通过HSV颜色计算圆点

Question

I have a color circle where the user can choose a color from. The color is calculated with this method

public int getColorForPoint(int x, int y, float[] hsv) {
        x -= fullCircleRadius;
        y -= fullCircleRadius;
        double centerDist = Math.sqrt(x * x + y * y);

        hsv[0] = (float) (Math.atan2(y, x) / Math.PI * 180f) + 180;
        hsv[1] = Math.max(0f, Math.min(1f, (float) (centerDist / innerCircleRadius)));

        return Color.HSVToColor(hsv);
    }

Now I need the reversed method to calculate the x and y coordinate by a given color (hsv array). To be more specific: The user can save a color and the indicator in the color circle should "jump" to the saved color on the circle. But I'm quite lost with this mathematics.

Answer 1

Looking at the way you calculate centerDist - I can tell your circle centre is at the origin (0,0).

Basically HSV is a polar co ordinate, all you need is to convert a polar co ordinate to cartesian co ordinate. which is done as follows.

public double[] getHSVtoCartesian(double[] hsv) {

    double [] xy;

     double theta = hsv[0];
     double r = hsv[1];

    xy[0] = r * Math.cos(theta);
    xy[1] = r * Math.sin(theta);

    return xy;
}