Phantasmal Site > Design > MUD Visibility

MUD Visibility and Perception for Phantasmal

Visibility should be important to Phantasmal -- light levels, lines of sight, ability to notice details. These things are linked.

Most MUDs place limited importance on visibility because allowing very perceptive characters to notice vast amounts of detail gets very distracting very quickly. In, say, a forest setting, there are simply too many things going on. The challenge, then, is not to determine whether a character can detect particular things, but to reduce the amount of detail coming in to a manageable level. Phantasmal will eventually attempt both tasks.

Detecting Detail

Detecting detail is a matter of determining what the player can determine about the environment around him. There are many events occurring constantly -- mobiles move, objects are gotten and dropped, mobiles speak or fidget. The question, then, is which ones the player or character can detect, and how those events appear.

Lines of sight are among the simplest ways to manage this -- in a given location, there is effectively a list of other locations that are visible. Since it isn't really possible to tell where a character is within that location (Phantasmal doesn't use a coordinate grid), we must simply assume that character can potentially see events in every location on the list of visible locations. Audible locations are similar -- a character can hear events occurring in any location on the "audible list", potentially.

Other senses -- taste, touch and smell -- are all localized. A character can only taste, touch or smell in his current location, or one containing it. Smells can propagate, but a character cannot instantaneously detect a smell in another location.

Locations that are visible or audible from the current location will still (usually) transmit sights and sounds less well than if the character were standing in that location. Each will effectively have a percentage of the visibility/audibility that is actually transmitted. Note that in the case of visibility, this is not transitive -- you can't see a location that is visible from another location automatically. Otherwise you could always see around corners! While it might make sense to propagate sounds automatically (and at some level, this will need to occur), Phantasmal will internally simply use an audible-list just like the visible-list since all of this information can be determined when the objects are connected by exits.

Objects in Phantasmal can have alternate low-light descriptions. These are usually part of the markup of the object description, though they can be detected programmatically if necessary. These are not specifically low-light descriptions, but are rather low-detail descriptions. For instance, an object seen through fog, or in darkness, or far away, or without glasses, would use this description. Thus a tall, brown-haired man might be "a man" or "somebody tall" at a distance. Similarly, to recognize another character you must be close enough and in good enough lighting and visibility to know who you're looking at.

Conceivably, this could be used to "mis-recognize" people for mysterious, dramatic or comedic effect. That's longer term, though.

And finally, some objects require appropriate skills, abilities or characteristics to recognize. For instance, you might need to be an Angel or Demon to recognize a "tin can of mighty slaying, blessed to the Lord", or have a good grasp of philately to notice a valuable misprint stamp on a postcard. Objects in the class heirarchy can mark themselves as requiring particular skills or attributes to recognize, and players without those skills or attributes will simply see the object as the next-most-general in the heirarchy -- the valuable misprint stamp would be simply a stamp, the blessed tin can would be simply a tin can, or garbage.

Managing Detail

The most difficult part is not creating all of this detail, but keeping the player from being overwhelmed. Phantasmal eventually hopes to have several mechanisms for this -- Object Grouping, Event Grouping, Perceptual Thresholds, and Automatic Detail Adjustment.

Object Grouping

Object Grouping is described in its own separate document, and relies heavily on the class heirarchy.

Event Grouping

Event Grouping is the idea that many events occurring simultaneously can be grouped into a single message. For instance, twenty balloons popping at once (perhaps a result of an air pressure change) might say that "a large cluster of balloons all pop at once" rather than having twenty separate messages about the balloons popping. The trick is to detect that these events are occurring roughly simultaneously.

Similarly, events of different types could be grouped in essentially the same way -- the sound of a cannon roaring, the smell of gunpowder and a small tremor in the earth could be grouped together into "a cannon fires nearby! It's incredibly loud!", but a character farther away would only feel the tremor, and a deaf character in the dark might only smell gunpowder. This combination, if implemented well, could also allow certain deception to occur. For instance, a spell that caused a tremor in the earth could be masked by cannonfire, or a magically-muffled cannon could be used to convince nearby enemies that such a spell had been cast (but the smell might give it away!).

Obviously there's a limit to what events can be grouped, but in many cases (such as the cannon above), the events could be dispatched all at once, specifically marked as being mergeable. Characters that could detect all of the events would see them as merged, while characters that couldn't perceive one or more would see only the relevant parts of the event. As the grouping system got better it could notice events like separate balloons popping independently and group them, or group all sounds or smells together if they occur quickly, and so on.

More difficult is grouping sequential events that are related. For instance, sharpening a sword might involve taking out a whetstone, oiling it, using it many times and then putting everything away again. It isn't necessary to give continual updates on the status of the activity unless something interrupts it. So the events should be grouped as a sequence, so that if all goes well the player will see only " you begin sharpening the sword" and, eventually, "you finish sharpening the sword". However, if the whetstone oil contains nasty grit which prevents you from using it, you might see:

  > sharpen sword
  You take out a whetstone from your backpack.
  You take out whetstone oil from your backpack.
  You pour the whetstone oil on the whetstone.
  Yuck!  Your whetstone oil is black and gritty, and now your
        whetstone is all dirty and greasy!
  > swear like a golfer

Perceptual Thresholds

Perceptual Thresholds are a name for preventing a character from detecting things that are too far apart in intensity. Thus, it's very difficult to smell something subtle when there's red herring in the air. It's hard to see the fine detail of a Ming vase when you're blinded by a flash of magnesium powder burning, and when a cannon goes off, it's hard to hear yourself think :-)

Mathematically, this means that any character, for a given sense, will have a dynamic range of detail. For instance, the character will have a perception for smell, which determines how minute an odor can be detected or how much can be found out about an odor, but then will also have a range of smells available, so a high-dynamic-range smeller (like a bloodhound) might be better at tracking traces of an odor past a very powerful other odor like pickled fish or rotten eggs. The higher the dynamic range, the more powerful the interfering odor can be or the more miniscule the traces of the other odor can be.

Due to Perceptual Thresholds, you might think it would be impossible to find small things for the sheer rush and bustle of large things. And that would be correct. Therefore, in implementing commands like "search", it is important to tune the Perceptual Thresholds appropriately. Essentially, a search command will broaden a character's dynamic range temporarily (and quite possibly increase his or her basic perceptiveness as well) in return for the character staying in one place and taking no other actions.

Similarly, it might be a good idea to have a "watch" or "concentrate" command so that the player can pay attention to a particular thing specifically, no matter what distractions are attempted. This would be useful to guard an item, to foil a thief's attempts to hide, or to notice when a particular signal is given.

Automatic Detail Adjustment

When a character has a vast amount of information coming in, even if none of that information is especially intense (as in Perceptual Thresholds above), the least noteworthy (probably approximated as the least-perceptible by default) will be lost until a reasonable amount of information is available. For instance, a character running rapidly through the woods will probably get shorter room descriptions (cutting out less perceptible or noteworthy bits) and won't see the ants crawling along or hear the birdsong -- those things aren't as noteworthy as the basic room description, and the information is simply coming in too fast.

If the character is perceiving many tiny events like the movement of ants and distant birdsong, then a few more obvious nearby events like the motion and sound of a river will drown out the smaller events automatically via Perceptual Thresholds (see above). However, if the forest is relatively quiet or the perceiver has a wide dynamic range, then all events will be at a fairly similar perceptual level and all will potentially be perceptible.

When a large number of events are all perceptible at once and Event Grouping (see above) is unable to reduce the amount of detail to something manageable, it becomes necessary to give the player a temporarily-reduced dynamic range of perception, just to reduce the flow of incoming information. Essentially, less perceptible events are dropped from the flow of information to the player, but not necessarily to the character. A character will still usually react to the stimuli in the normal way. However, most characters' reactions to most stimuli is to simply observe and ignore.

The subtlety about this reduced perceptual range is that events will continue to come in at different times, and what events cannot (usually) be predicted in advance. Therefore, the interface will need to detect when a player is overloaded and throttle back the character's effective dynamic range of perception until the number of events is again manageable. This is conceptually similar to old-style MUD commands like "verbose" and "terse" for room descriptions. The player is requesting a level of detail, and the interface adjusts itself to provide approximately that level of detail.