public void HandleNCCalcsize(IntPtr wParam, IntPtr lParam)
{
// lParam is an [in, out] that can be either a RECT* (wParam == FALSE) or an NCCALCSIZE_PARAMS*.
// Since the first field of NCCALCSIZE_PARAMS is a RECT and is the only field we care about
// we can unconditionally treat it as a RECT.
/* DefWindowProc must be called in both the maximized and non-maximized
* cases, otherwise tile/cascade windows won't work */
var nonclient = (RECT)Marshal.PtrToStructure(lParam, typeof(RECT));
DefWindowProcW(_framelessInfo.Handle, WM.NCCALCSIZE, wParam, lParam);
var client = (RECT)Marshal.PtrToStructure(lParam, typeof(RECT));
if (IsMaximized(_framelessInfo.Handle))
{
WINDOWINFO wi = new WINDOWINFO(null);
GetWindowInfo(_framelessInfo.Handle, ref wi);
/* Maximized windows always have a non-client border that hangs over
* the edge of the screen, so the size proposed by WM_NCCALCSIZE is
* fine. Just adjust the top border to remove the window title. */
var rect = new RECT();
rect.left = client.left;
rect.top = (int)(nonclient.top + wi.cyWindowBorders);
rect.right = client.right;
rect.bottom = client.bottom;
IntPtr mon = MonitorFromWindow(_framelessInfo.Handle, MONITOR.DEFAULTTOPRIMARY);
MONITORINFOEXW mi = new MONITORINFOEXW(null);
GetMonitorInfoW(mon, ref mi);
/* If the client rectangle is the same as the monitor's rectangle,
* the shell assumes that the window has gone fullscreen, so it removes
* the topmost attribute from any auto-hide appbars, making them
* inaccessible. To avoid this, reduce the size of the client area by
* one pixel on a certain edge. The edge is chosen based on which side
* of the monitor is likely to contain an auto-hide appbar, so the
* missing client area is covered by it. */
if (rect.AreEqual(mi.rcMonitor))
{
if (HasAutohideAppbar(ABE_BOTTOM, mi.rcMonitor))
{
rect.bottom--;
}
else if (HasAutohideAppbar(ABE_LEFT, mi.rcMonitor))
{
rect.left++;
}
else if (HasAutohideAppbar(ABE_TOP, mi.rcMonitor))
{
rect.top++;
}
else if (HasAutohideAppbar(ABE_RIGHT, mi.rcMonitor))
{
rect.right--;
}
}
Marshal.StructureToPtr(rect, lParam, false);
}
else
{
/* For the non-maximized case, set the output RECT to what it was
* before WM_NCCALCSIZE modified it. This will make the client size the
* same as the non-client size. */
Marshal.StructureToPtr(nonclient, lParam, false);
}
}