Transparent Borderless Forms in C#

The picturebox fills the entire draggable area of the form (those sections which are not visible cannot be used for a drag operation) and for that that reason the picture box controls mouse down event is used to support the borderless form dragging operations.

/// <summary>
/// Respond to the picture box mousedown event to
/// drag the borderless form around (left click and drag)/// </summary>

/// <param name="sender"></param>
/// <param name="e"></param>

private void pictureBox1_MouseDown(object sender, MouseEventArgs e)

{

// drag the form without the caption bar

// present on left mouse button

if (e.Button == MouseButtons.Left)

{

ReleaseCapture();

SendMessage(this.Handle, 0xa1, 0x2, 0);

}

}

The rest of the class code is pretty straightforward and is not particularly relevant to the topic. The code is annotation to explain the remaining event handlers.

/// <summary>

/// Close the Application

/// </summary>

/// <param name="sender"></param>

/// <param name="e"></param>

private void button1_Click(object sender, EventArgs e)

{

// dispose

this.Dispose();
}

/// <summary>

/// Creates a second transparent form

/// </summary>

/// <param name="sender"></param>

/// <param name="e"></param>

private void button2_Click(object sender, EventArgs e)

{

// open up another transparent form, this one with a hole in it

Form2 f = new Form2();

f.Show();

}

/// <summary>

/// Creates a third transparent form

/// </summary>

/// <param name="sender"></param>

/// <param name="e"></param>

private void button3_Click(object sender, EventArgs e)

{

Form3 f = new Form3();

f.Show();

}

Form 2 (Form2.cs)

The code behind Form2 is the same as it used in Form1; the only differences between the two forms are the complexity of the image used as the borderless form and that the background color and transparency key property values are different than that used on Form1.

Form 3 (Form3.cs)

Form3 is another spin on the same thing used in forms 1 and 2. The difference here is that the picture box contains a white rectangle; the transparency key value is set also to white which will defeat any attempts to drag the form. This form does have a border around it to enable dragging the form If you set the border style to None then the form will no longer be draggable.

Summary

This article was intended to demonstrate an approach to creating transparent backed, borderless draggable forms. The approach may be used to generate some sort of custom UI or may be used to build a classier looking splash screen.