Game Development Reference
In-Depth Information
Touchscreens
The touchscreen is the natural evolution of the icon-based operating systems we are
used to. Instead of selecting data represented by icons and then issuing commands
to manipulate them with a mouse, with touch interfaces there is a direct manipulation
of the data through a set of predefined, touch-based actions performed with our fin-
gers on the screen.
Mobile devices can use lots of different methods to detect a person's input on a
touchscreen. Many use sensors and circuitry to monitor changes in a specific state.
Many monitor changes in electrical current. Others monitor changes in the reflection
of sound waves or beams of near-infrared light. Some measure changes in vibration
caused when your finger hits the screen's surface, or cameras to monitor changes in
light and shadow.
Contemporary devices can process more than one touch at a time. This makes it pos-
sible to use multitouch gestures, which we will discuss later in the chapter. Earlier
touchscreen devices may or may not be able to process more than one touch.
For example, the Apple iPhone has a multitouch user interface that requires touching
multiple points on the screen simultaneously. One example is called spread and
pinch, where the thumb and forefinger touch the screen at the same time; bringing
the fingers together (pinching) zooms out the image while moving the fingers apart
(spread) zooms in.
The iPhone is not the only device that allows multitouch operations: Android and Win-
dows Phone-based devices do that too. To allow multitouch operations, screens have
capacitors arranged on a grid. When a touch occurs, the device detects its location
and direction of movement. A feature of this configuration is the ability to process
more than one touch simultaneously.
Generally, two methods are used to detect touch; mutual capacitance and self-capa-
citance. Mutual capacitance requires two distinct layers of material; one carries elec-
trical current and the other has electrical sensors. Self-capacitance combines the cur-
rent and sensors into a single layer.
