UPDATE 2017-04-02: https://twitter.com/anholt/status/840753745721937920 there might be a working driver now...
UPDATE: Latest OpenGL work status seems to be here, https://dri.freedesktop.org/wiki/VC4/ which is Required for Webkit2.
THE MISSION: Get Webkit2 working on the Alarm Rpi2!
Does Webkit2 work on Raspbian? Yes... but without hardware acceleration for compositing
Firstly their package is called libwebkitgtk-3.0-0. The source package from
where it is built from is confusingly called webkitgtk and their current
version at time of writing is 2.4.8-2+rpi1, which is about 6 months old.
After grabbing the source, you can see a scary amount of patches. 314 to be exact.
pi@raspberrypi ~/webkitgtk-2.4.1/debian/patches/rpi $ ls -1 *.patch | wc -l 314
So one of these patches probably might make Webkit2 work on ARMv7h. Well... actually I am not confident at all since I know for a fact webkit2gtk-2.6.5-1 works fine in Webconverger's Rpi2 port, and Raspbian's heavily patched version is 2.4.8... which is older!
Raspbian's libwebkit2gtk-4.0-37 and the source package webkit2gtk of version 2.9.3, which is newer than the last known Webkit2 in Alarm, 2.6.5.
Here there are thankfully only 12 patches (down from 314):
pi@raspberrypi ~/webkit2gtk-2.9.3+dfsg1/debian/patches/rpi $ ls -1 0001-GTK-Crash-performing-drag-and-drop.patch 0002-GTK-Empty-gtk-font-name-setting-causes-WebProcess-cr.patch 0003-CairoGL-should-be-checked-unconditionally.patch 0004-GTK-Forcefully-disable-gtk-doc-and-gobject-introspec.patch 0005-GTK-The-Missing-Plug-in-buttons-are-not-showing-up-o.patch 0006-GTK-Crash-when-spell-checker-returns-no-guesses.patch 0007-Fix-build-with-ENABLE-DATABASE_PROCESS-and-ENABLE-IN.patch 0008-RPI-Demote-GCC-4.9-requirement-if-ENABLE_DATABASE_PR.patch 0009-Fix-ENABLE_OPENGL-OFF-builds.patch 0010-CMake-Trigger-the-memory-reduction-tricks-on-armhf-t.patch 0011-CMake-Reduce-debug-info-on-32bit-arches-using-g1-to-.patch 0012-RPI-Disable-AC-by-default.patch
Summary: Emanuele tells me the proprietary GL stack for the Rpi2 is not reliable enough (Webkit may stress it too much) for Webkit2.
So the work around is to build with
-DENABLE_OPENGL=OFF which means no
accelerated composition at all. Emanuele is working upon a software only
compositor, but it's far from
Workaround that breaks accelerated composition for everyone else
Obviously a Archlinux Arm7 package for Webkit2 with
be detrimental to working GL implementations like Mali, so at this present time
the Alarm package
PKGBUILD is unlikely to
be fixed for Rpi2! Since the fix would disable GL working acceleration for the
likes of ODROID-XU4 and make them slow!
I asked Emanuele Aina about the possibility of fallback within Webkit runtime
itself and not a build switch and he said there is a
WebCore::Settings::setAcceleratedCompositingEnabled() setting but he has had
issues with it. There needs to be a custom check, though since he works on
Raspbian, he may not find time to implement it.
The future for Webkit on Rpi2
It doesn't look promising in the short term. Emanuele added on 2015-10-07 that it looks like one or two years from having a GL implementation we can rely on on the Broadcom based Raspberry Pi platform !