C#, GDI+ - Why are my rectangles truncated?

Answer 1

Your problem is DrawRectangle. The starting location of your rectangle reaches the end of your initial bitmap.

If you change the location of your rectangle you will be able to see it completely.

using (Graphics g2 = Graphics.FromImage(b))
{
    g2.DrawRectangle(new Pen(Color.White, 7.2f), 50, 50, 150, 100);
}

Answer 2

I tried your code with TryGdiPlus (very useful for these kind of things, BTW). I managed to make the rectangle draw without clipping with width of 99 pixels:

g2.DrawRectangle(new Pen(Color.White, 7.2f), 200, 100, 99, 100);

So it looks as though the bitmap's width is still 300 pixels even after rotating.