如何清除WriteableBitmap

Question

我有一个WriteableBitmap，我想反复澄清和重新绘制。

我已经看到了直接写入像素数组的引用，但是在WriteableBitmap中不能访问像素数组。我也尝试过每次重新创建WriteableBitmap的建议，但我的应用程序几乎立即耗尽了内存。

有简单的方法来清除WriteableBitmap吗？

Answer 1

要使用writeablebitmap.clear()，您需要WriteableBitmapEx库。http://writeablebitmapex.codeplex.com

Answer 2

我们阻止将空白字节数组复制到可写位图的后缓冲区以完成此操作。我们也可以复制原始帧超过30帧每秒1k x 1k位图。

两个例子快速或安全(而且仍然相当快)。我更喜欢不安全的版本。

    #region External
    [DllImport("kernel32.dll", EntryPoint = "RtlMoveMemory")]
    public static extern void CopyMemory(IntPtr destination, IntPtr source, uint length);
    #endregion
    private const int PixelHeight = 1024;
    private const int PixelWidth = 1024;
    private const int DpiHeight = 96;
    private const int DpiWidth = 96;
    private const int RgbBytesPerPixel = 3;
    WriteableBitmap _myBitmap = new WriteableBitmap(PixelHeight, PixelWidth, DpiHeight, DpiWidth, PixelFormats.Rgb24, null);
    private readonly byte[] _blankImage = new byte[PixelHeight * PixelWidth * RgbBytesPerPixel];


    private unsafe void FastClear()
    {
        fixed (byte* b = _blankImage)
        {
            CopyMemory(_myBitmap.BackBuffer, (IntPtr)b, (uint)_blankImage.Length);            
        Application.Current.Dispatcher.Invoke(() =>
        {
            _myBitmap.Lock();
            _myBitmap.AddDirtyRect(new Int32Rect(0, 0, _myBitmap.PixelWidth, _myBitmap.PixelHeight));
            _myBitmap.Unlock();
        });
       }
    }
    private void SafeClear()
    {
        GCHandle pinnedArray = new GCHandle();
        IntPtr pointer = IntPtr.Zero;
        try
        {
            //n.b. If pinnedArray is used often wrap it in a class with IDisopsable and keep it around
            pinnedArray = GCHandle.Alloc(_blankImage, GCHandleType.Pinned);
            pointer = pinnedArray.AddrOfPinnedObject();

            CopyMemory(_myBitmap.BackBuffer, pointer, (uint)_blankImage.Length);

            Application.Current.Dispatcher.InvokeAsync(() =>
            {
                _myBitmap.Lock();
                _myBitmap.AddDirtyRect(new Int32Rect(0, 0, _myBitmap.PixelWidth, _myBitmap.PixelHeight));
                _myBitmap.Unlock();
            });
        }

        finally
        {
            pointer = IntPtr.Zero;
            pinnedArray.Free();

        }

    }

Answer 3

CCondron给出的答案最终将开始抛出AccessViolationException。幸运的是，我们能够以一种更简单、更快、更稳定的方式解决这个问题：

[System.Runtime.InteropServices.DllImport("kernel32.dll")]
private static extern void RtlZeroMemory(IntPtr dst, int length);

protected void ClearWriteableBitmap(WriteableBitmap bmp)
{
    RtlZeroMemory(bmp.BackBuffer, bmp.PixelWidth * bmp.PixelHeight * (bmp.Format.BitsPerPixel / 8));

    bmp.Dispatcher.Invoke(() =>
    {
        bmp.Lock();
        bmp.AddDirtyRect(new Int32Rect(0, 0, bmp.PixelWidth, bmp.PixelHeight));
        bmp.Unlock();
    });
}