Converting byte array into texture2D XNA

Question

I have a byte array representing an image.

Each byte represents an intensity value (0-255) of either R,G or B of a particular pixel. So for a 640x480 image the byte array is of size 640*480*3 (each pixel has 3 bytes representing it).

The bytes are in order of pixels. For instance:

image[0] = the R value of x=0 y=0 
image[1] = the G value of x=0 y=0
image[2] = the B value of x=0 y=0
image[3] = the R value of x=1 y=0

and so on.

I am wondering what the most efficient way to draw this to screen in XNA is?

My thoughts are to do the following.

1. Create a new Texture2d object
2. During the draw() method, loop through the byte array and set the values on the Texture2D object
3. Draw this filled in object to the screen.

Is this the fastest way to do this? I can also store the byte array in a different order/format if it is more efficient. Is there any downside to doing the looping during the draw() method? Would it be better to do it during update()?

EDIT:

I have attempted to use setData() on a Texture2D inorder to create a new texture every time my byte array updates (usually once a frame). The fps is now below 15 whereas before it was at 60. The code is as follows:

    public static Texture2D getImageFrame(GraphicsDevice gd)
    {
        if (cameraTex == null)
        {
            cameraTex = new Texture2D(gd, 640, 480, false, SurfaceFormat.Color);
        }
        cameraTex.SetData(imageFrame);
        return cameraTex;
    }

Which is called every draw() cycle.

Surely there has to be a more efficient way of doing this?

Answer 1

Depending on the way in which the byte array is updated (may be worth noting), you can probably update a smaller segment of a texture using the SetData overloads that use index and count parameters.

Obviously you'll need to add some way of tracking what regions of pixels have last changed for this to work (again depends on the structure of your program). In any case, I had a similar performance hit with drawing a blood splatter texture on another texture recently, and managed to minimize the hit using this method.

public void SetData (T[] data, int startIndex, int elementCount)

public void SetData (int level, Nullable rect, T[] data, int startIndex, int elementCount)

http://msdn.microsoft.com/en-us/library/microsoft.xna.framework.graphics.texture2d.setdata.aspx