Graphical Errors on 3D games

Software related questions

Graphical Errors on 3D games

Postby MadKingCorduroy » Mon Oct 13, 2014 11:41 am

Hello guys, I have a PCjr fully decked out with 640k of ram running DOS 1.0 and my machine is totally stock. However when I run games that draw 3D graphics the screen turns into garbage, the runs it's just that the graphics glitch out and make it unplayable.

The games I have tested are Battlezone, Elite and Arctic Fox. At first Elite seems to be playable but when you go out into space and fire your weapon the graphics all turn to "garbage" and make the game unplayable.

Is there any work around for this? I've heard about a tandy graphics mod, would that help with software compatibility?
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Re: Graphical Errors on 3D games

Postby Trixter » Mon Oct 13, 2014 12:36 pm

MadKingCorduroy wrote:Hello guys, I have a PCjr fully decked out with 640k of ram running DOS 1.0 and my machine is totally stock. However when I run games that draw 3D graphics the screen turns into garbage, the runs it's just that the graphics glitch out and make it unplayable.


It's hard to diagnose without a picture or two, but what I think you're describing is: When the game switches to graphics mode, it displays something that looks like graphics but is scrambled. If that's the case, then what you're seeing is a PCjr incompatibility that cannot easily be fixed. Games made before the PCjr sometimes switched into and out of text/graphics mode by banging on the graphics hardware registers directly. This worked on CGA, but the registers do slightly different things on PCjr and so you get "garbage" displays. If this is what you are seeing, the Tandy graphics hardware mod will not help; all that does is mod the PCjr so that Tandy 16-color games display without artifacts.

The issue you're seeing isn't related to 3D graphics; it is just a coincidence given the programs you picked.

Some games had patches that fixed them for PCjr; others might be able to be hacked if they are simple enough programs. I know that there was a Tandy-specific version of Arctic Fox that used its 16-color mode; you should try that. (You'll need DOS 2.x or higher though, using JRCONFIG as a memory driver with these settings in config.sys:

device=jrconfig.nrd -t3 -v64

This allocates 64KB of lower RAM for graphics, allowing for two 320x200x16 video pages, which is what some Tandy games used. This is not a guarantee that Tandy 16-color games will work, but it can help with a few of them. The hardware Tandy mod can help with many more.)

If you try some other games and are still seeing glitches, post a photo or two so we can see what it looks like. If there is a game that you absolutely MUST play on PCjr, let me know and I can try to hack it so that it works.
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Re: Graphical Errors on 3D games

Postby MadKingCorduroy » Mon Oct 13, 2014 5:31 pm

Wow thanks! I appreciate the offer to modify an executable for me but I guess there isn't anything I absolutely need to run on the PCjr, it's merely one of those things where it would be nice since I don't have any other proper DOS only computers. That and it was always my intention from day one to be able to run the DOS version of Elite on my PCjr. But I guess I should be happy that there are so many games that do work flawlessly on this computer.

Btw speaking of compatibility how hard is it to get a serial mouse working when you have the adapter cable?
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Re: Graphical Errors on 3D games

Postby Trixter » Mon Oct 13, 2014 6:26 pm

Don't give up hope so quickly; I might be able to hack Elite to work on PCjr. First of all, try the version I'm familiar with: Grab ftp://ftp.oldskool.org/pub/misc/xtfiles.rar and look in games\ACTION\ELITE and try to run that. If that displays junk instead of graphics, let me know.

As for a serial mouse, I just used the PCjr serial port adapter cable and connected an old 9-pin serial mouse to it, then ran the CuteMouse (ctmouse.exe) mouse driver. Worked like a charm.

BTW, if you want to have some fun with your PCjr, try these lists of games; they should support the special 3-voice audio, the 16-color graphics, or both:

http://www.mobygames.com/browse/games/p ... c,2/ti,31/

http://www.mobygames.com/browse/games/p ... c,1/ti,32/

http://www.mobygames.com/browse/games/d ... i,31/1984/

http://www.mobygames.com/browse/games/d ... i,31/1985/

http://www.mobygames.com/browse/games/d ... i,32/1984/

http://www.mobygames.com/browse/games/d ... i,32/1985/

...and a few others after 1985 too, like Silpheed, Thexder, and most Sierra AGI games.
You're all insane and trying to steal my magic bag!
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Re: Graphical Errors on 3D games

Postby MadKingCorduroy » Mon Oct 13, 2014 7:00 pm

Wow thanks again! Haha! You rock, I'll have to try that version of elite but I just realized I'm actually using DOS 2.1 which was a bootleg copy from the previous owner so I should be set there. Currently I've been playing the crap out of Empire : Wargame of the Century, that game is just TOO COOL. I had no idea such an advanced strategy game existed during the 80's.
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Re: Graphical Errors on 3D games

Postby Trixter » Tue Oct 14, 2014 9:26 am

I agree, that game was one of the prototypical games of its genre.

Whenever you get a chance, snag ftp://ftp.oldskool.org/pub/misc/Softwar ... ITELJR.EXE and see if it works on your PCjr. I disabled the writes to ports 3d8 and 3d9 as those are not supported by the PCjr. The palette will be wrong and the cursor will be blinking, but it should run. If it runs for you, let me know and I can try to patch it further to restore the cursor and palette.

(edit 11:33am, missed a few references, got those too; download again if you grabbed it before now)
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Re: Graphical Errors on 3D games

Postby MadKingCorduroy » Thu Oct 16, 2014 8:29 am

Ok I just tried your hacked version and it suffered the same problems. :(

However, this time I recorded exactly what happens when I try to play it on my PCjr. Here is the video: https://www.youtube.com/watch?v=lvR_JOIjzCw

I appreciate your help! Thanks again! :D
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Re: Graphical Errors on 3D games

Postby Trixter » Thu Oct 16, 2014 10:28 am

That was interesting! One of two things is happening:

1. Based on the timing of when the glitches occur, I must have missed a palette and/or background color setting that writes to the wrong port. I'll go back and check.

2. Based on what the glitch actually looks like in the video (vertical blank bars), there is a 1% chance that the game is located in, or writing to, RAM below 128KB. Your boot disk should have a memory manager that enables memory above 128KB and also prevents programs from running below 128KB, so if you booted a vanilla DOS disk without one, that might be the culprit.

Scenario #1 is much more likely so I'll set up my PCjr tonight and make sure I get it working before updating the download. If there is room in the binary, I'll try to replace what I take out with BIOS calls that should work on PCjr. (And PC too)
You're all insane and trying to steal my magic bag!
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Re: Graphical Errors on 3D games

Postby MadKingCorduroy » Thu Oct 16, 2014 12:35 pm

Glad you liked the video. lol
The program itself requires 512k of RAM to run so I suppose I could tell it to run above the 128k but I'm really not sure what I'm looking for in terms of program to manage the memory. What was common? So I can see if this diskette has it.

Also it's kinda weird but it almost looks like the lines for the graphics are displaced one over, it's noticeable when my ship explodes because you can see movement on the left where there should only be the border.

Thanks again! This is really awesome!
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Re: Graphical Errors on 3D games

Postby Trixter » Thu Oct 16, 2014 1:13 pm

MadKingCorduroy wrote:The program itself requires 512k of RAM


No, MobyGames is wrong on that aspect. Elite Gold requires that much, but the version you're running doesn't seem to take up more than 128 K.

I'm really not sure what I'm looking for in terms of program to manage the memory. What was common? So I can see if this diskette has it.


Look at config.sys to see if there is a device= line referencing a PCjr memory manager. If there is, you're good. (I would also look at autoexec.bat and stop loading that print spooler I saw in one of your earlier videos.) If you don't see a memory manager, grab JRCONFIG and configure it similarly to how I referenced earlier in this thread. You can grab it from Mike's site.

I should have a chance to hack it more tonight.
You're all insane and trying to steal my magic bag!
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