How do you convert bytes of bitmap into x, y location of pixels?

Posted by Jon on Stack Overflow See other posts from Stack Overflow or by Jon
Published on 2010-05-25T17:59:07Z Indexed on 2010/05/25 18:01 UTC
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win32

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bitmap

I have a win32 program that creates a bitmap screenshot. I am trying to figure out the x and y coordinates of the bmBits. Below is the code I have so far:

UINT32 nScreenX = GetSystemMetrics(SM_CXSCREEN);



UINT32 nScreenY = GetSystemMetrics(SM_CYSCREEN);

HDC hdc = GetDC(NULL);  
HDC hdcScreen = CreateCompatibleDC(hdc);

HBITMAP hbmpScreen = CreateDIBSection( hdcDesk, ( BITMAPINFO* )&bitmapInfo.bmiHeader,DIB_RGB_COLORS, &bitmapDataPtr, NULL, 0 );

SelectObject(hdcScreen, hbmpScreen);

BitBlt(hdcScreen, 0, 0, nScreenX , nScreenY , hdc, 0, 0, SRCCOPY);   
ReleaseDC(NULL, hdc);

BITMAP bmpScreen;

GetObject(hbmpScreen, sizeof(bmpScreen), &bmpScreen);

DWORD *pScreenPixels = (DWORD*)bmpScreen.bmBits,


UINT32 x = 0;
UINT32 y = 0;
UINT32 nCntPixels = nScreenX * nScreenY;

for(int n = 0; n < nCntPixels; n++)
{

    x = n % nScreenX;
    y = n / nScreenX;

   //do stuff with the x and y vals
}

The code seem correct to me but, when I use this code the x and y values appear to be off. Where does the first pixel of bmBits start? When x and y are both 0. Is that the top left, bottom left, bottom right or top right?

Thanks.

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