Visual C++ 비트맵 중 특정 색을 투명하게 처리하기

// 기본적으론 흰색은 transparent
HRGN BitmapToRegion(HBITMAP hBmp, COLORREF cTransparentColor=RGB(255,255,255), COLORREF cTolerance = 0x101010);

// hBmp 비트맵 소스
// cTransparentColor Color base for the "transparent" pixels 예) RGB(255,255,255) : 흰색은 투명하게

// cTolerance   Color tolerance for the "transparent" pixels.
HRGN BitmapToRegion(HBITMAP hBmp, COLORREF cTransparentColor, COLORREF cTolerance)
{
 HRGN hRgn = NULL;
 if (hBmp)
 {
  // Create a memory DC inside which we will scan the bitmap content
  HDC hMemDC = CreateCompatibleDC(NULL);
  if (hMemDC)
  {
   // Get bitmap size
   BITMAP bm;
   GetObject(hBmp, sizeof(bm), &bm);

   // Create a 32 bits depth bitmap and select it into the memory DC
   BITMAPINFOHEADER RGB32BITSBITMAPINFO = {
     sizeof(BITMAPINFOHEADER), // biSize
     bm.bmWidth,     // biWidth;
     bm.bmHeight,    // biHeight;
     1,       // biPlanes;
     32,       // biBitCount
     BI_RGB,      // biCompression;
     0,       // biSizeImage;
     0,       // biXPelsPerMeter;
     0,       // biYPelsPerMeter;
     0,       // biClrUsed;
     0       // biClrImportant;
   };
   VOID * pbits32;

   HBITMAP hbm32 = CreateDIBSection(hMemDC, (BITMAPINFO *)&RGB32BITSBITMAPINFO, DIB_RGB_COLORS, &pbits32, NULL, 0);
   if (hbm32)
   {
    HBITMAP holdBmp = (HBITMAP)SelectObject(hMemDC, hbm32);

    // Create a DC just to copy the bitmap into the memory DC
    HDC hDC = CreateCompatibleDC(hMemDC);
    if (hDC)
    {
     // Get how many bytes per row we have for the bitmap bits (rounded up to 32 bits)
     BITMAP bm32;
     GetObject(hbm32, sizeof(bm32), &bm32);
     while (bm32.bmWidthBytes % 4)
      bm32.bmWidthBytes++;

     // Copy the bitmap into the memory DC
     HBITMAP holdBmp = (HBITMAP)SelectObject(hDC, hBmp);
     BitBlt(hMemDC, 0, 0, bm.bmWidth, bm.bmHeight, hDC, 0, 0, SRCCOPY);
     // For better performances, we will use the ExtCreateRegion() function to create the
     // region. This function take a RGNDATA structure on entry. We will add rectangles by
     // amount of ALLOC_UNIT number in this structure.
     #define ALLOC_UNIT 100
     DWORD maxRects = ALLOC_UNIT;
     HANDLE hData = GlobalAlloc(GMEM_MOVEABLE, sizeof(RGNDATAHEADER) + (sizeof(RECT) * maxRects));
     RGNDATA *pData = (RGNDATA *)GlobalLock(hData);
     pData->rdh.dwSize = sizeof(RGNDATAHEADER);
     pData->rdh.iType = RDH_RECTANGLES;
     pData->rdh.nCount = pData->rdh.nRgnSize = 0;
     SetRect(&pData->rdh.rcBound, MAXLONG, MAXLONG, 0, 0);

     // Keep on hand highest and lowest values for the "transparent" pixels
     BYTE lr = GetRValue(cTransparentColor);
     BYTE lg = GetGValue(cTransparentColor);
     BYTE lb = GetBValue(cTransparentColor);
     BYTE hr = min(0xff, lr + GetRValue(cTolerance));
     BYTE hg = min(0xff, lg + GetGValue(cTolerance));
     BYTE hb = min(0xff, lb + GetBValue(cTolerance));
   
     // Scan each bitmap row from bottom to top (the bitmap is inverted vertically)
     BYTE *p32 = (BYTE *)bm32.bmBits + (bm32.bmHeight - 1) * bm32.bmWidthBytes;
     for (int y = 0; y < bm.bmHeight; y++)
     {
      // Scan each bitmap pixel from left to right
      for (int x = 0; x < bm.bmWidth; x++)
      {
       // Search for a continuous range of "non transparent pixels"
       int x0 = x;
       LONG *p = (LONG *)p32 + x;
       while (x < bm.bmWidth)
       {
        BYTE b = GetRValue(*p);
        if (b >= lr && b <= hr)
        {
         b = GetGValue(*p);
         if (b >= lg && b <= hg)
         {
          b = GetBValue(*p);
          if (b >= lb && b <= hb)
           // This pixel is "transparent"
           break;
         }
        }
        p++;
        x++;
       }

       if (x > x0)
       {
        // Add the pixels (x0, y) to (x, y+1) as a new rectangle in the region
        if (pData->rdh.nCount >= maxRects)
        {
         GlobalUnlock(hData);
         maxRects += ALLOC_UNIT;
         hData = GlobalReAlloc(hData, sizeof(RGNDATAHEADER) + (sizeof(RECT) * maxRects), GMEM_MOVEABLE);
         pData = (RGNDATA *)GlobalLock(hData);
        }
        RECT *pr = (RECT *)&pData->Buffer;
        SetRect(&pr[pData->rdh.nCount], x0, y, x, y+1);
        if (x0 < pData->rdh.rcBound.left)
         pData->rdh.rcBound.left = x0;
        if (y < pData->rdh.rcBound.top)
         pData->rdh.rcBound.top = y;
        if (x > pData->rdh.rcBound.right)
         pData->rdh.rcBound.right = x;
        if (y+1 > pData->rdh.rcBound.bottom)
         pData->rdh.rcBound.bottom = y+1;
        pData->rdh.nCount++;

        // On Windows98, ExtCreateRegion() may fail if the number of rectangles is too
        // large (ie: > 4000). Therefore, we have to create the region by multiple steps.
        if (pData->rdh.nCount == 2000)
        {
         HRGN h = ExtCreateRegion(NULL, sizeof(RGNDATAHEADER) + (sizeof(RECT) * maxRects), pData);
         if (hRgn)
         {
          CombineRgn(hRgn, hRgn, h, RGN_OR);
          DeleteObject(h);
         }
         else
         {
          hRgn = h;
         }
         pData->rdh.nCount = 0;
         SetRect(&pData->rdh.rcBound, MAXLONG, MAXLONG, 0, 0);
        }
       }
      }
      // Go to next row (remember, the bitmap is inverted vertically)
      p32 -= bm32.bmWidthBytes;
     }

     // Create or extend the region with the remaining rectangles
     HRGN h = ExtCreateRegion(NULL, sizeof(RGNDATAHEADER) + (sizeof(RECT) * maxRects), pData);

     if (hRgn)
     {
      CombineRgn(hRgn, hRgn, h, RGN_OR);
      DeleteObject(h);
     }
     else
      hRgn = h;
     // Clean up
     SelectObject(hDC, holdBmp);
     DeleteDC(hDC);
    }
    DeleteObject(SelectObject(hMemDC, holdBmp));
   }
   DeleteDC(hMemDC);
  }
 }
 return hRgn;
}