Eliminate ScrollRootId

Just use WebRender's ClipId directly. This will allow us to create and
use ReferenceFrames in the future, if we need to do that. It will also
make it easier to have Servo responsible for creating the root
scrolling area, which will allow removing some old hacks in the future.

1 files changed, 41 insertions, 98 deletions

diff --git a/components/gfx_traits/lib.rs b/components/gfx_traits/lib.rs
index 0dae3d6fff1..14f168671d7 100644
--- a/components/gfx_traits/lib.rs
+++ b/components/gfx_traits/lib.rs
@@ -19,18 +19,6 @@ pub mod print_tree;
 use range::RangeIndex;
 use std::sync::atomic::{ATOMIC_USIZE_INIT, AtomicUsize, Ordering};
 
-/// The next ID that will be used for a special stacking context.
-///
-/// A special stacking context is a stacking context that is one of (a) the outer stacking context
-/// of an element with `overflow: scroll`; (b) generated content; (c) both (a) and (b).
-static NEXT_SPECIAL_STACKING_CONTEXT_ID: AtomicUsize = ATOMIC_USIZE_INIT;
-
-/// If none of the bits outside this mask are set, the stacking context is a special stacking
-/// context.
-///
-/// Note that we assume that the top 16 bits of the address space are unused on the platform.
-const SPECIAL_STACKING_CONTEXT_ID_MASK: usize = 0xffff;
-
 /// A newtype struct for denoting the age of messages; prevents race conditions.
 #[derive(PartialEq, Eq, Debug, Copy, Clone, PartialOrd, Ord, Deserialize, Serialize)]
 pub struct Epoch(pub u32);
@@ -46,89 +34,29 @@ impl Epoch {
 pub struct StackingContextId(
     /// The identifier for this StackingContext, derived from the Flow's memory address
     /// and fragment type.  As a space optimization, these are combined into a single word.
-    usize
+    u64
 );
 
 impl StackingContextId {
-    #[inline]
-    pub fn new(id: usize) -> StackingContextId {
-        StackingContextId::new_of_type(id, FragmentType::FragmentBody)
-    }
-
-    /// Returns a new stacking context ID for a special stacking context.
-    fn next_special_id() -> usize {
-        // We shift this left by 2 to make room for the fragment type ID.
-        ((NEXT_SPECIAL_STACKING_CONTEXT_ID.fetch_add(1, Ordering::SeqCst) + 1) << 2) &
-            SPECIAL_STACKING_CONTEXT_ID_MASK
-    }
-
-    #[inline]
-    pub fn new_of_type(id: usize, fragment_type: FragmentType) -> StackingContextId {
-        debug_assert_eq!(id & (fragment_type as usize), 0);
-        if fragment_type == FragmentType::FragmentBody {
-            StackingContextId(id)
-        } else {
-            StackingContextId(StackingContextId::next_special_id() | (fragment_type as usize))
-        }
-    }
-
     /// Returns the stacking context ID for the outer document/layout root.
     #[inline]
     pub fn root() -> StackingContextId {
         StackingContextId(0)
     }
-}
-
-/// A unique ID for every scrolling root.
-#[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, HeapSizeOf, PartialEq, Serialize)]
-pub struct ScrollRootId(
-    /// The identifier for this StackingContext, derived from the Flow's memory address
-    /// and fragment type.  As a space optimization, these are combined into a single word.
-    pub usize
-);
-
-impl ScrollRootId {
-    /// Returns a new stacking context ID for a special stacking context.
-    fn next_special_id() -> usize {
-        // We shift this left by 2 to make room for the fragment type ID.
-        ((NEXT_SPECIAL_STACKING_CONTEXT_ID.fetch_add(1, Ordering::SeqCst) + 1) << 2) &
-            SPECIAL_STACKING_CONTEXT_ID_MASK
-    }
-
-    #[inline]
-    pub fn new_of_type(id: usize, fragment_type: FragmentType) -> ScrollRootId {
-        debug_assert_eq!(id & (fragment_type as usize), 0);
-        if fragment_type == FragmentType::FragmentBody {
-            ScrollRootId(id)
-        } else {
-            ScrollRootId(ScrollRootId::next_special_id() | (fragment_type as usize))
-        }
-    }
-
-    /// Returns the stacking context ID for the outer document/layout root.
-    #[inline]
-    pub fn root() -> ScrollRootId {
-        ScrollRootId(0)
-    }
 
-    /// Returns true if this is a special stacking context.
-    ///
-    /// A special stacking context is a stacking context that is one of (a) the outer stacking
-    /// context of an element with `overflow: scroll`; (b) generated content; (c) both (a) and (b).
+    /// Returns a new sacking context id with the given numeric id.
     #[inline]
-    pub fn is_special(&self) -> bool {
-        (self.0 & !SPECIAL_STACKING_CONTEXT_ID_MASK) == 0
-    }
-
-    #[inline]
-    pub fn id(&self) -> usize {
-        self.0 & !3
+    pub fn new(id: u64) -> StackingContextId {
+        StackingContextId(id)
     }
+}
 
-    #[inline]
-    pub fn fragment_type(&self) -> FragmentType {
-        FragmentType::from_usize(self.0 & 3)
-    }
+int_range_index! {
+    #[derive(Deserialize, Serialize)]
+    #[doc = "An index that refers to a byte offset in a text run. This could \
+             point to the middle of a glyph."]
+    #[derive(HeapSizeOf)]
+    struct ByteIndex(isize)
 }
 
 /// The type of fragment that a stacking context represents.
@@ -146,22 +74,37 @@ pub enum FragmentType {
     AfterPseudoContent,
 }
 
-impl FragmentType {
-    #[inline]
-    pub fn from_usize(n: usize) -> FragmentType {
-        debug_assert!(n < 3);
-        match n {
-            0 => FragmentType::FragmentBody,
-            1 => FragmentType::BeforePseudoContent,
-            _ => FragmentType::AfterPseudoContent,
-        }
+/// The next ID that will be used for a special stacking context.
+///
+/// A special stacking context is a stacking context that is one of (a) the outer stacking context
+/// of an element with `overflow: scroll`; (b) generated content; (c) both (a) and (b).
+static NEXT_SPECIAL_STACKING_CONTEXT_ID: AtomicUsize = ATOMIC_USIZE_INIT;
+
+/// If none of the bits outside this mask are set, the stacking context is a special stacking
+/// context.
+///
+/// Note that we assume that the top 16 bits of the address space are unused on the platform.
+const SPECIAL_STACKING_CONTEXT_ID_MASK: usize = 0xffff;
+
+/// Returns a new stacking context ID for a special stacking context.
+fn next_special_id() -> usize {
+    // We shift this left by 2 to make room for the fragment type ID.
+    ((NEXT_SPECIAL_STACKING_CONTEXT_ID.fetch_add(1, Ordering::SeqCst) + 1) << 2) &
+        SPECIAL_STACKING_CONTEXT_ID_MASK
+}
+
+pub fn combine_id_with_fragment_type(id: usize, fragment_type: FragmentType) ->  usize {
+    debug_assert_eq!(id & (fragment_type as usize), 0);
+    if fragment_type == FragmentType::FragmentBody {
+        id
+    } else {
+        next_special_id() | (fragment_type as usize)
     }
 }
 
-int_range_index! {
-    #[derive(Deserialize, Serialize)]
-    #[doc = "An index that refers to a byte offset in a text run. This could \
-             point to the middle of a glyph."]
-    #[derive(HeapSizeOf)]
-    struct ByteIndex(isize)
+pub fn node_id_from_clip_id(id: usize) -> Option<usize> {
+    if (id & !SPECIAL_STACKING_CONTEXT_ID_MASK) != 0 {
+        return Some((id & !3) as usize);
+    }
+    None
 }