Does standard cover block line of effect?

Rules Discussion

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There seems to have been substantial change in the line of effect rules from first edition (link) to second edition (link). Additionally, line of effect was described differently in the playtest than in either edition. Here are the important differences:
1.) In PF1E, you had line of effect if you could draw a line from any corner of your square through any part of your target’s square.
2.) In the playtest, you had line of effect if there was an unblocked path between you and your target. To calculate if you path was blocked, you were told to calculate as if checking for cover, i.e. a line from your center to the center of your target. A great description of the straitjacketing effect the playtest rules had on spellcasting is presented in this previous post.
3.) Now, in the PF2E CRB, we are told that you have line of effect “unless a creature is entirely behind a solid physical barrier.” However, unlike both of the previous definitions, no methodology for calculation is described. I find it currently ambiguous whether standard cover blocks line of effect like it did in the playtest. I think a case can be made for the current Line of effect rules to work similarly to either PF1E or the playtest:

Pathfinder 1E case: If standard cover blocks line of effect, then some of the cover rules do not make sense. Specifically, the following methodology for determining if you have cover from an area spell is provided:

cover rules CRB p.477 wrote:
Standard cover gives you a +2 circumstance bonus to AC, to Reflex saves against area effects … Draw a line from the center of your space to the center of the target’s space. If that line passes through any terrain or object that would block the effect, the target has standard cover … When measuring cover against an area effect, draw the line from the effect’s point of origin to the center of the creature’s space.

But line of effect is necessary to even be affected by the spell in the first place:

line of effect rules CRB p.457 wrote:
In an area effect, creatures or targets must have line of effect to the point of origin to be affected.

So it is nonsensical to give +2 to AC and Reflex saves to a target behind cover if said cover makes the target immune to the spell’s effects.

Playtest case: It is arguable that in cases of ambiguity, the playtest’s precedent should be followed and any contradictions from PF1E rules are irrelevant and thus ignorable. If a rule was unchanged upon full release of PF2E, shouldn’t the rule work as it did in the playtest? For emphasis, line of effect rules in the PF2E CRB are clearly held over from the playtest:
playtest line of effect rules CRB p.298 wrote:
You usually need an unblocked path to the target of a spell, the origin point of an area, or the place where you create something with a spell or other ability. This is called the line of effect. If you need to check whether you have a line of effect, draw a line like you do when determining cover.
PF2E line of effect rules CRB p.457 wrote:
When creating an effect, you usually need an unblocked path to the target of a spell, the origin point of an effect’s area, or the place where you create something with a spell or other ability. This is called a line of effect. You have line of effect unless a creature is entirely behind a solid physical barrier.

Furthermore, the rules for cover can still make sense with “playtest line of effect rules” because the text from above: “When measuring cover against an area effect, draw the line from the effect’s point of origin to the center of the creature’s space.” Can be applied to lesser cover, or future types of unusual cover.

Lastly, a visual way of representing the problem:
W = wall square
C = caster
T = target
X = empty square

X W W W
T W W W
X W W W
X W W W
X C C X
X C C X
X X X X

Does the caster have line of effect to the target (i.e. an “unblocked path to the target of the spell”)?

Developer insight on this issue would be ideal (e.g. in an FAQ or on the Friday podcast), but hope is faint, and I’d greatly appreciate the community’s thoughts on the topic.

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The rules for determining cover also reference the idea of line of effect. So I would suspect that the intent is to use the same measuring/line drawing rules for line of effect as for cover.

It also lists that the difference between lesser cover, standard cover, and blocked line of effect are in the qualities of the object that is in the way. Another creature or something that doesn't block much provides lesser cover. Most things provide standard cover. Something that is completely solid blocks line of effect.

But I also agree that this should be presented properly in the rules for line of effect.

You usually need an unblocked path to the target of a spell. So you just need to be able to draw a line between the 2 that isn't blocked. That's it. "you have line of effect unless a creature is entirely behind a solid physical barrier." As long as any part of them isn't behind a barrier [ie, a line can be drawn], it's fine to target. So even greater cover doesn't affect line of effect as being able to "barely see one another" is still an "unblocked path to the target".

graystone wrote:
You usually need an unblocked path to the target of a spell. So you just need to be able to draw a line between the 2 that isn't blocked. That's it. "you have line of effect unless a creature is entirely behind a solid physical barrier." As long as any part of them isn't behind a barrier [ie, a line can be drawn], it's fine to target. So even greater cover doesn't affect line of effect as being able to "barely see one another" is still an "unblocked path to the target".

The issue I see with such quick dismissal is that the playtest also used the language "You usually need an unblocked path to the target of a spell" .... yet line of effect didn't go around corners. That's the language we still have.

Del_Taco_Eater wrote:
graystone wrote:
You usually need an unblocked path to the target of a spell. So you just need to be able to draw a line between the 2 that isn't blocked. That's it. "you have line of effect unless a creature is entirely behind a solid physical barrier." As long as any part of them isn't behind a barrier [ie, a line can be drawn], it's fine to target. So even greater cover doesn't affect line of effect as being able to "barely see one another" is still an "unblocked path to the target".
The issue I see with such quick dismissal is that the playtest also used the language "You usually need an unblocked path to the target of a spell" .... yet line of effect didn't go around corners. That's the language we still have.

I don't understand what you're talking about. If it needs line of affect, of course it can't go around corners.

If you're talking about "usually", then it means some spells don't require it. For instance, take Scrying. Range is planetary and you don't have to draw a line of effect for it.

graystone wrote:
Del_Taco_Eater wrote:
graystone wrote:
You usually need an unblocked path to the target of a spell. So you just need to be able to draw a line between the 2 that isn't blocked. That's it. "you have line of effect unless a creature is entirely behind a solid physical barrier." As long as any part of them isn't behind a barrier [ie, a line can be drawn], it's fine to target. So even greater cover doesn't affect line of effect as being able to "barely see one another" is still an "unblocked path to the target".
The issue I see with such quick dismissal is that the playtest also used the language "You usually need an unblocked path to the target of a spell" .... yet line of effect didn't go around corners. That's the language we still have.

I don't understand what you're talking about. If it needs line of affect, of course it can't go around corners.

If you're talking about "usually", then it means some spells don't require it. For instance, take Scrying. Range is planetary and you don't have to draw a line of effect for it.

Miscommunication, sorry. By "around corners" I meant like in the picture in my OP where casty's target has cover around a corner. To reiterate my point, the playtest had the exact same wording as you quoted above, i.e. "you usually need an unblocked path to the target of a spell." However, the playtest also seemed to deem many common examples of standard cover (e.g. said corner, or a pillar, etc) capable of blocking line of effect. So maybe line of affect is more restricted than you assume?

Del_Taco_Eater wrote:
Miscommunication, sorry. By "around corners" I meant like in the picture in my OP where casty's target has cover around a corner. To reiterate my point, the playtest had the exact same wording as you quoted above, i.e. "you usually need an unblocked path to the target of a spell." However, the playtest also seemed to deem many common examples of standard cover (e.g. said corner, or a pillar, etc) capable of blocking line of effect. So maybe line of affect is more restricted than you assume?

In the picture, there IS an unblocked path to #4: you can draw a single line between the two and not hit a barrier. For instance, you can draw a line from the right hand top corner of the monster to the top right hand corner of #4 and that is all you need for line of effect. Cover is different in that most of the target is blocked so the cover is greater cover.

I think you are combining cover and line of effect and they just aren't the same thing. "unblocked view" is explained on page 457: "usually a 1-foot-square gap is enough to maintain a line of effect". So if a 1' wide line can be draw to a target, from any part of one to any part of the other, you have line of effect.

graystone wrote:
Del_Taco_Eater wrote:
Miscommunication, sorry. By "around corners" I meant like in the picture in my OP where casty's target has cover around a corner. To reiterate my point, the playtest had the exact same wording as you quoted above, i.e. "you usually need an unblocked path to the target of a spell." However, the playtest also seemed to deem many common examples of standard cover (e.g. said corner, or a pillar, etc) capable of blocking line of effect. So maybe line of affect is more restricted than you assume?

In the picture, there IS an unblocked path to #4: you can draw a single line between the two and not hit a barrier. For instance, you can draw a line from the right hand top corner of the monster to the top right hand corner of #4 and that is all you need for line of effect. Cover is different in that most of the target is blocked so the cover is greater cover.

I think you are combining cover and line of effect and they just aren't the same thing. "unblocked view" is explained on page 457: "usually a 1-foot-square gap is enough to maintain a line of effect". So if a 1' wide line can be draw to a target, from any part of one to any part of the other, you have line of effect.

My reason for combining line of effect and cover is due to how intertwined they were in the playtest. I'm curious if your interpretation is the same as mine that by playtest rules the caster in the picture does not have line of effect.

Del_Taco_Eater wrote:
My reason for combining line of effect and cover is due to how intertwined they were in the playtest. I'm curious if your interpretation is the same as mine that by playtest rules the caster in the picture does not have line of effect.

I don't understand what the playtest has to do with the final rules: I'm 100% talking about the final rules, and by the final rules, there is line of effect. By the playtest rules, I don't know. I'm not pulling them out to see.

graystone wrote:
Del_Taco_Eater wrote:
My reason for combining line of effect and cover is due to how intertwined they were in the playtest. I'm curious if your interpretation is the same as mine that by playtest rules the caster in the picture does not have line of effect.
I don't understand what the playtest has to do with the final rules: I'm 100% talking about the final rules, and by the final rules, there is line of effect. By the playtest rules, I don't know. I'm not pulling them out to see.

I think they are relevant for two reasons.

1.) The playtest was of course the "beta" version of PF2E. There is arguably a precedent set by playtest rules for how PF2E works in cases where the new CRB (which ofc 100% trumps any old rules) uses the unchanged wording from the playtest. In the case of line of effect, it clearly does to meaningful extent.
2.) The justification I understand you are making for the caster in the picture having line of effect is that an unlocked path can be drawn. The playtest used (I think?) your language verbatim and still didn't grant line of effect.

I feel I may not be getting getting my point across if you read me to be saying that playtest rules should still be followed in 2E.

Just for me because I am not quite clear with the explainations so far?

Checking for cover is center to center, right?

Is line of effect also center to center? Or any corner to any corner? How about when you move along a line that borders both open space and a solid barrier?

Consider two guys C and O standing in alcoves. Can they hit each other with (non-AOE) spells?

XXXXXXXXXXX
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XXXCXXXOXXX
XXXXXXXXXXX

Ubertron_X wrote:

Just for me because I am not quite clear with the explainations so far?

Checking for cover is center to center, right?

Is line of effect also center to center? Or any corner to any corner? How about when you move along a line that borders both open space and a solid barrier?

Consider two guys C and O standing in alcoves. Can they hit each other with (non-AOE) spells?

XXXXXXXXXXX
........................
XXXCXXXOXXX
XXXXXXXXXXX

Re: cover - correct.

Re: line of effect - in 1E it was any line through both squares. In the playtest it was center to center. In the 2E CRB it is completely unspecified, which is what I want to draw attention to.

Re: the picture - The target demonstrably has no line of effect by playtest rules. In 1E I believe the line could originate from a corner of your square but had to pass through the interior of theirs (no line of effect). Although unspecified, I find no reasonable interpretation of 2E's rules to allow line of effect either.

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Ubertron_X wrote:
Checking for cover is center to center, right?

Yes.

Ubertron_X wrote:
Is line of effect also center to center? Or any corner to any corner? How about when you move along a line that borders both open space and a solid barrier?

There has to be a one foot open space between the two, that's all.

Ubertron_X wrote:
Consider two guys C and O standing in alcoves. Can they hit each other with (non-AOE) spells?

No line of effect. There is a solid barrier between the 2 and you can't draw a 1 foot lines connecting the 2. Now if there was a 1' wide hole in the 2 x's between the 2, they could fire through it at each other.

So it is either a min 1-foot-square "opening" in between target and point of origin (AoE) or a min 1 foot-square "opening" in between the caster and the target, which means that for caster <> target it really is any corner to any corner BUT with the additional requirement of the 1-foot-square "opening", which excludes cutting corners and passing alone lines.

Ubertron_X wrote:
So it is either a min 1-foot-square "opening" in between target and point of origin (AoE) or a min 1 foot-square "opening" in between the caster and the target, which means that for caster <> target it really is any corner to any corner BUT with the additional requirement of the 1-foot-square "opening", which excludes cutting corners and passing alone lines.

Sounds right: For line of effect, you can just think of it as a foot wide line and as long as you can connect the caster and the target without going through a solid object*, you're good.

* Having a 1'+ opening through an object is an exception to it stopping line of effect if the line would go through that opening.

But even with the 1' opening there's the Take Cover action which if you're near an opening would be to back away from it, maybe even put your back to the wall next to it. That should at least cut off angles where there's a 1' clear path to you even if you only get Greater Cover (and not Total Cover).

It seems that's exactly where a Magic Missile should be able to shoot through and connect (assuming you can see part of the target.)

Castilliano wrote:
But even with the 1' opening there's the Take Cover action which if you're near an opening would be to back away from it, maybe even put your back to the wall next to it. That should at least cut off angles where there's a 1' clear path to you even if you only get Greater Cover (and not Total Cover).

This doesn't matter for line of effect: if you are in the square with the 1' opening, you are in the line of effect. Your amount of cover changes your "circumstance bonus to AC, to Reflex saves against area effects, and to Stealth checks to Hide, Sneak, or otherwise avoid detection". Note line of effect isn't there.

Castilliano wrote:
It seems that's exactly where a Magic Missile should be able to shoot through and connect (assuming you can see part of the target.)

Yep, you ignore the circumstance bonus to AC with it's auto-hit.

One qualm I have with the one foot line method is that it depends too much on geometry. In the example of firing around a corner, how many squares from the corner your target is determines in you have line of effect. I doubt, if/when we get a ruling on the topic, that it will end up being that complicated.

Del_Taco_Eater wrote:
One qualm I have with the one foot line method is that it depends too much on geometry. In the example of firing around a corner, how many squares from the corner your target is determines in you have line of effect. I doubt, if/when we get a ruling on the topic, that it will end up being that complicated.

PF2 is very much game of 'ask the DM'. In this situation, the game isn't really expecting you to use "geometry". It's expecting the Dm to eyeball it, shug his shoulders and say 'looks like it [should or shouldn't] work'.

You'll note this in the rules. Look at cover: "Usually, the GM can quickly decide whether your target has cover. If you’re uncertain or need to be more precise, draw a line from the center of your space to the center of the target’s space." The default is "the GM can quickly decide whether your target has cover" and how much. It's only when they want to be precise that they even have to go center to center. Later, it's tells you "Your GM might let you reduce or negate cover by leaning around a corner to shoot or the like" and "the GM might measure cover from an edge or corner of your space instead of your center". This totally up to the DM fiat.

For myself, I wouldn't worry too much about a 1' wide line or exacting line graphs to calculate things. Just make a line from corner to corner and if there are no interruptions you're most likely fine.