port java game to dreamcast?

hansjak · Post by **hansjak** » Sat May 21, 2005 8:21 pm

me and some friends of mine developed a java game. we have to present our project in a month or so at our university...

now i tought it would be cool to present our game on my dreamcast too. that would rock for sure...

i started searching the internet for anything related to java and dreamcast... and the only thing i found, was that a company ported personalJava along with a web-browser... and i found out that it could be possible to use gcj (gnu java compiler), which uses the gcc backend which supports the sh-4.

i would be happy if i could port at least a limited version of the game (no network support, no sound, ...)

to make it short: should i even bother trying to port our game to the dreamcast? do i have a chance to complete this project in a month?

regards,
hansjak

things you might want to know about the game:
- it makes use of lwjgl (opengl, fmod)
- it's 2d only
- it's single-threaded

BlackAura · Post by **BlackAura** » Sat May 21, 2005 11:10 pm

You'd have to rewrite most of it from scratch, I'm afraid. There is no Java VM available on the Dreamcast (at least, none that aren't embedded in a web browser), and no OpenGL either (we have a work-alike called KGL, but it's not exactly compatible with OpenGL).

Ex-Cyber · Post by **Ex-Cyber** » Sun May 22, 2005 12:39 am

GCJ can compile to native code, so lack of a VM shouldn't be an issue, but I'd think you would essentially end up having to port Classpath as well, unless your code is highly self-contained.

hansjak · Post by **hansjak** » Sun May 22, 2005 9:15 am

so, that means "no"...

can you imagine other consoles i could port our game more easily to?

Post by **Quzar** » Sun May 22, 2005 4:10 pm

java enabled web phones probably. you'd just have to compile/interpret it using j2me instead (and maybe rewrite some things that may not be compliant).

hansjak · Post by **hansjak** » Mon May 23, 2005 1:02 am

rewrite some things? honestly... i don't think cell phones have enough power to run our game... but thanks for the suggestion.

BlackAura · Post by **BlackAura** » Mon May 23, 2005 2:27 am

I've been doing some work on J2ME over the past couple of days. Apps written for J2SE generally won't work. The packages available in both J2ME and J2SE are java.lang, java.io and java.util. Even those packages are stripped down somewhat for J2ME.

Other than that... I can't think of anything. Java generally isn't used for games at all, except for mobile phones, and that's only because native code games will only work on a single type of phone, while Java MIDlets tend to work more-or-less the same on anything that has an appropriate Java / J2ME implementation.

Depending on how it's written, it might be possible to get it running, but you'd either have to port a JVM (like Kaffe) to the Dreamcast, or somehow make GCJ work (I couldn't get it working last time I tried, although that was years ago). Either way, you'd need to port the base classes over, you'd have to write a load of JNI-style bindings to KallistiOS system calls, and you'd have to write a back-end for your game that uses those instead of lwjgl. Not fun. Possible, but not fun.

I'll have to have another look at getting a JVM running on the Dreamcast. Last time I looked, KOS's support for the C standard library and C++ wasn't good enough. It might be now though.

Ender · Post by **Ender** » Mon May 23, 2005 12:31 pm

I seem to remember BlueCrab telling me something one day about Java dev for DC. He had a whole dev environ up at one point apparently. You may want to ask him.

Post by **BlueCrab** » Mon May 23, 2005 12:43 pm

I did have enough of gcj working to get it to compile binaries for the dreamcast, however nothing ever really worked. (At least, not that I can remember)

I think that if I can get a chance to try to work on that again, I might try it. Exceptions would be a problem though, because I can't seem to get C++ exceptions to work at all on the dc.

hansjak · Post by **hansjak** » Mon May 23, 2005 5:01 pm

wow, thats soo cool... i didn't expect that much interest and support... if gcj really works, i'll try to port it. i couldn't get our game working with gcj 3.4.1. maybe gcc 4 works better...

thank you very much for your support!

Pale Rider · Post by **Pale Rider** » Mon May 23, 2005 6:04 pm

java's tuff on the dc,even in planetweb with suns pjava support,somethings,even supported apps dont run...or they run extremely sluggish.but i would imagine that is due to the overhead in memory being used by the browser while trying to run an applet.

hansjak · Post by **hansjak** » Mon May 23, 2005 7:33 pm

gcj isn't as polished as i tought. i can't even use it (cygwin-version crashes, mingw-version sometimes locks) for my project, because of command-path-limitations, gcj limitations (1.4 not very well supported), ... i can't even compile our project for x86.

i guess we're out of luck.

but thanks for looking into the issue.

BlackAura · Post by **BlackAura** » Thu May 26, 2005 5:53 am

Looking around, I basically see three possible ways to do Java stuff on the Dreamcast.

1 - GCJ, compiling to native SH-4 binaries. Assuming we can get GCC 4.0 working on the Dreamcast (GCJ 4 is much better than GCJ 3.x), that basically means we'd need to port libgcj (the GCJ runtime) over to KOS, and get the compiler itself building and generating working code. The runtime consists of a threading part (should be easy now we have pthreads support in KOS), a file handling part (should be easy now we have a POSIX-style libc), and a signal handling part to handle signals sent by the operating system and convert them into Java exceptions. That could be tough - not only does KOS not have anything like signals, it doesn't even use the SH-4's MMU so we will be completely unable to catch null pointer exceptions. That just leaves things like arithmetic exceptions (like divide by zero), but I don't think we can catch those either. So some modification of KOS itself might be in order, or we could just ignore it...

2 - Kaffe, or another JIT. Kaffe shouldn't be that much more difficult to port than GCJ. Might even be easier - the core library only has threading and file stuff, no signal handling to worry about. It already has an SH JIT backend, and has been ported to a number of embedded operating systems. Would require more memory than GCJ for the code cache, but it does also have an interpreter version, and the (now disappeared) DOS port ran on machines with 8MB of RAM. Doesn't leave that much room elsewhere, but you're not going to be doing 3D games with this thing anyway. Of course, if we have to write an SH-4 JIT, it's going to be bloody difficult.

3 - SableVM, or another interpreter. Slow, but probably a little easier than a JIT.

Once you have the interpreter up and running, that leaves you trying to do something useful with it. That would probably get you the core Java libraries - java.lang, java.io, java.util, and anything else that's part of the interpreter itself or implemented in pure Java. That's probably not all that hard, actually, but it would be a fair bit of work.

Might be interesting to try though.

Oh, one other possibility... Port Mono or Portable.Net over, and run Java code using IKVM. That's even more insane than porting a Java runtime (which, at least, we know is possible), but it'd also buy C# and Vb.Net (if you're using Microsoft's VB.Net compiler).

hansjak · Post by **hansjak** » Thu May 26, 2005 3:40 pm

phew... so many options... and everything sounds so easy

ok, BlackAura, you still got ~25 days to do all this stuff. i'm waiting...

well... i abandon the project. i think it would be easier to port everything to c++. but just to show off that's still too much effort.

i'll post a link where you can download the game when it's done.

so long...

hansjak · Post by **hansjak** » Sat Jun 04, 2005 11:17 am

http://cultris.ath.cx/

beta