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2D All the way! / Trig for getting spaceship to point in right direction

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Joined: 19th Apr 2013
Posted: 21st Apr 2013 10:38

I'm making a 2D spaceship-shooter game that moves in all directions, (i.e. ( -x, +x ),( -y, +y ) ).

I'm trying to make the spaceship face the direction of the movement according to a virtual joystick. The virtual joystick has it's x and y coordinates working correctly and they are normalized (ie. between -1 and +1) in both x and y.

I'm able to set the angle of the image I'm using by a call to

where the angle is in degrees. The problem I'm having is with the trigonometry involved.

I know from trig that calculating the angle is radius*cos(x), and I could be wrong on that, so I tried this:

Problem one is, there's no account for the Y direction, so I tried:

Still a problem, just not working correctly, so I tried arcsine and arccosine:

Now the image is just flipping in what seems like a random direction, and just in case it was calculating, instead of the total angle, perhaps it was the angle from the x intercept, so I tried:

Now it's only flipping as if angle is close to 0 and moving occasionally in a certain 270 degree position I believe,

So I guess I'm going to have to admit that my trigonometry skills aren't what they used to be and ask you guys for some help, by the way sin(x) is where x is in degrees and sinr(x) is where x is in radians, so I might be missing it there too, frankly I'm just too confused to get any farther right now.

Thanks guys!
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Joined: 19th Apr 2013
Posted: 21st Apr 2013 20:13
I was able to get the code to work with this small set of code:

using tan2( y, x )

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Joined: 16th Apr 2003
Location: Metropia
Posted: 27th Apr 2013 12:17 Edited at: 28th Apr 2013 10:11

"You're all wrong. You're all idiots." ~Fluffy Rabbit

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