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Using RenderTargetBitmap and DrawingVisual

Kenneth Haugland asked:

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Here goes:

I want to set a background image on a Canvas, using ImageBrush. The trouble starts when I want to resize the Canvas and leave the background picture intact. Meaning it will stay the same size in the topleft corner.

This is what I tried:
 Private Function GenerateImageBrush(ByVal image As ImageSource, Optional ByVal SizeNew As Boolean = False) As ImageBrush
        Dim result As New ImageBrush
        Dim drawingVisual As New DrawingVisual()
        Dim drawingContext As DrawingContext = drawingVisual.RenderOpen()
        drawingContext.DrawRectangle(Brushes.White, New Pen(Brushes.Black, 1), New Rect(New Size(Me.Height, Me.Width)))
        drawingContext.DrawImage(image, New Rect(0, 0, imgWidth, imgHeight))
        Dim bmp As New RenderTargetBitmap(Me.Height, Me.Width, 96, 96, PixelFormats.Pbgra32)
        result.ImageSource = bmp
        Return result
    End Function
    Dim imgWidth, imgHeight as Double
    Public Sub AddPicture(ByVal pic As String)
        Dim imgConv = New ImageSourceConverter()
        Dim imageSource As ImageSource
        imageSource = DirectCast(imgConv.ConvertFromString(pic), ImageSource)
        imgWidth = imageSource.Width
        imgHeight = imageSource.Height
        Me.Width = imageSource.Width
        Me.Height = imageSource.Height
        Me.Background = GenerateImageBrush(imageSource)
    End Sub

The idea is to return an Image that has preserved its original size, and filled the rest of the space with white color.

But When I try to resize the canvas, the picture starts to deform. It seems to want to preserve the original ratio Length/Width and adusts the image accordingly. But I cant seem to find out how to do this, does anybody know how to get this to work?
Tags: VB, VB.NET, .NET (.NET4.5), WPF


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