How create Stealth-like system?

[Snuux]

stealthview.jpg (6.72 KiB) Viewed 3386 times

This is simple example.

Player must detect enemies in some range. And function should be like this:

Code: Select all

if Player:see(enemy) then
  --do some staff
end

Pleasy give me advice and may be link to articles about this.
Thanks!)

(Sorry, my english is very bad )

[micha]

To check, if the player can see the enemy, you have to check three things:

• The enemy is not too far away (calculate the distance between player and enemy)
• The enemy is within the sight-cone (calculate the angle between the line (player-enemy) and the center line of the players view)
• There is no object in between. This would be solved with ray-casting.

I suggest checking these three conditions in this order, because the last one is computationally most expensive.

[bekey]

-snip-

[micha]

I just want to point out the difference between bekey's and my suggestions: My approach has three conditions and checks for a circular sector. Bekey's approach has only two conditions and checks for a triangular area.

If the angle of vision is small, the difference is small and you should go for the approach you find simpler. For larger angles, you should definitely go for circular sectors, otherwise the player can look very far diagonally, but not very far straight.

[bekey]

-snip-

[micha]

Here is my attempt for implementing the circular sector approach:

Code: Select all

function player:see(enemy)
	return player:isCloseTo(enemy) and player:withinAngle(enemy) and player:raycast(enemy)
end

function player:isCloseTo(enemy)
	local dx,dy = player.x-enemy.x, player.y-enemy.y
	return dx^2+dy^2 < player.maxViewDistance^2
end

function player:withinAngle(enemy)
	local dx,dy = player.x-enemy.x, player.y-enemy.y
	local anglePE = math.atan2(dy,dx)
	local dAngle = ((anglePE-player.angle+math.pi)%(2*math.pi)-math.pi)
	return dAngle < 0.5*player.sightAngle
end

function player:raycast(enemy)
	-- to be filled (depends on implementation)
end

Some notes:

• The and operator in Lua only evaluates the second argument, if the first one is true. So if the "isCloseTo" check fails, then the other functions are not called.
• The cone is defined by player.sightAngle and player.maxViewDistance.
• player.angle denotes the direction the player is currently looking.
• anglePE is the angle of the line between player and enemy
• dAngle is the angle between the line (player-enemy) and player.angle. The math.pi and stuff is needed so wrap the angles correctly

[Snuux]

Oh, with ray casting, is hard for me... I find some articles and now try learn it. I thought, that is not so hard Thanks all!

[bekey]

-snip-

[Roland_Yonaba]

Oh, with ray casting, is hard for me... I find some articles and now try learn it. I thought, that is not so hard Thanks all!

Well, in case you are using a tile-based world representation, Bresenham length of sight is the way to go. Or Bresenham-based supercover line algorithm for something more accurate.
If not, well, there is more work to do: you will have to emit a ligne from the player and check if this line is not intersecting any obstacle bounding shape (circle, polygon, whatever).