9.3 Specifying Points Within Coordinate Systems

A coordinate system describes points on the screen in terms of their horizontal (x) and vertical (y) positions. You specify a certain location by providing two values that map to a unique position.

Summary: Graphics functions usually use viewport and window coordinates.

Coordinates on the physical screen never change. Only five functions, listed in “Physical Coordinates” on this page use physical coordinates. All other graphics functions use one of these two coordinate systems:

Viewport coordinates (short integers)

Window coordinates (double-precision floating-point numbers)

Viewports and windows can occupy all of the physical screen or just part of it. The three coordinate systems and conventions for naming points and regions of the screen are described below.