C / C++ / MFC

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void CAnimateWnd::ChangeAppearanceAndPosition(HRGN hNewRgn, int iPosX, int iPosY)<br />
{<br />
CRect oldRect;<br />
GetWindowRect(&oldRect);<br />
<br />
SetWindowRgn(hNewRgn, FALSE); // change shape without redrawing<br />
SetWindowPos(&wndTopMost, iPosX, iPosY, 100, 100, SWP_NOACTIVATE);<br />
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::InvalidateRect( GetDesktopWindow()->GetSafeHwnd(), &oldRect, TRUE);<br />
}<br />

1. Do a ScreenToClient of the rectangle for the desktop window prior to using it in InvalidateRect.
   
2. Force the repainting of the desktop window with UpdateWindow after invalidating.

void CAnimateWnd::ChangeAppearanceAndPosition(HRGN hNewRgn, int iPosX, int iPosY)
{
CRgn oldRgn;
oldRgn.CreateRectRgn(0,0,0,0);
GetWindowRgn(oldRgn);
SetWindowRgn(hNewRgn, FALSE); // change shape without redrawing
GetDesktopWindow()->InvalidateRect(&oldRgn);
SetWindowPos(&wndTopMost, iPosX, iPosY, 100, 100, SWP_NOACTIVATE);
}

void CAnimateWnd::ChangeAppearanceAndPosition(HRGN hNewRgn, int iPosX, int iPosY)
{
  CRgn oldRgn;
  oldRgn.CreateRectRgn(0,0,0,0);
  GetWindowRgn(oldRgn);
  SetWindowRgn(hNewRgn, FALSE); // change shape without edrawing
  InvalidateRect(&oldRgn);
  SetWindowPos(&wndTopMost, iPosX, iPosY, 100, 100, SWP_NOACTIVATE);
}

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void CAnimateWnd::UpdateRgnAndPos(HRGN hNewRgn, int iPosX, int iPosY)<br />
{<br />
HRGN hOldRgn = CreateRectRgn(0, 0, 0, 0); // make blank region<br />
GetWindowRgn(hOldRgn);<br />
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HRGN hOffRgn = CreateRectRgn(0, 0, 0, 0); // make blank region<br />
CombineRgn(hOffRgn, hNewRgn, NULL, RGN_COPY); // make a copy<br />
OffsetRgn(hOffRgn, iPosX - m_iOldPosX, iPosY - m_iOldPosY); // compensate for later movment<br />
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HRGN hCombinedRgn = CreateRectRgn(0, 0, 0, 0); // make blank region<br />
CombineRgn(hCombineRgn, hOffRgn, hOldRgn, RGN_OR); // combine region so that lost area gets deleted<br />
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SetWindowRgn(hCombinedRgn, FALSE); // don't redraw yet<br />
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SetWindowPos(iPosX, iPosY, 100, 100, SWP_NOACTIVATE); // change position<br />
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SetWindowRgn(hNewRgn, TRUE); // redraw now so that lost areas of combined region are restored<br />
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Invalidate(TRUE); // make it pretty<br />
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m_iOldPosX = iPosX; // remember old position for next time<br />
m_iOldPosY = iPosY;<br />
}<br />