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Message: 5797

Author: andrewbroad

Date: 13/04/2006

Subject: Re: Willy's behaviour on conveyors during the toilet-run

 

Daniel wrote:

I was extremely upset by Andrew's message # 5784 and the
suggestion that:

1. "Jet Set Willy: The 2005 Megamix" is not toilet-completable;
2. A game can run differently on different emulators;
3. The emulator I normally use (ZX32) does not emulate ZX Spectrum
faithfully.

I apologise for any upset caused. It just never occurred to me that
different right-keys would behave differently during the toilet-run!
However, I /have/ experienced unfaithful emulator-behaviour in the
area of keyboard-handling:

1. The old emulator that I used on my Mac, MacSpectacle 1.8.2, can't
recognise more than two keys being pressed at once.

2. RealSpectrum behaves differently from a real Spectrum in JSW's
WRITETYPER mode. Keys '1' to '6' ('1' to '8' in JSW128) form a room-
number in binary, but some combinations don't take you to the room
they're supposed to. And the set of WRITETYPERable rooms are
different on a real Spectrum and in RealSpectrum!

JSW48 rooms which are NOT WRITETYPERable:
- real Spectrum: [18,19, 22,23, 26,27, 30,31, 34,35, 38,39, 42,43,
46,47,48,49, 52,53, 56,57, 60,61]
- RealSpectrum: [24-31, 58-63], i.e. RealSpectrum cannot
recognise '4', '5' and '9' being pressed together (in fact my PC
makes a weird beeping noise whenever '4', '5' and '9' are pressed
together).

I also found out, Andrew, that you usually play using the "P"
key for "Right", and "O" for "Left", isn't that true? :-)

Yes - I am right-handed, so I always use 'O' for left (index-finger)
and 'P' for right (middle finger).

For jumping I usually use Space (thumb), and sometimes Caps-Shift
(little finger) - although I have to be careful not to use them
together as this resets the game! ;-)

Here's what I found out - and it's very interesting! :-)

I.

[For all of the features mentioned in this section please discard
the key "P" - I am NOT referring to it. If I mention the "Right"
key, I mean: "W", "R", "Y", "I" and the cursor key, and if I
say "there is no way" to do something, this may exclude holding
"P".]

Pressing 'P' to stop during the toilet-run is just as valid as
pressing 'W' (or whatever) to move forwards on a right-conveyor.

In fact, from my perspective, 'P' is *the* right-key, and 'W' is
just a special key that I must use if I get stuck on a right-
conveyor during the toilet-run.

So here are the general rules of Willy's behaviour on conveyors
during the toilet-run:

- Willy runs smoothly over the left-, off- and sticky-conveyors.
There is no way to stop him there.

Except by pressing 'P'.

Unfortunately, if you stop on a left-conveyor, you cannot move on -
not even by pressing 'W'! :-(

Off-conveyors behave exactly the same as Water-cells in all
circumstances (cell-behaviour does not include conveyor-animation).

Running over a sticky conveyor during the toilet-run is like walking
over a right-conveyor (or walking right over a sticky conveyor) in
normal mode - you cannot stop, not even by pressing 'P'.

These are interesting extensions to the field of conveyor-mechanics,
and there's no reason why a patch-vector shouldn't put Willy in
toilet-run mode (POKE 34271,2) temporarily (perhaps on a per-room
basis, using POKE 34271,0 to restore him to normal mode in all other
rooms).

I might do that in Advanced MM/JSW Trainer, so that the player can
practise toilet-run mechanics without having bed-completed the game.

- Willy stops on a right-conveyor, at the edge of it. Then you can
nudge him rightwards by pressing the "Right" key - he goes to the
right step-by-step (or two-steps by two perhaps, because it's
still double speed). You can also turn Willy around - by pressing
the "Left" key - but you cannot move him to the left.
A right-conveyor IS a good way to stop Willy during the toilet-run
in order to introduce challenges which involve avoiding guardians.

But pressing 'P' is an even better way.

The above behaviour patterns are probably true also with conveyor-
ramps. I did not test this thoroughly, I have just checked that
Willy stops on a right-conveyor (and can be moved on with
the "Right" key).

They will be. In JSW48/128, the test for Conveyor's colour-attribute
under Willy's feet is independent of the test for Ramp's colour-
attribute.

And I'd be amazed if JSW64's Conveyor-Ramps were any different,
though I must confess that I have neither tested nor disassembled
JSW64 to verify this.

II.

The peculiar behaviour of the key "P":

- When you hold "P" and press one of the "Left" keys, Willy turns
around (but won't go left).

Which could be useful for avoiding a VG in a pixel-perfect situation.

- When you hold "P" and press one of the other "Right" keys, Willy
behaves similarly to being on a right-conveyor - he moves
rightwards every time you press another "Right" key (while holding
"P").

The above shows, IMO, that pressing "P" during the toilet-run
causes EXACTLY the same effect as if Willy were on a right-
conveyor.

Fascinating.

If you hold the key "P", it doesn't matter whether you are running
over Water or Earth - the effect is the same.

In JSW48/128, the code to check what Willy's standing on (#8E36)
works like this:
1. If there is a Fire-cell under Willy's feet - either in his left
cell-column OR his right cell-column, then go to Step 4.
2. If there are two Air-cells under Willy's feet - in both his left
cell-column AND his right cell-column, then go to Step 4.
3. Willy is standing, so go to Step 7.

[Falling]
4. (#8E62) If Willy is jumping, then go to #8FBC to handle
horizontal movement.
5. Code for falling...
6. Return from Willy's movement subroutine (do not continue to Step
7).

[Walking and Conveyors]
7. (#8ED4) Set the conveyor-mask to recognise the left- and right-
keys.
8. If there is a Conveyor-cell under Willy's feet, then set the
conveyor-mask to ignore the left-key (if it is a right-conveyor),
the right-key (left-conveyor) or both (sticky conveyor).
9. Detect keypresses, using the conveyor-mask to decide what to
ignore...

In short, anything other than Air or Fire is a stand-onable cell,
which may have conveyor-behaviour or not.

JSW48/128 uses the colour-attribute of a cell to determine its
behaviour (i.e. its effective cell-type), so cell-types can be
combined by giving them the same colour-attribute.

So in the above, where it says "if there is a X-cell...", this
actually means "if there is a cell that has the current room's
colour-attribute for X..."

It may help to understand that JSW48/128 constructs the secondary
attributes-buffer from the actual room-definition. Each cell in the
secondary attributes-buffer is simply a colour-attribute, and it is
these colour-attributes which determine cell-behaviour - not the
cell-types in the actual room-definition.

This whole thing is very interesting, because it means that "P" is
a very special key for the toilet-run. I was unaware of its
peculiar behaviour (which includes stopping Willy almost
anywhere), because I always play using "Q" for "Left" and "W" for
right (and usually "Space" for jumping). On the other hand Andrew
apparently uses "O" and "P" for left and right, respectively, and
that's why he wasn't aware of the "normal" behaviour of the other
"Right" keys.

It's a good job you realised that, or we'd probably both think the
other was mad by now! ;-)

So, to sum up, I can say with relief that "JSW: The 2005 Megamix"
IS PERFECTLY TOILET-COMPLETABLE :-) . I would also kindly suggest
that placing a right-conveyor on the route of the toilet-run might
be one of the features to take into account for the Advanced
Trainer (as well as using "P" to stop Willy elsewhere).

I plan to include all the quirks mentioned in this and Message 5787
when next I update my Advanced MM/JSW Trainer page (except off-
conveyors, which actually have no conveyor-behaviour at all).

At this point I see no need for further experiments with various
emulators, as I think they all behave in the same way. However, if
somebody should want to experiment, I have uploaded two files into
my folder ("Daniel Gromann"), called "ConvExp1.z80" and
"ConvExp2.z80". The first one lets you see easily what happens
on all four kinds of conveyors plus when falling on a right- and
left-conveyor, and the other one lets you see what happens when
you fall on an off- and sticky-conveyor.

ConvEx2.z80 is redundant to me, for I simply used runtime POKE
34271,0 to get past "Falling on LEFT-conveyor" and "Falling on
STICKY-conveyor" (and POKE 34271,2 once past the respective
obstacles).

ConvEx2.z80 would also be redundant if you used one of the three
methods for giving the player a choice of ways during the toilet-run:
1. Rope (as in _The 2005 Megamix_)
2. Vertical lift (press 'P' to stop)
3. Horizontal lift (keep stopping and starting to stay on the lift!)

Also, for the sake of completeness, I should say I have tested the
above-mentioned phenomena on the following emulators:

- ZX32 v. 1.03.98.0211 and v. 2.00.04.04 (beta)
- Real Spectrum v. 0.97.26
- Warajevo v. 2.51
- Spectaculator 6.10
- X128 v. 0.94
- MESS 0.104
- ZXSpin v. 0.504
- Spec256 v. 1.2
- Multi-machine emulator v. 1.30b
- EmuZWin v.2.7
- Aspectrum 0.1.8
- Es.pectrum v. 06b
- GLECK 0.0.5
- YaSE 2 v. 0.4.1
- Z80 v. 4.00

Good grief! There's dedication.

So I think that the picture is clear and we know exactly how Willy
behaves on various types of conveyors during the toilet-run and
how the player can influence it. I guess that now it is up to you,
technically-minded ones, to explain WHY that happens and why "P"
plays such a special role... :-)

I guess it's because Step 9 above (#8EFA) works roughly as follows:
9.1. Read Port #DFFE (keys 'Y' to 'P') and apply conveyor-mask.
9.2. If Willy is in toilet-run mode, then modify the conveyor-mask
to ignore left-keys in the following steps.
9.3. Read Port #FBFE (keys 'Q' to 'T') and apply conveyor-mask.
9.4. Read Port #EFFE (keys '6' to '0') and apply conveyor-mask.
9.5. If a Kempston-joystick is present, then read Port #001F and
apply conveyor-mask.
9.6. A keypress resets the pause-counter.
9.7. Modify the byte at #85D0 (Bit 0: Willy's direction; Bit 1:
horizontal movement on/off) according to what was pressed, so that
it will be acted on in the next time-frame.

So we see why the right-keys 'Y', 'I' and 'P' /could/ be treated
differently - it's because they are detected before Step 9.2.

So why is 'P' a special case? The explanation involves a lot of low-
level bit-twiddling, I'm afraid, so here's the gist of it. If 'P' is
pressed, then the LSb of Port #DFFE will be read as 0. And if Willy
is in toilet-run mode, then a 1 gets shifted into the accumulator
and XORed with that 0, giving a LSb of 1, which disables moving to
the right.

--
Dr. Andrew Broad
http://geocities.com/andrewbroad/
http://geocities.com/andrewbroad/spectrum/
http://geocities.com/andrewbroad/spectrum/willy/

 

 

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