Fast creation of 2D array from 1D array of objects

Question

I need to convert the following 1D array of my class Frames to a 2D byte array (I need the 2D byte array for sending to a GPU, I cannot use jagged arrays, Lists, or other enumerables).

Right now, my conversion is very slow and stupid:

public byte[,] allBytes()
{
    byte[,] output = new byte[this.frameListSize, this.ySize * this.xSize];
    for (int y = 0; y < this.frameListSize; y++)
    {
        byte[] bits = this.frameList[y].getBytes();
        for (int x = 0; x < this.ySize * this.xSize; x++)
        {
            output[y, x] = bits[x];
        }
    }
    return output;
}

The snippets that define of frameList and Frame are below:

public Frame[] frameList;

public class Frame
{

  public byte[] bits;

  public byte[] getBytes()
  {
    return bits;
  }
}

Mitja · Accepted Answer · 2014-12-25 21:50:56Z

2

If you use .NET Framework 4 or higher, you can use Parallel (for a first speeding up)

    public byte[,] allBytes()
    {
        int size1 = this.frameListSize;
        int size2 = this.ySize * this.xSize;
        byte[,] output = new byte[size1, size2];
        Parallel.For(0, size1, (y) =>
        {
            byte[] bits = this.frameList[y].getBytes();
            System.Buffer.BlockCopy(bits, 0, output, 0 + size2 * y, bits.Length);
        });
        return output;
    }

Buffer.BlockCopy is about 20 times faster than normal copying. Make sure bits.Length has the same value as size2. Otherwise you can run into errors

edited Dec 25, 2014 at 21:50

answered Dec 25, 2014 at 20:06

Mitja

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4 Comments

Dr.YSG Over a year ago

Yes, I am using .net 4.5.2, But I think the CPU usage is hurting my video frame grabber which is what is deliving all these bytes (I am getting buffer overflows when I do this in parallel with the fetching of the data). The resultant 2D byte array is [21, 1024x1024]

Dr.YSG Over a year ago

from the MSDN documentation you quote: ArgumentException The current Array does not have exactly one dimension.

Mitja Over a year ago

Im sorry, its my fault. Then you have to use Block.Copy (changed in my answer)

Dr.YSG Over a year ago

That's a dramatic improvement. Thanks.

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