Page 30 - DCAP504_Computer Graphics

Unit 3: Overview of Graphics I/O Devices

The figure 3.1 illustrates the communication between an input device, CPU, and output device.

Figure 3.1: Communication between Input Device, CPU and
Output Device

The keyboard and mouse are the common interactive devices that help in input operation. Apart from
the keyboard and mouse, there are many interactive devices that help in the input operation, such as the
tablet, light pen, joystick, control dial, button, data glove, and touch screen.
The display terminals generally provide an alphanumeric keyboard to type commands and enter data
for the program. However, in some applications the use of keyboard is inconvenient or inadequate. This
kind of a situation may arise when the user has to add lines or symbols to the pictures on the screen.
Even though the user can position the lines or symbols using coordinates, they can also perform this
task by pointing at the screen.
The graphical interactions happen either by positioning the items or by pointing at items. There are a
number of graphical input devices that are classified into pointing devices and positioning devices.
Pointing devices refer to devices that are used to select items on the screen, and positioning devices
refers to devices that are used to add new items on the screen. These devices provide position
information, that is, they provide the coordinate of a point.

Pointing devices are also known as selectors, whereas positioning devices are known as
locators.

Some of the pointing and positioning devices are discussed as follows:

1. Graphics Tablet: The graphics tablet is the most widely used device for pointing oriented
operations. It is a flat, touch-sensitive device that is used with a stylus (stylus is used to indicate a
location on the tablet surface). Anything that is written or drawn on this device is transferred
automatically to the PC in the form of a graphic. Typically tablets provide two-dimensional
coordinate information. The values returned are in tablet coordinates. This device provides an
accurate method of selecting the positions of the coordinates. There are different principles used to
implement tablets. Some of them are, using wires, sound waves and magnetic principles.

Graphic tablets are also known as digitizing tablets.

2. Joystick: A joystick is another locator device that controls the movement of the cursor. It provides
three types of controls, such as digital, direct and glide. The digital control allows movement in
limited directions, that is, up, down, left and right. The direct and glide control allows movement
in every direction, that is, 360 degrees.

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