Algorithms for region filling with mixed colors

Computer graphics applications are becoming widespread. Line drawing alone no longer satisfies the average user's needs. Region-filling is one advanced feature to make a computer graphics system more sophisticated. Roughly speaking, there are two categories of filling algorithms. One is to fill a pixel on the screen and recursively fill its four neighboring pixels. The other is to fill a whole line within the boundary, then fill the neighboring lines if they are not filled yet.

This study uses the latter algorithm to develop a package of software that fills bounded regions of a graphics screen with varied solid or halftone colors.

The package is implemented on the Apple II computer. It does line drawing, color filling and record keeping. It has a user friendly interface. A major effort has been dedicated to speed the process by converting critical parts of the code to machine language. Drawing a typical full-screen scene required 130 seconds in Pascal, and less than three seconds in assembly language.