STAR TIP 1

by Dominic Robinson

from Your Sinclair #20 (Aug.1987) - "Program Pitstop"

[files STARTIP1.*]



Ever looked at the flashy rainbow

coloured lettering on Hewson games and

thought "Corky! I wish I could do that

in my games!" Well now you can, because

those awfully nice Hewson people have

allowed Dominic Robinson, the

exceedingly talented chap behind the

Spectrum conversion of Uridium, to share

it with you. His programming life at

Hewson began when he worked on the team

that built Pyracurse, and after Uridium

and the game he's just completed,

Zynaps, he looks, at the tender age of

21, to be one of the top Spectrum

programmers of 1987.



The Rainbow Effects Processor is a very

tidy group of routines, used in both

Zynaps and Uridium to produce the

amazing rainbow 3D effects on the title

and hi-score screens. "In its simplest

form, the Rainbow Processor can be used

to increase the Spectrum's normal colour

resolution, giving you a different

colour on each pixel line, in a band

twenty characters wide in the centre of

the screen. With a little more work, the

bars can be animated to produce some

very un-Spectrum like effects. The

Rainbow Processor runs in Interrupt Mode

2, to keep it synchronised with the

generation of the TV picture, so that

different attribute values are fetched

for each pixel line."



Method



To use the Rainbow Processor, you must

set up a block of memory containing the

colour for each pixel line of your

display. This block can be 256 bytes

long, although at most 192 will be used

at one time, and it must not cross a

page boundary. Starting at a block at an

address which is a multiple of 256 will

ensure that this condition is met. For

example: 193*256-49408, which is

conveniently placed just above the end

of the code. Next POKE the address of

your data into 49189 and 49190; call the

routine at 49153 to initialise the

interrupts, then POKE 49188 with the

number of pixel lines you want

displayed. This value should be a

multiple of 8 for best results. Any

value outside of the range 1 to 192 will

switch off the rainbow effect until

another value is used. The deeper the

display you use, the less processor time

will be available for Basic or any other

code you have running. For this reason

the rainbow effect can only really be

used for title screens and special

effects.



Hex Dump



Feed this, eight bytes at a time, into

the Hex Loader from Peeker, and save it

as SAVE "democode" CODE 49153,145.



Demo Program



This small Basic program demonstrates

the facilities of the Rainbow Code. Save

it as SAVE "RAINBOW" LINE 2000. When you

run it, it will load and activate the

machine code, upon which the screen will

go black for a couple of minutes while

the demo picture is drawn. So be

patient; the result is stunning.