StretchBlt

[Hogger]

Hi all Guru's,

I need som help with the API call StretchBlt. I use it to scale a picture from one picturebox to another. This works fine... no to the problem. It only works on Windows 2000(so far). I have also tested it on Windows 95 and Windows Me and it just gives me a White area instead of my beautiful picture. Are there any problems with this API call and different OS's. And if there is... can I do it another way ?? I tried to putting the picture into an Image control which scales the picture but the resolution is crappy. Can't see anything... no good. Any ideas out there.

Best regards
Hogger

[John G Duffy]

I use the StretchBlt copying pictureboxes on Windows ME with no problems resizeing at will. Perhaps playing with autosize or Redraw properties or maybe the picture is coming outside the bounds of the Target picturebox.
below is a sample running program.
You need two picture boxes and a command button with a picture in Picture1

option Explicit
Const SRCCOPY = &HCC0020 ' Copies image exactly
Const TwipsperInch = 1440
private Declare Function CreateCompatibleDC Lib "gdi32" (byval hdc as Long) as Long
private Declare Function SelectObject Lib "gdi32" (byval hdc as Long, byval hObject as Long) as Long
private Declare Function DeleteObject Lib "gdi32" (byval hObject as Long) as Long
private Declare Function StretchBlt Lib "gdi32" (byval hdc as Long, byval X as Long, byval Y as Long, byval nWidth as Long, byval nHght as Long, byval hSrcDC as Long, byval XSrc as Long, byval YSrc as Long, byval nSrcWidth as Long, byval nSrcHeight as Long, byval dwRop as Long) as Long
private Declare Function DeleteDC Lib "gdi32" (byval hdc as Long) as Long

public Sub CopyPictureToTarget(Src as PictureBox, tgt as Variant, l, t, w, h)
' Do some Magic
Dim hMemoryDC as Long
Dim hOldBitMap as Long
Dim lret
' Do some Magic
hMemoryDC = CreateCompatibleDC(Src.hdc)
hOldBitMap = SelectObject(hMemoryDC, Src.Picture)
'
' Copy picture to the target hdc

lret = StretchBlt(tgt.hdc, l, t, w, h, _
hMemoryDC, 0, 0, Src.ScaleWidth, _
Src.ScaleHeight, SRCCOPY)
'
If lret = 0 then Stop
' Restore the magic
hOldBitMap = SelectObject(hMemoryDC, hOldBitMap)
' Cleanup
lret = DeleteDC(hMemoryDC)

End Sub

private Sub Command1_Click()
Dim OneInchX as Long
Dim OneInchY as Long

OneInchX = TwipsperInch / Screen.TwipsPerPixelY
OneInchY = TwipsperInch / Screen.TwipsPerPixelY
print OneInchX; " "; OneInchY
Picture1.ScaleMode = vbPixels
Picture2.ScaleMode = vbPixels
CopyPictureToTarget Picture1, Picture2, 0, 0, OneInchX, OneInchY
Picture2.Refresh
End Sub




John G

[Hogger]

Thanks John,

It seams to work. Only tried it on Windows Me. I didn't use the CreateCompatibleDC, SelectObject stuff you used. That might be my mistake. Anyway thanks a lot.... you just made my life a little easier... :-).

/Hogger