Transparent 之 AlphaBlend

• 函数:
  • The AlphaBlend function displays bitmaps that have transparent or semitransparent pixels.

  • BOOL AlphaBlend(
      HDC hdcDest,                 // handle to destination DC
      int nXOriginDest,            // x-coord of upper-left corner
      int nYOriginDest,            // y-coord of upper-left corner
      int nWidthDest,              // destination width
      int nHeightDest,             // destination height
      HDC hdcSrc,                  // handle to source DC
      int nXOriginSrc,             // x-coord of upper-left corner
      int nYOriginSrc,             // y-coord of upper-left corner
      int nWidthSrc,               // source width
      int nHeightSrc,              // source height
      BLENDFUNCTION blendFunction  // alpha-blending function
    );
    

• 代码:

  • 	static HBITMAP hBmp1;
    	static HBITMAP hBmp2;
    	static int cxBmp;
    	static int cyBmp;
    
    	case WM_CREATE:
    		{
    			//load bmp
    			hBmp1 = LoadBitmap(GetModuleHandle(NULL),MAKEINTRESOURCE(IDB_BITMAP1));
    			if (hBmp1 == NULL)
    			{
    				MessageBox(hWnd,L"failed to load bmp1!",NULL,MB_OK);
    			}
    			hBmp2 = LoadBitmap(GetModuleHandle(NULL),MAKEINTRESOURCE(IDB_BITMAP2));
    			if (hBmp2 == NULL)
    			{
    				MessageBox(hWnd,L"failed to load bmp2!",NULL,MB_OK);
    			}
    			//get bmp info
    			BITMAP bmpInfo;
    			GetObject(hBmp1,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 = cxBmp + 2 * GetSystemMetrics(SM_CXFRAME);
    			int cyWnd = cyBmp + 2 * GetSystemMetrics(SM_CXFRAME) + GetSystemMetrics(SM_CYCAPTION);
    			MoveWindow(hWnd,(cxScr-cxWnd)/2,(cyScr-cyWnd)/2,cxWnd,cyWnd,TRUE);
    		}
    		break;
    
    	case WM_PAINT:
    		hdc = BeginPaint(hWnd, &ps);
    		{
    			//disp bmp
    			HDC hMemDC1 = CreateCompatibleDC(hdc);
    			HDC hMemDC2 = CreateCompatibleDC(hdc);
    			SelectObject(hMemDC1, hBmp1);
    			SelectObject(hMemDC2, hBmp2);
    			
    			BLENDFUNCTION bf;
    			bf.BlendOp = AC_SRC_OVER;
    			bf.BlendFlags = 0;
    			bf.SourceConstantAlpha = 128;//alpha transparency value
    			bf.AlphaFormat = 0;
    			AlphaBlend(hMemDC1,0,0,cxBmp,cyBmp,hMemDC2,0,0,cxBmp,cyBmp,bf);
    
    			BitBlt(hdc, 0, 0,cxBmp, cyBmp, hMemDC1, 0, 0, SRCCOPY);			
    
    			DeleteDC(hMemDC1);
    			DeleteDC(hMemDC2);
    
    		}
    		EndPaint(hWnd, &ps);
    		break;
    

• 结果:
  • 
  • 
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