Scroll Colour

Scroll colour





Bill Longley,


Colchester,


Essex.





Most ZX-81 users will have a selection of machine-code


routines for inverting the display and scrolling in


different directions. Unhappily for those who upgrade to a


Spectrum, these are not compatible with the high-resolution


display file. But many of the principles remain the same


and here are three typical subroutines for the Spectrum.


The first two are the up-and-down scrolling routines, but


here they scroll colour while the text remains still.


The third is an ordinary screen invert routine. It will


exchange the ink dots for paper dots, and vice versa. This


probably only makes sense to Spectrum users.


Three separate REMs are used to store the routines, so


one routine can be used on its own. If you make sure each


REM has 32 characters - remember a colour control code is


two - then each routine starts at an address which is 38


greater than the last; so the first starts at 23760, the


next at 23798, the third at 23836 and so on.


One last point: it makes good sense to save each routine


on tape - with different line numbers - and MERGE them into


your program as you need them.


[In fact, all three routines are relocatable, so you


don't have to load them into REMs at all. Loading them into


any other available part of memory should work fine.]