当前例程使用一个函数BitmapToRegion()，用于把一个位图转换为区域。
它扫描位图内容，找到非透明象素的连续线，增加这些线到 RGNDATA结构，最后，用ExtCreateRgn()创建区域。
程序提供的、使用该函数的例子程序创建了一个非矩形区域的Windows NT启动屏幕，
参见下图。该区域与winnt256.bmp位图基本相同，并去掉了黑色和近乎黑色的象素。
所以窗口为非规则外形，窗体有镂空效果，如下图
上位机MFC将位图转换为区域
例程是在WIN32类型程序上调用上面函数实现，自己可以在MFC中使用。
用鼠标左键可以点着移动窗口，ESC键可以退出程序。
项目源代码下载：
下面是BitmapToRegion()函数可以复制使用
//
// BitmapToRegion : Create a region from the "non-transparent" pixels of a bitmap
//
// hBmp : Source bitmap
// cTransparentColor : Color base for the "transparent" pixels (default is black)
// cTolerance : Color tolerance for the "transparent" pixels.
//
// A pixel is assumed to be transparent if the value of each of its 3 components (blue, green and red) is
// greater or equal to the corresponding value in cTransparentColor and is lower or equal to the
// corresponding value in cTransparentColor + cTolerance.
//
HRGN BitmapToRegion (HBITMAP hBmp, COLORREF cTransparentColor = 0, COLORREF cTolerance = 0x101010)
{
HRGN hRgn = NULL;
ASSERT(hBmp);
if (hBmp)
{
// Create a memory DC inside which we will scan the bitmap content
HDC hMemDC = CreateCompatibleDC(NULL);
ASSERT(hMemDC);
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);
ASSERT(hbm32);
if (hbm32)
{
HBITMAP holdBmp = (HBITMAP)SelectObject(hMemDC, hbm32);
// Create a DC just to copy the bitmap into the memory DC
HDC hDC = CreateCompatibleDC(hMemDC);
ASSERT(hDC);
if (hDC)
{
// Get how many bytes per row we have for the bitmap bits (rounded up to 32 bits)
BITMAP bm32;
VERIFY(GetObject(hbm32, sizeof(bm32), &bm32));
while (bm32.bmWidthBytes % 4)
bm32.bmWidthBytes++;
// Copy the bitmap into the memory DC
HBITMAP holdBmp = (HBITMAP)SelectObject(hDC, hBmp);
VERIFY(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;
VERIFY(hData = GlobalReAlloc(hData, sizeof(RGNDATAHEADER) + (sizeof(RECT) * maxRects), GMEM_MOVEABLE));
pData = (RGNDATA *)GlobalLock(hData);
ASSERT(pData);
}
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);
ASSERT(h);
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);
ASSERT(h);
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;
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