GTIA RAINBOW

An Atari Kaleidoscope of 256 colors.

by MIKE WILDING

SYNOPSIS
Generates 256 colors on your monitor screen. Program requires 16K RAM, and your computer must be equippad with the GTIA chip. If used with an XL series Atari computer, Translator (see box page 85) must be run first.

This special program for ANTIC's international issue generates 256 colors on-screen simultaneously. Many programs generate 128 colors, but this is the first one we've seen that can handle twice that number.

Because GTIA Graphics Mode 9 can create16 intensities and display list interrupts (DLI's) can be used to produce16 basic colors, the Atari can now produce up to 256 (16 x 16) colors at one time. (The CTIA chip can generate only 128 colors, because it can handle only 8 intensities and 16 basic colors.)

The program draws 16 vertical bars (each of a different intensity) and then sets a DLI routine that "varies" the color 16 times over each bar. As a result, it generates 256 different intensities. The effect is a rainbow-like, subtle range of colors that is quite pleasing to the eye.

Mike Wilding, the author of this colorful program, sent it to ANTIC from England, but we understand that he is in Germany now, recovering from some sort of accident. We wish him a speedy recovery, and hope to see more of his multi- colored works of programming art. --ANTIC ED

Listing: GTIARAIN.BAS Download