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Does anybody know where I can find a good tutorial on using regions in a GDI Win32 Visual C++ application to set "transparent" areas in a bitmap or window? (like color-keying in DirectDraw) Either links to tutorials or a post describing the process would be extremely welcome. Thanks, Mike

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That is a great article. Thanks Lunatic. It was incredibly easy to apply regions to my window. But how would I do a transparent "BitBlt". I know this question has been asked a lot, but I have never found very good answers. Any thoughts?

Thanks,
Mike

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Here is a routine i use to get an HRGN... after setting my window to the HRGN passed back, all that is needed is to do a regular BitBlt in your WM_PAINT message and viola. *Note* The following code was created by Jean-Edouard Lachand-Robert.


    
HRGN BitmapToRegion (HBITMAP hBmp, COLORREF cTransparentColor , COLORREF cTolerance )
{
HRGN hRgn = NULL;

if (hBmp)
{
// Create a memory DC inside which we will scan the bitmap content

HDC hMemDC = CreateCompatibleDC(NULL);
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);
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 = ((RGBQUAD *) p)->rgbRed; // GetRValue(*p);

if (b >= lr && b <= hr)
{
b = ((RGBQUAD *) p)->rgbGreen; // GetGValue(*p);

if (b >= lg && b <= hg)
{
b = ((RGBQUAD *) p)->rgbBlue ; // 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

SelectObject(hDC, holdBmp);
DeleteDC(hDC);
}

DeleteObject(SelectObject(hMemDC, holdBmp));
}

DeleteDC(hMemDC);
}
}

return hRgn;
}


[edited by - xtrmntr on April 19, 2002 5:56:56 PM]

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