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[File] Jet Set Willy: Mono

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#1 jetsetdanny


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Posted 22 May 2019 - 11:59 PM

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File Name: Jet Set Willy: Mono

File Submitter: jetsetdanny

File Submitted: 23 May 2019

File Category: Jet Set Willy [Patched]

System: Sinclair
Original Author(s): Matthews Smith
Third Party Author(s): John Elliott


"Jet Set Willy: Mono" is a black-and-white variant of "Jet Set Willy" created by tweaking the game engine, thanks to a path written by John Elliott.


To make the items easier to spot, John Elliott he has also written 'companion' patches called "Wobble" and "Jiggle" to make the items move right and back left by one pixel column (Wobble), or up and back down by one pixel row (Jiggle).


The patches can be downloaded from his website.


The "Jet Set Willy: Mono" files currently hosted on World of Spectrum are impossible to complete, because they suffer from the same four bugs which make the original "JSW" incompletable:


1. It is impossible to climb the Banyan Tree (and reach the items in "Conservatory Roof") because of an Earth cell which stands in the way.


2. It is impossible to collect the rightmost item in "Conservatory Roof" because of the adjacent Fire cell.


3. It is impossible to collect an invisible, unreachable item in "First Landing".


4. A faulty arrow in "The Attic" corrupts the game.


Moreover, the files hosted on WoS (and elsewhere) are only the 'basic' version of the game, without either of the companion patches.


The ZIP file of this download contains fixed, completable files of the game in TAP and TZX formats. There are six files altogether: the 'basic' version of "Jet Set Willy: Mono" with items indistinguishable from the other elements in the room, the 'Wobble' version with the items moving sideways, and the 'Jiggle' version with the items moving up and down, each in TAP and TZX formats.


The files were created using John Elliott's JSWED 2.3.7 and Claus Jahn's ZX-Blockeditor. The four official Software Projects POKEs were applied (#A4C7,0B; #DE2C,04; #E9FD,52 and #EB47,00), and the tickable options on the main screen of JSWED were used to create the 'Wobble' and 'Jiggle' variants.


I did mean to make this ZIP available for download here ever since I created an individual page of this version of the game on JSW Central back in March 2018, but it slipped my mind - I've just remembered it was one of the things I planned to do. So here it is :).


Click here to download this file

#2 IRF


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Posted 23 May 2019 - 10:39 AM

I seem to recall that I identified a flaw with the Jiggle patch, which causes the bottom pixel-row of the graphic of an item located in the bottom cell-row of the screen, to spill over into the top pixel-row of the top cell-row on the screen, causing a permanent overwriting of that graphic byte.  Such graphical corruption would be prone to collision with guardians, imperilling Willy.


I identified an easy fix for that flaw, which is detailed somewhere in the Yahoo! Group.


This problem shouldn't affect the games you've just uploaded, since (as far as I can recall) there are no items in the game which are located in the bottom cell-row of any of the rooms.  But if the game were modified to that effect, then the flaw could rear its head.  Though if the graphical corruption were to occur in an air cell in the top cell-row, then it may not be visible unless the Air's PAPER and INK settings are different, such as in a room with a rope.

#3 IRF


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Posted 23 May 2019 - 11:22 AM

Having refreshed my memory, the flaw doesn't work in the way that I outlined in my previous post.  The items jiggle up from their default position, not down (as I had misremembered).


If you have an item in the top cell-row, then it discolours the cell in the bottom cell-row directly below it.  (The top graphic byte of the item is interpreted as an attribute byte, overwriting the primary attribute buffer.)


This is normally disguised, because in Mono mode, everything is overwritten in black-and-white anyway, even though technically all the room blocks remain retain their colour attributes (upon which Willy's interaction with them is based).


So it's normally a harmless effect (an 'invisible visual glitch'!)  But if the top pixel-row of an item's graphic definition matches the attribute byte of a defined room block type, then other effects can occur.


In the attached test file, I have defined an item shape in West Wing and added some items in the top and bottom cell-rows.  There is no collision with the vertical guardian, as I had initially expected, but there are a couple of effects:


(1) If you try to walk down to the bottom of the ramp, you will notice that Willy is killed for no apparent reason.  The item's top pixel-row is entirely filled in - all eight pixels are on; it holds the value #FF - this matches the defined attribute byte for Fire cells, so there are two invisible Fire cells created in the bottom cell-row;


(2) The bottom two items disappear after two time-frames - because the #FF Fire cells hold white INK, collecting the items.  (The slight time delay occurs as the secondary buffers take a while to catch up with the corruption of the primary buffers.)

Attached Files

Edited by IRF, 23 May 2019 - 11:23 AM.

#4 jetsetdanny


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Posted 25 May 2019 - 04:12 AM

Very interesting comments, Ian - thanks!  :thumbsup:

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