L_SetBitmapAlpha

L_INT SetBitmapAlphaExample(HWND hWnd,L_TCHAR*  szFilename) 
{ 
   L_INT nRet; 
   BITMAPHANDLE   MainBitmap;           /* Main bitmap */ 
   BITMAPHANDLE   AlphaBitmap;          /* Alpha channel bitmap */ 
   RGNXFORM       XFormToBitmap;        /* Structure for transforming display coordinates */ 
   HDC            hWindowDC;            /* Device context of the current window */ 
   RECT           rClientArea;          /* Client area of the current window */ 
   RECT           rRgnRect;             /* Rectangle that defines the current region */ 
   HPALETTE       hSavedPalette = NULL; /* Temporary copy of the current system palette */ 
   HPALETTE       hOurPalette = NULL;   /* The palette that we will use to paint */ 
 
   /* Get the device context of the current window */ 
   hWindowDC = GetDC (hWnd);  
   /* Get the client area of the current window */ 
   GetClientRect(hWnd,&rClientArea); 
 
   /* Load a bitmap at 16 bits per pixel */ 
   nRet = L_LoadBitmap(szFilename, &MainBitmap, sizeof(BITMAPHANDLE), 16, ORDER_BGR, NULL, NULL); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Set XFormToBitmap fields, assuming that the display rectangle is the same 
   as the client area of the current window */ 
   XFormToBitmap.uViewPerspective = TOP_LEFT; 
   XFormToBitmap.nXScalarNum      = BITMAPWIDTH(&MainBitmap); 
   XFormToBitmap.nXScalarDen      = rClientArea.right; 
   XFormToBitmap.nYScalarNum      = BITMAPHEIGHT(&MainBitmap); 
   XFormToBitmap.nYScalarDen      = rClientArea.bottom; 
   XFormToBitmap.nXOffset         = 0; 
   XFormToBitmap.nYOffset         = 0; 
 
   /* Specify a rectangle to define the region */ 
   SetRect(&rRgnRect, rClientArea.right/8, rClientArea.bottom/8,  
      rClientArea.right/2, rClientArea.bottom/2); 
 
   /* Create an elliptical region in the AlphaBitmap */ 
   nRet = L_SetBitmapRgnEllipse(&MainBitmap, &XFormToBitmap, &rRgnRect, L_RGN_SET); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Create a mask bitmap from the region */ 
   nRet = L_CreateMaskFromBitmapRgn ( &MainBitmap, &AlphaBitmap, sizeof(BITMAPHANDLE)  ); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Update the alpha channel in the main bitmap */ 
   nRet = L_SetBitmapAlpha(&MainBitmap, &AlphaBitmap); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Save the bitmap at 16 bits per pixel to keep the alpha channel */ 
   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("Result.TIF")), &MainBitmap, FILE_TIF, 16, 0, NULL); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Free the bitmaps */ 
   L_FreeBitmap(&MainBitmap); 
   L_FreeBitmap(&AlphaBitmap); 
 
   /* Load the bitmap that we just saved and get its alpha channel */ 
   nRet = L_LoadBitmap(MAKE_IMAGE_PATH(TEXT("Result.TIF")), &MainBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL); 
   if(nRet != SUCCESS) 
      return nRet; 
   nRet = L_GetBitmapAlpha(&MainBitmap, &AlphaBitmap, sizeof(BITMAPHANDLE)); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Use the AlphaBitmap as a mask to set the region in the MainBitmap */ 
   nRet = L_SetBitmapRgnFromMask ( &MainBitmap, NULL, &AlphaBitmap, L_RGN_SET ); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Create the palette that we will use to paint */ 
   hOurPalette = L_CreatePaintPalette(hWindowDC, &MainBitmap); 
   /* Select our palette and save the old one */ 
   hSavedPalette = SelectPalette (hWindowDC, hOurPalette, FALSE); 
   /* Realize our palette */ 
   RealizePalette (hWindowDC); 
   /* Paint the region */ 
   nRet = L_PaintRgnDC(hWindowDC,    /* Device context */ 
               &MainBitmap,   /* Bitmap handle */ 
               NULL,          /* Default source rectangle */ 
               NULL,          /* Default source clip area */ 
               &rClientArea,  /* Destination rectangle */ 
               NULL,          /* Default destination clipping rectangle */ 
               SRCCOPY);      /* ROP3 code for a Normal Paint */ 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Restore the old palette */ 
   SelectPalette (hWindowDC, hSavedPalette, FALSE); 
   if(hOurPalette) 
      DeleteObject(hOurPalette); 
   /* Release the device context */ 
   ReleaseDC(hWnd, hWindowDC); 
   /* Free the AlphaBitmap */ 
   L_FreeBitmap(&AlphaBitmap); 
   L_FreeBitmap(&MainBitmap); 
   return SUCCESS; 
}