Tip 113: Creating Transparent Forms

July 1, 1995

Abstract

When developing an application in Microsoft® Visual Basic®, you may need to design a transparent form. This article explains how to create transparent forms.

Using Transparent Forms

A transparent form is a form that, when displayed, does not cover up the underlying windows beneath it. The Microsoft® Windows® application programming interface (API) function SetWindowLong can be used to change the style settings of a form or window. You can create a transparent window by setting the WS_EX_TRANSPARENT style bit.

To use the SetWindowLong function within your Microsoft Visual Basic® program, include the following Declare statement in the General Declarations section of a form (note that it must be typed as a single line of code):

Private Declare Function SetWindowLong Lib "User" (ByVal hWnd As Integer, ByVal 
   nIndex As Integer, ByVal dwNewLong As Long) As Long

The SetWindowLong function takes the following arguments.

hWnd An integer value containing the window's handle.
nIndex An integer value that describes the type of information you want to set. This value may be one of the following:
GWL_EXSTYLE Set the extended window style
GWL_STYLE Set the window style
GWL_WNDPROC The window function's address
dwNewLong A long value containing the new style bits to be given to the window.

Because you want to make the specified form transparent, you call the SetWindowLong function with the nIndex argument set to GWL_EXSTYLE, specifying the transparency style bit.

When you run the example program shown below, the form will be displayed in transparent mode.

Example Program

This program shows how to create a transparent form.

  1. Create a new project in Visual Basic. Form1 is created by default. Set the form's Picture property to the ARCHES.BMP bitmap file (usually found in the \WINDOWS directory).

  2. Add a Command Button control to Form1. Command1 is created by default. Set its Caption property to "Show Form".

  3. Add the following code to the Click event for Command1:
    Private Sub Command1_Click()
    Form2.Show
End Sub
  4. From the Visual Basic Insert menu, select Form to create a new form. Form2 is created by default. Change the size of Form2 so that it is the same size as Form1. Position Form2 so that it is on top of Form1.

  5. Add the following Constant and Declare statements to the General Declarations section of Form2 (note that the Declare statement must be typed as one single line of code):
    Private Declare Function SetWindowLong Lib "User" (ByVal hWnd As Integer, ByVal 
   nIndex As Integer, ByVal dwNewLong As Long) As Long
Const WS_EX_TRANSPARENT = &H20&
Const GWL_EXSTYLE = (-20)
  6. Add the following code to the Form_Load event for Form2:
    Private Sub Form_Load()
   Dim Ret As Long
   Ret = SetWindowLong(Form2.hWnd, GWL_EXSTYLE, WS_EX_TRANSPARENT)
End Sub

Run the example program by pressing F5. Click the "Show Form" command button. Form2 is displayed directly over Form1. It appears as if only Form1 is displayed because Form2 has the transparent attribute.