stylo: Allow computing change hints during the traversal.

ports/geckolib/gecko_bindings/bindings.rs

@@ -294,10 +294,11 @@ extern "C" {
     pub fn Gecko_GetNodeFlags(node: *mut RawGeckoNode) -> u32;
     pub fn Gecko_SetNodeFlags(node: *mut RawGeckoNode, flags: u32);
     pub fn Gecko_UnsetNodeFlags(node: *mut RawGeckoNode, flags: u32);
-    pub fn Gecko_CalcAndStoreStyleDifference(element: *mut RawGeckoElement,
-                                             newstyle:
-                                                 *mut ServoComputedValues)
+    pub fn Gecko_CalcStyleDifference(oldstyle: *mut ServoComputedValues,
+                                     newstyle: *mut ServoComputedValues)
      -> nsChangeHint;
+    pub fn Gecko_StoreStyleDifference(node: *mut RawGeckoNode,
+                                      change: nsChangeHint);
     pub fn Gecko_EnsureTArrayCapacity(array: *mut ::std::os::raw::c_void,
                                       capacity: usize, elem_size: usize);
     pub fn Gecko_EnsureImageLayersLength(layers: *mut nsStyleImageLayers,

ports/geckolib/wrapper.rs

@@ -8,7 +8,9 @@ use gecko_bindings::bindings;
 use gecko_bindings::bindings::Gecko_ChildrenCount;
 use gecko_bindings::bindings::Gecko_ClassOrClassList;
 use gecko_bindings::bindings::Gecko_GetNodeData;
+use gecko_bindings::bindings::ServoComputedValues;
 use gecko_bindings::bindings::ServoNodeData;
+use gecko_bindings::bindings::{Gecko_CalcStyleDifference, Gecko_StoreStyleDifference};
 use gecko_bindings::bindings::{Gecko_ElementState, Gecko_GetDocumentElement};
 use gecko_bindings::bindings::{Gecko_GetFirstChild, Gecko_GetFirstChildElement};
 use gecko_bindings::bindings::{Gecko_GetLastChild, Gecko_GetLastChildElement};
@@ -21,8 +23,8 @@ use gecko_bindings::bindings::{Gecko_IsLink, Gecko_IsRootElement, Gecko_IsTextNo
 use gecko_bindings::bindings::{Gecko_IsUnvisitedLink, Gecko_IsVisitedLink};
 use gecko_bindings::bindings::{Gecko_LocalName, Gecko_Namespace, Gecko_NodeIsElement, Gecko_SetNodeData};
 use gecko_bindings::bindings::{RawGeckoDocument, RawGeckoElement, RawGeckoNode};
-use gecko_bindings::structs::nsIAtom;
 use gecko_bindings::structs::{NODE_HAS_DIRTY_DESCENDANTS_FOR_SERVO, NODE_IS_DIRTY_FOR_SERVO};
+use gecko_bindings::structs::{nsIAtom, nsChangeHint};
 use glue::GeckoDeclarationBlock;
 use libc::uintptr_t;
 use selectors::Element;
@@ -40,6 +42,7 @@ use style::dom::{OpaqueNode, PresentationalHintsSynthetizer};
 use style::dom::{TDocument, TElement, TNode, TRestyleDamage, UnsafeNode};
 use style::element_state::ElementState;
 use style::error_reporting::StdoutErrorReporter;
+use style::gecko_glue::ArcHelpers;
 use style::gecko_selector_impl::{GeckoSelectorImpl, NonTSPseudoClass};
 use style::parser::ParserContextExtraData;
 use style::properties::{ComputedValues, parse_style_attribute};
@@ -91,14 +94,36 @@ impl<'ln> GeckoNode<'ln> {
 }
 
 #[derive(Clone, Copy)]
-pub struct DummyRestyleDamage;
-impl TRestyleDamage for DummyRestyleDamage {
-    fn compute(_: Option<&Arc<ComputedValues>>, _: &ComputedValues) -> Self { DummyRestyleDamage }
-    fn rebuild_and_reflow() -> Self { DummyRestyleDamage }
+pub struct GeckoRestyleDamage(nsChangeHint);
+
+impl TRestyleDamage for GeckoRestyleDamage {
+    fn compute(previous_style: Option<&Arc<ComputedValues>>,
+               current_style: &Arc<ComputedValues>) -> Self {
+        type Helpers = ArcHelpers<ServoComputedValues, ComputedValues>;
+        let previous_style = match previous_style {
+            Some(previous) => previous,
+            None => return Self::rebuild_and_reflow(),
+        };
+
+        let previous = unsafe { Helpers::borrow(previous_style) };
+        let current = unsafe { Helpers::borrow(current_style) };
+        let hint = unsafe { Gecko_CalcStyleDifference(*previous, *current) };
+
+        GeckoRestyleDamage(hint)
+    }
+
+    fn rebuild_and_reflow() -> Self {
+        GeckoRestyleDamage(nsChangeHint::nsChangeHint_ReconstructFrame)
+    }
 }
-impl BitOr for DummyRestyleDamage {
+
+impl BitOr for GeckoRestyleDamage {
     type Output = Self;
-    fn bitor(self, _: Self) -> Self { DummyRestyleDamage }
+
+    fn bitor(self, other: Self) -> Self {
+        use std::mem;
+        GeckoRestyleDamage(unsafe { mem::transmute(self.0 as u32 | other.0 as u32) })
+    }
 }
 
 
@@ -106,7 +131,7 @@ impl BitOr for DummyRestyleDamage {
 impl<'ln> TNode for GeckoNode<'ln> {
     type ConcreteDocument = GeckoDocument<'ln>;
     type ConcreteElement = GeckoElement<'ln>;
-    type ConcreteRestyleDamage = DummyRestyleDamage;
+    type ConcreteRestyleDamage = GeckoRestyleDamage;
 
     fn to_unsafe(&self) -> UnsafeNode {
         (self.node as usize, 0)
@@ -243,9 +268,14 @@ impl<'ln> TNode for GeckoNode<'ln> {
         }
     }
 
-    fn restyle_damage(self) -> Self::ConcreteRestyleDamage { DummyRestyleDamage }
+    fn restyle_damage(self) -> Self::ConcreteRestyleDamage {
+        // Not called from style, only for layout.
+        unimplemented!();
+    }
 
-    fn set_restyle_damage(self, _: Self::ConcreteRestyleDamage) {}
+    fn set_restyle_damage(self, damage: Self::ConcreteRestyleDamage) {
+        unsafe { Gecko_StoreStyleDifference(self.node, damage.0) }
+    }
 
     fn parent_node(&self) -> Option<GeckoNode<'ln>> {
         unsafe {