Check if two objects are facing eachother

Question

I've searched all over and couldn't find an answer to this seemingly common question, surprisingly. The problem I'm currently facing is checking if the player is facing an enemy, then if so within what range of the players' view (adjustable) and if it's within that range then move away in the nearest safe direction.

Here's a picture :D

So, how would I accomplish this? I have the x, y, and direction, of every ship object. This is my last failed attempt, attempting to consider that the player's direction will be exactly 180 degrees away from the enemy's direction relative to the player.

var direction=Math.direction(this.x,this.y,player.x,player.y,1),
    playerview=Math.abs(direction)-Math.abs(player.direction-180)
if(Math.abs(playerview)<10) {
    console.log('in view')
    this.xVelocity+=AI.speed*Math.sin(playerview*Math.PI/180)
    this.xVelocity+=AI.speed*Math.cos(playerview*Math.PI/180)
    }

In this example, 10 would be the range. Of course, I've only managed to make ships rotate to the right, so aside from the detection only working on half a circle I can't make the enemy go to the right side either. Any ideas?

Answer 1

In Your code, You are modifying this.xVelocity twice instead of modifying this.yVelocity.

I guess, Math.direction is not in the JavaScript/ECMA standard. Are You sure, You are using it correctly? Consider Math.atan2.

Moreover, You should provide a definition of "facing each other".

If it's "seeing each other", then Your comment "in view" is misleading.

---

But the main issue is:

Math.abs(angleInDegrees) modifies the angle!

The correct way to build an absolute value of an angle is:

while (angleInDegrees < 0) 
{   
   angleInDegrees += 360;
}

// If necessary, add this too:
while (angleInDegrees >= 360)
{
   angleInDegrees -= 360;
}

-10 and 350 are identical, -10 and 10 are 20 degrees apart.

For further explanation, let's call the code above normalizeAngle

(Note: For huge values, the loop may run very long or even forever. If such values may occur, this should be checked.)

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The following should do the trick:

playerview = normalizeAngle(direction - player.direction - 180)
if (playerview < range || playerview > 360-range) {

By the way: "playerview" should be the mininum from the player's field of view and the enemy's field of view.