Fullscreen.hs: don't lay out windows obscured by fullscreen

There's no reason to return a rectangle for any window that is totally
obscured by a full-screen window, and not doing so has the nice property that
when hidden windows' borders overlap with a full-screen window's, the user
will not be confused by overlapping partially-drawn borders. It also makes the
Fullscreen modifiers combine much better with smartBorders.

CHANGES.md

@@ -135,6 +135,11 @@
     Added `sideNavigation` and a parameterised variant, providing a navigation
     strategy with fewer quirks for tiled layouts using X.L.Spacing.
 
+  * `XMonad.Layout.Fullscreen`
+    
+    The fullscreen layouts will now not render any window that is totally
+    obscured by fullscreen windows.
+    
   * `XMonad.Layout.Gaps`
 
     Extended the sendMessage interface with `ModifyGaps` to allow arbitrary

XMonad/Layout/Fullscreen.hs

@@ -109,7 +109,7 @@ instance LayoutModifier FullscreenFull Window where
   pureModifier (FullscreenFull frect fulls) rect _ list =
     (map (flip (,) rect') visfulls ++ rest, Nothing)
     where visfulls = intersect fulls $ map fst list
-          rest = filter (flip notElem visfulls . fst) list
+          rest = filter (not . (flip elem visfulls `orP` covers rect')) list
           rect' = scaleRationalRect rect frect
 
 instance LayoutModifier FullscreenFocus Window where
@@ -122,7 +122,7 @@ instance LayoutModifier FullscreenFocus Window where
   pureModifier (FullscreenFocus frect fulls) rect (Just (W.Stack {W.focus = f})) list
      | f `elem` fulls = ((f, rect') : rest, Nothing)
      | otherwise = (list, Nothing)
-     where rest = filter ((/= f) . fst) list
+     where rest = filter (not . ((== f) `orP` covers rect')) list
            rect' = scaleRationalRect rect frect
   pureModifier _ _ Nothing list = (list, Nothing)
 
@@ -240,3 +240,15 @@ fullscreenManageHook' isFull = isFull --> do
     sendMessageWithNoRefresh FullscreenChanged cw
   idHook
 
+-- | True iff one rectangle completely contains another.
+covers :: Rectangle -> Rectangle -> Bool
+(Rectangle x1 y1 w1 h1) `covers` (Rectangle x2 y2 w2 h2) =
+  let fi = fromIntegral
+      in x1 <= x2 &&
+         y1 <= y2 &&
+         x1 + fi w1 >= x2 + fi w2 &&
+         y1 + fi h1 >= y2 + fi h2
+
+-- | Applies a pair of predicates to a pair of operands, combining them with ||.
+orP :: (a -> Bool) -> (b -> Bool) -> (a, b) -> Bool
+orP f g (x, y) = f x || g y