The next example demonstrates the following technique. Rainbow number 1, with colour index 1, is given a colour table length of 4097, which is one entry for every colour value that will be displayed on screen. The RGB values are left blank, to be set up by the first FOR ... NEXT routine, that contains the RAIN command. The second FOR ... NEXT routine uses RAINBOW to display a pattern 255 lines long, starting at scan line 40. The DO ... LOOP structure is used to repeat the process.
E> Curs Off : Centre "OVER THE RAINBOW"
Set Rainbow 1,1,4097,"","",""
For L=0 To 4095
Rain(1,L)=L
Next L
Do
For 0=0 To 4095-255 Step 4
Rainbow 1,C,40,255
Wait Vbl
Next C
Loop
The copper list
The appearance of every line displayed on your screen is controlled by the Amiga's co-
processor, known as the "copper". The copper is a self-contained processor with its own special
set of instructions, and its own internal memory. A massive number of special effects can be
created by programming the copper, but the copper list is notoriously difficult to manipulate,
and many competent programmers have failed to master its mysteries.
A full discussion of the copper lists may be found in Appendix F of this User Guide.