Rotate a point around another point

Question

I have a task to draw a specific graphic. As part of this task I need to rotate some dot\'s on 45 degrees.

I\'ve spent already 2 days trying to calculate a formula,

Answer 1

The problem is int center = radius which you are setting int radius = 576. This doesn't make sense as surely you are rotating about a point that should have an x and y location.

Given you are rotating around the origin the center x and y should both be 0 not 576.

So, given that, try this.

/// 

/// Rotates one point around another
/// 
/// The point to rotate.
/// The center point of rotation.
/// The rotation angle in degrees.
/// Rotated point
static Point RotatePoint(Point pointToRotate, Point centerPoint, double angleInDegrees)
{
    double angleInRadians = angleInDegrees * (Math.PI / 180);
    double cosTheta = Math.Cos(angleInRadians);
    double sinTheta = Math.Sin(angleInRadians);
    return new Point
    {
        X =
            (int)
            (cosTheta * (pointToRotate.X - centerPoint.X) -
            sinTheta * (pointToRotate.Y - centerPoint.Y) + centerPoint.X),
        Y =
            (int)
            (sinTheta * (pointToRotate.X - centerPoint.X) +
            cosTheta * (pointToRotate.Y - centerPoint.Y) + centerPoint.Y)
    };
}

Use like so.

Point center = new Point(0, 0); 
Point newPoint = RotatePoint(blueA, center, 45);

Obviously if the center point is always 0,0 then you can simplify the function accordingly, or else make the center point optional via a default parameter, or by overloading the method. You would also probably want to encapsulate some of the reusable math into other static methods too.

e.g.

/// 

/// Converts an angle in decimal degress to radians.
/// 
/// The angle in degrees to convert.
/// Angle in radians
static double DegreesToRadians(double angleInDegrees)
{
   return angleInDegrees * (Math.PI / 180);
}

/// 

/// Rotates a point around the origin
/// 
/// The point to rotate.
/// The rotation angle in degrees.
/// Rotated point
static Point RotatePoint(Point pointToRotate, double angleInDegrees)
{
   return RotatePoint(pointToRotate, new Point(0, 0), angleInDegrees);
}

Use like so.

Point newPoint = RotatePoint(blueA, 45);

Finally, if you are using the GDI you can also simply do a RotateTransform. See: http://msdn.microsoft.com/en-us/library/a0z3f662.aspx

Graphics g = this.CreateGraphics();
g.TranslateTransform(blueA);
g.RotateTransform(45);