Border Patterns

BORDER PATTERNS


by Ben Machin & Fred O'Rourke


from Your Sinclair #26 (February 1988)


[files BORDPATT.*]





[NOTE: This is unlikely to work on many emulators, because of timing ]


[problems, and also because they don't have a border as wide as a real ]


[Spectrum in order to show a legible border display. Using WinZ80 with ]


[the "wide borders" setting gives some idea of what should appear, ]


[although even that is not very good. JimG]





I liked this program from Ben and Fred (sounds like a couple of Flint-


stones), partly because it was so well presented, and also because it


was so frivolous. By well presented I mean that they supplied a tape,


hex dump, assembly listing, a page of information about the program, and


demo listing. (If all the submissions were as well presented it would


make this job so much easier!) The demo program shows border graphic


units zooming along above normal screen limits.





The routine occupies RAM from 50000-50213 and 64980-65281. [This doesn't


tally with the printed listings, which end at 50215 and 65027. JimG] The


latter of the two addresses holds the interrupt handler and the vector


table, whereas the first area is the border display handler. Borderprint


is compatible with the 48K and 128K/+2 Spectrums. It automatically works


out which computer it is running on, and modifies itself to run on the


slightly faster 128k/+2 processor.





POKE 50005, lo-byte of display file start


POKE 50006, hi-byte of display file start


POKE 50008, (1-64) amount of pixel lines to be printed


POKE 50107, (1-255) scroll speed, 255=fast, 1=slow


POKE 50141, (1-8) size of chars printed by routine 50131


POKE 50168, (1-7) ink colour of chars


POKE 50176, (1-7) paper colour of chars


POKE 50212, 0=scroll on, 1=scroll off


POKE 50167,237: POKE 50168,95 multicolour chars


POKE 50167,62: POKE 50168,0 normal black chars


RANDOMIZE USR 50131 when scroll is off captures character at 0,0


RANDOMIZE USR 64980 turns the border display off


RANDOMIZE USR 65000 turns the border display on





The Basic listing of the demo program below requires a few lines of


modification, 'cos as it stands it doesn't load the machine code. Add


these lines for full operation:





140 STOP


150 CLEAR 49999


160 LOAD "BLOCK1" CODE


170 LOAD "BLOCK2" CODE


180 GO TO 5





When you save the Basic use SAVE "demo" LINE 150. The reason for this


omission was that there was a short program on the tape that loaded the


CODE before the Basic demo.





I haven't bothered to give you the assembly listing for three reasons:


1) There were no comments anyway; 2) It would have taken up space, and


finally; 3) Disassembling code is a good way to learn about it!





The authors add this small note: "If this routine is published in


Program Pitstop, please mention that readers can use it in their own


programs, but not in any commercial or published programs / games. Thank


you." Well, thank YOU, Ben and Fred.