Check if a point is in a rotated rectangle (C#)

Question

I have a program in C# (Windows Forms) which draws some rectangles on a picturebox. They can be drawn at an angle too (rotated).

I know each of the rectangles\' star

Answer 1

I know this was already answered but I had to do something similar a while ago. I created an extension method for the System.Windows.Point class that helped do exactly what Neil suggested:

    public static double GetAngle(this Point pt)
    {
        return Math.Atan2(pt.X, -pt.Y) * 180 / Math.PI;
    }

    public static Point SetAngle(this Point pt, double angle)
    {
        var rads = angle * (Math.PI / 180);
        var dist = Math.Sqrt(pt.X * pt.X + pt.Y * pt.Y);
        pt.X = Math.Sin(rads) * dist;
        pt.Y = -(Math.Cos(rads) * dist);
        return pt;
    }

This would allow me to work with the angles of points around 0, 0. So if you know the center of the rect that you are testing you would offset the point by the negative of this value (for example: pt.X -= 32; pt.Y -= 32) And then you would apply the negative rotation of the rectangle (as suggested by Neil: pt.SetAngle(-45);)...

Now if the point is within 64, 64 you know you hit the rectangle. More specifically I was checking a pixel of a rotated image to make sure I hit a pixel of a specific color.