Fixing effective touch point position inside the touched area

[Denis Dzyubenko]

Hi Chase,

On 7 September 2010 16:35, Chase Douglas <chase.douglas at canonical.com> wrote:
>> Touching a screen with a finger usually produces quite a big area of
>> touch and the problem raises is what is the effective touch point
>> inside the area - as I can see it supposed to be somewhere in the top
>> part of the touched area - usually when a user touches the screen with
>> a thumb, he means to interact with an item a bit above it - however
>> that position depends on the screen orientation. So _someone_ is
>> supposed to add an offset to the area of touch that is reported to the
>> windowing system - otherwise it will be really hard for the user to
>> interact with items on the screen - for example touching the top part
>> of a window will be almost impossible.
>
> It's up to the hardware to produce a set of coordinates for a touch.
> Some hardware also provides details such as the size of a touch, either
> in a general form or as two axes of an ellipse. I believe the hardware
> makers calibrate their touchscreens such that that touch coordinates are
> appropriate for finger touch interaction, so I don't think this is a
> huge issue for the X layer to deal with. X does have some extra
> calibration mechanisms if needed, though.

I am not convinced that calibration will help in that case - let's say
the screen is in the landscape mode and has been calibrated to offset
the touch point a bit above the actual area of touch. Then when
tilting the device to be in the portrait mode the touch point will be
a bit to the right side.

Thinking again about it and playing with the touch phones here - it
doesn't seem to be a big deal though... So it is safe to scrap the
idea and sorry for the noise :)

-- 
Best regards,
Denis.