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Editorial Team
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Asked: 2026-06-02T07:24:09+00:00

I want to use a single CDC , inwhich to draw 3 bitmaps, positioned

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I want to use a single CDC, inwhich to draw 3 bitmaps, positioned in the CDC, and then pass it into UpdateLayeredWindow. My problem is that I can’t get the SIZE* psize parameter of the UpdateLayeredWindow function right! Can Anyone help? What do I do?

BLENDFUNCTION bBlendFnc = {
    AC_SRC_OVER,
    0,
    255,
    AC_SRC_ALPHA
};

CBitmap btCdcBuff;
CBitmap* cache;
BITMAP hbCdcBuff;

btCdcBuff.CreateCompatibleBitmap(pCdcMain, szWndSize.cx, szWndSize.cy); btCdcBuff.GetBitmap(&hbCdcBuff);

cache = pCdcMain->SelectObject(&btCdcBuff); // pCdcMain is a compatible CDC with the screen (pCdcScreen)

Blend(&btIcon); // This function just creates a compatible CDC from a CPaintDC, selects the passed in CBitmap via SelectObject and AlphaBlends it to the pCdcMain.
pCdcMain->SelectObject(cache);

UpdateLayeredWindow(pCdcScreen, NULL, new CSize(hbCdcBuff.bmWidth, hbCdcBuff.bmHeight), pCdcMain, new CPoint(0, 0), 0, &bBlendFnc, ULW_ALPHA) // This fails and returns false
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1 Answer

  1. Editorial Team

    When using CreateCompatibleBitmap with UpdateLayeredWindow, make sure you pass in the CDC for the screen (ie, pCdcScreen not pCdcMain), so that the Bitmap created is of the correct format. See this thread: http://social.msdn.microsoft.com/Forums/en/windowsuidevelopment/thread/1fbcf5e4-b9eb-4537-bf0b-d330aa333fea

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