targetting and LOS

[will_asher]

One good reason is that in a symmetrical visibility system, it is easy and intuitive to determine which enemies have LOS on you. If there are many asymmetrical lines of sight, then it becomes difficult to avoid situations where enemies have asymmetrical LOS on you, and it also encourages the exploitation of AI which doesn't strive to avoid being the victim of asymmetrical LOS (the classic hockey stick).

With my suggestion (which I don't really expect many people to agree with), the player has the advantage that sleeping & stupid monsters don't hide behind corners. And also the fact that the player is much smarter than any of the monsters. Probably only intelligent creatures (people, orcs, dark elves..) should be considered smart enough to take advantage of the same things that the PC can take advantage of.
If you consider dragons intelligent, then there would still be the fact that there is a huge difference between a PC peeking around a corner (hard to notice) and a dragon peeking around a corner to breathe (big head == very easy to notice).

Additionally I would argue that certain asymmetrical lines of sight would make the game significantly more tactically frustrating in a bad way - consider breaking into a room with breathers in the corners with a system where the room inhabitants can see you at the door, but you can't see them. Effectively, they'd get two chances to breath on you before you could even see them, once at the door and once as you stepped into the room. The first aggressor in Angband is already at a disadvantage due to the turn-based nature of the game, and asymmetrical lines of sight only exacerbate the problem.

Remember my example:

    #.#    
#####@#
..M...#
#######

where the @ is peeking around the corner. The same situation would apply when the PC is entering a room. It would be almost the opposite of what you said: The PC would see the big breathers you mention before entering the room because he can peek around the corners while he is next to a corner. At the same time, he would be hiding most of his body around the corner of the doorway, making it unlikely that the monster would notice him. There is also the fact that most big breathers start out sleeping and are not very alert.

Taking advantage of situations where you can see your target but the target can't see you is a very realistic aspect of battle and should be allowed IMO. Ideally, intelligent monsters would be given AI to avoid being the victim of asymmetrical LOS.

Unfortunatly my suggestion has the disadvantage of being probably extremely hard to implement so that it works correctly. I guess my point is that I think that line of sight should not be symmetrical, and since my suggestion would be very hard to implement, I prefer that LOS stay as it is currently.

EDIT: sorry that I kindof contradicted myself by agreeing to Powerdiver's suggestion in the OP, but I've thought about it more since then. I agree that walls should not be considered to take up the whole square (that would go well with my ideal suggestion), but not if it makes line of sight symmetrical.

[PaulBlay]

Am I missing something here?

What about when the line exactly touches the edge of the 'blocked' area at the edge of the square. In the attachment can the @ see the G or not?

[Marble Dice]

Described like that you would not be able to see ghosts in the wall of corridors, nor would they be able to see you. (Because the middle of their tile is inside the wall)

Plus these two points:

1) Walls don't obstruct themselves. If the only obstruction is a wall at the final "observed destination", then that tile is visible (otherwise you'd never be able to see any walls, ever).
2) If an enemy is in a visible tile (wall or open), that enemy is visible.

Am I missing something here?

[PaulBlay]

Here's how the situation you describe would look from both perspectives, using a line from tile center to tile center for visibility, and walls obstructing from 1/4 to 3/4 inside of a tile.

Described like that you would not be able to see ghosts in the wall of corridors, nor would they be able to see you. (Because the middle of their tile is inside the wall)

[Marble Dice]

As far as I can tell, the biggest criticism of Eddie's original spec is that the shadows it casts aren't nice looking.

How much of a showstopper is this?

Considering that shadows also imply lack of visibility and thus the feasibility of cover, I think it's important. The problem isn't that they aren't nice looking so much as they don't provide adequate cover, and it's drastically inconsistent with the shadows cast on the horizontal/vertical (you're never going to fix that 100% in a square tile based system, but you can do a lot better than thin dotted line shadows).

Here's how the situation you describe would look from both perspectives, using a line from tile center to tile center for visibility, and walls obstructing from 1/4 to 3/4 inside of a tile.

Player                 Orc
#################      #################
#..............?#      #..............o#
#...........????#      #...............#
#.......@#??????#      #.......?#......#
#...........????#      #....???........#
#..............?#      #????...........#
#...............#      #??.............#
####.############      ####.############

This is a lot easier for me to believe than having a series of disconnected blind spots in a diagonal line behind a pillar. Using a line from center to center is necessarily symmetric because if you can draw a line from one direction without obstruction, you can draw the same line from the other direction without obstruction.

Paul - I agree with all your points, and I believe this system is compatible with all of them.

[PaulBlay]

I think we're all getting a little confused / off track here.

To sum up, "wouldn't it be nice if"

* What you see is what you can hit with a spell (and vice versa).
* What you see can also see you (and vice versa).
* Standing directly next to a pillar should produce an expanding shadow.
* Reasonably fast code can be produced to implement the FOV, etc.
* No 'trick shots' required (or possible) to hit monsters that you can't target directly.

Is everyone agreed on the above (if they are possible)?

How does the current system specifically differ from the above?

Are any of those points not possible?

[d_m]

As far as I can tell, the biggest criticism of Eddie's original spec is that the shadows it casts aren't nice looking.

How much of a showstopper is this? After some thought, I think that attractive shadows may be incompatible with symmetry, and I definitely prefer the latter. Consider the following:

###############
#........o
#.....
#.@#
#.....
#........
###############

The orc in the picture is not visible by @ (at least, according to one of the alternate proposals). However, it seems to me that if the positions of @ and o were reversed, @ would expect to see the orc (and currently would, I think). Thus, either the system is not symmetrical, we end up with some very strange LOS situations, or it is not coherent.

EDIT: I should say that I think this argument applies to most of the systems designed to create "expanding shadows" via Eddie's argument that asymmetric beholder-beholden relationships imply asymmetric visibility.

[PaulBlay]

If you want something along these lines, I think you'd have to define it as some sort of measure of the proportion of points in the two squares that can see each other.

I did come up with a variation that was symmetrical, but apart from being even more complicated I had to introduce 'special case' handling to stop people being able to see the whole of rooms when in the entrance.

I won't go into details unless I can think of a relatively easy (fast running) way to implement it.

[Magnate]

However, it is exceptionally hard to get these things right and still playable, and the D&D combination of evasion and damage reduction into a single value called AC makes it impossible. The only way to fix the rule is to throw it away. That is a lesson to be considered when thinking about things like "cover" bonuses in an angband framework.

If there was one radical change I could persuade Takkaria to make to V, it would be the separation of damage absorption (armour) and damage avoidance (evasion). So much else Just Works once you sort that out.

[Marble Dice]

Why is it so important that line of sight be symmetrical?

One good reason is that in a symmetrical visibility system, it is easy and intuitive to determine which enemies have LOS on you. If there are many asymmetrical lines of sight, then it becomes difficult to avoid situations where enemies have asymmetrical LOS on you, and it also encourages the exploitation of AI which doesn't strive to avoid being the victim of asymmetrical LOS (the classic hockey stick).

Additionally I would argue that certain asymmetrical lines of sight would make the game significantly more tactically frustrating in a bad way - consider breaking into a room with breathers in the corners with a system where the room inhabitants can see you at the door, but you can't see them. Effectively, they'd get two chances to breath on you before you could even see them, once at the door and once as you stepped into the room. The first aggressor in Angband is already at a disadvantage due to the turn-based nature of the game, and asymmetrical lines of sight only exacerbate the problem.

[PowerDiver]

Hmm, my gut instinct was that it would be symmetrical but it doesn't appear to be the case. :-(

If the definition is asymmetrical, a point in one square and an area in the other, the result is unlikely to be symmetrical. If you want something along these lines, I think you'd have to define it as some sort of measure of the proportion of points in the two squares that can see each other. The obvious starting point for such a def would be bounds on some sort of integral, but maybe its properties would be such that there would be a simpler equivalent def once you worked out exactly what you wanted.

[will_asher]

Take me with a grain of salt because I'm pretty sure I'm in the minority..

Why is it so important that line of sight be symmetrical?

In the following example (copied from another post), I would consider the @ to be both hiding behind the wall and peeking around it. So the @ should be able to see most of the hallway, but it should be pretty unlikely that the M would notice the @. This would involve having stealth as a factor in line of sight but I think it's much more realistic that way.

    #.#    
#####@#
..M...#
#######

The problem with assuming that the player and monsters always take the part of the grid in the middle is that any player or monster with sense is going to try to keep as much of their body as possible out of the line of fire (which should be the same as LOS).

[PaulBlay]

I think Paul's suggestion would be considerably more processor-intensive to implement. I don't see any way to get around having to track the visibility state of 16 subgrids per grid.

It's maths. But that doesn't mean that you can't fake it with tables and stuff.

[PaulBlay]

Also, Paul, I don't see how your system can be symmetrical --- compare your pictures in posts #33 and #35; they clearly don't describe symmetrical behaviour.

Hmm, my gut instinct was that it would be symmetrical but it doesn't appear to be the case. :-( I think I may have to drop my suggestion if so.

but I don't get exactly what you mean. In particular, I'm confused by your point 1 --- we had been discussing the suggestion that pillars take up a quarter of the area of a square, but placed at the centre, i.e. the central 2x2 squares of a 4x4 subdivision.

First point - I changed from needing to see all the square to needing to see half the square. This allows the 'ghost in wall' situation to be OK.

Second point that's exactly what I'm doing - pillars and walls have a 1/4 (25%) gap around them where they meet the open space (as seen in the pictures).

[EDIT] Changed text in first half.

[RogerN]

If I remember Angband's view code correctly, the existing view algorithm could be adapted to use the proposed center-to-center method without too much difficulty. I think Paul's suggestion would be considerably more processor-intensive to implement. I don't see any way to get around having to track the visibility state of 16 subgrids per grid.

Not that implementation concerns should always dictate decisions which affect gameplay, but I think performance is pretty important in this case. However Angband calculates the player view, the algorithm needs to be pretty fast.