Random scan systems
•An application program is input and stored in the system memory along
with a graphics package. Graphics commands in the program are translated
by the graphics package into a display file stored in the system memory
• This display file is then accessed by the display processor to refresh the
screen.
• The display processor cycles through each command in the display file
program once during every refresh cycle.
• Graphic patterns are drawn on a random scan system by directing the
electron beam along the component lines of the picture.
• Lines are defined by the values for their co-ordinate endpoints, and these
input co-ordinate values are converted to x and y deflection voltages. A
scene is then drawn one line at a time by positioning the beam to fill in the
line between specified endpoints.
4.
•Application and GraphicsPackage: When you run a program (for example, a game or a drawing tool), it
contains graphic instructions (commands) that tell the computer how to draw things on the screen. These
instructions are stored in the computer's memory.
•Display File: The graphics commands are passed through a special graphics package (software) that
translates them into a "display file." This display file is a collection of instructions that tells the computer
what needs to be shown on the screen. It is also stored in the computer's memory.
•Display Processor: The display processor is like a special part of the computer's hardware that reads the
display file. It processes these instructions and uses them to refresh the image on the screen.
•Refresh Cycle: The screen needs to be updated continuously to show the correct image. The display
processor goes through the display file one time in each "refresh cycle." A refresh cycle happens many
times per second, making sure the image stays up to date.
•Random Scan System: In this type of system, the computer uses an electron beam (like a tiny "pencil" of
light) to draw pictures on the screen. The beam moves randomly around the screen, drawing one line at a
time.
•Lines and Coordinates: Each line that the computer draws is defined by two points (called coordinates).
These points have x (horizontal) and y (vertical) values, which describe where the line starts and ends.
•Deflection Voltages: The x and y coordinates are converted into electrical signals called deflection
voltages. These signals tell the electron beam where to move on the screen to draw the line.
•Drawing the Scene: The electron beam follows the instructions in the display file, drawing one line at a
time between the start and end points, until the entire picture is created on the screen.
Input Devices
•The InputDevices are the hardware that is used to
transfer transfers input to the computer. The data can
be in the form of text, graphics, sound, and text.
Output device display data from the memory of the
computer. Output can be text, numeric data, line,
polygon, and other objects.
