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Q189736: BUG: Painting Model for BitBlt and StretchBlt Changed for VB6

Article: Q189736
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): kbGrpDSVB
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Learning Edition for Windows, version 6.0 
- Microsoft Visual Basic Professional Edition for Windows, version 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, version 6.0 
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SYMPTOMS
========

A program that paints correctly using the BitBlt or StretchBlt API functions
under Visual Basic 5.0 might no longer work under Visual Basic 6.0. Under Visual
Basic 5.0, the bitmap is correctly displayed no matter whether the AutoRedraw
property of the Form is set to True or False. However, under Visual Basic 6.0,
if the AutoRedraw property is set to True, nothing is displayed and no error
messages are generated.

RESOLUTION
==========

In Visual Basic 6.0, set the Form's AutoRedraw property to False or call Refresh
to view the result after calling BitBlt or StretchBlt if the AutoRedraw property
is set to True.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. We are researching this bug and will post new
information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

1. Create a new Standard EXE project in Visual Basic. Form1 is created by
  default.

2. Change the AutoRedraw property of Form1 to True.

3. Add a CommandButton (Command1) to Form1.

4. Add a PictureBox (Picture1) to Form1 and set its Picture property to a .bmp
  file.

5. Copy and paste the code below in Form1's code module:

        Option Explicit

        Private Declare Function BitBlt Lib "gdi32" ( _
           ByVal hDestDC As Long, ByVal x As Long, ByVal y As Long, _
           ByVal nWidth As Long, ByVal nHeight As Long, _
           ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, _
           ByVal dwRop As Long) As Long

        Private Sub Command1_Click()

           Call BitBlt(hdc, ScaleX(Width, vbTwips, vbPixels) * 0.5, _
              ScaleY(Height, vbTwips, vbPixels) * 0.5, _
              ScaleX(Picture1.Width, vbTwips, vbPixels), _
              ScaleY(Picture1.Height, vbTwips, vbPixels), _
              Picture1.hdc, 0, 0, vbSrcCopy)
           '**************************************************************
           'Refresh    'this line is required for Visual Basic 6.0 to
                       'work if Form1.AutoRedraw is TRUE
           '**************************************************************
        End Sub

  If the above project is run in Visual Basic 5.0, everything behaves as
  expected. If run under Visual Basic 6.0, the program will not run as
  expected. For the above code to work in Visual Basic 6.0, you must call
  Refresh (as commented above).

Additional query words: kbDSupport kbVBp500bug kbVBp600bug kbdss kbVBp kbAPI kbBitmap

======================================================================
Keywords          : kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB600Search kbVBA600 kbVB600
Issue type        : kbbug

=============================================================================

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