C# How to draw in front of objects?

.net graphics user-controls paint drawstring
Patrick picture Patrick · Jul 29, 2009 · Viewed 20.6k times · Source

How do you draw a string that is supposed to be on top of everything else? Right now in my panel i have some user controls in Panel1.Controls. So i added this to the Paint method:

Graphics g = Panel1.CreateGraphics();  
g.DrawString("BUSTED", new Font("Arial", 20f), new SolidBrush(Color.Black), new PointF(50, 50));

The problem is that the text is printed behind the user controls, so it can't be seen. (If i change the position of the text out in the open, it's displayed correctly).

Any ideas?

Answer

Michael A. McCloskey picture Michael A. McCloskey · Jul 29, 2009

All windows forms controls are HWND based, meaning they each have their own window handle and the z-order/parent-child of the controls determines what clips what. The panel paint event is painting onto the panel control, but the panel controls output is clipped by all it's child controls.

Transparency does not work correctly in windows forms. If you set something to have a transparent background, it will typically wind up having the form background show through, and not it's immediate parents.

I have worked around this in various ways.

  1. Do all the compositing yourself by rendering everything to a bitmap and then displaying that. This only works with static content.
  2. Create a windowless rendering model that renders everything like in #1, also handles mouse interaction with its constituent elements.
  3. Create a new top level, layered window (WS_EX_LAYERED) that overlays the control and renders the desired content. This prohibits interaction with the underlying control unless steps are taken to pass messages through. I believe this is the method Visual Studio 2008 uses for the windows form designer surface.

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