How can I copy a block of memory?

CopperCircle

Hi, I am trying to use the third party VideoCog componet with C# and I need to copy a image frame? Videocog drops the frame into an rgb array in memory and I can then fast process the pixels using pointers. How can I create another copy of the frame from memory so that I can also access that via another pointer? Thanks...

private void videoCogControl1_FrameReady(double SampleTime, IntPtr pBuffer,

                                     int BufferSize, int Width, int Height)

```
 {
```
```
      unsafe
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```
      {
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           byte\* p = (byte\*)(void\*)pBuffer;

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           int nWidth = Width \* 3;
```

           for (int y = 0; y < Height; y++)

```
           {
```

                for (int x = 0; x < nWidth; x++)

```
                {
```

                    p\[0\] = (byte)(255 - p\[0\]);

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                    p++;
```
```
                }
```
```
           }
```
```
       }   
```
```
 }
```

Lost User

Have you tried the Marshal.Copy[^] method from the interop namespace? regards

CopperCircle

Thanks for the reply, I am very new to C# and I am just working off the Videocog tutorials, do you have an example of how Marshal.Copy works?

Guffa

The documentation has. MSDN Library: Marshal.Copy method[^]

Despite everything, the person most likely to be fooling you next is yourself.

CopperCircle

Thanks, I got it to work, but there must be an faster/easyer way to copy a block of memory? This is what I did to get it to work with Marshal.ReadByte, it gives me p2 which I can use on the copied image:

byte[] bytes = new byte[BufferSize];
for (int i = 0; i < BufferSize; i++)
bytes[i] = Marshal.ReadByte(pBuffer, i);

fixed (byte* pTmp = bytes)
{
System.IntPtr pBuffer2 = new IntPtr((void*)pTmp);
byte* p2 = (byte*)(void*)pBuffer2;
}

Guffa

Use Marshal.Copy instead of Marshal.ReadByte. Now you are making a method call for every byte that you copy, that is bound to be slow. Why are you converting the pointer to an IntPtr value, then back to a pointer? Just copy the pointer:

fixed (byte* pTmp = bytes) {
byte* p2 = pTmp;
}

Despite everything, the person most likely to be fooling you next is yourself.

CopperCircle

Thanks, I tried to use Marshal.Copy but I could not get it to work, could you please show how to implement it? Cheers,

realJSOP

Have you tried the C++ forum?

"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

CopperCircle

Hi, I found a very quick method in the end using RtlMoveMemory:

[DllImport("kernel32")]
public static extern void RtlMoveMemory(IntPtr dest, IntPtr src, int len);

System.IntPtr pBuffer2 = Marshal.AllocHGlobal(BufferSize); //Assign unmanaged memory
RtlMoveMemory(pBuffer2, pBuffer, BufferSize); //Copy memory
byte* p2 = (byte*)(void*)pBuffer2;
// Use p2 to access image pixels
Marshal.FreeHGlobal(pBuffer2); //Free unmanaged memory

Thanks, for the help and hope this helps some one else.