I wonder when I became the kind of person for whom Michael Abrash's Graphics Programming Black Book became exciting and fun to read, instead of being daunting and terrifying

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. mastodon.social/media/Yg3wSvnV

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

Like I was convinced Mode X was black undocumented voodoo magic, instead of just, like, bankswitching? I had no concept that mode 13h was just throwing away 192kb of video memory because I had no concept of how RAM worked at all, really

I assumed interfacing with hardware was hard, when what was actually going on was that debugging was hard, and programs I wrote on my own without copying directly from tutorials were buggy

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 mastodon.social/media/uax66anG

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 mastodon.social/media/QGLwPAja

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! 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.

Ok, here’s what I definitely do understand:
Keen has two “pages” of video memory that it flips between. Each page represents an image slightly larger than the screen that it can smoothly pan around in. We’re talking, like, 16 pixels wider.

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.

This morning an old Michael Abrash article taught me exactly how to trivially speed up my current tile drawing routine 4x by caching tiles in video memory so this makes sense to me.

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 mastodon.social/media/LEqZ5yj7

I really wanted to play with the split screen register, so now there's a static footer and I can scroll around the map with the arrow keys. Scrolling is a bit slower 'cause I have an actual map in RAM now. Name is absolutely not final.

Trying to figure out how to efficiently draw semitransparent sprites in EGA. It is... not as simple as I thought. Reading the Graphics Programming Black Book chapters about fast animation and some of the methods he's describing are absurd - chapter 43 is like "if you don't mind having every sprite be 1 colour and only using 5 colours total, here's a neat trick" and no actually I do mind those constraints, that's not helpful advice

I'll probably have a quick look at the Keen Dreams source again and then just build something slow and naive

Came up with my own strategy for sprite drawing; so far it seems to be going pretty swell

Very important to document these glitches before I fix them IMO. I've almost got the sprites drawing in the right place, though they're not even close to the right data. I replaced the background tiles with the car sprites I drew just to make sure my TIF loader was reading them OK.

Hey, I can see a mangled version of my car sprite! And it moves around smoothly!

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I have unmangled my car sprite! Now to figure out why only the grass tile is being used as a background, and also wtf is going on with my pixel mask, jeez

Coding in C for the 286 is kind of like coding in a dynamic scripting language except the only data types are "array of bytes" and "little-endian words"

Like these bytes have structure but it's probably more trouble than it's worth to try to explain to the type system what it looks like

It's fun when figuring out a problem with something then uncovers exciting new problems with that thing

Implemented smooth horizontal scrolling, which in EGA makes the footer jitter. There’s a VGA-only fix but I think I’ll switch course a little and scroll the footer onscreen at times where the player can’t move. Of course getting rid of the footer ended up exposing a new delightful glitch

Starting to factor out the game loop; added the ability to pop-up the footer by tapping the space bar, which pauses normal game logic.

Nothing visually new today, just a bunch of overdue code cleanup. Everything used to be in one giant C file but now there's proper modules and header files. Fun Turbo C++ tip: to create a new multifile project, select "Open Project" and type in the name of a file that doesn't exist

I almost set up a Twitch stream but was having trouble with my headset making me sound like a weird glitchy robot for some reason

I’ve been frustrated at how difficult it is to log stuff for debugging when your only video card is currently in use, so I grabbed a null modem cable, connected my *other* 286, a Toshiba T3100e with a very dead hard drive but a working boot floppy, and wrote a dumb serial port byte-banging routine

I am SO tempted to write a little Forth REPL to drive my game logic right now, nnngggh

BTW if anyone has experience tricking old BIOSes that only know two possible hard disk geometries into booting from a big compact flash card, hit me up

Time to join my two retrodev threads: Jorth ( jean forth) now runs in-game over my serial port!

Michael Abrash: Here’s how you reprogram the PC’s timer, but be warned! It will fuck with your system clock until it reboots! Here’s exactly what happens for this particular application and why

André LaMothe: yolo just chain your ISRs and shit will probably work out? Don’t worry about it, paste the code in, I don’t have time to explain and you don’t care. Also let’s just run all of your game logic in the timer interrupt handler, this is how multitasking works, what could go wrong

I mean, LaMothe was _absolutely right_ when I was a kid reading Teach Yourself Game Programming in 21 Days, I didn’t care and I would not have understood. And he explained the concepts well enough that they were accessible to me when the time came to learn them for real.

Finally hit a bug where my computer doesn’t hang but it DOES corrupt the system state enough that when it crashes, subsequent runs stop working quite right and only a reboot clears it up

So, that’s fun

Oof! Got it. Two bugs conspired to cause a stack overflow:

* if a task was set to have its output ignored, it was leaving each character on the parameter stack. So the silent loading of the base definitions would leave a bunch of junk on the stack if there was any output. Usually there isn’t, so I didn’t notice.

* I added a definition that contained a comment before I defined the word that interprets comments, so the interpreter dumped a bunch of errors on the stack trying to figure THAT out

The tricky stuff I was messing with last night when I started noticing crashes - multitasking and compiler improvements - that was all totally fine. I just forgot a DROP in some I/O code last week.

went to implement simple text drawing yesterday but ended up writing Jorth code to do animation lerps

managed to successfully write a word that takes five parameters on the stack, so I assume I'll be receiving some sort of Forth Programmer Certificate of Achievement in the mail soon

(Jorth still has no words that can touch anything on the stack beyond the top three values)

Tried to implement text drawing but something is fucked and it only draws garbage

It _should_ be a very simple BIOS call to fetch a pointer to the built-in 8x8 EGA font and just use it, I’m clearly missing something fundamental

had the idea to peek at the DOSBox source to verify the BIOS call works like I expect and, yup, it's very not complicated :/

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(This is the Jorth ( jean forth) VM printing out the address of each C function being called while it’s executing its busy loop, btw. The idea was I’d make it crash and then do forensics on the last few numbers to figure out where it died. The last displayed number turned out to be 0, meaning I could easily check for null and set a real breakpoint in Turbo C++, and that’s how I caught the stack overflow.)

@SpindleyQ this looks incredible and I'm so glad I don't have to do this to debug anything

@hellojed my understanding is that a common setup was to have a second video card, using a different video standard so video memory didn’t overlap, to run your IDE / debugger on a second monitor

@SpindleyQ Holy shit! Is that an orange gas/plasma monochrome screen? on a laptop with mechanical keys?

Also I spent way too much time in Telix back in the day; would dial 4 or 5 BBSes a day. ... man I should get into telnet/ssh bbses ..

@djsumdog not quite a laptop; there’s no battery. But yes! en.m.wikipedia.org/wiki/Toshib

I’m using a Raspberry Pi as an etherdfs drive and at some point soon I’m definitely gonna plug a USB RS232 converter into it and turn it into a wifi modem

@jplebreton I could’ve just plugged it into my Raspberry Pi but it would’ve felt wrong

@SpindleyQ There is an compact flash to IDE adapter I'm sure is around here somewhere I used to use. I had a 4 MB card in it.

@AskChip yeah, I’m using one in my desktop 286, but that bios lets me enter custom geometry. The T3100 bios assumes you have one of the two hard disk configurations it shipped with, so finding a CF card that's an exact match would be... challenging. Plus I'd love to have more space if I can!

@SpindleyQ So 40 or 80 meg. This looks like it would work, as long as you formatted the drive in another machine: aetherwide.com/vignettes/20070

@SpindleyQ You want XTIDE: code.google.com/archive/p/xtid

You can burn that image and stick it in the socket of an ISA network card. Or you can buy this PCB and build your own ISA card to put it on: lo-tech.co.uk/product/8-bit-id

@SpindleyQ You also need an IDE->CF adapter and the appropriate CF card. You have to use a CF card that supports Fixed Disk mode. Anything on eBay sold as "industrial compact flash" should. Used to be that SanDisk cards could have the mode set with a DOS utility, but modern cards have removed support entirely and you have to pay SanDisk 2x for the industrial version now.

@ieure hmmmm... This is definitely what I want, but I'm working with an unusual form factor (Toshiba T3100e)... I know it's got an add-on modem in it, wonder if it's a standard ISA connector

@SpindleyQ Ooh, yeah. That's going to be challenging. Worst case, maybe you can use the CF card as the larger of the two built-in geometries.

@ieure Certainly no harm in trying, anyway. Thanks for the pointers!

@SpindleyQ Sure thing! Good luck, hope you work something out.

@ieure huh, i looked it up and kinda see how it works. that's... so bizarre!

@maple Yep. They're just the easiest way to do the thing.

@SpindleyQ Hrm, the GIF speed dropped quite a bit once uploaded and processed. Maybe it's better this way..

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