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Old 04-02-2018, 05:05 PM   #1
Anthony
 
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Default Area spells and walls

For some reason I've never considered this in GURPS, but I was suddenly wondering: how do area spells interact with walls? If I cast an area spell that envelops a building, does it affect both the inside and the outside of the building at the same time, or do I have to select one?
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Old 04-02-2018, 06:32 PM   #2
Not another shrubbery
 
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Default Re: Area spells and walls

We always assumed that physical effect area spells were stopped by physical barriers, and that most others would penetrate such things. It never occurred to us to question whether this was the official intent, though, which I'd chalk up to a desire to 'just play'. Reflecting on it now, that favoring of non-physical effects is unseemly, and it might be better to make them all be blocked or not, as you see fit, although some spells (like the Domes) probably ought to penetrate regardless.
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Old 04-02-2018, 07:37 PM   #3
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Default Re: Area spells and walls

I've always just had them as 'penetrating'.
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Old 04-02-2018, 11:19 PM   #4
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Default Re: Area spells and walls

Quote:
Originally Posted by Anthony View Post
. . . how do area spells interact with walls? . . .
That's a good question.

How should an area spell such as Fire Cloud behave if a wall was imposed after the casting? Should the wall push the effects?

To get extreme, for a character in the area of effect, you could assume his armor is like a "wall" that protects from the effects.

I might assume that the area effects grow from the target point and are contained by interposing barriers.

So in your building example the result would depend on whether you target the inside or outside regardless of any walls between you and the target (notwithstanding the usual casting penalties for not touching or seeing the subject.)

Last edited by Tom H.; 04-03-2018 at 12:33 PM. Reason: Correction
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Old 04-03-2018, 09:51 AM   #5
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Default Re: Area spells and walls

I'd have to think on it more to remember if I've been inconsistent on this, but as far as I can recall at the moment, I've always treated an area as the full area regardless of what's in it.

So I think I've always ignored walls when it comes to that (unless the caster chooses to stop at the walls).
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Old 04-03-2018, 10:25 AM   #6
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Default Re: Area spells and walls

So, create fire cast outside the castle wall, with a big area, will set fires to anything flammable inside the castle?

I’d tend to say it works on the other side of the barrier if
a) casting on the other side of the barrier would have succeeded
b) the spell manages to cross the barrier

In the second case, if you’d have a half circle of flame outside a wooden wall, but once the wall broke down, fire will tavel across the entire circle without anything fuel, because the entire area is magical fire. It would still have to make it way through the initial opening, as if flames were catching across dry firewood (that is, probably a yard every few seconds).
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Old 04-03-2018, 11:19 AM   #7
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Default Re: Area spells and walls

When this came up in play, I checked a few books, didn't find a conclusive answer, and ruled that area spells radiated from the center when cast. Things that block line of sight blocked to layout of the spell. This meant walls blocked it but most figures didn't. Once it was laid down, it wouldn't be blocked this way (like by closing a door).

The players were fine with it and we haven't had to rethink it yet.
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Old 04-03-2018, 11:27 AM   #8
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Default Re: Area spells and walls

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Originally Posted by ArchonShiva View Post
So, create fire cast outside the castle wall, with a big area, will set fires to anything flammable inside the castle?
If the caster doesn't exclude the castle's interior, yes.

This is implicit in the way Area spells work (like Regular spells with a few differences), such that Regular spells are not bound by barriers, and an Area spell fills the entirety of it's area excepting where the caster does not wish it to.

Quote:
In the second case, if you’d have a half circle of flame outside a wooden wall, but once the wall broke down, fire will tavel across the entire circle without anything fuel, because the entire area is magical fire. It would still have to make it way through the initial opening, as if flames were catching across dry firewood (that is, probably a yard every few seconds).
Once cast area spells do not change their area unless the the caster wishes it to and has some means to do so (like the spell allows for it, which Create Fire does not, or a Perk or Advantage that allows for it).

Note, that doesn't stop things from catching on fire normally and spreading normally, but then canceling the spell won't turn off the mundanely burning area.

I don't remember where I read it* but if an Area spell crosses a wall, it will not 'create' it's area where the wall is standing, even if the wall is later removed.



* Maybe a Krommquote, maybe a houseruling, might just be my own interpretation of the above being that Area spells do not change their area with being acted upon.
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Old 04-03-2018, 12:28 PM   #9
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Default Re: Area spells and walls

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Originally Posted by evileeyore View Post
This is implicit in the way Area spells work (like Regular spells with a few differences), such that Regular spells are not bound by barriers, and an Area spell fills the entirety of it's area excepting where the caster does not wish it to.
After rereading Spells 12-13, I agree that this is the simplest reading of the rules. Area spells are like Regular spells which explicitly ignore physical barriers.

I can easily see someone preferring to have area spells emanate from a particular point. This wouldn't break anything, and would make it a bit harder to light a whole castle on fire from outside the wall. But I would argue that the spell should emanate from the point that you pay the range penalty for. Normally, if you can't touch the area, you pay a range penalty to the closest point of the area (e.g., an edge). I suggest that the area emanates from that point. So if you wanted it to emanate from the center, you would need to pay a range penalty of the number of hexes from the caster to the center. If a caster were standing outside a wall, they would have to deal with at least a penalty of the wall's thickness. (And you could add the extra -5 for out-of-sight from Regular spells if you wanted to further clamp down on this.)
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Old 04-03-2018, 11:36 PM   #10
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Default Re: Area spells and walls

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Area spells are like Regular spells which explicitly ignore physical barriers.
Well... it's not 'ignore'. it's 'aren't bound by. They still interact with them in meaningful ways, mostly by penalizing the caster if he can't see where he's casting the spell.

In this case I only levy a penalty if the Area spell is completely on the other side of a barrier (in other words the caster can't touch a part of the area, so it's not only penalized for distance, but for LOS being blocked). If it's overlapping, then I just have it overlap. As most Area spells are more expensive to cast, I feel this evens out.
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