異步呈現WPF視覺到位圖

Question

我看到WinRT RenderTargetBitmap能夠通過「RenderAsync（visual）」異步渲染視覺效果;方法。 不幸的是.net RendertargetBitmap沒有RenderAsync方法。 有.net RenderTargetBitmap任何解決方法或擴展，以允許WPF視覺效果的異步呈現？ 感謝您的幫助！

Answer 1

我寫了一個方法來通過BitBlt函數渲染視覺到位圖。在像我這樣的沉重用戶界面中，這種方法比RenderTargetBitmap要快20倍。

你在這裏。

public static class VisualRender 
{ 
    [DllImport("user32.dll")] 
    static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int x, int y, int cx, int cy, uint uFlags); 

    static readonly IntPtr _HwndBottom = new IntPtr(1); 
    const UInt32 _SWP_NOSIZE = 0x0001; 
    const UInt32 _SWP_NOMOVE = 0x0002; 
    const UInt32 _SWP_NOACTIVATE = 0x0010; 


    public static async Task<BitmapSource> RenderAsync(this UIElement uiElement) 
    { 
     var brush = new VisualBrush(uiElement); 
     var topLeft = uiElement.PointToScreen(new System.Windows.Point(0, 0)); 
     var bottomRight = uiElement.PointToScreen(new System.Windows.Point(uiElement.RenderSize.Width, uiElement.RenderSize.Height)); 

     var helperWindowLocation = Rect.Empty; 
     helperWindowLocation.Union(topLeft); 
     helperWindowLocation.Union(bottomRight); 

     var width = helperWindowLocation.Width; 
     var height = helperWindowLocation.Height; 

     // 
     var windowsScaleTransform = uiElement.GetWindowsScaleTransform(); 
     helperWindowLocation.X /= windowsScaleTransform; 
     helperWindowLocation.Y /= windowsScaleTransform; 
     helperWindowLocation.Width /= windowsScaleTransform; 
     helperWindowLocation.Height /= windowsScaleTransform; 

     BitmapSource bitmapSourceT = await RenderAsync(brush, helperWindowLocation, new System.Windows.Size(width, height)); 
     bitmapSourceT.Freeze(); 
     return bitmapSourceT; 
    } 

    private static async Task<BitmapSource> RenderAsync(System.Windows.Media.Brush brush, Rect helperWindowLocation, System.Windows.Size snapshotSize) 
    { 
     // Create a tmp window with its own hwnd to render it later 
     var window = new Window { WindowStyle = WindowStyle.None, ResizeMode = ResizeMode.NoResize, ShowInTaskbar = false, Background = System.Windows.Media.Brushes.White }; 
     window.Left = helperWindowLocation.X; 
     window.Top = helperWindowLocation.Y; 
     window.Width = helperWindowLocation.Width; 
     window.Height = helperWindowLocation.Height; 
     window.ShowActivated = false; 
     var content = new Grid() { Background = brush }; 
     RenderOptions.SetBitmapScalingMode(content, BitmapScalingMode.HighQuality); 
     window.Content = content; 
     var handle = new WindowInteropHelper(window).EnsureHandle(); 
     window.Show(); 
     // Make sure the tmp window is under our mainwindow to hide it 
     SetWindowPos(handle, _HwndBottom, 0, 0, 0, 0, _SWP_NOMOVE | _SWP_NOSIZE | _SWP_NOACTIVATE); 

     //Wait for the element to render 
     //await popupChild.WaitForLoaded(); 
     await window.WaitForFullyRendered(); 

     ////Why we have to wait here fore the visualbrush to finish its lazy rendering Process? 
     //// Todo: It seems like very complex uielements does not finish its rendering process within one renderloop 
     //// Check https://stackoverflow.com/questions/2851236/rendertargetbitmap-resourced-visualbrush-incomplete-image 

     // Async BitBlt the tmp Window 
     var bitmapSourceT = await Task.Run(() => 
     { 
      Bitmap bitmap = VisualToBitmapConverter.GetBitmap(handle, 
      (int)snapshotSize.Width, (int)snapshotSize.Height); 

      var bitmapSource = new SharedBitmapSource(bitmap); 
      bitmapSource.Freeze(); 
      return bitmapSource; 
     }); 
     // Close the Window 
     window.Close(); 

     return bitmapSourceT; 
    } 

    public static class VisualToBitmapConverter 
    { 
     private enum TernaryRasterOperations : uint 
     { 
      SRCCOPY = 0x00CC0020, 
      SRCPAINT = 0x00EE0086, 
      SRCAND = 0x008800C6, 
      SRCINVERT = 0x00660046, 
      SRCERASE = 0x00440328, 
      NOTSRCCOPY = 0x00330008, 
      NOTSRCERASE = 0x001100A6, 
      MERGECOPY = 0x00C000CA, 
      MERGEPAINT = 0x00BB0226, 
      PATCOPY = 0x00F00021, 
      PATPAINT = 0x00FB0A09, 
      PATINVERT = 0x005A0049, 
      DSTINVERT = 0x00550009, 
      BLACKNESS = 0x00000042, 
      WHITENESS = 0x00FF0062, 
      CAPTUREBLT = 0x40000000 
     } 

     [DllImport("gdi32.dll", SetLastError = true)] 
     [return: MarshalAs(UnmanagedType.Bool)] 
     private static extern bool BitBlt(IntPtr hdc, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hdcSrc, int nXSrc, int nYSrc, TernaryRasterOperations dwRop); 

     public static Bitmap GetBitmap(IntPtr hwnd, int width, int height) 
     { 
      var bitmap = new Bitmap(width, height); 
      using (Graphics graphicsFromVisual = Graphics.FromHwnd(hwnd)) 
      { 
       using (Graphics graphicsFromImage = Graphics.FromImage(bitmap)) 
       { 
        IntPtr source = graphicsFromVisual.GetHdc(); 
        IntPtr destination = graphicsFromImage.GetHdc(); 

        BitBlt(destination, 0, 0, bitmap.Width, bitmap.Height, source, 0, 0, TernaryRasterOperations.SRCCOPY); 

        graphicsFromVisual.ReleaseHdc(source); 
        graphicsFromImage.ReleaseHdc(destination); 
       } 
      } 

      return bitmap; 
     } 
    } 
} 

static class Extensions 
{ 
    public static Task WaitForLoaded(this FrameworkElement element) 
    { 
     var tcs = new TaskCompletionSource<object>(); 
     RoutedEventHandler handler = null; 
     handler = (s, e) => 
     { 
      element.Loaded -= handler; 
      tcs.SetResult(null); 
     }; 
     element.Loaded += handler; 
     return tcs.Task; 
    } 


    public static Task WaitForFullyRendered(this Window window) 
    { 
     var tcs = new TaskCompletionSource<object>(); 
     EventHandler handler = null; 
     handler = (s, e) => 
     { 
      window.ContentRendered -= handler; 
      tcs.SetResult(null); 
     }; 
     window.ContentRendered += handler; 
     return tcs.Task; 
    } 

    public static double GetWindowsScaleTransform(this Visual visual) 
    { 
     Matrix m = Matrix.Identity; 
     var presentationSource = PresentationSource.FromVisual(visual); 
     if (presentationSource != null) 
     { 
      if (presentationSource.CompositionTarget != null) m = presentationSource.CompositionTarget.TransformToDevice; 
     } 
     double totalTransform = m.M11; 
     return totalTransform; 
    } 

} 

您可以在這裏找到SharedBitmapSource。 https://stackoverflow.com/a/32841840/690656

Answer 2

我不認爲你可以。

你可以嘗試向上執行使用類似await Task.Run(() => bitmap.Render(Button));後臺線程渲染，但它不會工作：後臺線程將不會被允許訪問Button。