Game Development Reference
In-Depth Information
event.preventDefault();
// ...
}
Again, just like a
touchend
event, the object passed into the registered
callback
function is an instance of the
TouchEvent
class, which contains the same three
TouchList
attributes. The context of the
touches
and
targetTouches
attributes
are the exact same as their version found in
touchstart
. The touch objects in
the
changedTouches
list in the
touchmove
event represent previously registered
touches that have moved about the input device.
One important thing about the
touchmove
event is that it can be associated with
a
drag
event. If you notice, the default behavior for a
drag
event is to scroll the
page in the direction of the scroll. In some applications involving dragging across
the screen with a finger, this behavior may not be desired. For this reason, the
event.preventDefault()
method is called, which produces the effect of alert-
ing the browser that no scrolling is desired. If, however, the intention is to scroll the
screen with a
touchmove
event, provided that the element being touched supports
such behavior, this can be accomplished by omitting the call to the prevent default
function.
The touch object
Now, you may have noticed that each
TouchList
object holds instances of a very
specific object which is an instance of the
Touch
class. This is important because
the input device needs to keep track of individual touches. Otherwise, the list of
changedTouches
would not be accurate thus limiting what we can accomplish with
the API.
The way that each touch can be uniquely identified is by having the input device as-
sign a unique ID to each event it captures. This ID remains the same for the same
touch object until that object is released (in other words, when that particular touch
leaves the input device).
Lets take a look at all the other properties of the
Touch
class and see what other
important information is contained therein.
