Why the DOS version? It had atrocious graphics compared to the original Mac version....
EDIT: I googled for screenshots and I never knew how many different versions of the game there were! Every platform had completely different artwork! Pretty amazing.
I actually prefer the PC VGA version; it has very nice graphics, but still in the same style as the original Apple II version, not a complete redraw in a different style and tone, like many of the ports.
And the DOS port came out years before the Mac port. No wonder it looks worse. I always thought the DOS version was the first port but apparently the PC-98 version beat it by a few months.
I think that title goes to Pac-Man[1]. It helps being older, not to mention one of the most recognizable games ever made. As well as the 80's being a time when many unique platforms rose and fell.
And honorable mention goes to Lode Runner[2] which doesn't have quite the fame as Pac-Man but has still managed to create a lasting legacy (pun intended).
What about Tetris? Though the line gets blurry about "official" ports of Tetris, I'd wager that the core game concept is one of the most ported of all time.
Note that Pong and Space War were both ported before Pac-Man, as well, though Space War didn't get a home version before Pac-Man to my knowledge, it did get ported from mainframe hardware to an arcade cabinet before Pac-Man existed.
It's a mess of copyright for sure. I doubt you could really exercise your rights as a 3rd party with the GPLv3 there. e.g. if Debian or Ubuntu were to include the game then they would be on shakey ground for redistributing copyrighted stuff. Presumably the original graphics are in there too, not just the "re-imagined" code.
It reminds me of the old New Kind - Oolite - Elite shenanigans from years ago. Somehow Oolite powered through and stuck around, despite using most of the New Kind code originally (they translated the C game logic to Objective C if memory serves me), while New Kind was shut down by Braben for copyright infringement. The New Kind author - Christian Pinder I think was his name - did all the disassembly work originally. I don't think it was ever a big legal challenge there, more like "hey! take that down" and the author complied because he was a nice guy.
> reverse engineering Windows to reimplement stuff in Wine would be illegal
That's legal though. Stuff like that is the whole purpose of reverse engineering. You can't copy the code but you can learn how it works so you can do it yourself.
>but you can learn how it works so you can do it yourself
This part is definitely illegal. You can learn how it works but you cannot write the code yourself, you have to write the specs for someone else to do it, who hasn't done the reverse engineering.
That's clean room reverse engineering, a rigorous method to make absolutely sure that the results are legal so it can't be questioned later. It's not a legal requirement and it does not prevent lawsuits. It just makes it more likely that the legal battle will be won.
I think GP is referring to the DMCA, which forbids reverse-engineering unless it's to understand how to interface your own code with something (although I'm not a lawyer).
Yes, even under the DMCA it's totally legal to reverse engineer for the purposes of interoperability. Wine was created to make Windows applications work on Linux. I reverse engineered my laptop's crappy manufacturer software in order to make a Linux version.
Yeah, the author's "Copyright (C) 2013-2021 Dávid Nagy" seems ridiculous and meaningless. I can see the appeal of a project like this, but the author's pretending that that copyright and the GPL licensing mean anything isn't helpful.
IANAL either, but I suppose the situation here is similar as with "abandonware": as long as the original publisher/copyright holder doesn't protest, old software is made available on various download sites. Of course, with a project like this, if the copyright holder would intervene, a lot more work would go down the drain, and claiming your own copyright without explicitly mentioning the original copyright is definitely not helping...
> but I suppose the situation here is similar as with "abandonware"
I don't know if this would hold up. Prince of Persia IP is far from dead or abandoned. I know it's not exhaustive, but a quick search on IMDB [0] shows a movie in 2010, and a video game as recently as 2008. Just because this particular game is old, doesn't mean the IP/Trademark is dead. Personally, I'd be wary of a legal battle, even though I think the project is pretty interesting.
Again, IANAL, but that's not really relevant. The old Super Mario games for Game Boy and SNES can be downloaded from various abandonware sites, while the Mario franchise is still ongoing. As long as Nintendo is Ok with that, that's not a problem. The original Prince of Persia is also available as "abandonware" and can even be played in the browser (https://www.retrogames.cz/play_102-DOS.php?language=EN)
Even if Nintendo is OK with that (are they really?), that does not mean that someone else can grab one of those copies and claim copyright on it! That's what the author of the reverse-engineered Prince of Persia seems to be doing.
Based on, but as far I remember it was rewritten rather then copied.
To be honest, the should claim same with PoP and I don't see any solicitor suing them, as it would be too much hustle to prove its a code copy instead of inspired by.
Wow that is really sad, we live in the world where this is even a discussion. Where a love project that will not be commercialized has to think about this bs :(
Apparently that may not be strictly required either, but it gives a good defense. I think I could disassemble a blob to figure out what the possible behaviors of a WinAPI call and then write my own implementation of those things.
Microsoft might bankrupt me before I won a court case, but there is nothing in copyright law as far as I know that says reading a copyright work forever contaminates your mind such that you would be incapable of creating a vaguely similar thing without infringing on it.
Yes, that's what they mean by "clean room" implementation. The implementer should not be "polluted" by the previous implementation. This is what Microsoft did when they revert engineered CPM and created DOS.
Right... But there is nearly (no?) work to port from 8086 to 8088. The work was to adapt to the underlying IBM system calls (BIOS) and to the specific wired electronics (video card, DMA, mass-storage media, clock, keyboard...).
ReactOS isn’t based on disassembly of the original Windows code. It’s based on publicly available documentation of Windows APIs (and reverse engineering those that aren’t documented, but that’s a whole different beast from disassembling).
In fact, ReactOS maintains a policy to prevent proprietary Windows source code (whether leaked or otherwise) from making its way to the ReactOS codebase [0]. When Windows source code leaked, in 2006, ReactOS did a complete codebase audit to ensure that it was not tainted.
As far as I know the ReactOS team does not disassemble Windows.
"Is ReactOS legal?
Yes. ReactOS is fully legal.
Developers (devs) have not looked at Microsoft Windows™ source code. They have used the public documentation of Microsoft Windows OSes. They have made several tests to understand how Microsoft Windows works. In fact, ReactOS does the same things that Windows does but it does it differently as we don't have the same source code and it is all programmed by different developers. All code in ReactOS is released under the GNU GPL (General Public License).
Is ReactOS based on Microsoft Windows™ original source code?
No! ReactOS consists only of clean-room engineered GNU GPL (General Public License) and GPL compatible licensed source code. "
It's not based on any Windows binary code, or the project would be forever poisoned with respect to copyright. They actively prevent anyone who has seen the Windows source code from working on the project.
React OS has come under fire before, and been audited, for including windows code[2]. Also the project would not be poisoned with respect to copyright, according to US law.
> Clean room design is usually employed as best practice, but not strictly required by law. In NEC Corp. v Intel Corp. (1990), NEC sought declaratory judgment against Intel's charges that NEC's engineers simply copied the microcode of the 8086 processor in their NEC V20 clone. A US judge ruled that while the early, internal revisions of NEC's microcode were indeed a copyright violation, the later one, which actually went into NEC's product, although derived from the former, were sufficiently different from the Intel microcode it could be considered free of copyright violations.[1]
ReactOS has not "been audited" because they came "under fire" for including Windows code as your post implies - they chose to audit themselves to ensure that they were free of Windows code (they were), to be safe, and for the optics: so that observers see that they're serious about being safe.
ReactOS was audited, it doesn’t matter if they agreed to it. The fact is that an engineer claimed it had copied windows code and it had an assembly function believed to be taken directly from windows. The reason I mention it is that this thread has been claiming it’s illegal to study and rewrite disassembled code but that isn’t the case. It’s illegal to copy it but clean room implementations depend on disassembling code and documenting it allowing for another person to then do the implementation.
Im definitely not taking shots at ReactOS here, I’m on their side and am fascinated with the project. You’re right I should have been clear that they shut down and has themselves audited instead of risking a court battle but I don’t think the difference matters much, either way they were gonna have a code audit to disprove these allegations. But in regards to them, there’s a lot of wrong information floating around this thread.
> claim was made on 17 January 2006 by developer Hartmut Birr on the ReactOS developers mailing list (ros-dev) that ReactOS contained code derived from disassembling Microsoft Windows.[25] The code that Birr disputed involved the function BadStack in syscall.S,[26] as well as other unspecified items.[27] Comparing this function to disassembled binaries from Windows XP, Birr argued that the BadStack function was simply copy-pasted from Windows XP, given that they were identical. Alex Ionescu, the author of the code, asserted that while the Windows XP binary in question was indeed disassembled and studied, the code was not merely copy-pasted, but reimplemented; the reason why the functions were identical, Ionescu claimed, was because there was only one possible way to implement the function
I doubt it costs that much time and money to sue a couple of people once in a blue moon. As far as I know, this is not exactly an every day occurance for them.
Not open source, merely available—or, using the terminology of US copyright laws, it changed status from being an unpublished work to a published work. Mechner's warning from the linked repo:
> As the author and copyright holder of this source code, I personally have no problem with anyone studying it, modifying it, attempting to run it, etc. Please understand that this does NOT constitute a grant of rights of any kind in Prince of Persia, which is an ongoing Ubisoft game franchise. Ubisoft alone has the right to make and distribute Prince of Persia games.
It seems it is open source by the wording, he just makes it clear, that you can’t distribute it under that name because while he owns the rights to the code, Ubisoft owns the trademark(s). So any distribution would be required to remove the name completely from the game.
Ironically the specific definition of what open source is is not universally agreed on hence why you have likely seen the acronyms FOSS and FLOSS used explicitly. E.g. if you ask someone of the FSF group what "open source" means and they'll say the obvious meaning is you can look at the source code which is what makes "open source" different than FLOSS (which includes rights to use/modify the source). On the other hand if you ask the open source initiative what "open source" means and they'd likely link you to the OSD which includes most of the things a FSF would consider part of the separate FLOSS definition.
Usually the definition of open source isn't what matters for all things legal though it's about what rights you were assigned and what those let you do as you point out. All the "what does open source mean" debate is just debate on the terminology of being able to view the source.
Is there a school or a correspondence course where people enroll in order to learn how to make up stuff about the FSF when posting online, instead of just familiarizing oneself with what the FSF actually has to say about a given topic?
> if you ask someone of the FSF group what "open source" means and they'll say the obvious meaning is you can look at the source code
Extremely inaccurate. FSF's definition of open source matches the OSI's. Here are some words that are not the product of my imagination—what FSF actually has to say about the relationship between the two: "Among all programs that are open source, only a minuscule fraction are not free".
While I appreciate the questions asking if I've taken a literal course in misunderstanding the topic instead of looking at what the FSF has to say I was actually referencing the article "Why Open Source Misses the Point of Free Software" which fsf.org links to for defining "free software" when writing my comment. From this article a key section I reread before posting:
> The official definition of “open source software” (which is published by the Open Source Initiative and is too long to include here) was derived indirectly from our criteria for free software. It is not the same; it is a little looser in some respects. Nonetheless, their definition agrees with our definition in most cases.
[n.b. the OSI definition agrees with that of free software not that OSS is interchangeable with FLOSS - hence the article and its title]
> However, the obvious meaning for the expression “open source software”—and the one most people seem to think it means—is “You can look at the source code.” That criterion is much weaker than the free software definition, much weaker also than the official definition of open source. It includes many programs that are neither free nor open source.
> Since the obvious meaning for “open source” is not the meaning that its advocates intend, the result is that most people misunderstand the term. According to writer Neal Stephenson, “Linux is ‘open source’ software meaning, simply, that anyone can get copies of its source code files.” I don't think he deliberately sought to reject or dispute the official definition. I think he simply applied the conventions of the English language to come up with a meaning for the term. The state of Kansas published a similar definition: “Make use of open-source software (OSS). OSS is software for which the source code is freely and publicly available, though the specific licensing agreements vary as to what one is allowed to do with that code.”
.
In regards to the material you quoted "Among all programs that are open source, only a minuscule fraction are not free". Yes, that the fsf thinks most OSS also happens to be FLOSS, not that the terms mean the same thing.
> ask someone of the FSF group what "open source" means and they'll say the obvious meaning is you can look at the source code which is what makes "open source" different than FLOSS
Completely wrong. FSF considers the “open source” term to have the meaning as ascribed to it by the OSI. The FSF does not want to use the term itself, precisely because it can lead to misunderstandings.
The definition of “open source” is universally agreed upon to have the OSI-defined meaning, except for some people:
1. Intelligence community people, who have long understood the term “open source” to mean a source of intelligence which is not itself secret.
2. People who, without having ever looked it up, assume it means that the source code is available for reading. These people are simply ignorant, and should be using the term “source available” instead, since it means exactly that.
3. People who want to be able to use the “open source” term for their software to gain goodwill, but don’t want to actually give all of the freedoms it should guarantee. These people are dishonest shills who try to confuse the debate in order to get away with fraudulent labeling.
> The official definition of “open source software” (which is published by the Open Source Initiative and is too long to include here) was derived indirectly from our criteria for free software. It is not the same; it is a little looser in some respects. Nonetheless, their definition agrees with our definition in most cases.
>
> However, the obvious meaning for the expression “open source software”—and the one most people seem to think it means—is “You can look at the source code.” That criterion is much weaker than the free software definition, much weaker also than the official definition of open source. It includes many programs that are neither free nor open source.
> Nonetheless, their definition agrees with our definition in most cases.
In context, they obviously mean “[The OSI’s] definition [of ‘open source’] agrees with [the FSF’s] definition [of “free software’] in most cases”. The FSF does not have an alternative definition of “open source”; they explicitly use
the OSI definition.
> the obvious meaning for the expression “open source software”—and the one most people seem to think it means—is “You can look at the source code.”
Contrary to what you seem to be implying, they are arguing against that definition of the term “open source”. This is evident by their phrasing: “That criterion […] includes many programs that are neither free nor open source.”
That's not clear at all. There is no reason to believe that Mechner's warning is narrowly referring to the trademark rights, rather than, you know, "rights of any kind".
Some ancient years ago, before I was an adult, I tried to help with this, even had MSN Messenger contact of Ecalot (he was leading the charge on such projects). And tried to contribute to a new map editor with integrated SDL-based engine, had to learn a lot back then, it was my first time seeing GAWK, and my first time seeing GDK, among other things.
Now people on this thread have some questions, I think I can answer, being involved in the community for a while.
1. Why?
PrincEd, the site mentioned there, is a map editor, after someone released that "Prince 4D" mod for the DOS version, PoP fans basically were amazed by it and it created a cool modding community, but the engine is seriously limited, a lot of things can't be done, thus people kept wanting a new updated engine, specially if we could port the graphics of the other versions to PC.
2. Why the DOS?
Probably because the first mod was Prince 4D for DOS, and all mods are for that version.
3. Won't Ubisoft be mad?
As far as I know this never been an issue, I believe as long we don't get tangled with the fourth-game and onwards that is the games made AFTER they bought the IP, seemly they don't care.
I've always wanted to learn some reverse engineering and eventually do this with a game. Unfortunately the ones I'd like to target are all written in C or C++, so I guess translating the disassembly would be even more meticulous than it already is with games originally written in assembly.
Disassembled code from a C or C++ compiler is generally better structured than hand written assembly.
I reverse engineered major parts of Westwood’s Blade Runner for ScummVM. It was compiled with the Borland C++ compiler in 1997 and a lot of it was relatively easy to decompile. The most difficult parts were video decoding and character rendering. The video decoder was older Westwood code, clearly hand optimized, and the character renderer was also very optimized.
Currently I’m working on Cryo’s Dune which is all hand-written assembly code. The code jumps all over the place, parameters are passed in arbitrary registers and have to be traced over several calls. I’ve seen a function that, instead of using ret to return, jumped to the ret-instruction of a different function.
Code generated by an older compiler that doesn’t do too
much optimization is vastly preferable.
I have been toying with doing this to simtower for awhile. The disassemblers are a bit all over the place with respect to Win16 NE code though. Bit annoying to do though as it uses a decent amount of the win16 API so those bits have to be done too sometimes to figure out what is going on. Though it is fairly decently documented so you can block off the game bits from the win16 bits and just skip past the crazy way win16 loads dlls up.
Thanks for the insight. I've assumed hand written assembly, except for those parts where you try to squeeze out the last bit of performance, would be structured more like a human would think, but alas I might be wrong. :-)
But then again the two games I tried were compiled with Watcom, which according to mmy research was pretty advanced when it comes to optimizations, for its time at least.
The biggest turnoff for me was finding the right tooling though. It's not like there are many tutorials for reverse engineering, and those that exist mostly aimed at security research or cracking, targeting modern software.
I found that Ghidra was unable to even load a Watcom binary, it crashed. A year later there was a patch for that, but then Ghidra didn't understand the Watcom calling convention. Found some incomplete plugin for this, but it was just blindly marking all functions as Watcom calling convention. Then I gave up. It might not be the best idea to start learning RE with a full blown game, but at the same time, if you wanna do this "for fun", it actually has to have a fun goal.
Jordan's diary from the period making this (and the Karateka one) are fun, easy reads that really give you insight into a young kid making video games in the 80's that became hugely popular.
Oh, now I will have to check whether I still have the QBasic code somewhere which I wrote to generate a savegame so I can start on any of the levels and I could set unlimited lives.
When i was 11, Prince of Persia was a brutally challenging game and I called could hardly get to level 5.
But sometime later in 2000 I came to possess and old 386 HP desktop, and I tried running Prince on it, and I was surprised how easy it was: I have beaten it easily on the first try and later learned to run through it without dying at all.
I am hoping for a similar result (also didn't finish Prince of Persia at the time). I mean - in the meantime, I got pretty far in Super Meat Boy. Prince of Persia looks like a walk in the park in comparison.
Maybe such controls were necessary for animation reasons. You can't jump while both feet are in the air from running, and you can't make doing that look realistic.
I think, beating Aladdin (1993) on PC did help a lot: it was a more challenging game that required getting used to precise controlling the character. Prince of Persia has rather slow animations, and thus you don't even need a quick reflexes to beat it, just learn the levels and know where you need to move in a certain way.
I ask because a lot of the early DOS games generated sound via a sound card, and most of those used FM synthesis at the time. And so if really want to recreate the original sound then FM synthesis should be used.
listening over to different versions[1] and it is amazing how different the game sounded on different systems (sometimes with completely different soundtrackks). The Apple II sounds like it uses two square waves only. While Amiga, DOS, PC-98, Sharp x68000 and Sega Genesis sound like FM synth, FM Towns and SNES sound like wavetable synth, Gameboy is two squares, NES is two squares and a triangle plus noise.
EDIT: I googled for screenshots and I never knew how many different versions of the game there were! Every platform had completely different artwork! Pretty amazing.
https://www.oldgames.sk/en/game/prince-of-persia/pictures/