Intent to ship: TouchEvents (Windows), touch-action (all platforms), accessible caret

[Kartikaya Gupta]

In Firefox 52 I intend to ship support for TouchEvents on Windows
e10s. TouchEvent support has already been enabled on Android for a
long time and has been enabled on Linux e10s as well (if you have
MOZ_USE_XINPUT2=1 in your environment). The pref that controls this
feature is dom.w3c_touch_events.enabled. The pref has been enabled on
Nightly for a number of months, and bug 1244402 is now letting it ride
the trains. Chrome/Opera and Safari on iOS all support Touch Events,
and it is specced at [1].

Additionally, I also intend to ship support for the CSS touch-action
property, which is defined in the Pointer Events spec [2]. Note that
our support for touch-action currently does NOT include support for
the Pointer Events Level 2 property values such as pan-up/pan-down.
Touch-action will be supported on all platforms that support touch
input (i.e. Android, Linux e10s with MOZ_USE_XINPUT2=1, and Windows
e10s). The pref that controls this feature is
layout.css.touch_action.enabled. This pref has also been enabled on
Nightly for a number of months now and bug 1244402 is letting it ride
the trains. Touch-action is supported in IE/Edge, Chrome/Opera, and
partly in Safari.

Note also that along with enabling these features, touch scrolling on
Windows e10s will now be handled natively by APZ in the compositor
rather than being converted into wheel events by the OS, which should
enhance scrolling responsiveness and control. To round out touch
support, we are also enabling the "accessible caret" for text
selection on desktop platforms where TouchEvents are supported. This
allows the user to manipulate text selection using the touch-friendly
carets you already see in Firefox for Android. This is controlled by
the pref layout.accessiblecaret.enabled_on_touch. As with the
web-facing features, these have been enabled on Nightly builds for a
while and now are going to ride the trains.

Aside 1: on current Nightly, you *still* need to set
browser.tabs.remote.force-enable to true on Windows touch devices to
get e10s enabled. This is due to the instability caused by some
accessibility code, but the plan is to have those bugs fixed and that
restriction eliminated in Firefox 52 as well, hopefully within the
next week or two.

Aside 2: sorry for lumping all these things in one email, but they're
all related and mostly need to ship together.

Cheers,
kats

[1] https://www.w3.org/TR/touch-events/
[2] https://www.w3.org/TR/pointerevents/ (section 9)

[smaug]

Sounds great!


-Olli

[alirezapi...@gmail.com]