【WPF】使用 WriteableBitmap 提升 Image 性能

本文介绍: 由于中所周不知的原因，WPF 中想要快速的更新图像的显示速率一直以来都是一大难题。在本文中，我将分享一些我对于 WPF 领域的经验和见解。虽然我并不是这方面的专家，但是希望通过我的分享，能够为大家提供一些有用的信息和思考角度。

WriteableBitmap 继承至 System.Windows.Media.Imaging.BitmapSource

“巨硬” 官方介绍： WriteableBitmap 类

特殊的应用场景，可以适当调整下自己写代码的策略：

测试 Demo 使用 OpenCvSharp 将视频帧读取出来，将视频帧图像数据通过 WriteableBitmap 渲染到界面的 Image 控件。

private void ShowImage()
{
    Bitmap.Lock();

    bitmap = frame.ToBitmap();

    bitmapData = bitmap.LockBits(new Rectangle(new System.Drawing.Point(0, 0), bitmap.Size),
        System.Drawing.Imaging.ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppPArgb);

    Bitmap.WritePixels(rect, bitmapData.Scan0, bitmapData.Height * bitmapData.Stride, bitmapData.Stride, 0, 0);

    bitmap.UnlockBits(bitmapData);
    bitmap.Dispose();

    Bitmap.Unlock();
}

完整的 ViewModel 代码

public class MainWindowViewModel : Prism.Mvvm.BindableBase
{
    #region 属性、变量、命令

    private WriteableBitmap _bitmap;
    /// <summary>
    /// UI绑定的资源对象
    /// </summary>                
    public WriteableBitmap Bitmap
    {
        get => _bitmap;
        set => SetProperty(ref _bitmap, value);
    }

    /// <summary>
    /// OpenCvSharp 视频捕获对象
    /// </summary>
    private static VideoCapture videoCapture;

    /// <summary>
    /// 视频帧
    /// </summary>
    private static Mat frame = new Mat();

    private static BitmapData bitmapData = new BitmapData();
	
	private static Bitmap bitmap;
    
    Int32Rect rect;

    static int width = 0, height = 0;

    /// <summary>
    /// 打开文件
    /// </summary>
    public DelegateCommand OpenFileCommand { get; set; }

    public DelegateCommand MNCommand { get; set; }

    #endregion

    public MainWindowViewModel()
    {
        videoCapture = new VideoCapture();

        OpenFileCommand = new DelegateCommand(OpenFile);
        MNCommand = new DelegateCommand(MN);
    }

    #region 私有方法

    private void OpenFile()
    {
        OpenFileDialog open = new OpenFileDialog()
        {
            Multiselect = false,
            Title = "请选择文件",
            Filter = "视频文件(*.mp4, *.wmv, *.mkv, *.flv)|*.mp4;*.wmv;*.mkv;*.flv|所有文件(*.*)|*.*"
        };

        if (open.ShowDialog() is true)
        {           
            ShowMove(open.FileName);
        }
    }

    /// <summary>
    /// 获取视频
    /// </summary>
    /// <param name="fileName">文件路径</param>
    private void ShowMove(string fileName)
    {
        videoCapture.Open(fileName, VideoCaptureAPIs.ANY);

        if (videoCapture.IsOpened())
        {
            var timer = (int)Math.Round(1000 / videoCapture.Fps) - 8;
            width = videoCapture.FrameWidth;
            height = videoCapture.FrameHeight;

            Bitmap = new WriteableBitmap(width, height, 96, 96, PixelFormats.Bgra32, null);
            rect = new Int32Rect(0, 0, Bitmap.PixelWidth, Bitmap.PixelHeight);

            while (true)
            {
                videoCapture.Read(frame);
                if (!frame.Empty())
                {
                    ShowImage();
                    Cv2.WaitKey(timer);
                }
            }
        }
    }

    private void ShowImage()
    {
        Bitmap.Lock();

        bitmap = frame.ToBitmap();

        bitmapData = bitmap.LockBits(new Rectangle(new System.Drawing.Point(0, 0), bitmap.Size),
            System.Drawing.Imaging.ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppPArgb);

        Bitmap.WritePixels(rect, bitmapData.Scan0, bitmapData.Height * bitmapData.Stride, bitmapData.Stride, 0, 0);

        bitmap.UnlockBits(bitmapData);
        bitmap.Dispose();

        Bitmap.Unlock();
    }
}