§3.7. Lighting
At any place (room, or inside a container) light is either fully present or fully absent. Inform does not usually try to track intermediate states of lighting, but see The Undertomb 2 for a single lantern with varying light levels and Zorn of Zorna for multiple candles that can be lit for cumulative changes to the light level.
Light can be added to, but not taken away: rooms and things can act as sources of light, by having the "lighted" and "lit" properties respectively, but they cannot be sinks which drain light away. The reason darkness is not a constant hazard in Inform-written games is that rooms always have the "lighted" property unless declared "dark". (We assume daylight or some always-on electric lighting.) A "dark" room may well still be illuminated if a light source happens to be present:
The Deep Crypt is a dark room. The candle lantern is a lit thing in the Deep Crypt.
Hymenaeus allows us to explicitly refer to torches as "lit" or "unlit", or (as synonyms) "flaming" or "extinguished".
For light produced electrically we might want a wall switch, as in Down Below, or a portable lamp, as in The Dark Ages Revisited.
The fierce, locally confined light thrown out by a carried lamp has a quality quite unlike weak but ambient daylight, and Reflections exploits this to make a lantern feel more realistic.
When the player experiences darkness in a location, Inform is usually very guarded in what it reveals. ("It is pitch dark, and you can't see a thing.") Hohmann Transfer gives darkness a quite different look, and Four Stars heightens the other senses so that a player in darkness can still detect her surroundings. The first of the two examples in Peeled allows exploration of a dark place by touch.
It is sometimes useful to check whether a room that is not the current location happens to contain a light source or be naturally lighted. This poses a few challenges. Unblinking demonstrates one way of doing this, so long as there are no backdrop light sources.
Cloak of Darkness is a short and sweet game based on a light puzzle.
See Room Descriptions for an item that can only be seen in bright light, when an extra lamp is switched on
See Looking Under and Hiding for a looking under action which is helped by the fiercer brightness of a light source
See Going, Pushing Things in Directions for making it hazardous to walk around in the dark
See Electricity and Magnetism for batteries to power a torch or flashlight
See Fire for a non-electrical way to produce light
This will be explored more in subsequent examples, but one of the things we can do with carry out rules is extend the function of existing commands so that they do more, or have special effects in specific situations. For instance, suppose we want to have a class of electric light:
This will not affect the behavior of any other devices when switched; it will also not change the way in which switching lights on and off is reported. The player will still see "You switch the sodium lamp on." or the like. In this case that is probably what we want. If we wanted a special way of describing turning on electric lights as opposed to all other devices, we could also add an after rule for the electric light class. Adding this rule to the carry out train does guarantee, though, that in no case will we manage to make the lamp lit without actually making it switched on (or vice versa).
So far so easy. Since we've built the description of its light or darkness into the lamp's description, though, we may want to get rid of the "...is switched on" line that automatically follows when we look at something. For this we do need to borrow from a later chapter:
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This will be explored more in subsequent examples, but one of the things we can do with carry out rules is extend the function of existing commands so that they do more, or have special effects in specific situations. For instance, suppose we want to have a class of electric light:
This will not affect the behavior of any other devices when switched; it will also not change the way in which switching lights on and off is reported. The player will still see "You switch the sodium lamp on." or the like. In this case that is probably what we want. If we wanted a special way of describing turning on electric lights as opposed to all other devices, we could also add an after rule for the electric light class. Adding this rule to the carry out train does guarantee, though, that in no case will we manage to make the lamp lit without actually making it switched on (or vice versa).
So far so easy. Since we've built the description of its light or darkness into the lamp's description, though, we may want to get rid of the "...is switched on" line that automatically follows when we look at something. For this we do need to borrow from a later chapter:
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