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using Manic Miner and Jet Set Willy game engines
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Message: 6239
Author: adban_de_corcy
Date: 30/08/2007
Subject: Re: Tweaking the JSW engine: One for the experts
Gosh! Thanks a lot, John. I will try to it on my own (for a couple of
rooms, only) and if I'm unable to do it, I will ask again. This is
really cool, you could get very interesting and mind-boggling effects
with this patch.
> The instructions are in Z80 assembly language. You can get the patch
> into JSW64 using the hex editor, but you need to have a certain
> familiarity with hex and the way memory is laid out.
>
> Here's how I did this particular patch in the Bathroom, for example.
> I've rather naughtily put the code in the space reserved for the
> guardian table, so any changes to the Bathroom guardians will corrupt
> it and cause a crash. The proper course of action is to reserve an
> area of memory with the memory map tool and use that.
>
> Start with JSW64 (variant W).
> Go to the hex editor. Select bank 3, offset #C210. Enter the following
> bytes:
>
> 16 22 3a 83 85 fe 30 28
> 06 fe 35 28 02 16 1d 7a
> 32 e9 80 c9
>
> Now go to offset #C2FD and enter
>
> 10 80
>
> Then press Ctrl+W to commit the changes, and F5 to playtest. If the
> last digit of the time is '0' or '5' the left exit will lead to the
> Top Landing; otherwise, to the Nightmare Room. Note that this only
> applies to the real Bathroom, not the four fake ones.
>
> Now, how to generalise this?
>
> In the hex bytes above, the second byte on the first row '22' is the
> number of the Top Landing, and the sixth byte on the second row '16'
> is the number of the Nightmare Room. So you can change where things
> lead by adjusting these bytes.
> The second byte on the third row 'e9' says which exit is changed.
> It's 'e9' for left, 'ea' for right, and 'eb' / 'ec' for up and down,
> but I can't remember which way round just now.
> The "10 80" says where the patch is loaded. If, for example, you had
> used the memory map to reserve page CC00, then use "00 cc" instead of
> "10 80", and enter the main body of the patch at #CC00 in bank 0.
>
> To put the patch in a different room, you have to work out where the
> room layout is stored. In JSW64:W, what you do is divide the room
> number by 32. The quotient will be 0, 1, 2 or 3, corresponding to
> memory banks 1, 3, 4, 6 respectively. Then take the remainder,
> multiply it by 512, convert to hex and add #C0FD. That gives you the
> address of the patch vector to change.
> Let's take 'A bit of tree' as an example. This is room 36.
>
> 36 / 32 = 1 remainder 4. The quotient is 1 so the room is in bank 3.
> The remainder is 4, so the address is 4 * 512 = 2048 = #800. Add #C0FD
> to give a room address of #C8FD.
>
> Oh yes. To take a patch vector out again, change the two bytes back
> to 9F 86.
>
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