Line of sight behind walls parallel to a door

[Sheco]

When peeking around corners, your character is exposed to the enemies, at the moment you exit the look around mode. There's a visual anomaly too.

How to reproduce, place an enemy turret following the friendly sample layout included here.

    +------
    |
    |@
2   '
    |
    |
    +------

Peek down, move the cursor anywhere you want. (X, down, then look around)
After pressing escape or q, your character will be placed at the look around cursor, getting damage from the turret.

The first issue is the visual glitch, where your character is placed at the look around cursor. This seems to be only a visual representation mistake, your character actually is in the location you're peeking, which is in sight and range of the turret.

It doesn't matter where your cursor is, you'll be hit by the turret.

[BevapDin]

It doesn't matter where your cursor is, you'll be hit by the turret.

The viewing range algorithm is not symmetric. If you invert the scenario (switch positions with the turret) you'll be able to see the turret, but it does not see you.

[Sheco]

Did you try the scenario?

The "doesn't matter where the cursor is" is a bug, your character will "teleport" to the location of the look around cursor, but the character will not be in that location, but it doesn't matter, even if the cursor was behind a wall that the turret could definitely not see through, the effect is the same. Your character will be hit while exiting the peek around mode if the location of "peek at" is visible to the turret.

That would mean peaking around is the same as just moving to the location for a turn and moving back. But this is definitely not the case.

[Sheco]

Your patch fixes the visual glitch. (just tested it)

But doesn't address the issue that you're hit after peeking around the corner.

[Sheco]

No wait, you're right, the turret sees me... I understand what you were trying to say.

[Sheco]

Is this asymetric viewing range a correct representation of the world for each actor?

I would assume I'm behind the wall, but I'm actually kind of exposed?

[BevapDin]

The problem is the asymmetric field-of-sight algorithm, see for example here:
http://www.roguebasin.com/index.php?title=Comparative_study_of_field_of_view_algorithms_for_2D_grid_based_worlds#Symmetry

[Sheco]

I think the FoV should be reduced when an actor is straight pointing to an opening with a wall obstructing the view, so it only sees 1 tile straight, right now, looking straight at a window or door, the character has a FoV of 3 tiles wide to the inside.

Or something like that, I obviously don't know what I'm talking about.

[Sheco]

I still think this issue should be looked into, I'll explain the scenario again.

The line of sight code should be tweaked so when an actor is looking in a straight line to an opening (surrounded by at least 1 blocking tile), some tiles inside should not be visible.

         +----
         |???? 
X.............
         |????
         +----

Currently the tiles marked as ? are visible to the actor (player or monster), giving the X actor an unfair advantage, as actors inside the building would not be able to see him, if they are in one of those ? tiles.

I've tried fiddling with the code, but it's out of my league.

Getting closer to the opening correctly broadens the line of sight cone further away, but the tiles behind the walls are still visible.

This affects hidding behind walls, because the character is clearly visible to enemies aligned with the opening.

I edited the title of this issue to reflect the twist from the original report.

[kevingranade]

For reference, if you look at the page BevapDin linked, we're using "Recursive Shadowcasting".
I honestly don't see addressing this until we have some kind of partial cover type system in place, at which point you'd both be partially visible to each other.

[Sheco]

Ok I see.

Shall I close this?

[KA101]

I've changed the tags (and struck "bug" from the title) to reflect that this is at best a long-term improvement request. With that, I'd leave it open.

[kevingranade]

My recent overhaul forces monster vision of the player to match the player's vision of monsters, so now you can see into the building the same way, but the monster can see you as well.
In some ways this makes monster/player vision even more asymmetric, but it makes it reciprocal.