[Fw_Os_Forum] How to detect devices that support touch

Venkat Gorla venkatagorla at gmail.com
Sat Mar 5 05:35:03 EST 2016

Thanks Aaron, for the detailed explanation. That was really helpful.

I am new to the UEFI world and still trying to get the hang of it.

It seems EDK and the console splitter absolute pointer abstraction that you
described, is an open source development environment for the UEFI
specification. Unfortunately we have some very tight restrictions in our
company when it comes to using open source components in our shipping
products. As such using EDK right now isn't a realistic option for me.

The idea itself is very interesting though; what is the best/ recommended
way to get the handle for a device that supports the absolute pointer
protocol? If there is something that can be done using just the UEFI
specification, please let me know.

Btw, to get the array of handles for the absolute pointer protocol in my
code, I am calling EFI API LocateHandle(). There is also a related API
called LocateHandleBuffer(). The only difference between these functions
seems to be whose responsibility it is to allocate space for the handle
buffer array. Otherwise, functionally they seem to be the same.

Please let me know if there is reason to be using one function over the


On Fri, Mar 4, 2016 at 11:56 PM, <Aaron.Pop at congatec.com> wrote:

> Hi Venkat,
> Your original question was "How do I determine if I have a physical touch
> device attached to the system?".  Locating a handle buffer of absolute
> pointer protocols and going through the handles to determine if any of them
> contain a device path will answer that.
> If, however, you want to interact with the absolute pointer devices, then
> you should only use the absolute pointer protocol that does not have a
> device path.
> The console splitter, which I described in the previous email, collects
> all absolute pointer devices under a single abstracted absolute pointer
> protocol interface.  It abstracts away the information regarding the
> current settings of the screen. I'll give you a case to help understand
> what I mean.
> Consider that you have two touch screen devices attached to the system.
> The first is a digitizer that sit on top of the monitor, and the second is
> a tablet like device (like a wacom tablet).  Each of these touch devices
> installs their own absolute pointer instance with their own
> EFI_ABSOLUTE_POINTER_MODE interface descriptions.  The monitor touch screen
> device returns absoluteX and absoluteY information that is not tied to the
> current video resolution (i.e absolutex is 800, absolutey is 600, and the
> monitor is currently in 1920x1080 resolution).   If you attempt to use this
> data directly, then you will only be able to access 800x600 of hte total
> 1920x1080 resolution.  This same limitation will be experienced with the
> wacom device.
> The console splitter's absolute pointer protocol abstraction has
> information about the current video display resolution, and it will perform
> a translation of the individual device's absolute pointer information to
> map the information into the current display resolution.  For example, if
> the monitor's absolute pointer returns that the display is at pixel
> 799x599, then that would be mapped by the console splitter to approximately
> the 1919x1079 pixel.
> So to answer your second question, you should not be enumerating handles
> when you want to use an absolute pointer. You should be using the absolute
> pointer protocol from the console splitter, which can be retrieved by
> opening the protocol on the gST->ConInHandle.
> As to why your individual device is not working when you use the first
> handle in the handle buffer, I do not know.  It is probably something that
> you will have to investigate.  Are you sure that your device is conforming
> to the absolute pointer protocol description in the EFI specification?  Are
> there any assumptions in your test code that conflict with the EFI
> specification?  Is there a bug in the EDK2 console splitter's absolute
> pointer abstraction (freely available to view online at
> https://github.com/tianocore/edk2 under
> MdeModulePkg/Universal/Console/ConSplitterDxe).
> From:        Venkat Gorla <venkatagorla at gmail.com>
> To:        Aaron.Pop at congatec.com,
> Cc:        fw_os_forum at mailman.uefi.org,
> fw_os_forum-bounces at mailman.uefi.org
> Date:        03/04/2016 01:50 AM
> Subject:        Re: [Fw_Os_Forum] How to detect devices that support touch
> ------------------------------
> Thanks Aaron. Now when I get the list of handles, I am testing for the
> device path protocol in addition to the absolute pointer protocol.
> By doing so, I am able to filter out the negative scenarios.
> I have another related question on this topic.
> On some of the touch hardware on which we are testing our product changes,
> when enumerating the handles, if we select the first handle that has both
> absolute pointer protocol and device path protocol, it doesn't seem to
> function always -- touch events aren't being received.
> On the other hand, if we select the **last** handle that has both
> protocols, it seems to work always.
> So is there something about this first handle vs last handle that will
> explain this behavior?
> Venkat
> On Thu, Mar 3, 2016 at 11:38 PM, <*Aaron.Pop at congatec.com*
> <Aaron.Pop at congatec.com>> wrote:
> EDK implements a console splitter for input device.  This console splitter
> creates a absolute pointer protocol instance that does not contain a device
> path.
> You can locate a handle buffer of all the handles that contain an absolute
> pointer protocol, and then you can go through the handles and make sure
> that there is a handle that contains a device path.  If there are no
> absolute pointer instances that contain a device path.
> From:        Venkat Gorla <*venkatagorla at gmail.com*
> <venkatagorla at gmail.com>>
> To:        *fw_os_forum at mailman.uefi.org* <fw_os_forum at mailman.uefi.org>,
> Date:        03/03/2016 01:06 AM
> Subject:        [Fw_Os_Forum] How to detect devices that support touch
> Sent by:        *fw_os_forum-bounces at mailman.uefi.org*
> <fw_os_forum-bounces at mailman.uefi.org>
> ------------------------------
> Hello,
> We are making some product changes that are specific to touch devices
> (such as a tablet) in the Windows pre-boot UEFI environment. I am referring
> the following document for the UEFI specification:
> *http://www.uefi.org/sites/default/files/resources/UEFI_Spec_2_3_1.pdf*
> <http://www.uefi.org/sites/default/files/resources/UEFI_Spec_2_3_1.pdf>
> However I haven't been able to definitively check for touch devices vs
> non-touch devices using the specification.
> For example, querying for the absolute pointer protocol interface succeeds
> even on a non-touch device such as a laptop or a desktop. Additionally, the
> absolute max X and max Y values are also being reported as non-zero when I
> query the "Mode" of the protocol interface.
> So my question is how do I filter out the negative scenarios (devices that
> don't support touch) using the UEFI specification?
> Any pointers or help will is much appreciated.
> Thanks,
> Venkat _______________________________________________
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