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doc: added explanation for touch dispatching

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Zen-CODE 2015-05-30 11:25:49 +02:00
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doc/sources/guide/inputs.rst
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@ -111,6 +111,35 @@ evaluates to True. For all touch events, you automatically have the X and Y
positions available, scaled to the Window width and height. In other words, all
touch events have the ``'pos'`` profile.
Touch event basics
~~~~~~~~~~~~~~~~~~
By default, touch events are dispatched to all currently displayed widgets.
This means widgets recieve the touch event whether it occurs within their
physical area or not.
This can be counter intuitive if you have experience with other GUI toolkits.
These typically divide the screen into geometric areas and only dispatch
touch or mouse events to the widget if the coordinate lies within the
widgets area.
This requirement becomes very restrictive when working with touch input.
Swipes, pinches and long presses may well originate from outside of the widget
that wants to know about them and react to them.
In order to provide the maximimum flexibility, Kivy dispatches the events to
all the widgets and lets them decide how to react to them. If you only want
to responce to touch events inside the widgets, you simply check.::
def on_touch_down(self, touch):
if self.collide_point(*touch.pos):
# The touch has occurred inside the widgets area. Do stuff!
pass
Coordinates
~~~~~~~~~~~
You must take care of matrix transformation in your touch as soon as you use
a widget with matrix transformation. Some widgets such as
:class:`~kivy.uix.scatter.Scatter` have their own matrix transformation,