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BitmapData pointer in C#

Posted on 2007-03-30
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Last Modified: 2013-12-17
In code I had in a Visual Studio C++ .NET Windows Form Application, I had a portion of code that looked like this:
bmd is a BitmapData object.

for(int y = 0; y < bmd->Height; y++)
{
      Byte* row = (Byte*)(void*)bmd->Scan0 +(y * bmd->Stride);
      for(int x = 0; x < bmd->Width*4; x++)
      {
              ...
        }
}

Now, I'm writing a function to do the same thing in C#.  However, I got a few errors.  I've been trying to find a C# equivalent that would give me the equivalent of the "Byte* row" line, but so far, I've got no luck.  This is what I have now, but its still not working. I've replaced that one entire line with this:

int rowPtr = y * bmd.Stride;
IntPtr scanPoint = bmd.Scan0;
Byte row;
unsafe
{
      void* bmdRow = scanPoint.ToPointer();
      //bmdRow+=rowPtr;   <- Gives error.
      row = (Byte)(bmdRow);
}

The code is basically supposed to give me a pointer to each row so I can set each pixel individually.  In that nested for loop was code that contained stuff like "row[x] = pixelvalue;"    If anyone can help me out with this, that'd be great.  Any questions to get a more detailed explanation of the problem, just ask.
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Question by:raw_enha
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Expert Comment

by:Babycorn-Starfish
ID: 18828275
Hi,

what error are you getting?
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Babycorn-Starfish earned 500 total points
ID: 18828305
If you want to walk over the image, pixel by pixel i'd do something like this (i've assumed it's all in an unsafe block):

Byte bPP = (Byte)(aData.Stride / aWidth); //determine how many bytes per pixel there are  
Byte rowOffset = (Byte)(aData.Stride - (aBPP * aWidth)); // determine whether there is a row offset

Byte* p = (Byte*)aData.Scan0; //pointer to beginning of image

for (Int32 y = 0; y < height; y++)
{
    for (Int32 x = 0; x < width; x++)
    {
        //do something to this pixel
      //e.g. p[0] = 255 etc

      //update position of pointer
        p += bPP;    
    }
    p += rowOffset;
}
 
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