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By Žan Doberšek. Although most of the Wayland porting work will be solved by UI toolkits like GTK+, when X dependencies go beyond an implementation detail and have an influence on how a particular feature was designed, porting the software to Wayland can be more challenging. WebKit2GTK+ is one such case due to the split process architecture that comes with WebKit2, where rendering happens across two processes that need optimal (zero-copy) mechanisms to share an accelerated graphics surface for its Accelerated Compositing feature. This talk is intended for developers interested in porting applications to Wayland that need to share accelerated graphics between two processes. The talk will focus on WebKit2GTK+ as a case study, explaining how WebKit2’s architecture and X influenced the original design and implementation of Accelerated Compositing and how this feature is redesigned and implemented for Wayland.
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Wayland support in WebKitGTK+Žan DoberšekIgalia
Strasbourg, July 28th, 2014
I - Overview of WebKit
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WebKit - a portable Web engine
In memoriam: Chromium, Qt
PCs, phones, TVs, IVI, smartwatchesMac, iOS, 2 flavors of the Windows port, EFL, GTK
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About the fork
via WebKit Memes
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WebKitGTK+, the GTK+ port
... but really a GNOME port.
Web, Evolution, Yelp, Liferea ...
Highlights of the past year:
WebKit1 removedMultiple WebProcessesThe NetworkProcessCMake replaced Autotools
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WebKitGTK+, the GNOME port
Future work
Stability and securityPerformanceWebRTC, WebCrypto and other W3C/WHATWG standardsMore processes! (storage, workers)Wayland support
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II - Overview of Wayland
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Wayland
The successor to the X windowing systemPCs, phones, TVs, IVI
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Wayland support in GNOME
Ever improving!
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III - Wayland support in WebKitGTK+
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General overview
Basic support relies on GTK+Accelerated Compositing requires an inventive approachThe problem with the Netscape plugins
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Accelerated Compositing
Triggered by specific content - HTML video, HTML canvas, WebGL, CSStransforms, CSS filters ...Also enforcable (no need for triggers)Hardware-accelerated compositing of rendered layers throughOpenGL/OpenGLES
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The obligatory WebKit2 diagram
via WebKit Trac
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Implementation under X
Relies on XcompositeUIProcess prepares an X windowThe window handle is passed to the WebProcessThe WebProcess creates a GL context for that handle
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Implementation under Wayland
Implemented using a nested Wayland compositor in the UIProcessWebProcess essentially an EGL client of that compositor
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Implementation under Wayland
A small extension to the Wayland protocol is required.
Necessary to map the compositor client to the correspondingWebKitWebViewAppropriate for 1:1 and 1:N UIProcess-to-WebProcess mappings
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Necessary bits
Basic Wayland support by your driver.
Hopefully you're using Intel.
Some additional EGL extensions are required.
GL_OES_EGL_image_externalEGL_KHR_image_baseEGL_WL_bind_wayland_display
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Testing under Wayland
WebKit has a large suite of layout tests (> 30,000).
Many of these compare pixel output to a specified baseline or a reftest.
Performance tests should measure performance - correctness ensured bythe layout tests.
Hardware rasterizer can produce varying results over different runsRunning the tests will probably require the software rasterizer
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Future work
The target is WebKitGTK+ 2.6.
Bug polishImprovements in performanceWebGL supportPossible subsurface-based implementationNetscape plugins?
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III.I - Demos
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IV - Putting it all on Raspberry Pi
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Because why not?
Everyone's favourite mini-computer.
Only prototyping for now.
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State of the drivers
Current drivers are only partially openWayland support is presentMesa drivers are on their way
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Alas, problems
The GtkWidget's Cairo surface draws into a shared memory buffer.
This buffer is attached to the wl_surface.
Constant redraws become inefficient.
The subsurface-based nested compositor allows to avoid queueingconstant redraws on the GtkWidget.
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Alas, more problems
Hardware.
Solution - treat it as a challenge.
Support for JavaScriptCore on non-iOS ARM targets.
Single-core 700MHz ARMv6 CPU512MB RAM(No complaints with the GPU)
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V - QuestionsThank you.
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