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

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> I tried to explain what a sequence is later on, and yes, I meant the
>> change in distance.
>
> I tried to fix this in a followup change.  But now I wonder if I
> understood the semantics correctly:
>
>> + All arguments after @var{position} are floating point numbers.
>
> Does this mean DX and DY are also floats?  If so, are they in pixels
> or are they some kind of relative change?  If they are relative, then
> relative to what?  And why does text-scale-pinch require that both DX
> and DY be zero?

When DX, DY and ANGLE are all zero, then the event is the start of a
pinch gesture sequence; text-scale-pinch uses it to set the "base"
scale, which is then modified by events further in the sequence.

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.

Thanks.