SetClip 将窗体的指定区域弄成可剪裁区域
IntersectClip 需找2个剪裁区交集区域
private void IntersectClipRectangleF2(PaintEventArgs e)
{
// Set clipping region.
Rectangle clipRect = new Rectangle(0, 0, 200, 200);
e.Graphics.SetClip(clipRect);
// Update clipping region to intersection of
// existing region with specified rectangle.
RectangleF intersectRectF = new RectangleF(100.0F, 100.0F, 200.0F, 200.0F);
e.Graphics.IntersectClip(intersectRectF);
// Fill rectangle to demonstrate effective clipping region.
e.Graphics.FillRectangle(new SolidBrush(Color.Blue), 0, 0, 500, 500);
// Reset clipping region to infinite.
e.Graphics.ResetClip();
// Draw clipRect and intersectRect to screen.
e.Graphics.DrawRectangle(new Pen(Color.Black), clipRect);
e.Graphics.DrawRectangle(new Pen(Color.Red), Rectangle.Round(intersectRectF));
}`