Stretchblt in .NET

[vitaloverdose]

Hi im new to .net 2010 and im having a problem with using stretchblt.

Im trying to load in a BMP , copy part of that image and paste it back in the same image but stretched out. Then display and save the result.

First i pieced some code together that grabbed an image from a picture box , coppied part of it and pasted it back into the image. This worked fine except that it also copied anythingthat was sat on top of the image in the picture box as well as the image data.

 
Private Sub but_Render_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles but_Render.Click

        pbx_main.Image = CType(RenderImage(pbx_main), Bitmap).Clone
    End Sub

    Private Function RenderImage(ByVal src As PictureBox) As Bitmap

        'Create bitmap from image file
        Dim srcBmp As New Bitmap(LoadedImageFileName)

        'Create a Graphics object in memory from that bitmap
        Dim srcMem As Graphics = Graphics.FromImage(srcBmp)

        'Get a Graphics Object from picture box
        Dim srcPic As Graphics = src.CreateGraphics

        'get the IntPtr's of the graphics
        Dim HDC1 As IntPtr = srcPic.GetHdc

        'get the IntPtr's of the graphics
        Dim HDC2 As IntPtr = srcMem.GetHdc

        'StretchBlt the picture 
        StretchBlt(HDC2, 200, 200, 200, 200, HDC1, 50, 50, 50, 50, TernaryRasterOperations.SRCCOPY)

        'Clone the bitmap so we can dispose this one 
        RenderImage = srcBmp.Clone()

        'Clean Up 
        srcPic.ReleaseHdc(HDC1)
        srcMem.ReleaseHdc(HDC2)
        srcPic.Dispose()
        srcMem.Dispose()
        srcBmp.Dispose()

    End Function

So ive been trying to load in the bitmap from a file rather than take the one displayed in the picture box but nothing seems to work.

[dglienna]

Can't do that with BMP. Use JPG or PNG

[vitaloverdose]

Ive tried doing something like

   
    Private Sub but_Render_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles but_Render.Click

        pbx_main.Image = CType(RenderImage(pbx_main), Bitmap).Clone
 end sub

 Private Function RenderImage(ByVal src As PictureBox) As Bitmap

        'Create bitmap from image file
        Dim srcBmp As New Bitmap(LoadedImageFileName)
        Dim DestBmp As New Bitmap(LoadedImageFileName)

        'Create a Graphics object in memory from that bitmap
        Dim srcMem As Graphics = Graphics.FromImage(srcBmp)
        Dim DestMem As Graphics = Graphics.FromImage(DestBmp)

        'get the IntPtr's of the graphics
        Dim HDC1 As IntPtr = srcMem.GetHdc
        Dim HDC2 As IntPtr = DestMem.GetHdc

        'StretchBlt the picture 
        StretchBlt(HDC2, 200, 200, 200, 200, HDC1, 50, 50, 50, 50, TernaryRasterOperations.SRCCOPY)

        'Clone the bitmap so we can dispose this one 
        RenderImage = DestBmp.Clone()

        'Clean Up 
        DestMem.ReleaseHdc(HDC1)
        srcMem.ReleaseHdc(HDC2)
        DestMem.Dispose()
        srcMem.Dispose()
        srcBmp.Dispose()

    End Function

But nothing happens.

[vitaloverdose]

What cant i do with a Bitmap dglienna?

Ive tried changing the line

Dim srcPic As Graphics = src.CreateGraphics

to something else but nothing seems to work.

[Craig Gemmill]

Or you can just use the Graphics.DrawImage method. It will stretch the image for you.

        Dim destinationImage As New Bitmap(100, 100)
        Dim sourceImage As Image = PictureBox1.Image
        Dim g As Graphics

        g = Graphics.FromImage(destinationImage)

        g.DrawImage(sourceImage, New Rectangle(0, 0, destinationImage.Width, destinationImage.Height), 0, 0, sourceImage.Width, sourceImage.Height, GraphicsUnit.Pixel)

        g.Dispose()

        PictureBox2.Image = destinationImage

[dglienna]

What cant i do with a Bitmap dglienna?

Ive tried changing the line

Dim srcPic As Graphics = src.CreateGraphics

to something else but nothing seems to work.

http://en.wikipedia.org/wiki/Lossless_compression

[vitaloverdose]

Thanks Craig, i was able to produce the effect i was after from the code example you provided.