We're reporting integer co-ordinate for both touch and mouse, right?  Touch is probably the high-priority case (don't want switching from TE to PE to regress behavior at all).  So I suggest inverting the blocking relationship with  issue 456625 .  

I.e. first upgrade MouseEvent (and hence PointerEvent) co-ordinates to be capable of including fractions, but continue to report integers for the WebMouseEvent case.  That should be pretty easy to do and get most of the value (but probably requires an intent since the behavior is web exposed due to events synthesized in JS).

Later (perhaps post PE-ship) you can upgrade all the WebMouseEvent plumbing to also support fractional co-ordinates for mouse devices ( issue 456625 ).

WDYT?

Right, a partial fix for  crbug.com/456625  unblocks this bug. Since the bigger fix for  crbug.com/456625  (WebMouseEvent plumbing) should follow this bug, I have inverted the blocking dependency.

 Issue 649221  has been merged into this issue.

The PEWG had reached consensus a while back:
https://github.com/w3c/pointerevents/issues/107

As discussed in #3, exposing fractional values for touch is probably urgent.  Otherwise switching from touch events to pointer events can be a regression in user experience (smooth dragging, line writing, etc.)

Observed one weirdness in Edge: even though it emits fractional clientX/Y for touches, the console seems to truncate clientX/Y to int even with a pointerType="touch" property.
  new PointerEvent('eventType', { clientX: 123.45 }).clientX;   =>   123

Fascinating.  Even a more realistic event like:
var e = new PointerEvent('pointerdown', {
  pointerType:"touch",
  clientX:10.5,
  clientY:10.5
});

Doesn't get fractional co-ordinates.  Can you reach out to Ted to see if he can explain when you will and will not see fractional co-ordinates?  I don't think this needs to block us though.

I do see some fractional values for pageX/pageY though but not the ones I input (maybe they're getting computed from the clientX/clientY values)!  See http://jsbin.com/hiraqow/1

Since shipping fractional PE coordinates w/o affecting ME coordinates seems hard, and my patch to even minimally change ME calls for an intent to ship (see https://codereview.chromium.org/2406263003/#ps160001), we will fix it in M56 instead.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/48a106897274196b5897f1b0967d28c49e4ec696

commit 48a106897274196b5897f1b0967d28c49e4ec696
Author: mustaq <mustaq@chromium.org>
Date: Wed Nov 16 13:45:45 2016

Make PointerEvent coordinates fractional for touch

The current PointerEvent spec doesn't override the UI
MouseEvent spec definition of (clientX, clientY) and
(screenX, screenY) coordinates: all of them are integers.
This is not great for the sites that currently use Touch
Events & trying to switch to Pointer Events for touch:
specially on high DPI devices Pointer Event coordinates
would feel less precise than fractional Touch Event
coodinates. The PEWG has already reached consensus that
all coordinates in Pointer Events should be floating
point values:
  https://github.com/w3c/pointerevents/issues/107

Edge already reports fractional client coordinates for
PointerEvents (and not MouseEvents).

This CL exposes fractional Pointer Event coordinates for
touch input. Although the CL changes the client & screen
coordinates in Mouse Event idl to floating points, the
integer plumbing for mouse is kept intact so that mouse
coordinates still appear unchanged to JS. Pointer Events
that are fired for touches propagate appropriate
fractional coordinates to JS.

Intent to Implement and Ship: https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/1kroHAnh3BU/uYZb6uZRBwAJ

BUG= 607948 

Review-Url: https://codereview.chromium.org/2406263003
Cr-Commit-Position: refs/heads/master@{#432473}

[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/LayoutTests/fast/events/constructors/mouse-event-constructor-expected.txt
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/LayoutTests/fast/events/constructors/mouse-event-constructor.html
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/LayoutTests/fast/events/constructors/pointer-event-constructor-expected.txt
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/LayoutTests/fast/events/constructors/pointer-event-constructor.html
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/LayoutTests/fast/events/constructors/wheel-event-constructor-expected.txt
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/LayoutTests/fast/events/constructors/wheel-event-constructor.html
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/LayoutTests/fast/events/pointerevents/touch-pointer-events-expected.txt
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/LayoutTests/fast/events/pointerevents/touch-pointer-events.html
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/core/events/MouseEvent.cpp
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/core/events/MouseEvent.idl
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/core/events/MouseEventInit.idl
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/core/events/MouseRelatedEvent.cpp
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/core/events/MouseRelatedEvent.h
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/core/html/forms/RangeInputType.cpp
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/core/html/shadow/SliderThumbElement.cpp
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/core/page/ContextMenuController.cpp
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/web/WebInputEventConversion.cpp
[modify] https://crrev.com/48a106897274196b5897f1b0967d28c49e4ec696/third_party/WebKit/Source/web/WebPluginContainerImpl.cpp