Angle Calculation

[lincore]

Hi folks,

first of all: hello community. I started playing around with mmf2 a few days ago and now I have encountered the first problem I can't solve on my own.

I am trying to create a top down shooter thingie with enemies walking around, shooting at mostly innocent players. I want to give them a line of sight to determine if they see the player or not.

First I used an invisble object to detect the players presence, but I don't like that solution. It produces too much overhead for my taste and seems to be quite dirty. So I went over to math. I want to calculate the direction from an enemy to the player and compare that to the enemies direction. If the direction to the player is somewhere between -60° and +60° of the enemy's, then he fires a detector at the player, and if it hits him (aka not a wall), the player has been spotted.

I put the x and y distances from the enemy to the player in alterable values, calculated the hypotenuse of these values and the arcsin of y-distance / hypotenuse.

Sounds good to me, but unfortunetely the angles are completely wrong. Here are the angles that I get (N S W E are directions):
N:90° E:180° S:90° W:0°

Here is what I should get:
N:90° E:0° S:270° w:180°

Can anybody give me a clue whats wrong here?
Thanks in advance,
lincore

[Algul]

ATan2(Y1-Y2,X2-X1) will give you N:90° E:0° S:-90° w:180°

[lincore]

It works. Thanks, Algul.
lincore

[lincore]

For the record:
ATan2 (Special Object>Sine and Cosine>Arc Tangent of y/x (expression)) returns a value between -180 and +180. To get correct angles from 0 to 359 degrees you have to do this (pseudocode):

if (atan2_result < 0) then:
    atan2_result = 360 + ANGLE;

lincore

[Werbad]

In MMF you can use:

(atan2(y2-y1,x2-x1) + 360) mod 360