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Old 05-03-2015, 08:51 PM   #31
Grouchy Chris
 
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Default Re: Building permanent magical traps with GURPS Magic

Quote:
Originally Posted by jeff_wilson View Post
The addition of the Link spell effectively removes the requirement to keep wearing or carrying:

"Postpones the activation of one or
more linked spells cast in its area of
effect, until a certain thing happens in
the Linkís presence."

As I said before, the trap-layer can act as the user and initiate the first zap, which the effect of the Link holds until later and parcels it out under its description. The example under Link shows it time-shifting the Continual Light effect past when it would otherwise end, so it ought to time-shift a Create Fire effect past when it would otherwise end.
I think that's a rather strained interpretation of the rules. The rules for Link do not allow indefinite maintenance at zero cost for the linked spell when cast directly by a mage ("Linked spells may not benefit from cost reductions for high skill," p. 131). I think it's pretty clear this was done to prevent such things as permanent Fire Cloud spells, and I think this roundabout method of getting a permanent Fire Cloud by casting it with an item violates the intention of the rules.

I think it's iffy whether you can use "always on" items to cast area spells with zero cost that last indefinitely (especially since whether the item is "always on" will depend on the radius of the area the spell is cast on), and I think it's iffy to say the Link spell discriminates between spells cast directly by a mage and spells cast with an item. Moreover, the rules for Link seem to be designed to prevent you from making a permanent Fire Cloud. So given all that, I would have to see an official ruling on this before I could accept that such a thing is allowed.

But you have made clear, at least, that the question of what the rules allow along these lines is more complicated than I realized. These kinds of complications are part of the reason I'd like to know if there are any published rules extending the magic system on trap-building before I'd want to make my own rules.
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Old 05-04-2015, 12:48 AM   #32
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Default Re: Building permanent magical traps with GURPS Magic

Could you create a Force Dome that traps the subject until he starves and thirsts to death? Preferably somewhere they can see food and water?
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Old 05-04-2015, 02:56 AM   #33
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Default Re: Building permanent magical traps with GURPS Magic

Quote:
Originally Posted by Grouchy Chris View Post
I think that's a rather strained interpretation of the rules. The rules for Link do not allow indefinite maintenance at zero cost for the linked spell when cast directly by a mage ("Linked spells may not benefit from cost reductions for high skill," p. 131). I think it's pretty clear this was done to prevent such things as permanent Fire Cloud spells
Enchanted spells don't benefit from cost reductions for high skills either, but they are absolutely, positively meant to be capable of permanence as the existence of the Power enchantment attests, and the large numbers of "always on" item descriptions attest.
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Old 05-04-2015, 04:44 PM   #34
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Default Re: Building permanent magical traps with GURPS Magic

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Originally Posted by jeff_wilson View Post
Enchanted spells don't benefit from cost reductions for high skills either, but they are absolutely, positively meant to be capable of permanence as the existence of the Power enchantment attests, and the large numbers of "always on" item descriptions attest.
I don't see that as relevant, since Enchant is a completely different spell, and the no-cost-reduction rule in this case is due to the necessity of ceremonial magic.

I think we're in a rather gray area of the rules and we aren't likely to agree on this, so I've emailed Kromm to ask. If he has time for an answer, I'll relay what I learn here.
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Old 05-04-2015, 09:01 PM   #35
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Default Re: Building permanent magical traps with GURPS Magic

So it turns out that "always on" does not work for items that cast area spells in the way I thought it did at all. Apparently I need to go back and think about it some more. Here's what Kromm had to say:

Quote:
Originally Posted by Kromm, in an email
> (1) If a magic items enchanted with an area spell (a ring of Fire
> Cloud, let's say) also has a Power enchantment of sufficient level,
> does it count as an "always on" item, allowing for the creation of a
> Fire Cloud spell that lasts until the ring is removed by the caster?

Items can be truly "always on" only if their Power enchantment will
cover all possible costs. If there's an open-ended range of costs -- as
for an Area spell -- then a given casting might endure indefinitely as
long the caster is awake, but the item per se isn't "always on."

> (2) If "yes" on (1), is the spell eligible for use with the Link
> spell? (The text for Link stipulates that cost reductions for high
> skill do not apply, making indefinite maintenance of a spell at zero
> cost impossible by direct casting, but the issue of casting via
> Powered magic item is what I'm wondering about.)

Well, the answer to (1) is "no" . . . but note that Link works *very*
differently for enchantments. In that event, Link isn't ever actually
cast by the item, making the issue of its energy cost irrelevant. For
enchanted items, Link simply controls operation.

> (3) If "yes" on (1) and (2), does the use of the Link spell mean
> that when the Fire Cloud is triggered, it persists indefinitely
> without regard to whether or not the caster removes the ring?

Again, given the previous answers, this is almost irrelevant, but . . .
Taking off a worn item ends the spell. It has to be worn to work, even
if it costs no energy to use. "Always on" items are by definition only
"always on while used in the prescribed manner." For worn items, that
means "while worn."

> (4) If "yes" on (1) and (2) but "no" on (3), what controls the
> duration of the Linked, item-cast Fire Cloud?

Someone with an item that has Fire Cloud, high Power, and Link can cast
a free-to-maintain Fire Cloud as long as the conditions of the Link are
met. However, as Power spells out clearly, the user still has to remain
awake -- and as I just said, taking the item off would end the spell.
So the practical limit on duration is the length of time the user can
remain awake while wearing the item.
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Old 11-27-2015, 03:22 PM   #36
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Default Re: Building permanent magical traps with GURPS Magic

I took a quick look at the ACTUAL example for an Item for the Link spell. It says (Magic, p. 132)

Quote:
A sword might be Linked with a Light spell and a Sense Life spell, so that it glows in the presence of Orcs.
Ignoring the "Sense Life" for right now, which is part of the Link's Detect, the Light spell is Regular and has a 1 minute duration, and the only items listed for it are "wand, staff, or jewelry." (Though, not "mages only") To me, this implies that <i>if you are using Link as an enchantment</i> you can enchant any other spell into the same item and have the Link become the "user" for the purpose of activating the spell at the right time.

The spell should be enchanted into the item as you would a Spell Stone, at an energy cost of 20x casting cost. (For the sword above, this is 20 points. For a "Fire Cloud" trap of area 1, 2d damage, this 40 points.)

For powering the item,
1 - For a "permanent" item, the spell should be powered by a Power enchantment with enough power to trigger the spell. (For the light sword, this is 500 points. For the 2d "Fire cloud" trap, this is 1000 points. The item/trap will activate when the link's condition is true, then cut off after the duration of the spell, then reactivate when the link's detect is true again. If maintainable, it will maintain as long as the link's condition is true.)
2 - For a cheaper version of the trap that needs to reset, the spell could be powered by an exclusive powerstone (much cheaper). (For the sword above, this is 20 points. For the Fire Cloud... this is also 20 points, due to the tripled nature of the power supplied by the power stone. In this case, the spell would activate (or maintain) when the link's condition is true only if the powerstone has enough power, and wouldn't if the powerstone is recharging.)

Opinions?

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Old 11-28-2015, 11:57 AM   #37
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Default Re: Building permanent magical traps with GURPS Magic

I find GURPS Magic is best used as a toolbox. When I determine which people (specific guilds, temples, libraries, tribes, etc) have which spells and resources etc., it can be interesting and consistent and manageable. However, even for one-off adventures, when I've tried to allow high magic including anyone might know any spell... I can't even come close to wrapping my brain around all the possibilities in a way that leaves me feeling I'm doing a good job of knowing what's going on in the world and having it make sense. Too many possibilities for my tastes.

I think the rules-as-written with no invented spells pretty clearly does not allow you to make a self-powered fire cloud spell with link to make a permanent fire cloud trap.

I think it's easy enough to add, but requires making the decision to do so. As has been suggested, you can add a Trap spell (prereq: Link) or other spells, or modify the description of Link.

I think that's probably good, for reasons of potential balance and world abuse. So it requires deliberately adding the ability, but makes it easy enough to do in a mechanically consistent way. Or even in the existing system, if you invent a spell to do it and the GM allows it, or if you luck out and your GM decides to allow that sort of use by stretching the rules interpretation a bit, as was suggested already.

I can see several balance and abuse issues, unless you as a GM want that kind of abuse, which for the most part it sounds like you do. But not every GM wants to discover that the magic system allows creating permanent trap zones (which players may want to do or hire people to do) or other interesting uses of permanent self-powered enchantment with link spells. In particular, I can see players with mechanical enthusiasm wanting self-powered furnaces for steam engines and such (which is actually relatively abusable just with a self-powered fire item) not to mention the rest of the spell list. I have players who can cause great mayhem with the basic Sound spell and their imaginations, so...

But if you want a world where it's relatively common to leave permanent magical traps lying about, it's easy enough to add a spell or a few. I tend to think that it would make sense to allow some limiting discounts for a static permanent enchantment, as a portable magic item with self-powered fire cloud is generally quite useful - probably much more so than a room that can't move. Except that as a trap, it's a feature if your targets can't pick up your trap and use it as a weapon against you.

However I think there's a logic/balance issue with magic room traps - if a wizard has enough time and energy to enchant various permanent traps like that, then I'd hate to see what magic he has on hand for his personal use, and the use of whatever army of powerful bodyguards I'd expect him to have. That is, I think a smart wizard (look at the IQ they generally have) would tend to put even more effort into enchanting the weapons he and his pals and bodyguards use, than he puts into static traps on some room or door, no?

In which case, it might make more sense if there were a set of more balanced trap spells or trap methods for existing spells, that don't involve permanent self-powered enchantments. How vital is it that the fire cloud room trap have infinite energy? Maybe if there were just a trap spell that lets you hook up and link a spell trap without the maintenance and -1 / spell issue, that would let you have far more routine traps, without implying that anyone with magic traps has to be some sort of uber arch mage who can make super-powerful enchantments.
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Old 12-02-2015, 06:20 AM   #38
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Default Re: Building permanent magical traps with GURPS Magic

Hmm... well we apparently take different approaches to Magic in general, Skarg, since I make it a general rule that wizards in my world can know any spell. Even people who are racially magical (have Magery 0 in their racial template) are likely to know some of the simple spells from any school (like Light). It's "divine casters," who are devoted to a god and get their spells from that god, that are limited in which spells they are allowed to have.

And yes, I have no problem with my characters wanting to "invent" things! In many cases I would rule that it takes a lot of extra time to do it since there are weird side-effects they were unaware of as they build something experimental, or that the item that they get also has weird quirks. However, magical inventions mimicing technology underpin the world (there are magical street lights and "trains" in my world), even though we are in TL-4.

I have also established a third enchantment method that brings the 60-800 power enchantment range down into the level of purchasing feasibility: you can get an item in this range in about a week, and because of the quickness you can get it at about $2/energy point. The risk is that if you are doing this on commission (and the people who do this generally work on commission!) there is a much higher chance of a critical failure completely destroying the awesome armor that you're trying to improve.

I guess that's why I considered it feasible to have 200-point Link spells with 500-point Power spells attached to them lying around in dungeons... Although I would also probably rule that people building a trap could specify the link spell's trigger area as "that area of floor" not an area around the current location of the enchanted item. If the item is moved so that the Link can't "see" that specific area of floor, it can't tell if it's being triggered, so it can't function. This gives another way of disarming the trap, but also makes it impossible to steal a Link trap.

Or, would that be the fundamental difference between a "Link" spell that can make a glowing sword and a theoretical, invented "Trap" spell? A "Link" enchanted item can be carried around and functions in an area around its current location, whereas a "Trap" spell functions for a particular area only?

--Christina
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Old 01-21-2016, 12:20 PM   #39
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Default Re: Building permanent magical traps with GURPS Magic

Apologies for the necromancy, but I addressed this in my blog during my exile:
http://papermenplasticmonster.blogsp...-trap.html?m=0
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