Long story short, I have managed to convert some of the assset files that come with "Sid Meier's Railroad Tycoon Deluxe" into a modern file format (png) and have a pretty good idea of what the other files are about. In the end this is not the tale of a great feat I would have hoped it would become. My moderate success was not due to some sudden spark of genius but due to more sleepless nights than I care to admit in which I banged my head at the disassembly.
Over years I have revisited and left the problem again many times, Years with pauses of several months between shorts bursts of renewed interest, the latter often coinciding with updates in Krishty's "Extracting Ace Combat" Thread here.
I don't even know what I did wrong over all that time. One evening without consciously doing anything different than before, I "just knew" I was, finally, looking at the disassembly of the right function (Figure 1). I ported the assembly verbatim to C (think: uint16_t ax = 0x0;) , and I was done. Subsequent restructuring of the code in a more high-level style did not reveal any hidden secrets, at least not to me. Totally anticlimactic.
Code: Alles auswählen
_071B:0010 _071B:0010 ; =============== S U B R O U T I N E ======================================= _071B:0010 _071B:0010 ; Attributes: bp-based frame _071B:0010 _071B:0010 sub_56E0 proc far ; CODE XREF: sub_1EE2+B2↑P _071B:0010 _071B:0010 arg_0 = dword ptr 6 _071B:0010 arg_4 = dword ptr 0Ah _071B:0010 arg_8 = word ptr 0Eh _071B:0010 _071B:0010 push bp _071B:0011 mov bp, sp _071B:0013 push si _071B:0014 push di _071B:0015 push ds _071B:0016 push es _071B:0017 push bx _071B:0018 cld _071B:0019 mov ax, [bp+arg_8] _071B:001C cmp ax, 1 _071B:001F ja short loc_56F3 _071B:0021 out 0A6h, al ; Interrupt Controller #2, 8259A _071B:0023 _071B:0023 loc_56F3: ; CODE XREF: sub_56E0+F↑j _071B:0023 les di, [bp+arg_4] _071B:0026 lds si, [bp+arg_0] _071B:0029 mov dx, 10h _071B:002C lodsw _071B:002D mov bp, ax _071B:002F _071B:002F loc_56FF: ; CODE XREF: sub_56E0+2C↓j _071B:002F ; sub_56E0+76↓j ... _071B:002F shr bp, 1 _071B:0031 dec dx _071B:0032 jnz short loc_5709 _071B:0034 lodsw _071B:0035 mov bp, ax _071B:0037 mov dl, 10h _071B:0039 _071B:0039 loc_5709: ; CODE XREF: sub_56E0+22↑j _071B:0039 jnb short loc_570E _071B:003B movsb _071B:003C jmp short loc_56FF _071B:003E ; ---------------------------------------------------------------------------
This post will probably make very little sense without the context of Krishty's thread as linked above. I suggest you read that thread first. It is the more interesting read anyway. I will reference that thread a lot, maybe to the point where it gets awkward. To avoid misunderstandings: Krishty and I never met. The number of PMs we exchanged over the years can be counted on one hand, I think. He does not know about this project until now and I do not know anything about him other that he did a cool thing and I wanted to do the same. I will go into my motivation some more now but part of me thinks, that is all hindsight rationalisation and basically this is about competition. "If Krishty can do it, I will be damned if I can't." Maybe I'm overthinking this.
"Sid Meier's Railroad Tycoon Deluxe" (what a title! let's call it RRT) was not the first videogame I played but the first one I owned. The first physical disc someone bought in a shop and gifted to me. The first disk that was inserted into the newly bought family computer to install a game, or probably any software, with little to no concept among the gathered users what that was: installing software. It was not a new game when I got it, I think the first release was 1990 - without the "Deluxe" back then - and this anecdote takes place ca. 1996. Many now classic gaming franchises were founded in that year, you can google for yourself, but the 1996 release surely most relevant for this story is "Sid Meier's Civilisation II", arguably marking the passage of a whole generation in the genre. I was late to the party.
Ten more years later, 2kgames made RRT available for free as part of the marketing campaign for "Sid Meier's Railroads!" an otherwise unremarkable game that does not run on Windowses newer than Windows XP. They bundled RRT with a Dosbox and a .pdf of the copy protection sheet that was so usual in these days. In preparation for this post, I checked and the link is now dead. There is no longer any sign on the 2K Homepage that "Railroads!", let alone RRT ever happened. So 2K seems to have abandoned RRT almost 30 years after its first release but RRT never again left me after downloading that full digital copy.
You can still get RRT at https://www.pcwelt.de/downloads/Sid-Mei ... 73103.html apparently, which seems legit, but I haven't tried it and you would proceed at your own risk.
As it is probably clear from the above, nostalgia is a main driver of what follows. Krishty speaks of "nostalgische Verstimmung" (an untranslatable play of words along the lines of "nostalgic moodiness" and the desire for conservation (here I won't even try to translate his exact words).
For me it is less about conservation and more about evolution. The interest in games, kindled by the one we discuss here, led to an interest in game development - who would have guessed, given were we are here - led quickly to the realisation that I am unable to produce even passable "programmers art". There are many reasons why I never produced a single game, however small, but this is the one reason which I would have put forward at age 14 or so. An age at which admitting any other reason would have been too much for a developing ego. One day around that time I realised that one of my games (not RRT) stored its assets as bitmaps which I could read. Since that day I had this fantasy that I could use the assets of an existing game to make a new one. Like I said, this never happened, but the idea somehow sticks with me until this day.
The second motivator, which I apparently also share with Krishty, is the urge to do something comparatively hard with no conceivable utility other than my own entertaiment just because it is possible. The analogy of a jigsaw-puzzle comes too mind. Simply knowing that it had to be possible to read these files because, of course, the original game did just that, helped me over many dead ends.
To manage expectations: Given how long it took to write down only this part, I am not sure I will ever complete the write-up. Given that it took me years to get to the point were I had something to write about, what are a few month for the write-up? If I get around to it you might eventually learn how I obtained Figure 2. For now you can find Part II here.
Figure 2: Teaser. Here is something you won't see in the game. A tile masked "Err", probably for debugging purposes.