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

If you know the coordinates of the corners of the rectangle, this is an fast, elegant solution that merely involves a couple of dot and scalar products: https://math.stackexchange.com/a/190373/178768