Do I need to restore the Graphics state after painting in my OnPaint override (for a .NET Control)

Question

Consider the following overriden OnPaint method for a .NET Control:

protected override void OnPaint(PaintEventArgs e)
{
   base.OnPaint(e);
   e.Graphics.RotateTransform(180);

   // lots of drawing code
}

Is it a problem that I do not restore the state of the e.Graphics object when I am finished?

In Java this is often done by making a copy of the passed Graphics object, thus the passed Graphics object is not altered and there is no need to restore it's state. Similar Java Question

I could achieve this in .NET by using the Save() / Restore() methods. So my questions are:

• is it neccessary/best practice in .NET to restore the graphics state ?
• how expensive are the Save() / Restore() methods?

Answer 1

Well, whomever is going to implement the Paint event for the control is going to have a bit of a surprise. It could be valid if it makes sense that everything is always rotated, but that is for you to decide.

Graphics.Save + Restore takes about 4 microseconds on my laptop. Nothing to worry about given the typical expense of drawing.