Exolon Crashing Bug Fix (when you jump too high)

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Ast A. Moore
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Exolon Crashing Bug Fix (when you jump too high)

Post by Ast A. Moore »

Woot! Finally managed to get to the bottom of this nasty bug. Visually, the solution is a tiny bit inelegant—the guy bounces slightly off the top of the screen—but, hey, the game no longer crashes! :D

Up for grabs at the usual place.
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
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Alessandro
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Re: Exolon Crashing Bug Fix (when you jump too high)

Post by Alessandro »

I never stumbled into this bug actually - but thank you for fixing it :D
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Ast A. Moore
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Re: Exolon Crashing Bug Fix (when you jump too high)

Post by Ast A. Moore »

Yeah, I thought it was pretty rare myself, but then I noticed I could trigger it every time on a multitude of screens (including some of the very early ones):

Image

And my fixed version:

Image
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
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Pegaz
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Re: Exolon Crashing Bug Fix (when you jump too high)

Post by Pegaz »

This is great, I really like your fixes.
Did you possibly try to analyze Dynamite Dan II and missing ending issue?
We discussed this on wos long ago, but still i'm not sure why the game can not end in the way described in the manual.
After all, it might be good to make at least a congratulations message if there was any free space at all.
Would it be possible to do such a fix?
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Ast A. Moore
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Re: Exolon Crashing Bug Fix (when you jump too high)

Post by Ast A. Moore »

Pegaz wrote: Sat Feb 02, 2019 11:41 am This is great, I really like your fixes.
Thank you!
Pegaz wrote: Sat Feb 02, 2019 11:41 amDid you possibly try to analyze Dynamite Dan II and missing ending issue?
We discussed this on wos long ago, but still i'm not sure why the game can not end in the way described in the manual.
After all, it might be good to make at least a congratulations message if there was any free space at all.
Would it be possible to do such a fix?
No, I haven’t looked at it. I didn’t play it much back in the day, so I’m not familiar with it.

I generally try to make minimal changes to the originals and—whenever possible—preserve the original loaders (which is particularly easy with some of the strongly encrypted ones). Often, there’s is barely enough room for even a simple fix. Exolon is a good example, actually. It’s very tight and I barely managed to find a few spare bytes.

But I’d be happy if someone pointed me in the direction of some compendium of known bugs in Spectrum games. The games that I provide fixes for are for the most part the ones I discovered personally.
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
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Pegaz
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Re: Exolon Crashing Bug Fix (when you jump too high)

Post by Pegaz »

It took me a while, but I found an interview with the author (Rod Bowkett) in the RetroGamer magazine (pages 56-61):
https://computerarchive.org/files/compu ... ue_062.pdf

Basically, the problem is that after the last eight level, theres no secret Blitzen lab, where you need to set up explosives (time bomb), as it says in the instructions.
Instead, the game returns back to the first level, without any congrats message or anything else.
I can only assume that its a lack of memory, but Rod Bowkett says he is sure he wouldnt leave the game unfinished in such a way.
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Ast A. Moore
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Re: Exolon Crashing Bug Fix (when you jump too high)

Post by Ast A. Moore »

Pegaz wrote: Sat Feb 02, 2019 3:02 pm I can only assume that its a lack of memory, but Rod Bowkett says he is sure he wouldnt leave the game unfinished in such a way.
Right, but the article also says:
Since speaking to Rod, a disassembly of his code has been posted on the World of Spectrum forums and it confirms that there is indeed no proper ending to the game.
Still, an interesting case. It’s possible that he accidentally sent in the wrong version (unfinished).

EDIT: Just took a very superficial look at the game, and boy is it packed! I don’t think there’s room for adding extra game logic.
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
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hitm4n
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Re: Exolon Crashing Bug Fix (when you jump too high)

Post by hitm4n »

Still, an interesting case. It’s possible that he accidentally sent in the wrong version (unfinished).
So... Where is the RIGHT version !!
I don't have anything cool to put here, so i'll just be off now to see a priest with yeast stuck between his teeth and his friend called Keith who's a hairpiece thief...
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Pegaz
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Re: Exolon Crashing Bug Fix (when you jump too high)

Post by Pegaz »

hitm4n wrote: Wed May 05, 2021 8:10 am
Still, an interesting case. It’s possible that he accidentally sent in the wrong version (unfinished).
So... Where is the RIGHT version !!
That's the good question, but I'm not sure even Rod knows the answer, now.
This is one of the best Spectrum games ever in every sense and honestly, I would be more happy to find the complete version, than the discovery of Mire Mare.
I'm not sure if theres an disassembled version, which would help to find out, if theres a trace of the Blitzen lab or if there was no space at all...
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