Page 12 - DCAP313_LAB_ON_COMPUTER_GRAPHICS

Lab on Computer Graphics

Notes Graphics Commands
• Draw point
• Draw polygon

• Draw text
• Clear frame buffer

• Change drawing colour
Graphics Processor
Two kinds of graphics processors:
2D Graphics Processors: Execute commands in 2D coordinates, when objects not be separate,
the one being drawn will obscure objects drawn formerly in the region. Bitable operations (Bit
Block Transfer) are usually provided for moving/copying one rectangular region of frame buffer
contents to another region.

3D Graphics Processors: Execute commands in 3D coordinates, When objects overlap, it is required
to determine the visibility of the objects according to the z values.
Display Controller for a raster display device reads the frame buffer and generates the control
signals for the screen, i.e. the signals for horizontal scanning and vertical scanning. Most display
controllers include a colour map (or video look-up table). The major purpose of a colour map
is to provide a mapping between the input pixel values to the output colour.

Figure 1.5: Display Controller

1.2.2 Input Devices

Common Devices: keyboard, mouse, trackball and joystick Specialized devices.
Data Gloves : are electronic gloves for detecting fingers’ movement. In some applications, a
sensor is also close to the glove to notice the hand movement as a whole in 3D space. A tablet
contains a stylus and a drawing surface and it is mainly used for the input of drawings. A tablet
is usually more accurate than a mouse, and is commonly used for large drawings.
Scanners : are used to convert drawings or pictures in hardcopy format into digital signal for
computer processing.
Touch Panel : allow displayed objects or screen positions to be selected with the touch of a finger.
In these devices a touch-sensing mechanism is fitted over the video monitor screen. Touch input
can be recorded using optical, electrical, or acoustical methods.

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