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I'm working on a side scroller, and for the enemy I'm making a turret. I'm trying to make the turret aim at the player but I cant seem to get it right. Below is a rough sketch of what I want to achieve:

enter image description here

I want the barrel (dark blue), to aim/rotate to its pointing at the player.

I have uploaded a YouTube video of my scene:

http://www.youtube.com/watch?v=eeP47VoX9uA&feature=youtu.be

This is what I have so far (loop):

function enterFrameHandler(e : Event) : void{
   _turretBarrel.rotation = Math.atan2(enTarget.x, enTarget.y) * 180/Math.PI;
}

What this does is only rotate the barrel when I jump, and the barrel isn't even aiming at the player, also the barrel doesn't change rotation when I walk on the other side of the turret.

My enTarget.x is always central to the stage and the scene (including the turret) moves around the player left and right (x)... Only the enTarget.y moves (jump/high platform).

I'm slightly new to Flash and ActionScript. If anyone could help me out, or point me in the right direction then that would be great.

Thanks

Oliver Jones
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2 Answers2

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Oliver, it looks like you are calculating the tangens of wrong angle (between player and X-axis). You need something like the following:

function enterFrameHandler(e : Event) : void{
   _turretBarrel.rotation = Math.atan2(enTarget.x - barrel.x, enTarget.y - barrel.y) * 180/Math.PI;
}
Eugeny89
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    It should probably be `Math.atan2(enTarget.y - barrel.y, enTarget.x - barrel.x)` – Jonatan Hedborg Mar 16 '12 at 08:43
  • Still not working correctly. I forgot to mention that my player.x is always central to the stage, and that the scene (including the turret) moves left/right. ALthough my player.y does move. – Oliver Jones Mar 16 '12 at 09:20
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1) Make sure you got the right numbers and the position of the avatar and the turret are in the same coordinate space. A simple trace of each would do. In this case you probably want the world (relative to stage) position of both clips. Make sure they make sense compared to top left corner of the screen (0, 0).

2) Remember that _turretBarrel.rotation is a rotation that ranges from -180 to 180 so this would need to be taken into consideration when calculating angles.

3) Make sure you use the corresponding degrees/radians where appropriate.

4) force focus on avatar, run the game and see if the bounds looks ok. Then do the same thing with the turret.

Another good thing in general for debugging purposes is to setup some kind of debug graphics. i.e. draw a line of what you think is the direction vector to verify your numbers and calculations.

On a side note: This is what the majority of programming is; Debugging. Assume nothing but hard facts, get your numbers from the debugger (probably quicker), or trace output. If you're still using the horrible flash professional IDE. I would really recommend getting one with a proper debugger like FlashDevelop (free) or Flash Builder (commercial)

Kristian Moström
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  • I'm struggling to follow this. I'm really new to AS3, and its hard to get my head around your instructions – Oliver Jones Mar 17 '12 at 09:11
  • No worries. First calculate the direction vector from the turret towards the avatar. DirectionVector = PlayerPosition - TurretPosition. Both positions needs to be in the same space (somewhat explained here http://www.actionscriptmoron.com/?p=1062). I'm guessing one source of the problem could be that one (or both) clips are child clips of other clips. Which would make i.e. avatar_movieclip.x not a reliable value as it could be relative to the parent clip of the avatar clip (if it has one). Make sure to use absolut positions unless both clips are direct children of the same parent clip. – Kristian Moström Mar 18 '12 at 21:56