Resize composite overlay window when the root window changes.

- This allows some compositing managers to work, even after randr12 has changed the root window size.
- Thanks to ajax for figuring out the best place to put this.
- Example:
	- xf86RandR12SetMode() calls EnableDisableFBAccess().
	- That calls xf86SetRootClip() which in turn calls ResizeChildrenWinSize().
	- The final step is the call to PositionWindow().

composite/compwindow.c

@@ -165,6 +165,29 @@ compCheckRedirect (WindowPtr pWin)
     return TRUE;
 }
 
+static int
+updateOverlayWindow(ScreenPtr pScreen)
+{
+	CompScreenPtr cs;
+	WindowPtr pWin; /* overlay window */
+	XID vlist[2];
+
+	cs = GetCompScreen(pScreen);
+	if ((pWin = cs->pOverlayWin) != NULL) {
+		if ((pWin->drawable.width == pScreen->width) &&
+			(pWin->drawable.height == pScreen->height))
+			return Success;
+
+		/* Let's resize the overlay window. */
+		vlist[0] = pScreen->width;
+		vlist[1] = pScreen->height;
+		return ConfigureWindow(pWin, CWWidth | CWHeight, vlist, wClient(pWin));
+	}
+
+	/* Let's be on the safe side and not assume an overlay window is always allocated. */
+	return Success;
+}
+
 Bool
 compPositionWindow (WindowPtr pWin, int x, int y)
 {
@@ -203,6 +226,8 @@ compPositionWindow (WindowPtr pWin, int x, int y)
     cs->PositionWindow = pScreen->PositionWindow;
     pScreen->PositionWindow = compPositionWindow;
     compCheckTree (pWin->drawable.pScreen);
+    if (updateOverlayWindow(pScreen) != Success)
+	ret = FALSE;
     return ret;
 }