无法将像素着色器渲染到 RenderTargetBitmap！请帮忙！

Question

我编写了一个非常简单的 WPF 应用程序来测试渲染具有与 RenderTargetBitmap 关联的像素着色器的控件的能力。然后我将位图写入文件（jpeg）。该控件被渲染到位图上，但是像素着色器效果不会应用于该控件。

代码和 XAML 如下：

namespace TestPixelShader
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void OnSaveSnapshot(object sender, RoutedEventArgs e)
        {
            SaveFileDialog dlg = new SaveFileDialog();
            dlg.DefaultExt = "jpg";

            if ((bool)dlg.ShowDialog() == true)
            {
                String fileName = dlg.FileName;

                int Height = (int)CanvasControl.ActualHeight;
                int Width = (int)CanvasControl.ActualWidth;

                RenderTargetBitmap bmp = new RenderTargetBitmap(
                    Width, Height, 96, 96, PixelFormats.Pbgra32);
                bmp.Render(CanvasControl);

                string Extension = System.IO.Path.GetExtension(fileName).ToLower();

                BitmapEncoder encoder;
                if (Extension == ".gif")
                    encoder = new GifBitmapEncoder();
                else if (Extension == ".png")
                    encoder = new PngBitmapEncoder();
                else if (Extension == ".jpg")
                    encoder = new JpegBitmapEncoder();
                else
                    return;

                encoder.Frames.Add(BitmapFrame.Create(bmp));
                using (Stream stm = File.Create(fileName))
                {
                    encoder.Save(stm);
                }
            }
        }
    }
}

XAML：

<Window x:Class="TestPixelShader.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:TestPixelShader"
    Height="400"
    Width="300"
    Title="Test Pixel Shader">

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <Canvas Grid.Column="0" x:Name="CanvasControl" Margin="5"
                HorizontalAlignment="Stretch"
                VerticalAlignment="Stretch" >
            <Canvas.Effect>
                <local:TestPixelShaderEffect />
            </Canvas.Effect>
            <Canvas.Background>
                <ImageBrush ImageSource="/TestPixelShader;component/Images/DSCF0225.JPG" />
            </Canvas.Background>
        </Canvas>
        <Button x:Name="SaveSnapshotButton" Grid.Row="1" Click="OnSaveSnapshot" Height="40"
                Content="Take Snapshot" Margin="5"/>
    </Grid>
</Window>

Answer 1

您的目标是哪个 Pixel Shader 版本？

我尝试了你的代码，它为 PS 2.0 着色器正确保存了图像。 RenderTargetBitmap 使用软件渲染器，而 PS 3.0 没有软件回退，因此如果您使用 PS 3.0 着色器，它将被忽略。

Answer 2

 public class SnapshotHelper
{
    public static BitmapSource Capture(Rect absoluteControlRect)
    {
        using (var screenBmp = new System.Drawing.Bitmap(
            (int)absoluteControlRect.Width,
            (int)absoluteControlRect.Height,
            PixelFormat.Format32bppArgb))
        {
            using (var bmpGraphics = System.Drawing.Graphics.FromImage(screenBmp))
            {
                bmpGraphics.CopyFromScreen((int)absoluteControlRect.Left, (int)absoluteControlRect.Top, 0, 0, screenBmp.Size);
                return System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(
                    screenBmp.GetHbitmap(),
                    IntPtr.Zero,
                    Int32Rect.Empty,
                    BitmapSizeOptions.FromEmptyOptions());
            }
        }
    }

    public static Rect GetAbsoltutePlacement(FrameworkElement visual)
    {
        Point absolutePos = visual.PointToScreen(new Point(0, 0));
        return new Rect(absolutePos.X, absolutePos.Y, visual.ActualWidth, visual.ActualHeight);
    }

}

用法：

var rect = SnapshotHelper.GetAbsoltutePlacement(yourControl);
var image = SnapshotHelper.Capture(rect);