Difference between revisions of "User:Dee/Flicker handling"
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{{VB6}} | {{VB6}} | ||
| − | VB6 seems to | + | VB6 seems to ignores the WM_ERASEBKGND message and deso its background drawing internally in the WM_PAINT message. |
| − | This can cause flickering so to "fix" this, we | + | This can cause flickering so to "fix" this, we handle both messages and override VB's own WM_PAINT handling, set everything up and call the paint event ourselves. |
| − | We make sure the messages are not passed on to the next handler by telling the subclasser not to call CallWindowProc() but return | + | We make sure the messages are not passed on to the next handler by telling the subclasser not to call CallWindowProc() but return immediately. |
<pre> | <pre> | ||
Latest revision as of 21:32, 5 April 2010
| This article is currently work in progress. Please come back later. |
| This article is based on Visual Basic 6. Find other Visual Basic 6 articles. |
VB6 seems to ignores the WM_ERASEBKGND message and deso its background drawing internally in the WM_PAINT message. This can cause flickering so to "fix" this, we handle both messages and override VB's own WM_PAINT handling, set everything up and call the paint event ourselves. We make sure the messages are not passed on to the next handler by telling the subclasser not to call CallWindowProc() but return immediately.
Private Function SubClassed_WindowProc(ByVal hWnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long, Handled As Boolean) As Long
Dim PaintInfo As PAINTSTRUCT
Dim hDC As Long
Select Case hWnd
Case GraphFrame.hWnd
Select Case Msg
Case &HF 'WM_PAINT
'We handle WM_PAINT ourselves as VB6 seems to explicitly draw the background in its handler
hDC = BeginPaint(hWnd, PaintInfo)
GraphFrame_Paint
EndPaint hWnd, PaintInfo
'We've handled it so VB doesn't do anything further
SubClassed_WindowProc = 0
Handled = True
Case &H14 'WM_ERASEBKGND
'WM_ERASEBKGND seems to be a noop, but we handle it here anyway
SubClassed_WindowProc = -1
Handled = True
Case &H137 'WM_CTLCOLORSCROLLBAR
'Ignore the message to fix the scrollbar background
Handled = True
End Select
End Select
End Function
