777 wrote: ↑Wed Apr 27, 2022 2:26 pm
something weird did happen when i tried to put a too high a number into the width poke, which looks like parallax, spooky...
type goto 9900
https://easyupload.io/dplksm
no idea why thats happening...
Out of interest, where's that from?
I had a quick look. The BASIC program seems to have 4 POKEs that affects what the code does.
Code: Select all
9921 POKE 58679,0
9922 POKE 58680,64
9923 POKE 58681,50
9924 POKE 58682,100
The first two POKEs are the screen position to start the scroll at (picked up by HL in the assembly code).
So it's 0 + (64 * 256) =
16384 (start of screen display).
I think you might want to change this to the position at the end of the row because it's it's scrolling left (though I may have missed something). So try setting them to 31 and 64 (respectively) to put the screen address at the rightmost character of the row.
The third POKE at 9923 seems to be the number of pixel rows to scroll. So you could POKE it to 16 to scroll two full character rows.
The fourth POKE at 9924 is the column row to start at I think [Edit: Sorry, number of columns (counting from the right, as it's scrolling left)]. So if you're scrolling the whole row left, try poking it at 32.
I think that should scroll the top two character rows of the screen. If you POKE too high for the third & fourth parameters, you're possibly to get odd effects.
I reckon you'd have to refine/adapt the routine a bit for a game though (unless it was a Frogger-type game which just scrolls one line at a time). Maybe trying to get the top two character rows scrolling twice as fast as the next two would be a good practice exercise.
