efl_ui/box: optimize position_set operations with boxes

if a box is moved and no other changes are made to the box or its children,
e.g., if the box is scrolled, then there is no need to loop over the box's
items repeatedly in order to accurately calculate all the item geometries
and positions.

instead, simply apply an offset from the last box calc position to each child
item and handle the position changes more transparently

this yields roughly a 12% perf improvement to the 'efl.ui.scroller simple' test
and brings rendering up to nearly 60fps

Reviewed-by: Cedric BAIL <cedric.bail@free.fr>
Differential Revision: https://phab.enlightenment.org/D9342

src/lib/elementary/efl_ui_box.c

@@ -138,7 +138,7 @@ EOLIAN static void
 _efl_ui_box_efl_gfx_entity_size_set(Eo *obj, Efl_Ui_Box_Data *_pd EINA_UNUSED, Eina_Size2D sz)
 {
    efl_gfx_entity_size_set(efl_super(obj, MY_CLASS), sz);
-   efl_canvas_group_change(obj);
+   efl_pack_layout_request(obj);
 }
 
 EOLIAN static void
@@ -186,6 +186,7 @@ _efl_ui_box_efl_object_constructor(Eo *obj, Efl_Ui_Box_Data *pd)
    pd->dir = EFL_UI_LAYOUT_ORIENTATION_VERTICAL;
    pd->align.h = 0.5;
    pd->align.v = 0.5;
+   pd->full_recalc = EINA_TRUE;
 
    return obj;
 }
@@ -360,8 +361,9 @@ _efl_ui_box_efl_pack_linear_pack_index_get(Eo *obj EINA_UNUSED, Efl_Ui_Box_Data
 }
 
 EOLIAN static void
-_efl_ui_box_efl_pack_layout_layout_request(Eo *obj, Efl_Ui_Box_Data *pd EINA_UNUSED)
+_efl_ui_box_efl_pack_layout_layout_request(Eo *obj, Efl_Ui_Box_Data *pd)
 {
+   pd->full_recalc = EINA_TRUE;
    efl_canvas_group_need_recalculate_set(obj, EINA_TRUE);
 }
 

src/lib/elementary/efl_ui_box_layout.c

@@ -27,6 +27,28 @@ _weight_sort_cb(const void *l1, const void *l2)
    return it2->weight_factor <= it1->weight_factor ? -1 : 1;
 }
 
+/* this function performs a simplified layout when the box has changed position
+ * but no other changes have occurred, e.g., when a box is being scrolled
+ */
+static void
+_efl_ui_box_layout_simple(Efl_Ui_Box *ui_box, Efl_Ui_Box_Data *pd)
+{
+   Eo *child;
+   Eina_List *l;
+   Eina_Position2D pos = efl_gfx_entity_position_get(ui_box);
+
+   EINA_LIST_FOREACH(pd->children, l, child)
+     {
+        Eina_Position2D child_pos = efl_gfx_entity_position_get(child);
+
+        efl_gfx_entity_position_set(child,
+          EINA_POSITION2D(pos.x - pd->last_pos.x + child_pos.x,
+                          pos.y - pd->last_pos.y + child_pos.y));
+     }
+   pd->last_pos = pos;
+   efl_event_callback_call(ui_box, EFL_PACK_EVENT_LAYOUT_UPDATED, NULL);
+}
+
 void
 _efl_ui_box_custom_layout(Efl_Ui_Box *ui_box, Efl_Ui_Box_Data *pd)
 {
@@ -49,8 +71,14 @@ _efl_ui_box_custom_layout(Efl_Ui_Box *ui_box, Efl_Ui_Box_Data *pd)
         efl_gfx_hint_size_restricted_min_set(ui_box, EINA_SIZE2D(0, 0));
         return;
      }
-
+   if (!pd->full_recalc)
+     {
+        _efl_ui_box_layout_simple(ui_box, pd);
+        return;
+     }
    _efl_ui_container_layout_init(ui_box, box_calc);
+   pd->last_pos.x = box_calc[0].pos - box_calc[0].margin[0];
+   pd->last_pos.y = box_calc[1].pos - box_calc[1].margin[0];
 
    /* Item_Calc struct is currently 152 bytes.
     * this is pretty big to be allocating a huge number of, and we don't want to explode the stack
@@ -207,6 +235,7 @@ _efl_ui_box_custom_layout(Efl_Ui_Box *ui_box, Efl_Ui_Box_Data *pd)
    want[1] += (box_calc[1].margin[0] + box_calc[1].margin[1]) +
               (box_calc[1].pad * (count - 1));
 
+   pd->full_recalc = EINA_FALSE;
    efl_gfx_hint_size_restricted_min_set(ui_box, EINA_SIZE2D(want[0], want[1]));
 
    efl_event_callback_call(ui_box, EFL_PACK_EVENT_LAYOUT_UPDATED, NULL);

src/lib/elementary/efl_ui_box_private.h

@@ -27,7 +27,10 @@ struct _Efl_Ui_Box_Data
       double h, v;
    } align;
 
+   Eina_Position2D last_pos;
+
    Eina_Bool homogeneous : 1;
+   Eina_Bool full_recalc : 1; //whether to force full recalc
 };
 
 #endif