Star Tip

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.