[Fw_Os_Forum] How to detect devices that support touch

Aaron.Pop at congatec.com Aaron.Pop at congatec.com
Fri Mar 4 13:26:26 EST 2016

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 

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?


On Thu, Mar 3, 2016 at 11:38 PM, <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> 
To:        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 


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: 

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. 

Venkat _______________________________________________
Fw_os_forum mailing list
Fw_os_forum at mailman.uefi.org

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