I love the 1990-ass design of Railroad Tycoon's save system.
not "which directory do you want to save your game?", but "which drive has your save game disk?"
You know, cause you'd put the game in drive A:, and if you were fancy, you'd save to a blank disk in drive B:
Too poor to have two drives? Gotta swap them to save, then swap back to keep playing.
now when you save your game, it saves two files: RR1.SVE and RR1.MAP.
(The 1 can be 0-5 depending on which slot you save into/if it's an autosave).
Now the obvious guess is that the game saves things like "how much money you have" and "where your trains are" in the .SVE, and the current state of the map in the .MAP file, since the game world dynamically changes over time.
now that's super interesting because PIC files are compressed!
And the game can SAVE them, not just load them! that's unusual for games of this age!
that's why it has to save the whole map when you make a save game: because your map is unique.
(and presumably re-generating it from the seed would take too long on some of the computers this game ran on)
okay so I hacked it to go into an infinite loop after showing the first image of the intro sequence, then wrote a script to copy every image into the first image of the intro, start dosbox-x, then wait a couple seconds then screenshot it. So I now have all the images.
Here's the faces:
man I thought this game just had a bunch of random white-guy (well, redish-guys) portraits that it matched with some names of historical-guys-who-built-railroads.
NOPE! every name is matched to a face.
interestingly, these values don't seem to actually correspond to train performance.
I set my train up to have a very high max speed with lots of (positive) horsepower, and it managed to drive 26 miles at 42 miles an hour.
that's... better than a plain 0-4-0 Grasshopper, but not by the amount you'd expect
I figured out two more bytes: There's a "year this train is invented" short int, and it seems that when you start a game, it adjusts the years randomly.
So although the EXE says the 4-2-0 Norris says 1836, when I started a game, it changed to 1833.
"Interrupt 43: Note: This is not a callable vector!"
SO WHY IS INT 0x43 IN THIS CODE
Annoyingly it turns out I have two different versions of Railroad Tycoon here: 455.00 and 455.02
And all my copies of 445.00 are cracked
why does this code have "SUB AX,AX"?
that just changes AX to 0. But... the normal (and faster, I think) way to do that is XOR AX,AX.
Other than some flags (which this code doesn't use), they're the same. Strange.
god I hate hacking 16bit games.
GET A LINEAR ADDRESS SPACE YOU FUCKERS
oh god they interleaved fwrite and fread because they both end up calling the same DOS interrupt.
They basically wrote fwrite and made the fread function do a JMP into it.
the tell tale signs of this being hand-written assembly and not a compiler, because no compiler would generate something this weird
@sekoiatree MOV AX, 0 takes more bytes to encode than XOR AX, AX, so it's less compact and thus slower.
it looks like SUB AX, AX and XOR AX, AX are equivalently fast. I don't know why XOR AX,AX is the "standard" encoding for "clear AX", but it is.
@foone ah, right, x86 is variable length.
Looking it up a little: https://randomascii.wordpress.com/2012/12/29/the-surprising-subtleties-of-zeroing-a-register/
I remember copy protection systems with self modifying code relying on the icache needing explicit invalidate!
@foone ...isn't interrupt 33 one of the really old and basic ways to do mouse support under DOS?
Allegro has it as a fallback if that newfangled "mickeys" stuff doesn't work IIRC.
@foone this post has a documentation of the MS mouse protocol attached https://roborooter.com/post/serial-mice/
it's been like 25 years since I messed with this and I don't have my original references anymore but it looks right
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