Transparent 之 mask bmp

• 条件:
  • the colour image must be black in all areas that we want to display as transparent
  • the mask image must be white in the areas we want transparent, and black elsewhere
    
• 原理:
  • SRCAND:Combines the colors of the source and destination rectangles by using the Boolean AND operator.
  • SRCPAINT:Combines the colors of the source and destination rectangles by using the Boolean OR operator.

  • SelectObject(hMemDC, hMaskBmp);//mask bmp
    BitBlt(hdc, 0, 0, cxBmp, cyBmp, hMemDC, 0, 0, SRCAND);
    
    SelectObject(hMemDC, hColorBmp);//color bmp
    BitBlt(hdc, 0, 0, cxBmp, cyBmp, hMemDC, 0, 0, SRCPAINT);
    

    
    
• 代码:

  • HBITMAP CreateBitmapMask(HBITMAP hbmColour, COLORREF crTransparent)
    {
    	HDC hdcMem, hdcMem2;
    	HBITMAP hbmMask;
    	BITMAP bm;
    
    	// Create monochrome (1 bit) mask bitmap.  
    
    	GetObject(hbmColour, sizeof(BITMAP), &bm);
    	hbmMask = CreateBitmap(bm.bmWidth, bm.bmHeight, 1, 1, NULL);
    
    	// Get some HDCs that are compatible with the display driver
    
    	hdcMem = CreateCompatibleDC(0);
    	hdcMem2 = CreateCompatibleDC(0);
    
    	SelectObject(hdcMem, hbmColour);
    	SelectObject(hdcMem2, hbmMask);
    
    	// Set the background colour of the colour image to the colour
    	// you want to be transparent.
    	SetBkColor(hdcMem, crTransparent);
    
    	// Copy the bits from the colour image to the B+W mask... everything
    	// with the background colour ends up white while everythig else ends up
    	// black...Just what we wanted.
    
    	BitBlt(hdcMem2, 0, 0, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);
    
    	// Take our new mask and use it to turn the transparent colour in our
    	// original colour image to black so the transparency effect will
    	// work right.
    	BitBlt(hdcMem, 0, 0, bm.bmWidth, bm.bmHeight, hdcMem2, 0, 0, SRCINVERT);
    
    	// Clean up.
    
    	DeleteDC(hdcMem);
    	DeleteDC(hdcMem2);
    
    	return hbmMask;
    }

  • 	static HBITMAP hColorBmp;
    	static HBITMAP hMaskBmp;
    	static int cxBmp;
    	static int cyBmp;
    
    	case WM_CREATE:
    		{
    			//load bmp and get bmp info
    			hColorBmp = LoadBitmap(GetModuleHandle(NULL),MAKEINTRESOURCE(IDB_BALL));
    			if (hColorBmp == NULL)
    			{
    				MessageBox(hWnd,L"failed to load color bmp!",NULL,MB_OK);
    			}
    			hMaskBmp = CreateBitmapMask(hColorBmp,RGB(255,255,255));
    			if (hMaskBmp == NULL)
    			{
    				MessageBox(hWnd,L"failed to create mask bmp!",NULL,MB_OK);
    			}
    
    			BITMAP bmpInfo;
    			GetObject(hColorBmp,sizeof(BITMAP),&bmpInfo);
    			cxBmp = bmpInfo.bmWidth;
    			cyBmp = bmpInfo.bmHeight;
    			//put window int the middle screen
    			int cxScr = GetSystemMetrics(SM_CXSCREEN);
    			int cyScr = GetSystemMetrics(SM_CYSCREEN);
    			int cxWnd = 400;
    			int cyWnd = 400;
    			MoveWindow(hWnd,(cxScr-cxWnd)/2,(cyScr-cyWnd)/2,cxWnd,cyWnd,TRUE);
    		}
    		break;
    
    	case WM_PAINT:
    		hdc = BeginPaint(hWnd, &ps);
    		{
    			//bg color
    			RECT rcWnd;
    			HBRUSH hBrush;
    			GetClientRect(hWnd,&rcWnd);
    			hBrush = CreateSolidBrush(RGB(0,128,128));
    			FillRect(hdc,&rcWnd,hBrush);
    			DeleteObject(hBrush);
    			//disp bmp
    			HDC hMemDC = CreateCompatibleDC(hdc);
    
    			SelectObject(hMemDC, hMaskBmp);
    			BitBlt(hdc, 73,58, cxBmp, cyBmp, hMemDC, 0, 0, SRCAND);
    
    			SelectObject(hMemDC, hColorBmp);
    			BitBlt(hdc, 73,58, cxBmp, cyBmp, hMemDC, 0, 0, SRCPAINT);
    
    			DeleteDC(hMemDC);
    
    		}
    		EndPaint(hWnd, &ps);
    		break;
    

• 结果:
  •