Hello, old friend, today you're going to teach me how to hook the keyboard interrupt again https://mastodon.social/media/q_jH0jjh9xYy3GlHgKs
I have successfully loaded tiles from a TIF file that I drew in NeoPaint, converted them internally into EGA planar format, and drawn them to the screen. https://mastodon.social/media/Yg3wSvnVGXp8Foz1Te4
Just implemented page flipping, as a prelude to maybe implementing smooth scrolling.
It’s pretty amazing how little code this is? Like once you have a grasp on how EGA memory is laid out and you’ve got Michael Abrash telling you which registers you can poke to do neat stuff, it’s not complicated? This shit DESTROYED me as a teenager though, I never got ANY of it working outside the basic mode 13h linear framebuffer
It’s really astonishing to me how different the experience of programming a 286 is compared to what I do at my job, how starkly the priorities are different
At my job, I make sure the code I write is flexible and correct. I build safeguards to ensure bad things will not happen when someone makes a change or grows the system
For this project, I put together a pile of purpose-built subroutines and macros, kept simple enough that I could delete and rewrite any of them a dozen different ways
Mouse support is trickier than I expected! It would be easy if I just polled the state every frame but I decided to try to install a callback. I think I need to set the DS register at the start of the callback in order to access my data - I’m scribbling over something important and the computer hangs. But how do I know the value I should set it to? Is it even possible to do this in the small memory model? Argh
Got it! I looked at the generated ASM and figured out that DS was being ASSUMEd to a symbol called “DGROUP”; so I just explicitly set DS to that at the start of the callback and no more crashy!
I am definitely doing something to confuse CuteMouse’s cursor-drawing routine though... probably it assumes I have writing to all four planes enabled https://mastodon.social/media/uax66anGIreYRARWjGs
Well, definitely that, but it also plays _very_ badly with my page flipping implementation - you can see it writing into video memory when I’m flipped to the second page! sooo I guess I’ll be drawing my own damn mouse cursor https://mastodon.social/media/QGLwPAjaEOSkSqTnnq4
I’ve been pondering scrolling for a few days, and whether I could figure out how to write a huge smooth-scrolling playfield or whether I’d just flip from one screen to the next. This evening it occurred to me that surely at some point the Commander Keen source code must’ve been released and I could just see how they handled scrolling. And indeed Keen Dreams is GPLed! https://github.com/keendreams/keen
Hmmmm this is... a little overwhelming. Lots of extra stuff that makes me wonder if I’m missing something important. Gotta keep in mind that it’s an entire game, after many rounds of optimization, instead of a week’s worth of occasional hacking, and my slower, dumber code can still lead to an outcome I’m happy with.
Keen keeps track of which 16x16 tiles are dirty via a dirt-simple byte array where they mark each tile position 1 or 0 - because only 21x15 tiles are onscreen, this only costs a few hundred bytes and is a huge optimization. I’ll probably steal this idea. (Extremely common retroprogramming pattern that has basically disappeared from modern computing: knowing there are, at most, N of something, where N is small.)
The tiles are redrawn by copying from what the code refers to as the “master screen”, which is an area of video memory after the two pages.
I don’t know how this memory is structured, but I don’t really need to - because of the page sizes, I know that a full redraw into a page MUST happen regularly without slowing everything down. So as long as the tiles live in video memory and I have a reasonably efficient copy loop I should be fine.
Also thanks to @darius reminding me of its existence I now have Dangerous Dave in Copyright Infringement running on my 286, along with John Romero’s tilemap editor, and I’m kinda thinking it’d be fucking rad to use it to build my maps instead of slogging through writing my own
Implemented my tile-blitting speedup
Pro: it is indeed much faster
Con: don't quite have all the bugs worked out yet https://mastodon.social/media/LEqZ5yj7ynPKv3PK5YU
@SpindleyQ I feel like the source for Dangerous Dave in Copyright Infringement would be way more useful but alas, no such source I can find
@darius yeah, definitely! Honestly if I could look at the raw video memory while that runs that’d be enough
@SpindleyQ tbh john LOVES talking about this stuff and would probably happily answer any email you sent him
@mogwai_poet @darius oh definitely! Most of what’s actually driving me is that I spent like 20 years thinking of VGA as a dumb slow framebuffer and the discovery that it’s dumb and slow but actually has some neat bells and whistles makes me wanna try them out. I don’t actually want to become 1991 John Carmack and will be very content with being 1991 Steve Moraff.
@SpindleyQ if yer gonna scroll that shit the trick is getting the framebuffer memory to be one tile-size larger in all directions so you can utilize the EGA's built in hardware scrolling support. that thing also destroyed me as a teenager. i had to write down register maps from the EGA/VGA Programmer's Reference book in the bookstore cuz i couldnt afford the damn book.
@dildog yep, that's what I ultimately did! I spent a while trying to figure out if there was some trick that would mean I didn't have to redraw the whole screen once I hit the edge, like the NES mirroring, but the closest I came was not redrawing tiles that didn't change
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