c# - LockBits 性能关键代码

Question

我有一个方法需要尽可能快，它使用不安全的内存指针，这是我第一次尝试这种类型的编码，所以我知道它可能会更快。

    /// <summary>
    /// Copies bitmapdata from one bitmap to another at a specified point on the output bitmapdata
    /// </summary>
    /// <param name="sourcebtmpdata">The sourcebitmap must be smaller that the destbitmap</param>
    /// <param name="destbtmpdata"></param>
    /// <param name="point">The point on the destination bitmap to draw at</param>
    private static unsafe void CopyBitmapToDest(BitmapData sourcebtmpdata, BitmapData destbtmpdata, Point point)
    {
        // calculate total number of rows to draw.
        var totalRow = Math.Min(
            destbtmpdata.Height - point.Y,
            sourcebtmpdata.Height);


        //loop through each row on the source bitmap and get mem pointers
        //to the source bitmap and dest bitmap
        for (int i = 0; i < totalRow; i++)
        {
            int destRow = point.Y + i;

            //get the pointer to the start of the current pixel "row" on the output image
            byte* destRowPtr = (byte*)destbtmpdata.Scan0 + (destRow * destbtmpdata.Stride);
            //get the pointer to the start of the FIRST pixel row on the source image
            byte* srcRowPtr = (byte*)sourcebtmpdata.Scan0 + (i * sourcebtmpdata.Stride);

            int pointX = point.X;
            //the rowSize is pre-computed before the loop to improve performance
            int rowSize = Math.Min(destbtmpdata.Width - pointX, sourcebtmpdata.Width);
            //for each row each set each pixel
            for (int j = 0; j < rowSize; j++)
            {
                int firstBlueByte = ((pointX + j)*3);

                int srcByte = j *3;
                destRowPtr[(firstBlueByte)] = srcRowPtr[srcByte];
                destRowPtr[(firstBlueByte) + 1] = srcRowPtr[srcByte + 1];
                destRowPtr[(firstBlueByte) + 2] = srcRowPtr[srcByte + 2];
            }


        }
    }

那么有什么办法可以让它更快吗？暂时忽略待办事项，一旦我有了一些基线性能测量，我会稍后修复它。

更新:抱歉，应该提到我使用这个而不是 Graphics.DrawImage 的原因是因为我实现了多线程，因此我不能使用 DrawImage。

更新 2:我对性能仍然不满意，我确信还可以再多几毫秒。

Answer 1

我无法相信我直到现在才注意到代码存在根本性错误。

byte* destRowPtr = (byte*)destbtmpdata.Scan0 + (destRow * destbtmpdata.Stride);

这会获取指向目标行的指针，但不会获取要复制到的列，在旧代码中，它是在 rowSize 循环内完成的。现在看起来像:

byte* destRowPtr = (byte*)destbtmpdata.Scan0 + (destRow * destbtmpdata.Stride) + pointX * 3;

现在我们有了目标数据的正确指针。现在我们可以去掉那个 for 循环了。使用来自 Vilx- 的建议和 Rob代码现在看起来像:

        private static unsafe void CopyBitmapToDestSuperFast(BitmapData sourcebtmpdata, BitmapData destbtmpdata, Point point)
    {
        //calculate total number of rows to copy.
        //using ternary operator instead of Math.Min, few ms faster
        int totalRows = (destbtmpdata.Height - point.Y < sourcebtmpdata.Height) ? destbtmpdata.Height - point.Y : sourcebtmpdata.Height;
        //calculate the width of the image to draw, this cuts off the image
        //if it goes past the width of the destination image
        int rowWidth = (destbtmpdata.Width - point.X < sourcebtmpdata.Width) ? destbtmpdata.Width - point.X : sourcebtmpdata.Width;

        //loop through each row on the source bitmap and get mem pointers
        //to the source bitmap and dest bitmap
        for (int i = 0; i < totalRows; i++)
        {
            int destRow = point.Y + i;

            //get the pointer to the start of the current pixel "row" and column on the output image
            byte* destRowPtr = (byte*)destbtmpdata.Scan0 + (destRow * destbtmpdata.Stride) + point.X * 3;

            //get the pointer to the start of the FIRST pixel row on the source image
            byte* srcRowPtr = (byte*)sourcebtmpdata.Scan0 + (i * sourcebtmpdata.Stride);

            //RtlMoveMemory function
            CopyMemory(new IntPtr(destRowPtr), new IntPtr(srcRowPtr), (uint)rowWidth * 3);

        }
    }

将 500x500 图像复制到网格中的 5000x5000 图像 50 次耗时:00:00:07.9948993 秒。现在进行上述更改需要 00:00:01.8714263 秒。好多了。