Using RenderTargetBitmap and DrawingVisual

Question

5.00/5 (2 votes)

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.NET4.5

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))
       drawingContext.Close()

       Dim bmp As New RenderTargetBitmap(Me.Height, Me.Width, 96, 96, PixelFormats.Pbgra32)
       bmp.Render(drawingVisual)

       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?

Posted 22-Sep-12 23:15pm

Kenneth Haugland

Updated 22-Sep-12 23:16pm

v2

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Comments

Sandeep Mewara 23-Sep-12 6:14am

5! for proper structured question!

Kenneth Haugland 23-Sep-12 17:07pm

Thanks. A hard problem, and I did not find a solution, but found a workaround that is ok.

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Kenneth Haugland · Accepted Answer · 2012-09-23T10:47:00

I changed the code to make it work. I generated an own picture class:

VB

Public Class PictureElement
    Inherits FrameworkElement

    Private _children As VisualCollection

    Public Sub New(p_position As Point, ByVal Url As String)
        'You have to set the position before creating the Visual collection
        'Other wise the object will be placed on point (0,0)

        PositionOnCanvas = p_position

        _children = New VisualCollection(Me)
        _children.Add(CreateDrawingVisualImage(Url))
    End Sub

    Private Function CreateDrawingVisualImage(ByVal img As String) As DrawingVisual
        Dim imgConv = New ImageSourceConverter()
        Dim imageSource As ImageSource
        imageSource = DirectCast(imgConv.ConvertFromString(img), ImageSource)
        Dim imgHeight = imageSource.Height
        Dim imgWidth = imageSource.Width


        ' Create a circle and draw it in the DrawingContext.
        Dim drawingVisual As New DrawingVisual()
        Dim drawingContext As DrawingContext = drawingVisual.RenderOpen()
        drawingContext.DrawImage(imageSource, New Rect(0, 0, imgWidth, imgHeight))
        drawingContext.Close()

        ' Persist the drawing content.
        ' drawingContext.Close()

        Return drawingVisual
    End Function

......

Would love to know how to do it with my original method though....