Question 69312 in IOS Swift Question posted in
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How to determine the rotation angle? – Ios swift

I’m trying to implement a russian roulette game and want it to brute-force the solution for it. Here is my problem. I’m going to hard code the relative angles of the numbers on the wheel (eg. there are 36 numbers and each number would have 10 degree offset to each other, the one on the top, 12 o’clock position, will have the 0 and the next 10 and vice versa). I will rotate the wheel randomly and then determine the rotation of it based on some values that I can calculate (startPosition to finishedPosition). The wheel is an ImageView. Is there a way to actually do this? For example, get the top left x,y pos for its start and end, then by some formula to calculate how much it rotated. Or is there a better way to do this? There is not much of a source code to show it, so this is more like a mathematical question rather than a swift one. Any feedback is much appreciated.

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  1. 0

    To calculate rotation, you need coordinates of three points: start location sx, sy, end location ex, ey of the same point after rotation and center of rotation cx, cy

    Then you can find angle using atan2 function

    rot_angle = atan2((ex-cx)*(sx-cx)+(ey-cy)*(sy-cy), (ex-cx)*(sy-cy)-(ey-cy)*(sx-cx))

    Note – I used argument order (x,y) from here, while most languages use reverse order (y,x), so check what order you really need (I have no experience in IOS languages). Also result value might be in radians or in degrees (above link doesn’t specify it clearly)

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  2. 0

    Your question doesn’t make much sense. If you rotate the wheel randomly, calculate the random value as an angle. If you want to change the previous rotation by some random angle, then do the math on the starting rotation and ending rotation. That is just adding and subtracting angles (modulo 2π). Then you will know how far it is rotated, and not have to calculate it.

    Assuming you’re talking about a roulette wheel, and not "Russian Roulette" (In American English at least, that term involves pointing a loaded revolver at your head) you’ll need to track both the wheel rotation and the ball rotation. To apply the rotation to the wheel, you’ll just take the image of the wheel and rotate it on the Z axis around it’s x/y center point.

    To plot the ball, you’ll need to use trig to calculate the center of the ball based on the radius of the track the ball follows and the angle. But again, always track the angle, and then convert the angle to an x/y center point for the ball to plot it. Don’t forget the angle and then have to convert back from the ball position to its angle. That’s silly.

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