MFC 创建不规则窗体

//准备两张位图，一张位图为彩色位图，是要作为窗体背景的图片，另一张则为黑白图，黑色是窗体最后要镂空的部分，白色为显示区域

//关键代码：根据一张黑白位图获取Rgn区域

HRGN CMyDlg::BitmapToRegion(HBITMAP hBmp, COLORREF cTransparentColor, COLORREF cTolerance)
{
	HRGN hRgn = NULL;
	
	if (hBmp)
	{
		HDC hMemDC = CreateCompatibleDC(NULL);
		if (hMemDC)
		{
			BITMAP bm;
			GetObject(hBmp, sizeof(bm), &bm);
			
			//创建一个32位色的位图，并选进内存设备环境
			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
					GlobalFree(hData);
					SelectObject(hDC, holdBmp);
					DeleteDC(hDC);
				}				
				DeleteObject(SelectObject(hMemDC, holdBmp));
			}			
			DeleteDC(hMemDC);
		}
	}	
	return hRgn;	
}

//在对话框初始化或窗口创建时中添加以下代码

BOOL CMyDlg::OnInitDialog()
{

        // TODO: 在此添加额外的初始化代码
        CBitmap bmp;	
        if(bmp.LoadBitmap(IDB_BITMAP2))
        {
		HRGN rgn;
		rgn = BitmapToRegion((HBITMAP)bmp, RGB(0,0,0));//RGB(0,0,0)纯黑色作为透明色，是需要裁剪掉的区域
                //设置窗体的有效区域
		SetWindowRgn(rgn, TRUE);
		bmp.DeleteObject();
         }
         return TRUE;  // 除非将焦点设置到控件，否则返回 TRUE
}