|The Clock Tower|
The Clock Tower
If you think about it, the Missed Island clock tower puzzle is just another version of the combination lock. This time, there are two "digits", each with 12 possible settings: one with hours from 1 to 12, the other with minutes from 00 to 55 in increments of 5.
The clock tower in Myst is an analog clock, and in fact I could have done an analog version in a manner very similar to the existing combination lock puzzle. The hours indicator would be textured with a strip of 12 clock faces, with the hour hand in different positions. The minutes indicator would be a transparent strip of minute hands in different positions, overlaying the hours indicator. The only problem is the 128 pixel height of textures: each clock image could be no more than 10 pixels high. This would have been more of a wristwatch than a clock tower...
So, I decided to implement a digital clock instead, since that could
be made as large as needed. (Not to mention the laugh value of a digital clock
tower. It would have been even funnier if an idea of mine had proved
practical: have the clock initially be flashing 12:00,
like a VCR whose owner doesn't know how to set its clock.)
The clock display itself contains no moving parts: it's all done with lights. I used a custom texture (actually, parts of the same texture containing the combination lock digits) for a very realistic-looking digital display. It would also be possible to build digits out of existing textures: Mike Trinder's Gemini Station map for Marathon 2 has a good example of this, using the lava texture. However:
Here is a sample clock digit for you to examine (Editors Note:
in the demo map it is " just prior to this terminal"
- gls). It is in a slightly incomplete state, so that you can
see it better: the polygon floors and ceilings have not been
blanked out, and the digit still has a lot of depth to it (the
polygons are easier to select in this state, but should be "flattened"
It's obvious that the two segments composing the tens-of-hours
digit can use the same light. But would you have guessed that
the top and bottom segments of the tens-of-minutes digit can
also be wired together (light 31)? That digit only displays numbers
from 0 to 5,
which coincidentally all have the top and bottom segments in
the same state: only the number 7
has them different. The ones-of-minutes digit is the simplest
of all, since it never displays anything other than 0
Obviously, most of the individual hour and minute numbers require more lights to be turned on than the two that can be controlled by a single platform. This is not a problem...
...since the platform can control another platform (via the Activate Adjacent On Activating flag), which can control two more lights. Either platform can control yet another platform, so an arbitrary number of lights can be activated by a single platform activation.
The ideas developed so far would be sufficient to make a working clock, but it would be horribly inefficient. Consider the implementation of hour 8: the digit 8 has seven lit segments, so four platforms would be needed to activate all the necessary lights (one platform would have the same light for both floor and ceiling, to avoid affecting an unrelated light). It would take about 32 platforms (half the number available!) just to implement all twelve hours, never mind the minutes. So back to the drawing board...
The design can be simplified by a process best described as "factoring out common terms". It is possible to identify individual lights, or pairs of lights, that are activated by many different hour/minute settings. Instead of independently activating these lights for each setting, have a single platform that activates each common light or pair of lights. Each setting that uses common lights would have its own platform adjacent to the appropriate common platforms. Note that the common platforms cannot control any further platforms, since they would also activate ALL of the platforms adjacent to them.
This scheme requires extensive (possibly illegal) use of 5D
space in order to have everything adjacent to the proper platforms.
Not a problem, since the player has no access to the area.
The final optimization of the clock was based on the following observation: most of the digit segments are lit most of the time (in fact, only the digits 1 and 7 have less than half of their segments lit). Therefore, it is better to have those lights ON by default, and only turn them OFF in the few situations that need to. Since platforms don't have a Deactivate Polygon Lights On Activating flag, this requires lights wired backwards (0% intensity when active, 100% when inactive).
After months of
research and extensive simulation done on a Cray XMP supercomputer
(well, I might be exaggerating just a bit), I came up with the
following set of segments that should be lit by default: 9:30. This is what you'd see on the tower
in Forge, where the shooting galleries are inoperative: in the
actual game, the Enforcers in the galleries will be triggered
well before your first sight of the clock tower. (The Visible
Trigger polygon that starts the clock is between the library
and fountain: the trigger message travels down to the clock tower,
through a 5D space polygon behind the tower, to the galleries
north of the island. There are a LOT of Zone Border polygons
used to define this path. You can't see the connecting 5D polygon
on your automap because the entrance to it is sealed off by a
solid, nontransparent line.)
Gaze in stunned disbelief at the implementation of the most complicated Marathon mechanism ever built...
The minutes portion is similar in design, although it didn't work out quite as efficiently (it required 12 platforms, one more than the theoretical minimum).
The final piece of the puzzle is a 3-input AND gate, using
the liquid-controlled version, that triggers the bridge and clock
tower door. The 3 inputs are the proper hours setting, the proper
minutes setting, and the rightmost switch on the clock setting
CLOCK TOWER PUZZLE
|Download Jason Harper's prize winning map, "Missed Island". This is not only a playable puzzle map, it is also an example map and tutorial. This tutorial was taken from that map. The tutorial on this page can be reached by "warping" to level 3. You must use the provided shapes file to make any sense of this map.|