Workprint – September 2018

I spent the previous weekend visiting family dahn sarf and, after a particularly harrowing coach trip home, had to spend a few days “recovering” so this post is a bit later than expected… on the plus side, I picked up a copy of Compute’s First Book Of Atari Graphics from the lovely folks at Level Up in Canterbury…

…which I hope is not too advanced for me! It even came with a hand-written page – poking out of the book in the picture above – of display lists as decimal from a previous owner which seems to have been used as a bookmark since it’s a few pages into the chapter titled Introduction To Player/Missile Graphics, one of the few places where the display list isn’t particularly relevant.

Sorry, drifted off a little there… so I’ve been working on the project I’m still not really talking about, although it’s probably safe to say I’ve been a little lazy recently; the intro is done and there’s two complete parts still waiting to be linked, but I haven’t found the time for a prolonged coding session to get any of that done and it’s one of those jobs I don’t want to stop halfway through for fear of losing my place. I also have a list of potential ideas which is coming along nicely and a couple of existing prototypes which can be improved and re-purposed so stuff is still happening.

I did find a couple of hours to doodle some code whilst away though; an interesting thread at the Plus/4 World forums mentioned using the registers $FF1A and $FF1B to scroll a bitmapped screen around in a form similar to AGSP on the C64 except without the “dead air” at the top of the screen, so I spent some time experimenting to get my head around it. The code I wrote works but this method only affects the bitmap itself so colour data would need to be moved by brute force, a bit of an ask considering the Plus/4 uses 2K for bitmapped graphics regardless of mode. It’s something to experiment with later, although I’m seeing an odd, almost FLI-like glitch in the version I wrote which added splits for a character-based scrolling message and can’t think for the life of me why it’d be there!