背景
我正在开发一个silverlight(1.0)应用程序,该应用程序动态构建美国地图,在特定位置叠加图标和文本。该地图在浏览器中运行良好,现在我需要获得显示地图的静态(可打印并可插入到文档/幻灯片中)副本。
目标:
为了获得地图的可打印副本,该副本也可用于powerpoint幻灯片、word等。我选择创建一个ASP。NET HttpHandler在WPF的服务器端重新创建xaml,然后将WPF渲染为位图图像,该图像以png文件的形式返回,以300dpi的分辨率生成,以获得更好的打印质量。
问题:
这很好地解决了一个问题,我无法将图像缩放到指定的大小。我尝试了几种不同的方法,其中一些可以在评论中看到。我需要能够指定图像的高度和宽度,以英寸或像素为单位,我不一定在乎哪一个,并将生成的位图的xaml比例设置为该大小。目前,如果我将大小设置为大于根画布,画布将以指定的大小在生成图像的左上角以原始大小渲染。下面是我的httphandler的重要部分。存储为“MyImage”的根画布的高度为600,宽度为800。为了使内容缩放到指定的大小,我缺少什么?
我并不完全理解传递给Arrange()和Measure()的维度的作用,因为其中一些代码来自在线示例。我也不完全理解RenderTargetBitmap的东西。任何指导都将不胜感激。
Public Sub Capture(ByVal MyImage As Canvas)
' Determine the constraining scale to maintain the aspect ratio and the bounds of the image size
Dim scale As Double = Math.Min(Width / MyImage.Width, Height / MyImage.Height)
'Dim vbox As New Viewbox()
'vbox.Stretch = Stretch.Uniform
'vbox.StretchDirection = StretchDirection.Both
'vbox.Height = Height * scale * 300 / 96.0
'vbox.Width = Width * scale * 300 / 96.0
'vbox.Child = MyImage
Dim bounds As Rect = New Rect(0, 0, MyImage.Width * scale, MyImage.Height * scale)
MyImage.Measure(New Size(Width * scale, Height * scale))
MyImage.Arrange(bounds)
'MyImage.UpdateLayout()
' Create the target bitmap
Dim rtb As RenderTargetBitmap = New RenderTargetBitmap(CInt(Width * scale * 300 / 96.0), CInt(Height * scale * 300 / 96.0), 300, 300, PixelFormats.Pbgra32)
' Render the image to the target bitmap
Dim dv As DrawingVisual = New DrawingVisual()
Using ctx As DrawingContext = dv.RenderOpen()
Dim vb As New VisualBrush(MyImage)
'Dim vb As New VisualBrush(vbox)
ctx.DrawRectangle(vb, Nothing, New Rect(New System.Windows.Point(), bounds.Size))
End Using
rtb.Render(dv)
' Encode the image in the format selected
Dim encoder As System.Windows.Media.Imaging.BitmapEncoder
Select Case Encoding.ToLower
Case "jpg"
encoder = New System.Windows.Media.Imaging.JpegBitmapEncoder()
Case "png"
encoder = New System.Windows.Media.Imaging.PngBitmapEncoder()
Case "gif"
encoder = New System.Windows.Media.Imaging.GifBitmapEncoder()
Case "bmp"
encoder = New System.Windows.Media.Imaging.BmpBitmapEncoder()
Case "tif"
encoder = New System.Windows.Media.Imaging.TiffBitmapEncoder()
Case "wmp"
encoder = New System.Windows.Media.Imaging.WmpBitmapEncoder()
End Select
encoder.Frames.Add(System.Windows.Media.Imaging.BitmapFrame.Create(rtb))
' Create the memory stream to save the encoded image.
retImageStream = New System.IO.MemoryStream()
encoder.Save(retImageStream)
retImageStream.Flush()
retImageStream.Seek(0, System.IO.SeekOrigin.Begin)
MyImage = Nothing
End Sub