10.2. Liquids

| Chapter 10: Physics: Substances, Ropes, Energy and Weight |

| 10.2. Liquids

Liquids are notoriously difficult to simulate well. A fully thorough approach consumes endless storage and can be very finicky to write and keep realistic. It is essential to decide what aspect of a liquid's behaviour is actually needed in a given story, and to simulate only that. For instance, if we only need a little chemistry, where a player can add (say) water to salt and make a solution, we do not want to fool around with calculating quantities or concentrations: what's important is that "some water" (amount unspecified) combines with "some salt" to produce "some salty water". We should no more calculate precisely here than we would work out where all the furniture is to the nearest inch. Good advice for handling liquids is to simulate the least amount of realism possible, but no less.

Sometimes all we want is a down-in-one drink: we needn't simulate the actual liquid, just the bottle it comes in, and all we need is to handle the "drinking" action. See Beverage Service, and also 3 AM, where carbonated drinks can be shaken - again simulating the vessel, not the liquid.

Some elementary biochemistry in Xylan is done simply by... well, the point is that two different liquids are represented by single things each, and a chemical reaction simply switches one for the other.

In Frizz, we allow any container to be filled (only) with water (only) and we simulate what happens to any solid objects also inside: some waterproof, some not. Flotation provides a well (always full of water), with rules to determine whether things dropped into it should sink or float.

Next we move up to quantitative approaches, where we remember not just whether a liquid is present, but how much of it. In its simplest form, we could have a drinking vessel from which we draw in sips, so that it can be full, half-empty or empty: see Thirst.

The example with the best compromise between simulation quality and complexity is Lemonade. Here we provide a kind of container called a "fluid container", not just a single cup, and each such vessel has a given "fluid capacity". Each holds only a single liquid at a time (so no mixtures) and can be empty or full to any level (rounded off to the nearest 0.1 fl oz). We can fill one vessel from another (unless it would make a mixture). But liquids leaving these vessels must be consumed - drunk or poured away without trace: we cannot make pools on the floor, or carry liquids in our cupped hands. There is no object representing "lemonade": there are only fluid containers, but which can be called LEMONADE if that is what they now contain.

Savannah is a light elaboration of Lemonade, showing how liquids might be poured on other objects, as for instance to extinguish a fire.

Noisy Cricket extends Lemonade to allow for mixing, though then the number of different possible mixtures is so large that complexity increases greatly. Lakeside Living extends Lemonade differently to add a "liquid source" kind, a form of fluid container which has infinite fluid capacity and is scenery - ideal for a lake, river or spring.

See Bags, Bottles, Boxes and Safes for stoppered bottles which could also be used for carrying liquids around in

See Heat for keeping liquids warm in insulated containers

122
| Example Beverage Service A potion that the player can drink. |
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193
| Example 3 AM A shake command which agitates soda and makes items thump around in boxes. |
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192
| Example Frizz Liquid flows within containers and soaks objects that are not waterproof; any contact with a wet object can dampen our gloves. |
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385
| Example Flotation Objects that can sink or float in a well, depending on their own properties and the state of the surrounding environment. |
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277
| Example Xylan Creating a new command that does require an object to be named; and some comments about the choice of vocabulary, in general. |
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118
| Example Thirst A waterskin that is depleted as the player drinks from it. |
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255
| Example Lemonade Containers for liquid which keep track of how much liquid they are holding and of what kind, and allow quantities to be moved from one container to another. |
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256
| Example Savannah Using the liquid implementation demonstrated in Lemonade for putting out fires. |
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265
| Example Noisy Cricket Implementing liquids that can be mixed, and the components automatically recognized as matching one recipe or another. |
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320
| Example Lakeside Living Similar to "Lemonade", but with bodies of liquid that can never be depleted, and some adjustments to the "fill" command so that it will automatically attempt to fill from a large liquid source if possible. |
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Much of what follows is identical to "Lemonade" earlier; the new material begins at Part 2. "Lakeside Living" A volume is a kind of value. 15.9 fl oz specifies a volume with parts ounces and tenths (optional, preamble optional). A fluid container is a kind of container. A fluid container has a volume called a fluid capacity. A fluid container has a volume called current volume. The fluid capacity of a fluid container is usually 12.0 fl oz. The current volume of a fluid container is usually 0.0 fl oz. Liquid is a kind of value. The liquids are water, absinthe, and iced tea. A fluid container has a liquid. Instead of examining a fluid container: if the noun is empty, say "You catch just a hint of [the liquid of the noun] at the bottom."; otherwise say "[The noun] contains [current volume of the noun in rough terms] of [liquid of the noun]." To say (amount - a volume) in rough terms: if the amount is less than 0.5 fl oz: say "a swallow or two"; otherwise if tenths part of amount is greater than 3 and tenths part of amount is less than 7: let estimate be ounces part of amount; say "[estimate in words] or [estimate plus 1 in words] fluid ounces"; otherwise: if tenths part of amount is greater than 6, increase amount by 1.0 fl oz; say "about [ounces part of amount in words] fluid ounce[s]". Before printing the name of a fluid container (called the target) while not drinking or pouring: if the target is empty: say "empty "; otherwise: do nothing. After printing the name of a fluid container (called the target) while not examining or pouring: unless the target is empty: say " of [liquid of the target]"; omit contents in listing. Instead of inserting something into a fluid container: say "[The second noun] has too narrow a mouth to accept anything but liquids." Definition: a fluid container is empty if the current volume of it is 0.0 fl oz. Definition: a fluid container is full if the current volume of it is the fluid capacity of it. Understand "drink from [fluid container]" as drinking. Instead of drinking a fluid container: if the noun is empty: say "There is no more [liquid of the noun] within." instead; otherwise: decrease the current volume of the noun by 0.2 fl oz; if the current volume of the noun is less than 0.0 fl oz, now the current volume of the noun is 0.0 fl oz; say "You take a sip of [the liquid of the noun][if the noun is empty], leaving [the noun] empty[end if]." Part 2 - Filling Understand the command "fill" as something new. Here we want Inform to prefer full liquid sources to other containers when it chooses an end to a player's unfinished or ambiguous command. And so: Understand "fill [fluid container] with/from [full liquid source]" as filling it with. Understand "fill [fluid container] with/from [fluid container]" as filling it with. Both grammar lines point to the same ultimate outcome; the purpose of specifying both is to tell Inform to check thoroughly for full liquid sources before falling back on other fluid containers when making its decisions. Understand "fill [something] with/from [something]" as filling it with. Filling it with is an action applying to two things. Carry out filling it with: try pouring the second noun into the noun instead. Understand "pour [fluid container] in/into/on/onto [fluid container]" as pouring it into. Understand "empty [fluid container] into [fluid container]" as pouring it into. Understand "pour [something] in/into/on/onto [something]" as pouring it into. Understand "empty [something] into [something]" as pouring it into. Pouring it into is an action applying to two things. Check pouring it into: if the noun is not a fluid container, say "You can't pour [the noun]." instead; if the second noun is not a fluid container, say "You can't pour liquids into [the second noun]." instead; if the noun is the second noun, say "You can hardly pour [the noun] into itself." instead; if the liquid of the noun is not the liquid of the second noun: if the second noun is empty, now the liquid of the second noun is the liquid of the noun; otherwise say "Mixing [the liquid of the noun] with [the liquid of the second noun] would give unsavory results." instead; if the noun is empty, say "No more [liquid of the noun] remains in [the noun]." instead; if the second noun is full, say "[The second noun] cannot contain any more than it already holds." instead. Carry out pouring it into: let available capacity be the fluid capacity of the second noun minus the current volume of the second noun; if the available capacity is greater than the current volume of the noun, now the available capacity is the current volume of the noun; increase the current volume of the second noun by available capacity; decrease the current volume of the noun by available capacity. Report pouring it into: say "[if the noun is empty][The noun] is now empty;[otherwise][The noun] now contains [current volume of the noun in rough terms] of [liquid of the noun]; [end if]"; say "[the second noun] contains [current volume of the second noun in rough terms] of [liquid of the second noun][if the second noun is full], and is now full[end if]." Understand the liquid property as describing a fluid container. Understand "of" as a fluid container. And now we add our liquid source kind, which will represent lakes, absinthe fountains, and any other infinite supplies of liquid we might need. Note that 3276.7 is the largest possible number of fluid ounces available to us. A liquid source is a kind of fluid container. A liquid source has a liquid. A liquid source is usually scenery. The fluid capacity of a liquid source is usually 3276.7 fl oz. The current volume of a liquid source is usually 3276.7 fl oz. Instead of examining a liquid source: say "[The noun] is full of [liquid of the noun]." Carry out pouring a liquid source into something: now the current volume of the noun is 3276.7 fl oz. We want filling things from liquid sources to work the same way as usual, with the distinction that a) the liquid source never depletes in quantity (hence the carry-out rule resetting its fullness); and b) we should report the results a bit differently as well: After pouring a liquid source into a fluid container: say "You fill [the second noun] up with [liquid of the noun] from [the noun]." On the other hand, pouring liquids into a liquid source needs to work completely differently from pouring liquids into anything else. Let's say we're going to allow any liquid at all to be dumped into rivers and streams (environmental protections evidently are not very well-enforced in this scenario): Instead of pouring a fluid container into a liquid source: if the noun is empty, say "[The noun] is already empty." instead; now the current volume of the noun is 0.0 fl oz; say "You dump out [the noun] into [the second noun]." A couple of minor refinements: Swimming is an action applying to nothing. Understand "swim" or "dive" as swimming. Instead of swimming in the presence of a liquid source: say "You don't feel like a dip just now." Before inserting something into a liquid source: say "[The noun] would get lost and never be seen again." instead. Part 3 - Scenario The Lakeside is a room. The Lakeside swing is an enterable supporter in the Lakeside. "Here you are by the lake, enjoying a summery view." The glass is a fluid container carried by the player. The liquid of the glass is absinthe. The current volume of the glass is 0.8 fl oz. The pitcher is a fluid container in the Lakeside. The fluid capacity of the pitcher is 32.0 fl oz. The current volume of the pitcher is 20.0 fl oz. The liquid of the pitcher is absinthe. The lake is a liquid source. It is in the Lakeside. The player wears a bathing outfit. The description of the bathing outfit is "Stylishly striped in blue and white, and daringly cut to reveal almost all of your calves, and quite a bit of upper arm, as well. You had a moral struggle, purchasing it; but mercifully the lakeshore is sufficiently secluded that no one can see you in this immodest apparel." Instead of taking off the outfit: say "What odd ideas come into your head sometimes!" Test me with "fill glass / empty absinthe into lake / fill glass / swim / drink lake / drink / x water / x lake".

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