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IE implementation of navigator.maxTouchPoints

From: Rick Byers <rbyers@chromium.org>
Date: Wed, 10 Sep 2014 13:25:40 -0400
Message-ID: <CAFUtAY-_x--+HnA9J791BHTRk0pmzL8Qm-OCBPDdkq-vCwnpDg@mail.gmail.com>
To: Jacob Rossi <Jacob.Rossi@microsoft.com>
Cc: "public-pointer-events@w3.org" <public-pointer-events@w3.org>, David Bokan <bokan@chromium.org>
Hey Jacob,
We're getting reports of some complaints of navigator.maxTouchPoints
returning 1 on Chrome when there is in fact no touchscreen.  IE11 correctly
returns 0.  http://crbug.com/352942.  Scott (from MS OpenTech) wrote the
code
<https://code.google.com/p/chromium/codesearch#chromium/src/ui/base/touch/touch_device_win.cc&q=MAXTOUCHPOINTS&sq=package:chromium&type=cs&l=17>
for this for us, basically just:

int MaxTouchPoints() {
  return GetSystemMetrics(SM_MAXIMUMTOUCHES);
}

Apparently, despite what we'd expect fro the MSDN docs, this is
insufficient.  Users report that it returns 1 in scenarios with both an
internal and external mouse plugged in - although we haven't been able to
reproduce it (and they've confirmed they see those values from the API
directly, so it's not some bug in chrome).

Any chance you can share the algorithm with us that IE uses to compute
maxTouchPoints on windows?  Ideally Chrome and IE would always agree here,
and there's obviously some special cases.

Thanks,
   Rick
Received on Wednesday, 10 September 2014 17:26:31 UTC

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