Convert X,Y to angle

Question

I need a way to convert X and Y coordinates to an angle. I have this code but I need this layout:

 180

90 270

360

private double getAngle(double xTouch, double yTouch) {
    double x = xTouch - (slideBtn.getWidth() / 2d);
    double y = slideBtn.getHeight() - yTouch - (slideBtn.getHeight() / 2d);
    switch (getQuadrant(x, y)) {
        case 1:
            return Math.asin(y / Math.hypot(x, y)) * 180 / Math.PI;
        case 2:
            return 180 - Math.asin(y / Math.hypot(x, y)) * 180 / Math.PI;
        case 3:
            return 180 + (-1 * Math.asin(y / Math.hypot(x, y)) * 180 / Math.PI);
        case 4:
            return 360 + Math.asin(y / Math.hypot(x, y)) * 180 / Math.PI;
        default:
            return 0;
    }
}

/**
 * @return The selected quadrant.
 */
private static int getQuadrant(double x, double y) {
    if (x >= 0) {
        return y >= 0 ? 1 : 4;
    } else {
        return y >= 0 ? 2 : 3;
    }
}

Edit, to clarify the problem: The problem I had was that I was getting the wrong angles for the x,y angles. For instance: 0/360 degrees is the top side of the circle and 180 degrees is the bottom side of the circle. I tried to fix it using the code above (with different quadrants, but that didn't work). The accepted answer did the trick for me.

Answer 1

I'm not really sure what are you trying to achieve, but isn't it easier to just use the atan2 function to get an angle?

http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html#atan2(double, double)

If you are not familiar with the function you can read here:

http://en.wikipedia.org/wiki/Atan2

Edit, code example:

So, here is some code I think that is useful, after the discussion

public static double getAngle(int x, int y)
{
    return 1.5 * Math.PI - Math.atan2(y,x); //note the atan2 call, the order of paramers is y then x
}

Basically, it calculates an angle between the negative Y-axis with the positive clockwise direction. I hope that is what you have been looking for.