AT&T 6300 Programmer's Manual page 137

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SCREEN COORDINATES

Graphics images are positioned on the screen in

accordance with screen coordinates. These

coordinates comprise two parameters generally

referred to as x and y, where x defines the

horizontal screen position and y defines the

vertical screen position. Screen coordinates may

be of two types:

• absolute coordinates

• relative coordinates

Whereas absolute coordinates refer to the actual

position of a pixel on the screen, relative

coordinates indicate the position of a pixel

relative to the coordinates of the last pixel

referenced. The x and y relative coordinates are

therefore 'offset' values from the last pixel

referenced (known as the "current point").

Screen coordinates are described fully in the

Reference section (refer particularly to the

WINDOW statement); however, the following

example illustrates the use of both types of

coordinates:

20 PSET (100,50] 'absolute coordinates

30 PSET STEP (10,-5] 'relative coordinates

This program example illuminates two pixels on

the screen: the first at coordinates (100,50) and

the second at actual coordinates (110,45.)

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