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Q108710: PRB: Extra Repaint of VB CDK Graphical Custom Control

Article: Q108710
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:3.0
Operating System(s): 
Keyword(s): 
Last Modified: 26-APR-2000

3.00
WINDOWS
kbtool kbprg kbprb

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The information in this article applies to:

- Microsoft Visual Basic Professional Edition for Windows, version 3.0 
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SYMPTOMS
========

You can use the Visual Basic Control Development Kit (CDK) to design a graphical
custom control to perform visual effects. However, when another control such as
a Visual Basic button becomes visible on the same form as your custom control,
the graphical control repaints even though its client area has not been
invalidated.

CAUSE
=====

The repaint logic in Visual Basic causes this behavior. Graphical controls get a
VBM_PAINT message every time their container gets a WM_PAINT message, regardless
of whether the graphical control is in the invalidated area.

The VBM_PAINT message is the paint notification for graphical controls. The value
of the VBM_PAINT constant is defined in the VBAPI.H file in Visual Basic's CDK
directory. WM_PAINT is a message for windowed controls. For examples of
VBM_PAINT and WM_PAINT, see the PIX.C file in Visual Basic's CDK directory.

WORKAROUND
==========

You can work around this behavior in the VBM_PAINT handler with the following C
code:

     if (!RectVisible((HDC)wParam,(LPRECT)lParam)) {
        // Control is not in the paint region
        // Don't bother to repaint
        break;
        }

Additional query words: 3.00 flash flicker

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Keywords          :  
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB300Search kbVB300
Version           : WINDOWS:3.0

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