Digging for undocumented system calls

After much reverse engineering and stepping through MS source code looking for how the .net framework renders the simple black X close button for maximized MDI windows, I’ve found something which is well documented. DrawCaptionButton. Sigh. Well, here it is in case I forget.

Image ControlImage;

protected override void OnPaint(PaintEventArgs pe)
{
pe.Graphics.Clear(BackColor);
pe.Graphics.DrawImage(ControlImage, 0 , 0);
}

Image GetImage()
{
Bitmap image = new Bitmap(0x10, 0x10);
using (Graphics graphics = Graphics.FromImage(image))
{
ControlPaint.DrawCaptionButton(graphics, new Rectangle(Point.Empty, image.Size), CaptionButton.Close, ButtonState.Flat);
graphics.DrawRectangle(SystemPens.Control, 0, 0, image.Width - 1, image.Height - 1);
}
image.MakeTransparent(SystemColors.Control);
return image;
}