Predator bug ?

reminisce about bbc micro & electron games like chuckie egg, repton, elite & exileRelated forum: adventures


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sorvad
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Predator bug ?

Post by sorvad » Wed Sep 07, 2005 12:22 pm

Back years ago I used to write my own cheats for various games, usually on the same day I bought the game (I was never any good at playing them properly).

I wrote some for predator, I can't remember specifics but they were probably lives and ammo.

I've not played Predator since then so my memory is a little fuzzy, but I used to be able to play quite a bit into the game and then it would crash, I seem to rememeber a constant sound and I think something was supposed to be appearing at the right of the screen but the game just froze.

I know Peter frequents these forums and wondered if any version got out with a bug in ? It's more than most likley my hack for the cheats caused the problem, but after all these years it's laid in the back of my mind whether some copies got out with a bug in.

I'd have been playing the game on a Master 128.

Did anyone else write there own cheats or am I the only one to go to the dark side :shock:

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Post by PeterScott » Wed Sep 07, 2005 7:01 pm

hi,

mmmm a tricky one - me and superior used to spend ages playtesting stuff to make sure nothing odd could creep through. however predator went from a C64 loading screen and some maps out of c&vg to a finished game on elk and beeb in 6 weeks' flat, so things were compressed somewhat.

having said that, master compatibility and/or cheat stuff seem the most likely causes. my money's on the latter - some infinite lives cheats caused problems as I'd often try and cram data all over the shop...

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Post by Fraser » Thu Sep 08, 2005 10:23 am

Would it not have been useful to have source code in a high level language to do a conversion? Most conversions appear to have been done without it. Spy vs. Spy doesn't even have the same game rules as the original versions. Thrust is one game that does appear to have the same source code on the C64 and Acorns.

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Post by PeterScott » Thu Sep 08, 2005 11:58 am

it would be very sensible to try and use an overarching language to do conversions in. many new games do that, written in C or proprietary languages, and compiled for different hardware.

however it's very inefficient of memory use (not as much of an issue now as it was then) and much, much slower. there's also an argument that if you want to get the best out of a machine, use the hardware to the full and any original features etc, you need to program the bare metal.

my games tended to have a BBC basic core to save time programming them, and every programmer either has access to, or builds, a set of global routines for graphics, sound etc etc.

I was sometimes sent source code - the stuff in C for sim city was v useful - but the big game publishers saw the beeb as a way to earn some quick dosh for no work so I rarely got much. some even didn't send a copy of the game! I was left to fend for myself and rummage through magazines for maps and cheats, play the game and try to reproduce it.

it kinda worked though!

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Post by sorvad » Thu Sep 08, 2005 12:43 pm

Yes, most likely my cheat code. I can't remember details of exactly what I did. But most of my code would simply overwrite the decrement of lives opcode and operand with NOP codes. In 90% of cases lives, ammo etc. were located in zero page for speed, so I used to load the machine code part of a game somewhere into memory and scan it for the code for decrement zero page address. I would write all the ones down it found and then one by one experiment by replacing them with two NOP's at the location found.

Sometimes it was an easy task to do this as the loader would be written in basic, and it would load the machine code and then execute a call, I could then alter the loader to alter the address I wanted before it called the code. Sometimes this wasn't always possible and I would have to resort to other sneaky techniques to do the work. Writing some code that resided in memory somewhere (hopefully not overwritten by the game).

So all my cheat code ever bolied down to usually was a couple of NOP's replacing two bytes of program code. But I may in this case have resorted to something a little more complex which probably caused the problem.

I should still have all this stuff somewhere on disks. I intend to get all my stuff out again in a few months when I've the space, but what are the odds of the disks being readable ?

Thanks for the reply Peter.

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Post by billcarr2005 » Fri Sep 09, 2005 4:16 pm

No, you're not the only one. I worked at removing the protection (for my own enjoyment, not distribution) and then after a days play, I'd see if I could cheat successfully.

Although the Cheat It Again Joe disks covered a lot of games, the later ones weren't covered. Also, sometimes, the loading routine had been altered by transferring to disk, or if the game had been cracked which made the CIAJ cheats work incorrectly.

I wrote a cheat for Predator for infinite lives, energy, grenades, time and bullets. Looking at it now, I've changed the DEC instruction to an LDA rather than NOPping them out - this was due to the DEC being following by a conditional branch, BNE.

I used to look for LDA #&03 or similar for the number of lives, etc and then found where that memory location was being DECremented and work from there.

I used to have occasional problems with roms interfering with some games, but this usually made itself apparent when the game was loading, or just loaded.

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Post by sorvad » Sun Sep 11, 2005 6:42 pm

Sounds much like I did. I often got more enjoyment out of trying to create cracks than playing the game, mostly because I'm not the best gamer around :oops:

I will one day in the fairly near future have access to all my kit and disks again and it will be interesting to see what i did for predator. That's of course if the disks still work, the drive still works and I kept the code !

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Post by Kecske Bak » Mon Sep 12, 2005 6:07 pm

PeterScott wrote:it kinda worked though!
Kinda worked!?!?!

My BBC B still has the dent in it where my jaw dropped when I first saw Sim City.

And the other one when I saw the animation (and the size of the sprites) in Barbarian 2.

You're a genuis Peter!

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