHost.InputController or just use StubInputController.SystemInputInjector if necessary.OzonePlatform that owns instances of the above subclasses and provide a static constructor function for these objects. This constructor will be called when your platform is selected and the returned objects will be used to provide implementations of all the ozone platform interfaces. If your platform does not need some of the interfaces then you can just return a Stub* instance or a nullptr.The recommended way to add your platform to the build is as follows. This walks through creating a new ozone platform called foo.
chromium/src.git.ui/ozone/platform/ alongside internal platforms.ui/ozone/ozone_extra.gni to add your foo platform.To build chrome, do this from the src directory:
gn args out/OzoneChromeOS --args="use_ozone=true target_os=\"chromeos\"" ninja -C out/OzoneChromeOS chrome
Then to run for example the X11 platform:
./out/OzoneChromeOS/chrome --ozone-platform=x11
Warning: Only some targets such as content_shell or unit tests are currently working for embedded builds.
To build content_shell, do this from the src directory:
gn args out/OzoneEmbedded --args="use_ozone=true toolkit_views=false" ninja -C out/OzoneEmbedded content_shell
Then to run for example the headless platform:
./out/OzoneEmbedded/content_shell --ozone-platform=headless \ --ozone-dump-file=/tmp/
By default, Linux enables the following Ozone backends - X11, Wayland and Headless.
If you want to disable Ozone/X11 in the build, do this from the src directory:
gn args out/OzoneLinuxDesktop --args="ozone_platform_x11=false" ninja -C out/OzoneLinuxDesktop chrome
If you want to disable all, but Wayland Ozone backend, do this from the src directory:
gn args out/OzoneLinuxDesktop --args="ozone_auto_platforms=false ozone_platform_wayland=true" ninja -C out/OzoneLinuxDesktop chrome
Chrome/Linux uses X11 Ozone backend by default. Thus, simply start the browser without any parameters:
./out/OzoneLinuxDesktop/chrome
Or run for example the Wayland platform:
./out/OzoneLinuxDesktop/chrome --ozone-platform=wayland
You can turn properly implemented ozone platforms on and off by setting the corresponding flags in your GN configuration. For example ozone_platform_headless=false ozone_platform_drm=false will turn off the headless and DRM (GBM) platforms. This will result in a smaller binary and faster builds. To turn ALL platforms off by default, set ozone_auto_platforms=false.
You can also specify a default platform to run by setting the ozone_platform build parameter. For example ozone_platform="x11" will make X11 the default platform when --ozone-platform is not passed to the program. If ozone_auto_platforms is true then ozone_platform is set to headless by default.
Specify the platform you want to use at runtime using the --ozone-platform flag. For example, to run content_shell with the DRM (GBM) platform:
content_shell --ozone-platform=drm
Caveats:
content_shell always runs at 800x600 resolution.This platform draws graphical output to a PNG image (no GPU support; software rendering only) and will not output to the screen. You can set the path of the directory where to output the images by specifying --ozone-dump-file=/path/to/output-directory on the command line:
content_shell --ozone-platform=headless \ --ozone-dump-file=/tmp/
This is Linux direct rending with acceleration via mesa GBM & linux DRM/KMS (EGL/GLES2 accelerated rendering & modesetting in GPU process) and is in production use on Chrome OS.
Note that all Chrome OS builds of Chrome will compile and attempt to use this. See Building Chromium for Chromium OS for build instructions.
This platform is used for Chromecast.
This platform provides support for the X window system.
X11 is the default Ozone backend. You can try to compile and run it with the following configuration:
gn args out/OzoneX11 ninja -C out/OzoneX11 chrome ./out/OzoneX11/chrome
This platform provides support for the Wayland display protocol. It was initially developed by Intel as a fork of chromium and then partially upstreamed.
Currently, the Ozone/Wayland is actively being developed by Igalia in the Chromium mainline repository with some features missing at the moment. The progress can be tracked in the issue #578890.
Below are some quick build & run instructions. It is assumed that you are launching chrome from a Wayland environment such as weston. Execute the following commands (make sure a system version of gbm and drm is used, which are required by Ozone/Wayland by design, when running on Linux platforms.):
Please note that the Wayland Ozone backend is built by default unless ozone_auto_platforms=false is set (the same as the X11 Ozone backend).
gn args out/OzoneWayland ninja -C out/OzoneWayland chrome ./out/OzoneWayland/chrome --ozone-platform=wayland
Native file dialogs are currently supported through the GTK toolkit. That implies that the browser is compiled with glib and gtk enabled. Please append the following gn args to your configuration:
use_ozone=true use_system_minigbm=true use_system_libdrm=true use_xkbcommon=true use_glib=true use_gtk=true
Running some test suites requires a Wayland server. If you're not running one you can use a locally compiled version of Weston or Mutter. This is what the build bots do. Please note that this is required for interactive_ui_tests, as those tests use a patched version of the compositor.
Mutter and its dependencies are not checked out by default to keep the disk usage optimal for most developers. In order to checkout mutter, add the checkout_mutter custom var in your .gclient file and set it to True and run gclient sync.
solutions = [
{
"url": "https://chromium.googlesource.com/chromium/src.git",
"managed": False,
"name": "src",
"custom_deps": {},
"custom_vars": {
"checkout_mutter": True,
},
},
]
For weston, simply add this to your gn args:
use_bundled_weston = true
Then after building the test executable, run the xvfb.py wrapper script and tell it to start the compositor with the tests:
cd out/debug # or your out directory
# For weston ../../testing/xvfb.py --use-weston --no-xvfb ./views_unittests --ozone-platform=wayland
# For mutter ../../testing/xvfb.py --use-mutter --no-xvfb ./views_unittests --ozone-platform=wayland
Feel free to discuss with us on freenode.net, #ozone-wayland channel or on ozone-dev, or on #ozone-wayland-x11 channel in chromium slack.
This platform draws graphical output to text using libcaca (no GPU support; software rendering only). In case you ever wanted to test embedded content shell on tty. It has been removed from the tree and is no longer maintained but you can build it as an out-of-tree port.
Alternatively, you can try the latest revision known to work. First, install libcaca shared library and development files. Next, move to the git revision 0e64be9cf335ee3bea7c989702c5a9a0934af037 (you will probably need to synchronize the build dependencies with gclient sync --with_branch_heads). Finally, build and run the caca platform with the following commands:
gn args out/OzoneCaca \ --args="use_ozone=true ozone_platform_caca=true use_sysroot=false ozone_auto_platforms=false toolkit_views=false" ninja -C out/OzoneCaca content_shell ./out/OzoneCaca/content_shell
Note: traditional TTYs are not the ideal browsing experience.
Ash-chrome client implementation.
For fuchsia.
There is a public mailing list: ozone-dev@chromium.org