Re: IE implementation of navigator.maxTouchPoints

Thank you!  Indeed it looks like this is Windows 7 only, and unlike IE we
do still want to support touchscreens on Windows 7 (a small but non-trivial
fraction of our touchscreen users are still on Windows 7).  It looks
like SM_DIGITIZER
is false in these cases, so I think we can try looking at SM_MAXIMUMTOUCHES
only when SM_DIGITIZER is true. Sound reasonable to you?

Thanks,
Rick


On Wed, Sep 10, 2014 at 7:44 PM, Jacob Rossi <Jacob.Rossi@microsoft.com>
wrote:

>  Definitely happy to help here. Our code is roughly:
>
>
>
> lMaxTouchPoints = 0;
>
> if (Win8+)
>
> {
>
>     lMaxTouchPoints = GetSystemMetrics(SM_MAXIMUMTOUCHES);
>
> }
>
> return lMaxTouchPoints;
>
>
>
> The OS check is there because we don’t support touch in the IE platform on
> Windows 7 and usage of touchscreen devices on Win7 is extremely low (most
> have moved to Win8+).
>
> Have you seen reports of this on Windows 8/8.1 or just Windows 7?
>
>
>
> There definitely are touchpad drivers that like to install a fake touch
> driver in order to fake zoom gestures (e.g. pinch to zoom). I don’t think
> there’s a way for the Windows input stack to tell the difference between
> that and an actual touchscreen. But if you’d like, I can loop you in with
> our Win32 input team.
>
>
>
> -Jacob
>
>
>
> *From:* rbyers@google.com [mailto:rbyers@google.com] *On Behalf Of *Rick
> Byers
> *Sent:* Wednesday, September 10, 2014 10:26 AM
> *To:* Jacob Rossi
> *Cc:* public-pointer-events@w3.org; David Bokan
> *Subject:* IE implementation of navigator.maxTouchPoints
>
>
>
> 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
>
>
>
>
>
>
>
>
>