layout: Add a `REPOSITION` restyle damage type.

Separating out `REPOSITION` from `REPAINT` allows us to compute
stacking-context-relative positions without rebuilding the display list.
This saves a lot of time when responding to script-to-layout queries.

1 files changed, 32 insertions, 28 deletions

diff --git a/components/script_layout_interface/restyle_damage.rs b/components/script_layout_interface/restyle_damage.rs
index ef33370e064..ff0e26af03f 100644
--- a/components/script_layout_interface/restyle_damage.rs
+++ b/components/script_layout_interface/restyle_damage.rs
@@ -15,31 +15,36 @@ bitflags! {
         #[doc = "Currently unused; need to decide how this propagates."]
         const REPAINT = 0x01,
 
+        #[doc = "The stacking-context-relative position of this node or its descendants has \
+                 changed."]
+        #[doc = "Propagates both up and down the flow tree."]
+        const REPOSITION = 0x02,
+
         #[doc = "Recompute the overflow regions (bounding box of object and all descendants)."]
         #[doc = "Propagates down the flow tree because the computation is bottom-up."]
-        const STORE_OVERFLOW = 0x02,
+        const STORE_OVERFLOW = 0x04,
 
         #[doc = "Recompute intrinsic inline_sizes (minimum and preferred)."]
         #[doc = "Propagates down the flow tree because the computation is"]
         #[doc = "bottom-up."]
-        const BUBBLE_ISIZES = 0x04,
+        const BUBBLE_ISIZES = 0x08,
 
         #[doc = "Recompute actual inline-sizes and block-sizes, only taking out-of-flow children \
                  into account. \
                  Propagates up the flow tree because the computation is top-down."]
-        const REFLOW_OUT_OF_FLOW = 0x08,
+        const REFLOW_OUT_OF_FLOW = 0x10,
 
         #[doc = "Recompute actual inline_sizes and block_sizes."]
         #[doc = "Propagates up the flow tree because the computation is"]
         #[doc = "top-down."]
-        const REFLOW = 0x10,
+        const REFLOW = 0x20,
 
         #[doc = "Re-resolve generated content. \
                  Propagates up the flow tree because the computation is inorder."]
-        const RESOLVE_GENERATED_CONTENT = 0x20,
+        const RESOLVE_GENERATED_CONTENT = 0x40,
 
         #[doc = "The entire flow needs to be reconstructed."]
-        const RECONSTRUCT_FLOW = 0x40
+        const RECONSTRUCT_FLOW = 0x80
     }
 }
 
@@ -63,7 +68,8 @@ impl TRestyleDamage for RestyleDamage {
     /// `RestyleDamage::all()` will result in unnecessary sequential resolution
     /// of generated content.
     fn rebuild_and_reflow() -> RestyleDamage {
-        REPAINT | STORE_OVERFLOW | BUBBLE_ISIZES | REFLOW_OUT_OF_FLOW | REFLOW | RECONSTRUCT_FLOW
+        REPAINT | REPOSITION | STORE_OVERFLOW | BUBBLE_ISIZES | REFLOW_OUT_OF_FLOW | REFLOW |
+            RECONSTRUCT_FLOW
     }
 }
 
@@ -72,9 +78,10 @@ impl RestyleDamage {
     /// returns the damage that we should add to the *parent* of this flow.
     pub fn damage_for_parent(self, child_is_absolutely_positioned: bool) -> RestyleDamage {
         if child_is_absolutely_positioned {
-            self & (REPAINT | STORE_OVERFLOW | REFLOW_OUT_OF_FLOW | RESOLVE_GENERATED_CONTENT)
+            self & (REPAINT | REPOSITION | STORE_OVERFLOW | REFLOW_OUT_OF_FLOW |
+                    RESOLVE_GENERATED_CONTENT)
         } else {
-            self & (REPAINT | STORE_OVERFLOW | REFLOW | REFLOW_OUT_OF_FLOW |
+            self & (REPAINT | REPOSITION | STORE_OVERFLOW | REFLOW | REFLOW_OUT_OF_FLOW |
                     RESOLVE_GENERATED_CONTENT)
         }
     }
@@ -90,7 +97,7 @@ impl RestyleDamage {
                 // Absolute children are out-of-flow and therefore insulated from changes.
                 //
                 // FIXME(pcwalton): Au contraire, if the containing block dimensions change!
-                self & REPAINT
+                self & (REPAINT | REPOSITION)
             }
             (true, false) => {
                 // Changing the position of an absolutely-positioned block requires us to reflow
@@ -103,7 +110,7 @@ impl RestyleDamage {
             }
             _ => {
                 // TODO(pcwalton): Take floatedness into account.
-                self & (REPAINT | REFLOW)
+                self & (REPAINT | REPOSITION | REFLOW)
             }
         }
     }
@@ -115,6 +122,7 @@ impl fmt::Display for RestyleDamage {
 
         let to_iter =
             [ (REPAINT, "Repaint")
+            , (REPOSITION, "Reposition")
             , (STORE_OVERFLOW, "StoreOverflow")
             , (BUBBLE_ISIZES, "BubbleISizes")
             , (REFLOW_OUT_OF_FLOW, "ReflowOutOfFlow")
@@ -163,14 +171,8 @@ fn compute_damage(old: &ServoComputedValues, new: &ServoComputedValues) -> Resty
     // FIXME: Test somehow that every property is included.
 
     add_if_not_equal!(old, new, damage,
-                      [
-                          REPAINT,
-                          STORE_OVERFLOW,
-                          BUBBLE_ISIZES,
-                          REFLOW_OUT_OF_FLOW,
-                          REFLOW,
-                          RECONSTRUCT_FLOW
-                      ], [
+                      [REPAINT, REPOSITION, STORE_OVERFLOW, BUBBLE_ISIZES, REFLOW_OUT_OF_FLOW,
+                       REFLOW, RECONSTRUCT_FLOW], [
         get_box.float, get_box.display, get_box.position, get_counters.content,
         get_counters.counter_reset, get_counters.counter_increment,
         get_inheritedbox._servo_under_display_none,
@@ -191,8 +193,8 @@ fn compute_damage(old: &ServoComputedValues, new: &ServoComputedValues) -> Resty
         get_column.column_width, get_column.column_count
     ]) || (new.get_box().display == display::T::inline &&
            add_if_not_equal!(old, new, damage,
-                             [REPAINT, STORE_OVERFLOW, BUBBLE_ISIZES, REFLOW_OUT_OF_FLOW, REFLOW,
-                              RECONSTRUCT_FLOW], [
+                             [REPAINT, REPOSITION, STORE_OVERFLOW, BUBBLE_ISIZES,
+                              REFLOW_OUT_OF_FLOW, REFLOW, RECONSTRUCT_FLOW], [
         // For inline boxes only, border/padding styles are used in flow construction (to decide
         // whether to create fragments for empty flows).
         get_border.border_top_width, get_border.border_right_width,
@@ -200,7 +202,8 @@ fn compute_damage(old: &ServoComputedValues, new: &ServoComputedValues) -> Resty
         get_padding.padding_top, get_padding.padding_right,
         get_padding.padding_bottom, get_padding.padding_left
     ])) || add_if_not_equal!(old, new, damage,
-                            [ REPAINT, STORE_OVERFLOW, BUBBLE_ISIZES, REFLOW_OUT_OF_FLOW, REFLOW ],
+                            [REPAINT, REPOSITION, STORE_OVERFLOW, BUBBLE_ISIZES,
+                             REFLOW_OUT_OF_FLOW, REFLOW],
         [get_border.border_top_width, get_border.border_right_width,
         get_border.border_bottom_width, get_border.border_left_width,
         get_margin.margin_top, get_margin.margin_right,
@@ -225,11 +228,14 @@ fn compute_damage(old: &ServoComputedValues, new: &ServoComputedValues) -> Resty
         get_position.flex_shrink,
         get_position.align_self
     ]) || add_if_not_equal!(old, new, damage,
-                            [ REPAINT, STORE_OVERFLOW, REFLOW_OUT_OF_FLOW ], [
+                            [REPAINT, REPOSITION, STORE_OVERFLOW, REFLOW_OUT_OF_FLOW], [
         get_position.top, get_position.left,
-        get_position.right, get_position.bottom
+        get_position.right, get_position.bottom,
+        get_effects.opacity,
+        get_effects.transform, get_effects.transform_style, get_effects.transform_origin,
+        get_effects.perspective, get_effects.perspective_origin
     ]) || add_if_not_equal!(old, new, damage,
-                            [ REPAINT ], [
+                            [REPAINT], [
         get_color.color, get_background.background_color,
         get_background.background_image, get_background.background_position,
         get_background.background_repeat, get_background.background_attachment,
@@ -245,9 +251,7 @@ fn compute_damage(old: &ServoComputedValues, new: &ServoComputedValues) -> Resty
         get_inheritedtext._servo_text_decorations_in_effect,
         get_pointing.cursor, get_pointing.pointer_events,
         get_effects.box_shadow, get_effects.clip, get_inheritedtext.text_shadow, get_effects.filter,
-        get_effects.transform, get_effects.backface_visibility, get_effects.transform_style,
-        get_effects.transform_origin, get_effects.perspective, get_effects.perspective_origin,
-        get_effects.mix_blend_mode, get_effects.opacity, get_inheritedbox.image_rendering,
+        get_effects.mix_blend_mode, get_inheritedbox.image_rendering,
 
         // Note: May require REFLOW et al. if `visibility: collapse` is implemented.
         get_inheritedbox.visibility