How to inflate a rectangular shape given its vertices

Question

I have 5 vertices of a Rectangle. I want to inflate the rectangle to a certain no. say x. How can I dot that? The rectangle is a custom struct not System.Drawing.Rectangle object. Please suggest.

Answer 1

This inflates rectangle relative to its center:

    struct Rect {
        public PointF p1 { get; set; }
        public PointF p2 { get; set; }
        public PointF p3 { get; set; }
        public PointF p4 { get; set; }
        public PointF p5 { get; set; }
    }

    void RectResize()
    {
        // input rectangle and sample vertices
        Rect input = new Rect();
        input.p1 = new PointF(80, 200);
        input.p2 = new PointF(160, 340);
        input.p3 = new PointF(470, 160);
        input.p4 = new PointF(390, 20);
        input.p5 = new PointF(80, 200);  // same as p1

        PointF[] r1 = { input.p1, input.p2, input.p3, input.p4 }; // conversion to array, easier to manipulate
        float ratio = .3F;  // inflation factor
        PointF center = new PointF(r1[0].X + (r1[2].X - r1[0].X) / 2, r1[0].Y + (r1[2].Y - r1[0].Y) / 2);
        PointF[] r2 = new PointF[4];  // output array
        for (int i = 0; i < 4; i++)
        {
            r2[i].X = center.X + (r1[i].X - center.X) * ratio;
            r2[i].Y = center.Y + (r1[i].Y - center.Y) * ratio;
        }

        // convert output to struct Rect if needed
        Rect output = new Rect();
        output.p1 = r2[0]; output.p2 = r2[1]; output.p3 = r2[2]; output.p4 = r2[3]; output.p5 = r2[0];

        // demo
        Graphics g = this.CreateGraphics();
        g.DrawPolygon(Pens.Blue, r1);
        g.DrawPolygon(Pens.Red, r2);
    }