使用RenderTargetBitmap和DrawingVisual [英] Using RenderTargetBitmap and DrawingVisual

问题描述

这儿去了:

我想使用ImageBrush在Canvas上设置背景图像.当我想调整画布大小并保持背景图片完好无损时，麻烦就开始了.这意味着它将在左上角保持相同的大小.

这是我尝试过的:

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

这个想法是返回一个保留其原始大小并用白色填充其余空间的图像.

但是，当我尝试调整画布大小时，图片开始变形.似乎要保留原始的长/宽比并相应调整图像.但是我似乎无法找出执行该操作的方法，有人知道如何使它工作吗?

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?

推荐答案

我更改了代码以使其正常工作.我生成了自己的图片类:

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

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

......

不过，我很想知道如何使用我的原始方法来做....

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

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