How Can I Create a Semi-Transparent Overlay on a Windows Form Without Obscuring Child Controls?

Achieving a Semi-Transparent Overlay in Windows Forms Without Hiding Child Controls

Creating a semi-transparent overlay on a Windows Form without obscuring underlying controls necessitates using a second form layered on top. This overlay form utilizes the Opacity property to control its transparency level.

To build this overlay, add a new class to your project and implement the Plexiglass class (as shown in the example code below). This class will represent our overlay form.

public class Plexiglass : Form
{
    // ... Code implementation ...
}

Create an instance of the Plexiglass class, passing the main form as a parameter:

var overlay = new Plexiglass(this);

The Plexiglass form will dynamically adjust its position and size to match the main form, ensuring consistent coverage. Closing the overlay via overlay.Close() will restore the main form's full visibility.

For a smoother visual effect, consider disabling Aero transitions on the main form to prevent jarring animations:

if (Environment.OSVersion.Version.Major >= 6)
{
    int value = 1;
    DwmSetWindowAttribute(this.Handle, DWMWA_TRANSITIONS_FORCEDISABLED, ref value, 4);
}

This code snippet (assuming DwmSetWindowAttribute is appropriately defined and imported) disables Aero transitions, resulting in a more seamless overlay appearance.

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