VB Forum / Win API / November 2007

I'm running into some trouble getting BitBlt and StretchBlt to work
for me.  I declare the function in my form like the following:

Private Declare Auto Function StretchBlt Lib "GDI32.DLL" _
       (ByVal hdcDest As IntPtr, ByVal nXOriginDest As Integer, _
       ByVal nYOriginDest As Integer, ByVal nWidthDest As Integer, _
       ByVal nHeightDest As Integer, ByVal hdcSrc As IntPtr, _
       ByVal nXOriginSrc As Integer, ByVal nYOriginSrc As Integer, _
       ByVal nWidthSrc As Integer, ByVal nHeightSrc As Integer, _
       ByVal dwRop As Int32) As Boolean

What I'm having trouble with is getting three images pasted into one
larger image.  I have a function called drawDiagram() that creates my
graphs and returns them as a Graphics object.  I make an initial call
to StretchBlt with my first graph.  I think I then have to release the
HDC to my destination image.  The result of this is that my
destination image is wiped clean.  By the time I go to save my larger
destination image it is a plain white picture with no graphs located
on it.  I'm also having trouble getting StretchBlt to save my graphs
in different XY coordinates on the destination graph.  When I try to
StretchBlt just one graph in various places on the destination image
the graph always ends up at the top of the picture.  Finally, I'm sure
I'm not disposing of all the objects that I should, I would appreciate
any help here as well.  Here is my code:

ImageFile = New Bitmap(500, 660)
ImgFileGrphcs = Graphics.FromImage(ImageFile)
ImgFileGrphcs.FillRectangle(Brushes.White, 0, 0, ImageFile.Width,
ImageFile.Height)

If Color1.SelectedIndex = -1 Then
    colorIndex = 0
Else
    colorIndex = Color1.SelectedIndex
End If

SrcBitmap = drawDiagram(Cell1Image, Solution1.SelectedIndex - 1,
colorIndex)

Dim imghdc As IntPtr = ImgFileGrphcs.GetHdc
StretchBlt(imghdc, 0, 0, 500, 220, SrcBitmap.GetHdc, 0, 0, 500, 220,
SRCCOPY)
ImgFileGrphcs.ReleaseHdc(imghdc)

If Color3.SelectedIndex = -1 Then
  colorIndex = 0
Else
  colorIndex = Color3.SelectedIndex
End If

SrcBitmap.Dispose()

SrcBitmap = drawDiagram(Cell1Image, Solution3.SelectedIndex - 1,
colorIndex)

Dim imghdc2 As IntPtr = ImgFileGrphcs.GetHdc
StretchBlt(imghdc2, 0, 220, 500, 220, SrcBitmap.GetHdc, 0, 0, 500,
220, SRCCOPY)
ImgFileGrphcs.ReleaseHdc(imghdc2)

If Color5.SelectedIndex = -1 Then
  colorIndex = 0
Else
  colorIndex = Color5.SelectedIndex
End If

SrcBitmap.Dispose()

SrcBitmap = drawDiagram(Cell1Image, Solution5.SelectedIndex - 1,
colorIndex)

Dim imghdc3 As IntPtr = ImgFileGrphcs.GetHdc
StretchBlt(imghdc3, 0, 440, 500, 220, SrcBitmap.GetHdc, 0, 0, 500,
220, SRCCOPY)
ImgFileGrphcs.ReleaseHdc(imghdc3)

Brian