BUG: Painting Model for BitBlt and StretchBlt Changed for VB6

• Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 6.0

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 : kbGrpVB
Version :
Platform : WINDOWS
Issue type : kbbug