# Ozone Overview 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. ## Guiding Principles 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: 1. **Interfaces, not ifdefs**. Differences between platforms are handled by calling a platform-supplied object through an interface instead of using conditional compilation. Platform internals remain encapsulated, and the public interface acts as a firewall between the platform-neutral upper layers (aura, blink, content, etc) and the platform-specific lower layers. The platform layer is relatively centralized to minimize the number of places ports need to add code. 2. **Flexible interfaces**. The platform interfaces should encapsulate just what chrome needs from the platform, with minimal constraints on the platform's implementation as well as minimal constraints on usage from upper layers. An overly prescriptive interface is less useful for porting because fewer ports will be able to use it unmodified. Another way of stating is that the platform layer should provide mechanism, not policy. 3. **Runtime binding of platforms**. Avoiding conditional compilation in the upper layers allows us to build multiple platforms into one binary and bind them at runtime. We allow this and provide a command-line flag to select a platform (`--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. 4. **Easy out-of-tree platforms**. Most ports begin as forks. Some of them later merge their code upstream, others will have an extended life out of tree. This is OK, and we should make this process easy to encourage ports, and to encourage frequent gardening of chromium changes into the downstream project. If gardening an out-of-tree port is hard, then those projects will simply ship outdated and potentially insecure chromium-derived code to users. One way we support these projects is by providing a way to inject additional platforms into the build by only patching one `ozone_extra.gni` file. ## Ozone Platform Interface 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. ## Ozone in Chromium Our implementation of Ozone required changes concentrated in these areas: * Cleaning up extensive assumptions about use of X11 throughout the tree, protecting this code behind the `USE_X11` ifdef, and adding a new `USE_OZONE` path that works in a relatively platform-neutral way by delegating to the interfaces described above. * a `WindowTreeHostOzone` to send events into Aura and participate in display management on the host system, and * an Ozone-specific flavor of `GLSurfaceEGL` which delegates allocation of accelerated surfaces and refresh syncing to the provided implementation of `SurfaceFactoryOzone`. ## Porting with Ozone Users of the Ozone abstraction need to do the following, at minimum: * Write a subclass of `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. * Write a subclass of `SurfaceFactoryOzone` that handles allocating accelerated surfaces. I'll call this `SurfaceFactoryOzoneImpl`. * Write a subclass of `CursorFactory` to manage cursors, or use the `BitmapCursorFactory` implementation if only bitmap cursors need to be supported. * Write a subclass of `OverlayManagerOzone` or just use `StubOverlayManager` if your platform does not support overlays. * Write a subclass of `NativeDisplayDelegate` if necessary or just use `FakeDisplayDelegate`, and write a subclass of `PlatformScreen`, which is used by aura::ScreenOzone then. * Write a subclass of `GpuPlatformSupportHost` or just use `StubGpuPlatformSupportHost`. * Write a subclass of `InputController` or just use `StubInputController`. * Write a subclass of `SystemInputInjector` if necessary. * Write a subclass of `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`. ## Adding an Ozone Platform to the build (instructions for out-of-tree ports) The recommended way to add your platform to the build is as follows. This walks through creating a new ozone platform called `foo`. 1. Fork `chromium/src.git`. 2. Add your implementation in `ui/ozone/platform/` alongside internal platforms. 3. Patch `ui/ozone/ozone_extra.gni` to add your `foo` platform. ## Building with Ozone ### Chrome OS - ([waterfall](https://build.chromium.org/p/chromium.chromiumos/waterfall?builder=Linux+ChromiumOS+Ozone+Builder&builder=Linux+ChromiumOS+Ozone+Tests+%281%29&builder=Linux+ChromiumOS+Ozone+Tests+%282%29&reload=none)) To build `chrome`, do this from the `src` directory: ``` shell gn args out/OzoneChromeOS --args="use_ozone=true target_os=\"chromeos\"" ninja -C out/OzoneChromeOS chrome ``` Then to run for example the X11 platform: ``` shell ./out/OzoneChromeOS/chrome --ozone-platform=x11 ``` ### Embedded **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: ``` shell 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: ``` shell ./out/OzoneEmbedded/content_shell --ozone-platform=headless \ --ozone-dump-file=/tmp/ ``` ### Linux Desktop - ([X11 waterfall](https://ci.chromium.org/p/chromium/builders/try/linux-rel) && [Wayland waterfall](https://ci.chromium.org/p/chromium/builders/try/linux-wayland-rel)) 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: ``` shell 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: ``` shell 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: ``` shell ./out/OzoneLinuxDesktop/chrome ``` Or run for example the Wayland platform: ``` shell ./out/OzoneLinuxDesktop/chrome --ozone-platform=wayland ``` It is also possible to choose an Ozone backend via the chrome://flags/#ozone-platform-hint. The following options are available - Default, X11, Wayland, and Auto. The default one is "X11". "Auto" selects Wayland if possible, X11 otherwise. ### GN Configuration notes 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. ## Running with Ozone 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: ``` shell content_shell --ozone-platform=drm ``` Caveats: * `content_shell` always runs at 800x600 resolution. * For the DRM (GBM) platform, you may need to terminate your X server (or any other display server) prior to testing. * During development, you may need to configure [sandboxing](linux/sandboxing.md) or to disable it. ## Ozone Platforms ### Headless 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: ``` shell content_shell --ozone-platform=headless \ --ozone-dump-file=/tmp/ ``` ### DRM/GBM 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](https://www.chromium.org/chromium-os). Note that all Chrome OS builds of Chrome will compile and attempt to use this. See [Building Chromium for Chromium OS](https://www.chromium.org/chromium-os/how-tos-and-troubleshooting/building-chromium-browser) for build instructions. ### Cast This platform is used for [Chromecast](https://www.google.com/intl/en_us/chromecast/). ### X11 This platform provides support for the [X window system](https://www.x.org/). X11 is the default Ozone backend. You can try to compile and run it with the following configuration: ``` shell gn args out/OzoneX11 ninja -C out/OzoneX11 chrome ./out/OzoneX11/chrome ``` ### Wayland This platform provides support for the [Wayland](http://wayland.freedesktop.org/) display protocol. It was initially developed by Intel as [a fork of chromium](https://github.com/01org/ozone-wayland) 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](https://crbug.com/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). ``` shell 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: ``` shell 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. 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 Weston's test plugin. Add this to your gn args: ``` shell use_bundled_weston = true ``` Then run the xvfb.py wrapper script and tell it to start Weston: ``` shell cd out/debug # or your out directory ../../testing/xvfb.py --use-weston --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](https://www.chromium.org/developers/slack). ### Caca This platform draws graphical output to text using [libcaca](http://caca.zoy.org/wiki/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](https://codereview.chromium.org/2445323002/) and is no longer maintained but you can [build it as an out-of-tree port](https://github.com/fred-wang/ozone-caca). 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: ``` shell 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.
![Picture of a workstation using Ozone/caca to display the Google home page in a text terminal](./images/ozone_caca.jpg) ### drm Ash-chrome client implementation. ### flatland / scenic For fuchsia. ## Communication There is a public mailing list: [ozone-dev@chromium.org](https://groups.google.com/a/chromium.org/forum/#!forum/ozone-dev)