Re: master 101bbd1392: Add support for pinch gestures to the XI2 build

[Po Lu <luangruo@yahoo.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Po Lu <luangruo@yahoo.com>
>> Cc: emacs-devel@gnu.org
>> Date: Sun, 26 Dec 2021 18:58:50 +0800
>> 
>> >> DX and DY are represented in an imaginary unit where 1.0 is the
>> >> horizontal width and vertical height of the touchpad (or more precisely,
>> >> depedent touch device, which might include Wacom tablets if their
>> >> drivers are configured in a special way) respectively.
>> 
>> > This should be documented.
>> 
>> Yes, I'll do that.
>> 
>> > But I wonder how these two values are useful, if their units are not
>> > pixels and not anything that can be converted to pixels?
>> 
>> You are supposed to multiply it by the dimensions of whatever object is
>> onscreen: in image-mode, it could be the dimensions of the image, while
>> in a message buffer it could instead be the dimensions of the window's
>> text area.
>
> But you said above that the value 1.0 is the size of the touchpad, not
> of the image or text window?  So now I'm confused.

Yes.  The idea is that the size of the touchpad corresponds (in the mind
of the user) to the size of whatever is displayed onscreen underneath
the mouse pointer.