Fix performance regression

basis/ui/gadgets/gadgets.factor

@@ -166,14 +166,13 @@ DEFER: relayout
 
 DEFER: in-layout?
 
-: do-invalidate ( gadget -- gadget )
-    in-layout? get [ dup invalidate ] [ dup invalidate* ] if ;
+GENERIC: dim-changed ( gadget -- )
+
+M: gadget dim-changed
+    in-layout? get [ invalidate ] [ invalidate* ] if ;
 
 M: gadget (>>dim) ( dim gadget -- )
-   2dup dim>> =
-     [ 2drop ]
-     [ tuck call-next-method do-invalidate drop ]
-   if ;
+    2dup dim>> = [ 2drop ] [ tuck call-next-method dim-changed ] if ;
 
 GENERIC: pref-dim* ( gadget -- dim )
 

basis/ui/gadgets/incremental/incremental.factor

@@ -4,17 +4,6 @@ USING: io kernel math namespaces math.vectors ui.gadgets
 ui.gadgets.packs accessors math.geometry.rect ;
 IN: ui.gadgets.incremental
 
-! Incremental layout allows adding lines to panes to be O(1).
-! Note that incremental packs are distinct from ordinary packs
-! defined in layouts.factor, since you don't want all packs to
-! be incremental. In particular, incremental packs do not
-! support non-default values for pack-align, pack-fill and
-! pack-gap.
-
-! The cursor is the current size of the incremental pack.
-! New gadgets are added at
-!   incremental-cursor gadget-orientation v*
-
 TUPLE: incremental < pack cursor ;
 
 : <incremental> ( -- incremental )
@@ -29,29 +18,33 @@ M: incremental pref-dim*
 
 : next-cursor ( gadget incremental -- cursor )
     [
-        swap rect-dim swap cursor>>
-        2dup v+ >r vmax r>
+        [ rect-dim ] [ cursor>> ] bi*
+        [ vmax ] [ v+ ] 2bi
     ] keep orientation>> set-axis ;
 
 : update-cursor ( gadget incremental -- )
-    [ next-cursor ] keep (>>cursor) ;
+    tuck next-cursor >>cursor drop ;
 
 : incremental-loc ( gadget incremental -- )
     [ cursor>> ] [ orientation>> ] bi v*
     >>loc drop ;
 
-: prefer-incremental ( gadget -- )
+: prefer-incremental ( gadget -- ) USE: slots.private
     dup forget-pref-dim dup pref-dim >>dim drop ;
 
+M: incremental dim-changed drop ;
+
 : add-incremental ( gadget incremental -- )
     not-in-layout
     2dup swap (add-gadget) drop
-    over prefer-incremental
-    over layout-later
-    2dup incremental-loc
-    tuck update-cursor
-    dup prefer-incremental
-    parent>> [ invalidate* ] when* ;
+    t in-layout? [
+        over prefer-incremental
+        over layout-later
+        2dup incremental-loc
+        tuck update-cursor
+        dup prefer-incremental
+        parent>> [ invalidate* ] when*
+    ] with-variable ;
 
 : clear-incremental ( incremental -- )
     not-in-layout