c# - 不安全的每像素访问，30ms 访问 1756000 像素

Question

所以我一直在我的网站上分享关于快速、不安全像素访问的上述主题标题的一些想法。一位先生给了我一个粗略的例子，说明他如何在 C++ 中做到这一点，但这对我在 C# 中没有帮助，除非我可以互操作它，而且互操作也很快。我在互联网上找到了一个使用 MSDN 帮助编写的类，用于不安全地访问像素。上课速度特别快，但还不够快。这是类(class):

using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;

namespace DCOMProductions.Desktop.ScreenViewer {
public unsafe class UnsafeBitmap {
    Bitmap bitmap;

    // three elements used for MakeGreyUnsafe
    int width;
    BitmapData bitmapData = null;
    Byte* pBase = null;

    public UnsafeBitmap(Bitmap bitmap) {
        this.bitmap = new Bitmap(bitmap);
    }

    public UnsafeBitmap(int width, int height) {
        this.bitmap = new Bitmap(width, height, PixelFormat.Format32bppArgb);
    }

    public void Dispose() {
        bitmap.Dispose();
    }

    public Bitmap Bitmap {
        get {
            return (bitmap);
        }
    }

    private Point PixelSize {
        get {
            GraphicsUnit unit = GraphicsUnit.Pixel;
            RectangleF bounds = bitmap.GetBounds(ref unit);

            return new Point((int)bounds.Width, (int)bounds.Height);
        }
    }

    public void LockBitmap() {
        GraphicsUnit unit = GraphicsUnit.Pixel;
        RectangleF boundsF = bitmap.GetBounds(ref unit);
        Rectangle bounds = new Rectangle((int)boundsF.X,
      (int)boundsF.Y,
      (int)boundsF.Width,
      (int)boundsF.Height);

        // Figure out the number of bytes in a row
        // This is rounded up to be a multiple of 4
        // bytes, since a scan line in an image must always be a multiple of 4 bytes
        // in length. 
        width = (int)boundsF.Width * sizeof(Pixel);
        if (width % 4 != 0) {
            width = 4 * (width / 4 + 1);
        }
        bitmapData =
      bitmap.LockBits(bounds, ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);

        pBase = (Byte*)bitmapData.Scan0.ToPointer();
    }

    public Pixel GetPixel(int x, int y) {
        Pixel returnValue = *PixelAt(x, y);
        return returnValue;
    }

    public void SetPixel(int x, int y, Pixel colour) {
        Pixel* pixel = PixelAt(x, y);
        *pixel = colour;
    }

    public void UnlockBitmap() {
        bitmap.UnlockBits(bitmapData);
        bitmapData = null;
        pBase = null;
    }
    public Pixel* PixelAt(int x, int y) {
        return (Pixel*)(pBase + y * width + x * sizeof(Pixel));
    }
}

基本上我所做的是复制整个屏幕并将每个像素与旧副本进行比较。在 1680x1050 位图上，使用以下代码这大约需要 300 毫秒。

private Bitmap GetInvalidFrame(Bitmap frame) {
        Stopwatch sp = new Stopwatch();
        sp.Start();

        if (m_FrameBackBuffer == null) {
            return frame;
        }

        Int32 pixelsToRead = frame.Width * frame.Height;
        Int32 x = 0, y = 0;

        UnsafeBitmap unsafeBitmap = new UnsafeBitmap(frame);
        UnsafeBitmap unsafeBuffBitmap = new UnsafeBitmap(m_FrameBackBuffer);
        UnsafeBitmap retVal = new UnsafeBitmap(frame.Width, frame.Height);

        unsafeBitmap.LockBitmap();
        unsafeBuffBitmap.LockBitmap();
        retVal.LockBitmap();

        do {
            for (x = 0; x < frame.Width; x++) {
                Pixel newPixel = unsafeBitmap.GetPixel(x, y);
                Pixel oldPixel = unsafeBuffBitmap.GetPixel(x, y);

                if (newPixel.Alpha != oldPixel.Alpha || newPixel.Red != oldPixel.Red || newPixel.Green != oldPixel.Green || newPixel.Blue != oldPixel.Blue) {
                   retVal.SetPixel(x, y, newPixel);
                }
                else {
                    // Skip pixel
                }
            }

            y++;
        } while (y != frame.Height);

        unsafeBitmap.UnlockBitmap();
        unsafeBuffBitmap.UnlockBitmap();
        retVal.UnlockBitmap();

        sp.Stop();

        System.Diagnostics.Debug.WriteLine(sp.Elapsed.Milliseconds.ToString());

        sp.Reset();

        return retVal.Bitmap;
    }

是否有任何可能的方法/手段/方法可以将其加速到大约 30 毫秒？我可以使用 Graphics.CopyFromScreen() 在大约 30 毫秒内复制屏幕，这样每秒大约产生 30 帧。但是，一个程序的运行速度只能与其较慢的对应程序一样快，因此 GetInvalidFrame 中的 300 毫秒延迟会将其减慢到每秒大约 1 - 3 帧。这不适合 session 软件。

任何正确方向的建议、方法和指示都将非常棒!此外，用于在客户端绘制位图的代码也在下面。

评论 Dmitriy 的回答/评论:

#region RootWorkItem

    private ScreenClient m_RootWorkItem;
    /// <summary>
    /// Gets the RootWorkItem
    /// </summary>
    public ScreenClient RootWorkItem {
        get {
            if (m_RootWorkItem == null) {
                m_RootWorkItem = new ScreenClient();
                m_RootWorkItem.FrameRead += new EventHandler<FrameEventArgs>(RootWorkItem_FrameRead);
            }
            return m_RootWorkItem;
        }
    }

    #endregion

    private void RootWorkItem_FrameRead(Object sender, FrameEventArgs e) {
        if (e.Frame != null) {
            if (uxSurface.Image != null) {
                Bitmap frame = (Bitmap)uxSurface.Image;

                Graphics g = Graphics.FromImage(frame);
                g.DrawImage(e.Frame, 0, 0); // Draw only updated pixels

                uxSurface.Image = frame;
            }
            else {
                uxSurface.Image = e.Frame; // Draw initial, full image
            }
        }
        else {
            uxSurface.Image = null;
        }
    }

Answer 1

使用整数而不是像素和单循环的不安全方法:

private static Bitmap GetInvalidFrame(Bitmap oldFrame, Bitmap newFrame)
{
    if (oldFrame.Size != newFrame.Size)
    {
        throw new ArgumentException();
    }
    Bitmap result = new Bitmap(oldFrame.Width, oldFrame.Height, oldFrame.PixelFormat);

    Rectangle lockArea = new Rectangle(Point.Empty, oldFrame.Size);
    PixelFormat format = PixelFormat.Format32bppArgb;
    BitmapData oldData = oldFrame.LockBits(lockArea, ImageLockMode.ReadOnly, format);
    BitmapData newData = newFrame.LockBits(lockArea, ImageLockMode.ReadOnly, format);
    BitmapData resultData = result.LockBits(lockArea, ImageLockMode.WriteOnly, format);

    int len = resultData.Height * Math.Abs(resultData.Stride) / 4;

    unsafe
    {
        int* pOld = (int*)oldData.Scan0;
        int* pNew = (int*)newData.Scan0;
        int* pResult = (int*)resultData.Scan0;

        for (int i = 0; i < len; i++)
        {
            int oldValue = *pOld++;
            int newValue = *pNew++;
            *pResult++ = oldValue != newValue ? newValue : 0 /* replace with 0xff << 24 if you need non-transparent black pixel */;
            // *pResult++ = *pOld++ ^ *pNew++; // if you can use XORs.
        }
    }

    oldFrame.UnlockBits(oldData);
    newFrame.UnlockBits(newData);
    result.UnlockBits(resultData);

    return result;
}

我认为你真的可以在这里使用 XORed 帧，我希望这可以在双方都有更好的性能。

    private static void XorFrames(Bitmap leftFrame, Bitmap rightFrame)
    {
        if (leftFrame.Size != rightFrame.Size)
        {
            throw new ArgumentException();
        }

        Rectangle lockArea = new Rectangle(Point.Empty, leftFrame.Size);
        PixelFormat format = PixelFormat.Format32bppArgb;
        BitmapData leftData = leftFrame.LockBits(lockArea, ImageLockMode.ReadWrite, format);
        BitmapData rightData = rightFrame.LockBits(lockArea, ImageLockMode.ReadOnly, format);

        int len = leftData.Height * Math.Abs(rightData.Stride) / 4;

        unsafe
        {
            int* pLeft = (int*)leftData.Scan0;
            int* pRight = (int*)rightData.Scan0;

            for (int i = 0; i < len; i++)
            {
                *pLeft++ ^= *pRight++;
            }
        }

        leftFrame.UnlockBits(leftData);
        rightFrame.UnlockBits(rightData);
    }

您可以通过以下方式在两侧使用此过程:
在服务器端，您需要评估新旧框架之间的差异，将其发送到客户端并用新框架替换旧框架。服务器代码应如下所示:

  XorFrames(oldFrame, newFrame); // oldFrame ^= newFrame
  Send(oldFrame); // send XOR of two frames
  oldFrame = newFrame;

在客户端，您需要使用从服务器收到的异或帧来更新当前帧:

  XorFrames((Bitmap)uxSurface.Image, e.Frame);