Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2310 insertions, 0 deletions

diff --git a/gfx/wr/webrender/src/clip.rs b/gfx/wr/webrender/src/clip.rs
new file mode 100644
index 0000000000..f6bf55e967
--- /dev/null
+++ b/gfx/wr/webrender/src/clip.rs
@@ -0,0 +1,2310 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Internal representation of clips in WebRender.
+//!
+//! # Data structures
+//!
+//! There are a number of data structures involved in the clip module:
+//!
+//! - ClipStore - Main interface used by other modules.
+//!
+//! - ClipItem - A single clip item (e.g. a rounded rect, or a box shadow).
+//!              These are an exposed API type, stored inline in a ClipNode.
+//!
+//! - ClipNode - A ClipItem with an attached GPU handle. The GPU handle is populated
+//!              when a ClipNodeInstance is built from this node (which happens while
+//!              preparing primitives for render).
+//!
+//! ClipNodeInstance - A ClipNode with attached positioning information (a spatial
+//!                    node index). This is stored as a contiguous array of nodes
+//!                    within the ClipStore.
+//!
+//! ```ascii
+//! +-----------------------+-----------------------+-----------------------+
+//! | ClipNodeInstance      | ClipNodeInstance      | ClipNodeInstance      |
+//! +-----------------------+-----------------------+-----------------------+
+//! | ClipItem              | ClipItem              | ClipItem              |
+//! | Spatial Node Index    | Spatial Node Index    | Spatial Node Index    |
+//! | GPU cache handle      | GPU cache handle      | GPU cache handle      |
+//! | ...                   | ...                   | ...                   |
+//! +-----------------------+-----------------------+-----------------------+
+//!            0                        1                       2
+//!    +----------------+    |                                              |
+//!    | ClipNodeRange  |____|                                              |
+//!    |    index: 1    |                                                   |
+//!    |    count: 2    |___________________________________________________|
+//!    +----------------+
+//! ```
+//!
+//! - ClipNodeRange - A clip item range identifies a range of clip nodes instances.
+//!                   It is stored as an (index, count).
+//!
+//! - ClipChainNode - A clip chain node contains a handle to an interned clip item,
+//!                   positioning information (from where the clip was defined), and
+//!                   an optional parent link to another ClipChainNode. ClipChainId
+//!                   is an index into an array, or ClipChainId::NONE for no parent.
+//!
+//! ```ascii
+//! +----------------+    ____+----------------+    ____+----------------+   /---> ClipChainId::NONE
+//! | ClipChainNode  |   |    | ClipChainNode  |   |    | ClipChainNode  |   |
+//! +----------------+   |    +----------------+   |    +----------------+   |
+//! | ClipDataHandle |   |    | ClipDataHandle |   |    | ClipDataHandle |   |
+//! | Spatial index  |   |    | Spatial index  |   |    | Spatial index  |   |
+//! | Parent Id      |___|    | Parent Id      |___|    | Parent Id      |___|
+//! | ...            |        | ...            |        | ...            |
+//! +----------------+        +----------------+        +----------------+
+//! ```
+//!
+//! - ClipChainInstance - A ClipChain that has been built for a specific primitive + positioning node.
+//!
+//!    When given a clip chain ID, and a local primitive rect and its spatial node, the clip module
+//!    creates a clip chain instance. This is a struct with various pieces of useful information
+//!    (such as a local clip rect). It also contains a (index, count)
+//!    range specifier into an index buffer of the ClipNodeInstance structures that are actually relevant
+//!    for this clip chain instance. The index buffer structure allows a single array to be used for
+//!    all of the clip-chain instances built in a single frame. Each entry in the index buffer
+//!    also stores some flags relevant to the clip node in this positioning context.
+//!
+//! ```ascii
+//! +----------------------+
+//! | ClipChainInstance    |
+//! +----------------------+
+//! | ...                  |
+//! | local_clip_rect      |________________________________________________________________________
+//! | clips_range          |_______________                                                        |
+//! +----------------------+              |                                                        |
+//!                                       |                                                        |
+//! +------------------+------------------+------------------+------------------+------------------+
+//! | ClipNodeInstance | ClipNodeInstance | ClipNodeInstance | ClipNodeInstance | ClipNodeInstance |
+//! +------------------+------------------+------------------+------------------+------------------+
+//! | flags            | flags            | flags            | flags            | flags            |
+//! | ...              | ...              | ...              | ...              | ...              |
+//! +------------------+------------------+------------------+------------------+------------------+
+//! ```
+//!
+//! # Rendering clipped primitives
+//!
+//! See the [`segment` module documentation][segment.rs].
+//!
+//!
+//! [segment.rs]: ../segment/index.html
+//!
+
+use api::{BorderRadius, ClipMode, ComplexClipRegion, ImageMask, ClipId, ClipChainId};
+use api::{BoxShadowClipMode, FillRule, ImageKey, ImageRendering};
+use api::units::*;
+use crate::image_tiling::{self, Repetition};
+use crate::border::{ensure_no_corner_overlap, BorderRadiusAu};
+use crate::box_shadow::{BLUR_SAMPLE_SCALE, BoxShadowClipSource, BoxShadowCacheKey};
+use crate::spatial_tree::{SpatialTree, SpatialNodeIndex};
+use crate::ellipse::Ellipse;
+use crate::gpu_cache::GpuCache;
+use crate::gpu_types::{BoxShadowStretchMode};
+use crate::intern;
+use crate::internal_types::{FastHashMap, FastHashSet, LayoutPrimitiveInfo};
+use crate::prim_store::{VisibleMaskImageTile};
+use crate::prim_store::{PointKey, SizeKey, RectangleKey, PolygonKey};
+use crate::render_task_cache::to_cache_size;
+use crate::resource_cache::{ImageRequest, ResourceCache};
+use crate::scene_builder_thread::Interners;
+use crate::space::SpaceMapper;
+use crate::util::{clamp_to_scale_factor, MaxRect, extract_inner_rect_safe, project_rect, ScaleOffset};
+use euclid::approxeq::ApproxEq;
+use std::{iter, ops, u32, mem};
+
+/// A (non-leaf) node inside a clip-tree
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(MallocSizeOf)]
+pub struct ClipTreeNode {
+    pub handle: ClipDataHandle,
+    pub parent: ClipNodeId,
+
+    children: Vec<ClipNodeId>,
+
+    // TODO(gw): Consider adding a default leaf for cases when the local_clip_rect is not relevant,
+    //           that can be shared among primitives (to reduce amount of clip-chain building).
+}
+
+/// A leaf node in a clip-tree. Any primitive that is clipped will have a handle to
+/// a clip-tree leaf.
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(MallocSizeOf)]
+pub struct ClipTreeLeaf {
+    pub node_id: ClipNodeId,
+
+    // TODO(gw): For now, this preserves the ability to build a culling rect
+    //           from the supplied leaf local clip rect on the primitive. In
+    //           future, we'll expand this to be more efficient by combining
+    //           it will compatible clip rects from the `node_id`.
+    pub local_clip_rect: LayoutRect,
+}
+
+/// ID for a ClipTreeNode
+#[derive(Debug, Copy, Clone, PartialEq, MallocSizeOf, Eq, Hash)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipNodeId(u32);
+
+impl ClipNodeId {
+    pub const NONE: ClipNodeId = ClipNodeId(0);
+}
+
+/// ID for a ClipTreeLeaf
+#[derive(Debug, Copy, Clone, PartialEq, MallocSizeOf, Eq, Hash)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipLeafId(u32);
+
+/// A clip-tree built during scene building and used during frame-building to apply clips to primitives.
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipTree {
+    nodes: Vec<ClipTreeNode>,
+    leaves: Vec<ClipTreeLeaf>,
+    clip_root_stack: Vec<ClipNodeId>,
+}
+
+impl ClipTree {
+    pub fn new() -> Self {
+        ClipTree {
+            nodes: vec![
+                ClipTreeNode {
+                    handle: ClipDataHandle::INVALID,
+                    children: Vec::new(),
+                    parent: ClipNodeId::NONE,
+                }
+            ],
+            leaves: Vec::new(),
+            clip_root_stack: vec![
+                ClipNodeId::NONE,
+            ],
+        }
+    }
+
+    /// Add a set of clips to the provided tree node id, reusing existing
+    /// nodes in the tree where possible
+    fn add_impl(
+        id: ClipNodeId,
+        clips: &[ClipDataHandle],
+        nodes: &mut Vec<ClipTreeNode>,
+    ) -> ClipNodeId {
+        if clips.is_empty() {
+            return id;
+        }
+
+        let handle = clips[0];
+        let next_clips = &clips[1..];
+
+        let node_index = nodes[id.0 as usize]
+            .children
+            .iter()
+            .find(|n| nodes[n.0 as usize].handle == handle)
+            .cloned();
+
+        let node_index = match node_index {
+            Some(node_index) => node_index,
+            None => {
+                let node_index = ClipNodeId(nodes.len() as u32);
+                nodes[id.0 as usize].children.push(node_index);
+                let node = ClipTreeNode {
+                    handle,
+                    children: Vec::new(),
+                    parent: id,
+                };
+                nodes.push(node);
+                node_index
+            }
+        };
+
+        ClipTree::add_impl(
+            node_index,
+            next_clips,
+            nodes,
+        )
+    }
+
+    /// Add a set of clips to the provided tree node id, reusing existing
+    /// nodes in the tree where possible
+    pub fn add(
+        &mut self,
+        root: ClipNodeId,
+        clips: &[ClipDataHandle],
+    ) -> ClipNodeId {
+        ClipTree::add_impl(
+            root,
+            clips,
+            &mut self.nodes,
+        )
+    }
+
+    /// Get the current clip root (the node in the clip-tree where clips can be
+    /// ignored when building the clip-chain instance for a primitive)
+    pub fn current_clip_root(&self) -> ClipNodeId {
+        self.clip_root_stack.last().cloned().unwrap()
+    }
+
+    /// Push a clip root (e.g. when a surface is encountered) that prevents clips
+    /// from this node and above being applied to primitives within the root.
+    pub fn push_clip_root_leaf(&mut self, clip_leaf_id: ClipLeafId) {
+        let leaf = &self.leaves[clip_leaf_id.0 as usize];
+        self.clip_root_stack.push(leaf.node_id);
+    }
+
+    /// Push a clip root (e.g. when a surface is encountered) that prevents clips
+    /// from this node and above being applied to primitives within the root.
+    pub fn push_clip_root_node(&mut self, clip_node_id: ClipNodeId) {
+        self.clip_root_stack.push(clip_node_id);
+    }
+
+    /// Pop a clip root, when exiting a surface.
+    pub fn pop_clip_root(&mut self) {
+        self.clip_root_stack.pop().unwrap();
+    }
+
+    /// Retrieve a clip tree node by id
+    pub fn get_node(&self, id: ClipNodeId) -> &ClipTreeNode {
+        assert!(id != ClipNodeId::NONE);
+
+        &self.nodes[id.0 as usize]
+    }
+
+    /// Retrieve a clip tree leaf by id
+    pub fn get_leaf(&self, id: ClipLeafId) -> &ClipTreeLeaf {
+        &self.leaves[id.0 as usize]
+    }
+
+    /// Debug print the clip-tree
+    #[allow(unused)]
+    pub fn print(&self) {
+        use crate::print_tree::PrintTree;
+
+        fn print_node<T: crate::print_tree::PrintTreePrinter>(
+            id: ClipNodeId,
+            nodes: &[ClipTreeNode],
+            pt: &mut T,
+        ) {
+            let node = &nodes[id.0 as usize];
+
+            pt.new_level(format!("{:?}", id));
+            pt.add_item(format!("{:?}", node.handle));
+
+            for child_id in &node.children {
+                print_node(*child_id, nodes, pt);
+            }
+
+            pt.end_level();
+        }
+
+        fn print_leaf<T: crate::print_tree::PrintTreePrinter>(
+            id: ClipLeafId,
+            leaves: &[ClipTreeLeaf],
+            pt: &mut T,
+        ) {
+            let leaf = &leaves[id.0 as usize];
+
+            pt.new_level(format!("{:?}", id));
+            pt.add_item(format!("node_id: {:?}", leaf.node_id));
+            pt.add_item(format!("local_clip_rect: {:?}", leaf.local_clip_rect));
+            pt.end_level();
+        }
+
+        let mut pt = PrintTree::new("clip tree");
+        print_node(ClipNodeId::NONE, &self.nodes, &mut pt);
+
+        for i in 0 .. self.leaves.len() {
+            print_leaf(ClipLeafId(i as u32), &self.leaves, &mut pt);
+        }
+    }
+
+    /// Find the lowest common ancestor of two clip tree nodes. This is useful
+    /// to identify shared clips between primitives attached to different clip-leaves.
+    pub fn find_lowest_common_ancestor(
+        &self,
+        mut node1: ClipNodeId,
+        mut node2: ClipNodeId,
+    ) -> ClipNodeId {
+        // TODO(gw): Consider caching / storing the depth in the node?
+        fn get_node_depth(
+            id: ClipNodeId,
+            nodes: &[ClipTreeNode],
+        ) -> usize {
+            let mut depth = 0;
+            let mut current = id;
+
+            while current != ClipNodeId::NONE {
+                let node = &nodes[current.0 as usize];
+                depth += 1;
+                current = node.parent;
+            }
+
+            depth
+        }
+
+        let mut depth1 = get_node_depth(node1, &self.nodes);
+        let mut depth2 = get_node_depth(node2, &self.nodes);
+
+        while depth1 > depth2 {
+            node1 = self.nodes[node1.0 as usize].parent;
+            depth1 -= 1;
+        }
+
+        while depth2 > depth1 {
+            node2 = self.nodes[node2.0 as usize].parent;
+            depth2 -= 1;
+        }
+
+        while node1 != node2 {
+            node1 = self.nodes[node1.0 as usize].parent;
+            node2 = self.nodes[node2.0 as usize].parent;
+        }
+
+        node1
+    }
+}
+
+/// Represents a clip-chain as defined by the public API that we decompose in to
+/// the clip-tree. In future, we would like to remove this and have Gecko directly
+/// build the clip-tree.
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipChain {
+    parent: Option<usize>,
+    clips: Vec<ClipDataHandle>,
+}
+
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipStackEntry {
+    /// Cache the previous clip-chain build, since this is a common case
+    last_clip_chain_cache: Option<(ClipChainId, ClipNodeId)>,
+
+    /// Set of clips that were already seen and included in clip_node_id
+    seen_clips: FastHashSet<ClipDataHandle>,
+
+    /// The build clip_node_id for this level of the stack
+    clip_node_id: ClipNodeId,
+}
+
+/// Used by the scene builder to build the clip-tree that is part of the built scene.
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipTreeBuilder {
+    /// Clips defined by the display list
+    clip_map: FastHashMap<ClipId, ClipDataHandle>,
+
+    /// Clip-chains defined by the display list
+    clip_chains: Vec<ClipChain>,
+    clip_chain_map: FastHashMap<ClipChainId, usize>,
+
+    /// List of clips pushed/popped by grouping items, such as stacking contexts and iframes
+    clip_stack: Vec<ClipStackEntry>,
+
+    /// The tree we are building
+    tree: ClipTree,
+
+    /// A temporary buffer stored here to avoid constant heap allocs/frees
+    clip_handles_buffer: Vec<ClipDataHandle>,
+}
+
+impl ClipTreeBuilder {
+    pub fn new() -> Self {
+        ClipTreeBuilder {
+            clip_map: FastHashMap::default(),
+            clip_chain_map: FastHashMap::default(),
+            clip_chains: Vec::new(),
+            clip_stack: vec![
+                ClipStackEntry {
+                    clip_node_id: ClipNodeId::NONE,
+                    last_clip_chain_cache: None,
+                    seen_clips: FastHashSet::default(),
+                },
+            ],
+            tree: ClipTree::new(),
+            clip_handles_buffer: Vec::new(),
+        }
+    }
+
+    /// Define a new rect clip
+    pub fn define_rect_clip(
+        &mut self,
+        id: ClipId,
+        handle: ClipDataHandle,
+    ) {
+        self.clip_map.insert(id, handle);
+    }
+
+    /// Define a new rounded rect clip
+    pub fn define_rounded_rect_clip(
+        &mut self,
+        id: ClipId,
+        handle: ClipDataHandle,
+    ) {
+        self.clip_map.insert(id, handle);
+    }
+
+    /// Define a image mask clip
+    pub fn define_image_mask_clip(
+        &mut self,
+        id: ClipId,
+        handle: ClipDataHandle,
+    ) {
+        self.clip_map.insert(id, handle);
+    }
+
+    /// Define a clip-chain
+    pub fn define_clip_chain<I: Iterator<Item = ClipId>>(
+        &mut self,
+        id: ClipChainId,
+        parent: Option<ClipChainId>,
+        clips: I,
+    ) {
+        let parent = parent.map(|ref id| self.clip_chain_map[id]);
+        let index = self.clip_chains.len();
+        let clips = clips.map(|clip_id| {
+            self.clip_map[&clip_id]
+        }).collect();
+        self.clip_chains.push(ClipChain {
+            parent,
+            clips,
+        });
+        self.clip_chain_map.insert(id, index);
+    }
+
+    /// Push a clip-chain that will be applied to any prims built prior to next pop
+    pub fn push_clip_chain(
+        &mut self,
+        clip_chain_id: Option<ClipChainId>,
+        reset_seen: bool,
+    ) {
+        let (mut clip_node_id, mut seen_clips) = {
+            let prev = self.clip_stack.last().unwrap();
+            (prev.clip_node_id, prev.seen_clips.clone())
+        };
+
+        if let Some(clip_chain_id) = clip_chain_id {
+            if clip_chain_id != ClipChainId::INVALID {
+                self.clip_handles_buffer.clear();
+
+                let clip_chain_index = self.clip_chain_map[&clip_chain_id];
+                ClipTreeBuilder::add_clips(
+                    clip_chain_index,
+                    &mut seen_clips,
+                    &mut self.clip_handles_buffer,
+                    &self.clip_chains,
+                );
+
+                clip_node_id = self.tree.add(
+                    clip_node_id,
+                    &self.clip_handles_buffer,
+                );
+            }
+        }
+
+        if reset_seen {
+            seen_clips.clear();
+        }
+
+        self.clip_stack.push(ClipStackEntry {
+            last_clip_chain_cache: None,
+            clip_node_id,
+            seen_clips,
+        });
+    }
+
+    /// Push a clip-id that will be applied to any prims built prior to next pop
+    pub fn push_clip_id(
+        &mut self,
+        clip_id: ClipId,
+    ) {
+        let (clip_node_id, mut seen_clips) = {
+            let prev = self.clip_stack.last().unwrap();
+            (prev.clip_node_id, prev.seen_clips.clone())
+        };
+
+        self.clip_handles_buffer.clear();
+        let clip_index = self.clip_map[&clip_id];
+
+        if seen_clips.insert(clip_index) {
+            self.clip_handles_buffer.push(clip_index);
+        }
+
+        let clip_node_id = self.tree.add(
+            clip_node_id,
+            &self.clip_handles_buffer,
+        );
+
+        self.clip_stack.push(ClipStackEntry {
+            last_clip_chain_cache: None,
+            seen_clips,
+            clip_node_id,
+        });
+    }
+
+    /// Pop a clip off the clip_stack, when exiting a grouping item
+    pub fn pop_clip(&mut self) {
+        self.clip_stack.pop().unwrap();
+    }
+
+    /// Add clips from a given clip-chain to the set of clips for a primitive during clip-set building
+    fn add_clips(
+        clip_chain_index: usize,
+        seen_clips: &mut FastHashSet<ClipDataHandle>,
+        output: &mut Vec<ClipDataHandle>,
+        clip_chains: &[ClipChain],
+    ) {
+        // TODO(gw): It's possible that we may see clip outputs that include identical clips
+        //           (e.g. if there is a clip positioned by two spatial nodes, where one spatial
+        //           node is a child of the other, and has an identity transform). If we ever
+        //           see this in real-world cases, it might be worth checking for that here and
+        //           excluding them, to ensure the shape of the tree matches what we need for
+        //           finding shared_clips for tile caches etc.
+
+        let clip_chain = &clip_chains[clip_chain_index];
+
+        if let Some(parent) = clip_chain.parent {
+            ClipTreeBuilder::add_clips(
+                parent,
+                seen_clips,
+                output,
+                clip_chains,
+            );
+        }
+
+        for clip_index in clip_chain.clips.iter().rev() {
+            if seen_clips.insert(*clip_index) {
+                output.push(*clip_index);
+            }
+        }
+    }
+
+    /// Main entry point to build a path in the clip-tree for a given primitive
+    pub fn build_clip_set(
+        &mut self,
+        clip_chain_id: ClipChainId,
+    ) -> ClipNodeId {
+        let clip_stack = self.clip_stack.last_mut().unwrap();
+
+        if clip_chain_id == ClipChainId::INVALID {
+            clip_stack.clip_node_id
+        } else {
+            if let Some((cached_clip_chain, cached_clip_node)) = clip_stack.last_clip_chain_cache {
+                if cached_clip_chain == clip_chain_id {
+                    return cached_clip_node;
+                }
+            }
+
+            let clip_chain_index = self.clip_chain_map[&clip_chain_id];
+
+            self.clip_handles_buffer.clear();
+
+            ClipTreeBuilder::add_clips(
+                clip_chain_index,
+                &mut clip_stack.seen_clips,
+                &mut self.clip_handles_buffer,
+                &self.clip_chains,
+            );
+
+            // We mutated the `clip_stack.seen_clips` in order to remove duplicate clips from
+            // the supplied `clip_chain_id`. Now step through and remove any clips we added
+            // to the set, so we don't get incorrect results next time `build_clip_set` is
+            // called for a different clip-chain. Doing it this way rather than cloning means
+            // we avoid heap allocations for each `build_clip_set` call.
+            for handle in &self.clip_handles_buffer {
+                clip_stack.seen_clips.remove(handle);
+            }
+
+            let clip_node_id = self.tree.add(
+                clip_stack.clip_node_id,
+                &self.clip_handles_buffer,
+            );
+
+            clip_stack.last_clip_chain_cache = Some((clip_chain_id, clip_node_id));
+
+            clip_node_id
+        }
+    }
+
+    /// Recursive impl to check if a clip-chain has complex (non-rectangular) clips
+    fn has_complex_clips_impl(
+        &self,
+        clip_chain_index: usize,
+        interners: &Interners,
+    ) -> bool {
+        let clip_chain = &self.clip_chains[clip_chain_index];
+
+        for clip_handle in &clip_chain.clips {
+            let clip_info = &interners.clip[*clip_handle];
+
+            if let ClipNodeKind::Complex = clip_info.key.kind.node_kind() {
+                return true;
+            }
+        }
+
+        match clip_chain.parent {
+            Some(parent) => self.has_complex_clips_impl(parent, interners),
+            None => false,
+        }
+    }
+
+    /// Check if a clip-chain has complex (non-rectangular) clips
+    pub fn clip_chain_has_complex_clips(
+        &self,
+        clip_chain_id: ClipChainId,
+        interners: &Interners,
+    ) -> bool {
+        let clip_chain_index = self.clip_chain_map[&clip_chain_id];
+        self.has_complex_clips_impl(clip_chain_index, interners)
+    }
+
+    /// Check if a clip-node has complex (non-rectangular) clips
+    pub fn clip_node_has_complex_clips(
+        &self,
+        clip_node_id: ClipNodeId,
+        interners: &Interners,
+    ) -> bool {
+        let mut current = clip_node_id;
+
+        while current != ClipNodeId::NONE {
+            let node = &self.tree.nodes[current.0 as usize];
+            let clip_info = &interners.clip[node.handle];
+
+            if let ClipNodeKind::Complex = clip_info.key.kind.node_kind() {
+                return true;
+            }
+
+            current = node.parent;
+        }
+
+        false
+    }
+
+    /// Finalize building and return the clip-tree
+    pub fn finalize(self) -> ClipTree {
+        self.tree
+    }
+
+    /// Get a clip node by id
+    pub fn get_node(&self, id: ClipNodeId) -> &ClipTreeNode {
+        assert!(id != ClipNodeId::NONE);
+
+        &self.tree.nodes[id.0 as usize]
+    }
+
+    /// Get a clip leaf by id
+    pub fn get_leaf(&self, id: ClipLeafId) -> &ClipTreeLeaf {
+        &self.tree.leaves[id.0 as usize]
+    }
+
+    /// Build a clip-leaf for a tile-cache
+    pub fn build_for_tile_cache(
+        &mut self,
+        clip_node_id: ClipNodeId,
+        extra_clips: &[ClipId],
+    ) -> ClipLeafId {
+        self.clip_handles_buffer.clear();
+
+        for clip_id in extra_clips {
+            let handle = self.clip_map[clip_id];
+            self.clip_handles_buffer.push(handle);
+        }
+
+        let node_id = self.tree.add(
+            clip_node_id,
+            &self.clip_handles_buffer,
+        );
+
+        let clip_leaf_id = ClipLeafId(self.tree.leaves.len() as u32);
+
+        self.tree.leaves.push(ClipTreeLeaf {
+            node_id,
+            local_clip_rect: LayoutRect::max_rect(),
+        });
+
+        clip_leaf_id
+    }
+
+    /// Build a clip-leaf for a picture
+    pub fn build_for_picture(
+        &mut self,
+        clip_node_id: ClipNodeId,
+    ) -> ClipLeafId {
+        let node_id = self.tree.add(
+            clip_node_id,
+            &[],
+        );
+
+        let clip_leaf_id = ClipLeafId(self.tree.leaves.len() as u32);
+
+        self.tree.leaves.push(ClipTreeLeaf {
+            node_id,
+            local_clip_rect: LayoutRect::max_rect(),
+        });
+
+        clip_leaf_id
+    }
+
+    /// Build a clip-leaf for a normal primitive
+    pub fn build_for_prim(
+        &mut self,
+        clip_node_id: ClipNodeId,
+        info: &LayoutPrimitiveInfo,
+        extra_clips: &[ClipItemKey],
+        interners: &mut Interners,
+    ) -> ClipLeafId {
+
+        let node_id = if extra_clips.is_empty() {
+            clip_node_id
+        } else {
+            // TODO(gw): Cache the previous build of clip-node / clip-leaf to handle cases where we get a
+            //           lot of primitives referencing the same clip set (e.g. dl_mutate and similar tests)
+            self.clip_handles_buffer.clear();
+
+            for item in extra_clips {
+                // Intern this clip item, and store the handle
+                // in the clip chain node.
+                let handle = interners.clip.intern(item, || {
+                    ClipInternData {
+                        key: item.clone(),
+                    }
+                });
+
+                self.clip_handles_buffer.push(handle);
+            }
+
+            self.tree.add(
+                clip_node_id,
+                &self.clip_handles_buffer,
+            )
+        };
+
+        let clip_leaf_id = ClipLeafId(self.tree.leaves.len() as u32);
+
+        self.tree.leaves.push(ClipTreeLeaf {
+            node_id,
+            local_clip_rect: info.clip_rect,
+        });
+
+        clip_leaf_id
+    }
+
+    // Find the LCA for two given clip nodes
+    pub fn find_lowest_common_ancestor(
+        &self,
+        node1: ClipNodeId,
+        node2: ClipNodeId,
+    ) -> ClipNodeId {
+        self.tree.find_lowest_common_ancestor(node1, node2)
+    }
+}
+
+// Type definitions for interning clip nodes.
+
+#[derive(Copy, Clone, Debug, MallocSizeOf, PartialEq, Eq, Hash)]
+#[cfg_attr(any(feature = "serde"), derive(Deserialize, Serialize))]
+pub enum ClipIntern {}
+
+pub type ClipDataStore = intern::DataStore<ClipIntern>;
+pub type ClipDataHandle = intern::Handle<ClipIntern>;
+
+/// Helper to identify simple clips (normal rects) from other kinds of clips,
+/// which can often be handled via fast code paths.
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(Debug, Copy, Clone, MallocSizeOf)]
+pub enum ClipNodeKind {
+    /// A normal clip rectangle, with Clip mode.
+    Rectangle,
+    /// A rectangle with ClipOut, or any other kind of clip.
+    Complex,
+}
+
+// Result of comparing a clip node instance against a local rect.
+#[derive(Debug)]
+enum ClipResult {
+    // The clip does not affect the region at all.
+    Accept,
+    // The clip prevents the region from being drawn.
+    Reject,
+    // The clip affects part of the region. This may
+    // require a clip mask, depending on other factors.
+    Partial,
+}
+
+// A clip node is a single clip source, along with some
+// positioning information and implementation details
+// that control where the GPU data for this clip source
+// can be found.
+#[derive(Debug)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+#[derive(MallocSizeOf)]
+pub struct ClipNode {
+    pub item: ClipItem,
+}
+
+// Convert from an interning key for a clip item
+// to a clip node, which is cached in the document.
+impl From<ClipItemKey> for ClipNode {
+    fn from(item: ClipItemKey) -> Self {
+        let kind = match item.kind {
+            ClipItemKeyKind::Rectangle(rect, mode) => {
+                ClipItemKind::Rectangle { rect: rect.into(), mode }
+            }
+            ClipItemKeyKind::RoundedRectangle(rect, radius, mode) => {
+                ClipItemKind::RoundedRectangle {
+                    rect: rect.into(),
+                    radius: radius.into(),
+                    mode,
+                }
+            }
+            ClipItemKeyKind::ImageMask(rect, image, polygon_handle) => {
+                ClipItemKind::Image {
+                    image,
+                    rect: rect.into(),
+                    polygon_handle,
+                }
+            }
+            ClipItemKeyKind::BoxShadow(shadow_rect_fract_offset, shadow_rect_size, shadow_radius, prim_shadow_rect, blur_radius, clip_mode) => {
+                ClipItemKind::new_box_shadow(
+                    shadow_rect_fract_offset.into(),
+                    shadow_rect_size.into(),
+                    shadow_radius.into(),
+                    prim_shadow_rect.into(),
+                    blur_radius.to_f32_px(),
+                    clip_mode,
+                )
+            }
+        };
+
+        ClipNode {
+            item: ClipItem {
+                kind,
+                spatial_node_index: item.spatial_node_index,
+            },
+        }
+    }
+}
+
+// Flags that are attached to instances of clip nodes.
+bitflags! {
+    #[cfg_attr(feature = "capture", derive(Serialize))]
+    #[cfg_attr(feature = "replay", derive(Deserialize))]
+    #[derive(MallocSizeOf)]
+    pub struct ClipNodeFlags: u8 {
+        const SAME_SPATIAL_NODE = 0x1;
+        const SAME_COORD_SYSTEM = 0x2;
+        const USE_FAST_PATH = 0x4;
+    }
+}
+
+// When a clip node is found to be valid for a
+// clip chain instance, it's stored in an index
+// buffer style structure. This struct contains
+// an index to the node data itself, as well as
+// some flags describing how this clip node instance
+// is positioned.
+#[derive(Debug, MallocSizeOf)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipNodeInstance {
+    pub handle: ClipDataHandle,
+    pub flags: ClipNodeFlags,
+    pub visible_tiles: Option<ops::Range<usize>>,
+}
+
+impl ClipNodeInstance {
+    pub fn has_visible_tiles(&self) -> bool {
+        self.visible_tiles.is_some()
+    }
+}
+
+// A range of clip node instances that were found by
+// building a clip chain instance.
+#[derive(Debug, Copy, Clone)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipNodeRange {
+    pub first: u32,
+    pub count: u32,
+}
+
+impl ClipNodeRange {
+    pub fn to_range(&self) -> ops::Range<usize> {
+        let start = self.first as usize;
+        let end = start + self.count as usize;
+
+        ops::Range {
+            start,
+            end,
+        }
+    }
+}
+
+/// A helper struct for converting between coordinate systems
+/// of clip sources and primitives.
+// todo(gw): optimize:
+//  separate arrays for matrices
+//  cache and only build as needed.
+//TODO: merge with `CoordinateSpaceMapping`?
+#[derive(Debug, MallocSizeOf)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+enum ClipSpaceConversion {
+    Local,
+    ScaleOffset(ScaleOffset),
+    Transform(LayoutToWorldTransform),
+}
+
+impl ClipSpaceConversion {
+    /// Construct a new clip space converter between two spatial nodes.
+    fn new(
+        prim_spatial_node_index: SpatialNodeIndex,
+        clip_spatial_node_index: SpatialNodeIndex,
+        spatial_tree: &SpatialTree,
+    ) -> Self {
+        //Note: this code is different from `get_relative_transform` in a way that we only try
+        // getting the relative transform if it's Local or ScaleOffset,
+        // falling back to the world transform otherwise.
+        let clip_spatial_node = spatial_tree.get_spatial_node(clip_spatial_node_index);
+        let prim_spatial_node = spatial_tree.get_spatial_node(prim_spatial_node_index);
+
+        if prim_spatial_node_index == clip_spatial_node_index {
+            ClipSpaceConversion::Local
+        } else if prim_spatial_node.coordinate_system_id == clip_spatial_node.coordinate_system_id {
+            let scale_offset = prim_spatial_node.content_transform
+                .inverse()
+                .accumulate(&clip_spatial_node.content_transform);
+            ClipSpaceConversion::ScaleOffset(scale_offset)
+        } else {
+            ClipSpaceConversion::Transform(
+                spatial_tree
+                    .get_world_transform(clip_spatial_node_index)
+                    .into_transform()
+            )
+        }
+    }
+
+    fn to_flags(&self) -> ClipNodeFlags {
+        match *self {
+            ClipSpaceConversion::Local => {
+                ClipNodeFlags::SAME_SPATIAL_NODE | ClipNodeFlags::SAME_COORD_SYSTEM
+            }
+            ClipSpaceConversion::ScaleOffset(..) => {
+                ClipNodeFlags::SAME_COORD_SYSTEM
+            }
+            ClipSpaceConversion::Transform(..) => {
+                ClipNodeFlags::empty()
+            }
+        }
+    }
+}
+
+// Temporary information that is cached and reused
+// during building of a clip chain instance.
+#[derive(MallocSizeOf)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+struct ClipNodeInfo {
+    conversion: ClipSpaceConversion,
+    handle: ClipDataHandle,
+}
+
+impl ClipNodeInfo {
+    fn create_instance(
+        &self,
+        node: &ClipNode,
+        clipped_rect: &LayoutRect,
+        gpu_cache: &mut GpuCache,
+        resource_cache: &mut ResourceCache,
+        mask_tiles: &mut Vec<VisibleMaskImageTile>,
+        spatial_tree: &SpatialTree,
+        request_resources: bool,
+    ) -> Option<ClipNodeInstance> {
+        // Calculate some flags that are required for the segment
+        // building logic.
+        let mut flags = self.conversion.to_flags();
+
+        // Some clip shaders support a fast path mode for simple clips.
+        // TODO(gw): We could also apply fast path when segments are created, since we only write
+        //           the mask for a single corner at a time then, so can always consider radii uniform.
+        let is_raster_2d =
+            flags.contains(ClipNodeFlags::SAME_COORD_SYSTEM) ||
+            spatial_tree
+                .get_world_viewport_transform(node.item.spatial_node_index)
+                .is_2d_axis_aligned();
+        if is_raster_2d && node.item.kind.supports_fast_path_rendering() {
+            flags |= ClipNodeFlags::USE_FAST_PATH;
+        }
+
+        let mut visible_tiles = None;
+
+        if let ClipItemKind::Image { rect, image, .. } = node.item.kind {
+            let request = ImageRequest {
+                key: image,
+                rendering: ImageRendering::Auto,
+                tile: None,
+            };
+
+            if let Some(props) = resource_cache.get_image_properties(image) {
+                if let Some(tile_size) = props.tiling {
+                    let tile_range_start = mask_tiles.len();
+
+                    // Bug 1648323 - It is unclear why on rare occasions we get
+                    // a clipped_rect that does not intersect the clip's mask rect.
+                    // defaulting to clipped_rect here results in zero repetitions
+                    // which clips the primitive entirely.
+                    let visible_rect =
+                        clipped_rect.intersection(&rect).unwrap_or(*clipped_rect);
+
+                    let repetitions = image_tiling::repetitions(
+                        &rect,
+                        &visible_rect,
+                        rect.size(),
+                    );
+
+                    for Repetition { origin, .. } in repetitions {
+                        let layout_image_rect = LayoutRect::from_origin_and_size(
+                            origin,
+                            rect.size(),
+                        );
+                        let tiles = image_tiling::tiles(
+                            &layout_image_rect,
+                            &visible_rect,
+                            &props.visible_rect,
+                            tile_size as i32,
+                        );
+                        for tile in tiles {
+                            if request_resources {
+                                resource_cache.request_image(
+                                    request.with_tile(tile.offset),
+                                    gpu_cache,
+                                );
+                            }
+                            mask_tiles.push(VisibleMaskImageTile {
+                                tile_offset: tile.offset,
+                                tile_rect: tile.rect,
+                            });
+                        }
+                    }
+                    visible_tiles = Some(tile_range_start..mask_tiles.len());
+                } else if request_resources {
+                    resource_cache.request_image(request, gpu_cache);
+                }
+            } else {
+                // If the supplied image key doesn't exist in the resource cache,
+                // skip the clip node since there is nothing to mask with.
+                warn!("Clip mask with missing image key {:?}", request.key);
+                return None;
+            }
+        }
+
+        Some(ClipNodeInstance {
+            handle: self.handle,
+            flags,
+            visible_tiles,
+        })
+    }
+}
+
+impl ClipNode {
+    pub fn update(
+        &mut self,
+        device_pixel_scale: DevicePixelScale,
+    ) {
+        match self.item.kind {
+            ClipItemKind::Image { .. } |
+            ClipItemKind::Rectangle { .. } |
+            ClipItemKind::RoundedRectangle { .. } => {}
+
+            ClipItemKind::BoxShadow { ref mut source } => {
+                // Quote from https://drafts.csswg.org/css-backgrounds-3/#shadow-blur
+                // "the image that would be generated by applying to the shadow a
+                // Gaussian blur with a standard deviation equal to half the blur radius."
+                let blur_radius_dp = source.blur_radius * 0.5;
+
+                // Create scaling from requested size to cache size.
+                let mut content_scale = LayoutToWorldScale::new(1.0) * device_pixel_scale;
+                content_scale.0 = clamp_to_scale_factor(content_scale.0, false);
+
+                // Create the cache key for this box-shadow render task.
+                let cache_size = to_cache_size(source.shadow_rect_alloc_size, &mut content_scale);
+
+                let bs_cache_key = BoxShadowCacheKey {
+                    blur_radius_dp: (blur_radius_dp * content_scale.0).round() as i32,
+                    clip_mode: source.clip_mode,
+                    original_alloc_size: (source.original_alloc_size * content_scale).round().to_i32(),
+                    br_top_left: (source.shadow_radius.top_left * content_scale).round().to_i32(),
+                    br_top_right: (source.shadow_radius.top_right * content_scale).round().to_i32(),
+                    br_bottom_right: (source.shadow_radius.bottom_right * content_scale).round().to_i32(),
+                    br_bottom_left: (source.shadow_radius.bottom_left * content_scale).round().to_i32(),
+                    device_pixel_scale: Au::from_f32_px(content_scale.0),
+                };
+
+                source.cache_key = Some((cache_size, bs_cache_key));
+            }
+        }
+    }
+}
+
+#[derive(Default)]
+pub struct ClipStoreScratchBuffer {
+    clip_node_instances: Vec<ClipNodeInstance>,
+    mask_tiles: Vec<VisibleMaskImageTile>,
+}
+
+/// The main clipping public interface that other modules access.
+#[derive(MallocSizeOf)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+pub struct ClipStore {
+    pub clip_node_instances: Vec<ClipNodeInstance>,
+    mask_tiles: Vec<VisibleMaskImageTile>,
+
+    active_clip_node_info: Vec<ClipNodeInfo>,
+    active_local_clip_rect: Option<LayoutRect>,
+    active_pic_coverage_rect: PictureRect,
+}
+
+// A clip chain instance is what gets built for a given clip
+// chain id + local primitive region + positioning node.
+#[derive(Debug)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+pub struct ClipChainInstance {
+    pub clips_range: ClipNodeRange,
+    // Combined clip rect for clips that are in the
+    // same coordinate system as the primitive.
+    pub local_clip_rect: LayoutRect,
+    pub has_non_local_clips: bool,
+    // If true, this clip chain requires allocation
+    // of a clip mask.
+    pub needs_mask: bool,
+    // Combined clip rect in picture space (may
+    // be more conservative that local_clip_rect).
+    pub pic_coverage_rect: PictureRect,
+    // Space, in which the `pic_coverage_rect` is defined.
+    pub pic_spatial_node_index: SpatialNodeIndex,
+}
+
+impl ClipChainInstance {
+    pub fn empty() -> Self {
+        ClipChainInstance {
+            clips_range: ClipNodeRange {
+                first: 0,
+                count: 0,
+            },
+            local_clip_rect: LayoutRect::zero(),
+            has_non_local_clips: false,
+            needs_mask: false,
+            pic_coverage_rect: PictureRect::zero(),
+            pic_spatial_node_index: SpatialNodeIndex::INVALID,
+        }
+    }
+}
+
+impl ClipStore {
+    pub fn new() -> Self {
+        ClipStore {
+            clip_node_instances: Vec::new(),
+            mask_tiles: Vec::new(),
+            active_clip_node_info: Vec::new(),
+            active_local_clip_rect: None,
+            active_pic_coverage_rect: PictureRect::max_rect(),
+        }
+    }
+
+    pub fn get_instance_from_range(
+        &self,
+        node_range: &ClipNodeRange,
+        index: u32,
+    ) -> &ClipNodeInstance {
+        &self.clip_node_instances[(node_range.first + index) as usize]
+    }
+
+    /// Setup the active clip chains for building a clip chain instance.
+    pub fn set_active_clips(
+        &mut self,
+        prim_spatial_node_index: SpatialNodeIndex,
+        pic_spatial_node_index: SpatialNodeIndex,
+        clip_leaf_id: ClipLeafId,
+        spatial_tree: &SpatialTree,
+        clip_data_store: &ClipDataStore,
+        clip_tree: &ClipTree,
+    ) {
+        self.active_clip_node_info.clear();
+        self.active_local_clip_rect = None;
+        self.active_pic_coverage_rect = PictureRect::max_rect();
+
+        let clip_root = clip_tree.current_clip_root();
+        let clip_leaf = clip_tree.get_leaf(clip_leaf_id);
+
+        let mut local_clip_rect = clip_leaf.local_clip_rect;
+        let mut current = clip_leaf.node_id;
+
+        while current != clip_root {
+            let node = clip_tree.get_node(current);
+
+            if !add_clip_node_to_current_chain(
+                node.handle,
+                prim_spatial_node_index,
+                pic_spatial_node_index,
+                &mut local_clip_rect,
+                &mut self.active_clip_node_info,
+                &mut self.active_pic_coverage_rect,
+                clip_data_store,
+                spatial_tree,
+            ) {
+                return;
+            }
+
+            current = node.parent;
+        }
+
+        self.active_local_clip_rect = Some(local_clip_rect);
+    }
+
+    /// Setup the active clip chains, based on an existing primitive clip chain instance.
+    pub fn set_active_clips_from_clip_chain(
+        &mut self,
+        prim_clip_chain: &ClipChainInstance,
+        prim_spatial_node_index: SpatialNodeIndex,
+        spatial_tree: &SpatialTree,
+        clip_data_store: &ClipDataStore,
+    ) {
+        // TODO(gw): Although this does less work than set_active_clips(), it does
+        //           still do some unnecessary work (such as the clip space conversion).
+        //           We could consider optimizing this if it ever shows up in a profile.
+
+        self.active_clip_node_info.clear();
+        self.active_local_clip_rect = Some(prim_clip_chain.local_clip_rect);
+        self.active_pic_coverage_rect = prim_clip_chain.pic_coverage_rect;
+
+        let clip_instances = &self
+            .clip_node_instances[prim_clip_chain.clips_range.to_range()];
+        for clip_instance in clip_instances {
+            let clip = &clip_data_store[clip_instance.handle];
+            let conversion = ClipSpaceConversion::new(
+                prim_spatial_node_index,
+                clip.item.spatial_node_index,
+                spatial_tree,
+            );
+            self.active_clip_node_info.push(ClipNodeInfo {
+                handle: clip_instance.handle,
+                conversion,
+            });
+        }
+    }
+
+    /// Given a clip-chain instance, return a safe rect within the visible region
+    /// that can be assumed to be unaffected by clip radii. Returns None if it
+    /// encounters any complex cases, just handling rounded rects in the same
+    /// coordinate system as the clip-chain for now.
+    pub fn get_inner_rect_for_clip_chain(
+        &self,
+        clip_chain: &ClipChainInstance,
+        clip_data_store: &ClipDataStore,
+        spatial_tree: &SpatialTree,
+    ) -> Option<PictureRect> {
+        let mut inner_rect = clip_chain.pic_coverage_rect;
+        let clip_instances = &self
+            .clip_node_instances[clip_chain.clips_range.to_range()];
+
+        for clip_instance in clip_instances {
+            // Don't handle mapping between coord systems for now
+            if !clip_instance.flags.contains(ClipNodeFlags::SAME_COORD_SYSTEM) {
+                return None;
+            }
+
+            let clip_node = &clip_data_store[clip_instance.handle];
+
+            match clip_node.item.kind {
+                // Ignore any clips which are complex or impossible to calculate
+                // inner rects for now
+                ClipItemKind::Rectangle { mode: ClipMode::ClipOut, .. } |
+                ClipItemKind::Image { .. } |
+                ClipItemKind::BoxShadow { .. } |
+                ClipItemKind::RoundedRectangle { mode: ClipMode::ClipOut, .. } => {
+                    return None;
+                }
+                // Normal Clip rects are already handled by the clip-chain pic_coverage_rect,
+                // no need to do anything here
+                ClipItemKind::Rectangle { mode: ClipMode::Clip, .. } => {}
+                ClipItemKind::RoundedRectangle { mode: ClipMode::Clip, rect, radius } => {
+                    // Get an inner rect for the rounded-rect clip
+                    let local_inner_rect = match extract_inner_rect_safe(&rect, &radius) {
+                        Some(rect) => rect,
+                        None => return None,
+                    };
+
+                    // Map it from local -> picture space
+                    let mapper = SpaceMapper::new_with_target(
+                        clip_chain.pic_spatial_node_index,
+                        clip_node.item.spatial_node_index,
+                        PictureRect::max_rect(),
+                        spatial_tree,
+                    );
+
+                    // Accumulate in to the inner_rect, in case there are multiple rounded-rect clips
+                    if let Some(pic_inner_rect) = mapper.map(&local_inner_rect) {
+                        inner_rect = inner_rect.intersection(&pic_inner_rect).unwrap_or(PictureRect::zero());
+                    }
+                }
+            }
+        }
+
+        Some(inner_rect)
+    }
+
+    /// The main interface external code uses. Given a local primitive, positioning
+    /// information, and a clip chain id, build an optimized clip chain instance.
+    pub fn build_clip_chain_instance(
+        &mut self,
+        local_prim_rect: LayoutRect,
+        prim_to_pic_mapper: &SpaceMapper<LayoutPixel, PicturePixel>,
+        pic_to_world_mapper: &SpaceMapper<PicturePixel, WorldPixel>,
+        spatial_tree: &SpatialTree,
+        gpu_cache: &mut GpuCache,
+        resource_cache: &mut ResourceCache,
+        device_pixel_scale: DevicePixelScale,
+        world_rect: &WorldRect,
+        clip_data_store: &mut ClipDataStore,
+        request_resources: bool,
+    ) -> Option<ClipChainInstance> {
+        let local_clip_rect = match self.active_local_clip_rect {
+            Some(rect) => rect,
+            None => return None,
+        };
+        profile_scope!("build_clip_chain_instance");
+
+        let local_bounding_rect = local_prim_rect.intersection(&local_clip_rect)?;
+        let mut pic_coverage_rect = prim_to_pic_mapper.map(&local_bounding_rect)?;
+        let world_clip_rect = pic_to_world_mapper.map(&pic_coverage_rect)?;
+
+        // Now, we've collected all the clip nodes that *potentially* affect this
+        // primitive region, and reduced the size of the prim region as much as possible.
+
+        // Run through the clip nodes, and see which ones affect this prim region.
+
+        let first_clip_node_index = self.clip_node_instances.len() as u32;
+        let mut has_non_local_clips = false;
+        let mut needs_mask = false;
+
+        // For each potential clip node
+        for node_info in self.active_clip_node_info.drain(..) {
+            let node = &mut clip_data_store[node_info.handle];
+
+            // See how this clip affects the prim region.
+            let clip_result = match node_info.conversion {
+                ClipSpaceConversion::Local => {
+                    node.item.kind.get_clip_result(&local_bounding_rect)
+                }
+                ClipSpaceConversion::ScaleOffset(ref scale_offset) => {
+                    has_non_local_clips = true;
+                    node.item.kind.get_clip_result(&scale_offset.unmap_rect(&local_bounding_rect))
+                }
+                ClipSpaceConversion::Transform(ref transform) => {
+                    has_non_local_clips = true;
+                    node.item.kind.get_clip_result_complex(
+                        transform,
+                        &world_clip_rect,
+                        world_rect,
+                    )
+                }
+            };
+
+            match clip_result {
+                ClipResult::Accept => {
+                    // Doesn't affect the primitive at all, so skip adding to list
+                }
+                ClipResult::Reject => {
+                    // Completely clips the supplied prim rect
+                    return None;
+                }
+                ClipResult::Partial => {
+                    // Needs a mask -> add to clip node indices
+
+                    // TODO(gw): Ensure this only runs once on each node per frame?
+                    node.update(device_pixel_scale);
+
+                    // Create the clip node instance for this clip node
+                    if let Some(instance) = node_info.create_instance(
+                        node,
+                        &local_bounding_rect,
+                        gpu_cache,
+                        resource_cache,
+                        &mut self.mask_tiles,
+                        spatial_tree,
+                        request_resources,
+                    ) {
+                        // As a special case, a partial accept of a clip rect that is
+                        // in the same coordinate system as the primitive doesn't need
+                        // a clip mask. Instead, it can be handled by the primitive
+                        // vertex shader as part of the local clip rect. This is an
+                        // important optimization for reducing the number of clip
+                        // masks that are allocated on common pages.
+                        needs_mask |= match node.item.kind {
+                            ClipItemKind::Rectangle { mode: ClipMode::ClipOut, .. } |
+                            ClipItemKind::RoundedRectangle { .. } |
+                            ClipItemKind::Image { .. } |
+                            ClipItemKind::BoxShadow { .. } => {
+                                true
+                            }
+
+                            ClipItemKind::Rectangle { mode: ClipMode::Clip, .. } => {
+                                !instance.flags.contains(ClipNodeFlags::SAME_COORD_SYSTEM)
+                            }
+                        };
+
+                        // Store this in the index buffer for this clip chain instance.
+                        self.clip_node_instances.push(instance);
+                    }
+                }
+            }
+        }
+
+        // Get the range identifying the clip nodes in the index buffer.
+        let clips_range = ClipNodeRange {
+            first: first_clip_node_index,
+            count: self.clip_node_instances.len() as u32 - first_clip_node_index,
+        };
+
+        // If this clip chain needs a mask, reduce the size of the mask allocation
+        // by any clips that were in the same space as the picture. This can result
+        // in much smaller clip mask allocations in some cases. Note that the ordering
+        // here is important - the reduction must occur *after* the clip item accept
+        // reject checks above, so that we don't eliminate masks accidentally (since
+        // we currently only support a local clip rect in the vertex shader).
+        if needs_mask {
+            pic_coverage_rect = pic_coverage_rect.intersection(&self.active_pic_coverage_rect)?;
+        }
+
+        // Return a valid clip chain instance
+        Some(ClipChainInstance {
+            clips_range,
+            has_non_local_clips,
+            local_clip_rect,
+            pic_coverage_rect,
+            pic_spatial_node_index: prim_to_pic_mapper.ref_spatial_node_index,
+            needs_mask,
+        })
+    }
+
+    pub fn begin_frame(&mut self, scratch: &mut ClipStoreScratchBuffer) {
+        mem::swap(&mut self.clip_node_instances, &mut scratch.clip_node_instances);
+        mem::swap(&mut self.mask_tiles, &mut scratch.mask_tiles);
+        self.clip_node_instances.clear();
+        self.mask_tiles.clear();
+    }
+
+    pub fn end_frame(&mut self, scratch: &mut ClipStoreScratchBuffer) {
+        mem::swap(&mut self.clip_node_instances, &mut scratch.clip_node_instances);
+        mem::swap(&mut self.mask_tiles, &mut scratch.mask_tiles);
+    }
+
+    pub fn visible_mask_tiles(&self, instance: &ClipNodeInstance) -> &[VisibleMaskImageTile] {
+        if let Some(range) = &instance.visible_tiles {
+            &self.mask_tiles[range.clone()]
+        } else {
+            &[]
+        }
+    }
+}
+
+pub struct ComplexTranslateIter<I> {
+    source: I,
+    offset: LayoutVector2D,
+}
+
+impl<I: Iterator<Item = ComplexClipRegion>> Iterator for ComplexTranslateIter<I> {
+    type Item = ComplexClipRegion;
+    fn next(&mut self) -> Option<Self::Item> {
+        self.source
+            .next()
+            .map(|mut complex| {
+                complex.rect = complex.rect.translate(self.offset);
+                complex
+            })
+    }
+}
+
+// The ClipItemKey is a hashable representation of the contents
+// of a clip item. It is used during interning to de-duplicate
+// clip nodes between frames and display lists. This allows quick
+// comparison of clip node equality by handle, and also allows
+// the uploaded GPU cache handle to be retained between display lists.
+// TODO(gw): Maybe we should consider constructing these directly
+//           in the DL builder?
+#[derive(Copy, Debug, Clone, Eq, MallocSizeOf, PartialEq, Hash)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub enum ClipItemKeyKind {
+    Rectangle(RectangleKey, ClipMode),
+    RoundedRectangle(RectangleKey, BorderRadiusAu, ClipMode),
+    ImageMask(RectangleKey, ImageKey, Option<PolygonDataHandle>),
+    BoxShadow(PointKey, SizeKey, BorderRadiusAu, RectangleKey, Au, BoxShadowClipMode),
+}
+
+impl ClipItemKeyKind {
+    pub fn rectangle(rect: LayoutRect, mode: ClipMode) -> Self {
+        ClipItemKeyKind::Rectangle(rect.into(), mode)
+    }
+
+    pub fn rounded_rect(rect: LayoutRect, mut radii: BorderRadius, mode: ClipMode) -> Self {
+        if radii.is_zero() {
+            ClipItemKeyKind::rectangle(rect, mode)
+        } else {
+            ensure_no_corner_overlap(&mut radii, rect.size());
+            ClipItemKeyKind::RoundedRectangle(
+                rect.into(),
+                radii.into(),
+                mode,
+            )
+        }
+    }
+
+    pub fn image_mask(image_mask: &ImageMask, mask_rect: LayoutRect,
+                      polygon_handle: Option<PolygonDataHandle>) -> Self {
+        ClipItemKeyKind::ImageMask(
+            mask_rect.into(),
+            image_mask.image,
+            polygon_handle,
+        )
+    }
+
+    pub fn box_shadow(
+        shadow_rect: LayoutRect,
+        shadow_radius: BorderRadius,
+        prim_shadow_rect: LayoutRect,
+        blur_radius: f32,
+        clip_mode: BoxShadowClipMode,
+    ) -> Self {
+        // Get the fractional offsets required to match the
+        // source rect with a minimal rect.
+        let fract_offset = LayoutPoint::new(
+            shadow_rect.min.x.fract().abs(),
+            shadow_rect.min.y.fract().abs(),
+        );
+
+        ClipItemKeyKind::BoxShadow(
+            fract_offset.into(),
+            shadow_rect.size().into(),
+            shadow_radius.into(),
+            prim_shadow_rect.into(),
+            Au::from_f32_px(blur_radius),
+            clip_mode,
+        )
+    }
+
+    pub fn node_kind(&self) -> ClipNodeKind {
+        match *self {
+            ClipItemKeyKind::Rectangle(_, ClipMode::Clip) => ClipNodeKind::Rectangle,
+
+            ClipItemKeyKind::Rectangle(_, ClipMode::ClipOut) |
+            ClipItemKeyKind::RoundedRectangle(..) |
+            ClipItemKeyKind::ImageMask(..) |
+            ClipItemKeyKind::BoxShadow(..) => ClipNodeKind::Complex,
+        }
+    }
+}
+
+#[derive(Debug, Copy, Clone, Eq, MallocSizeOf, PartialEq, Hash)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipItemKey {
+    pub kind: ClipItemKeyKind,
+    pub spatial_node_index: SpatialNodeIndex,
+}
+
+/// The data available about an interned clip node during scene building
+#[derive(Debug, MallocSizeOf)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipInternData {
+    pub key: ClipItemKey,
+}
+
+impl intern::InternDebug for ClipItemKey {}
+
+impl intern::Internable for ClipIntern {
+    type Key = ClipItemKey;
+    type StoreData = ClipNode;
+    type InternData = ClipInternData;
+    const PROFILE_COUNTER: usize = crate::profiler::INTERNED_CLIPS;
+}
+
+#[derive(Debug, MallocSizeOf)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub enum ClipItemKind {
+    Rectangle {
+        rect: LayoutRect,
+        mode: ClipMode,
+    },
+    RoundedRectangle {
+        rect: LayoutRect,
+        radius: BorderRadius,
+        mode: ClipMode,
+    },
+    Image {
+        image: ImageKey,
+        rect: LayoutRect,
+        polygon_handle: Option<PolygonDataHandle>,
+    },
+    BoxShadow {
+        source: BoxShadowClipSource,
+    },
+}
+
+#[derive(Debug, MallocSizeOf)]
+#[cfg_attr(feature = "capture", derive(Serialize))]
+#[cfg_attr(feature = "replay", derive(Deserialize))]
+pub struct ClipItem {
+    pub kind: ClipItemKind,
+    pub spatial_node_index: SpatialNodeIndex,
+}
+
+fn compute_box_shadow_parameters(
+    shadow_rect_fract_offset: LayoutPoint,
+    shadow_rect_size: LayoutSize,
+    mut shadow_radius: BorderRadius,
+    prim_shadow_rect: LayoutRect,
+    blur_radius: f32,
+    clip_mode: BoxShadowClipMode,
+) -> BoxShadowClipSource {
+    // Make sure corners don't overlap.
+    ensure_no_corner_overlap(&mut shadow_radius, shadow_rect_size);
+
+    let fract_size = LayoutSize::new(
+        shadow_rect_size.width.fract().abs(),
+        shadow_rect_size.height.fract().abs(),
+    );
+
+    // Create a minimal size primitive mask to blur. In this
+    // case, we ensure the size of each corner is the same,
+    // to simplify the shader logic that stretches the blurred
+    // result across the primitive.
+    let max_corner_width = shadow_radius.top_left.width
+                                .max(shadow_radius.bottom_left.width)
+                                .max(shadow_radius.top_right.width)
+                                .max(shadow_radius.bottom_right.width);
+    let max_corner_height = shadow_radius.top_left.height
+                                .max(shadow_radius.bottom_left.height)
+                                .max(shadow_radius.top_right.height)
+                                .max(shadow_radius.bottom_right.height);
+
+    // Get maximum distance that can be affected by given blur radius.
+    let blur_region = (BLUR_SAMPLE_SCALE * blur_radius).ceil();
+
+    // If the largest corner is smaller than the blur radius, we need to ensure
+    // that it's big enough that the corners don't affect the middle segments.
+    let used_corner_width = max_corner_width.max(blur_region);
+    let used_corner_height = max_corner_height.max(blur_region);
+
+    // Minimal nine-patch size, corner + internal + corner.
+    let min_shadow_rect_size = LayoutSize::new(
+        2.0 * used_corner_width + blur_region,
+        2.0 * used_corner_height + blur_region,
+    );
+
+    // The minimal rect to blur.
+    let mut minimal_shadow_rect = LayoutRect::from_origin_and_size(
+        LayoutPoint::new(
+            blur_region + shadow_rect_fract_offset.x,
+            blur_region + shadow_rect_fract_offset.y,
+        ),
+        LayoutSize::new(
+            min_shadow_rect_size.width + fract_size.width,
+            min_shadow_rect_size.height + fract_size.height,
+        ),
+    );
+
+    // If the width or height ends up being bigger than the original
+    // primitive shadow rect, just blur the entire rect along that
+    // axis and draw that as a simple blit. This is necessary for
+    // correctness, since the blur of one corner may affect the blur
+    // in another corner.
+    let mut stretch_mode_x = BoxShadowStretchMode::Stretch;
+    if shadow_rect_size.width < minimal_shadow_rect.width() {
+        minimal_shadow_rect.max.x = minimal_shadow_rect.min.x + shadow_rect_size.width;
+        stretch_mode_x = BoxShadowStretchMode::Simple;
+    }
+
+    let mut stretch_mode_y = BoxShadowStretchMode::Stretch;
+    if shadow_rect_size.height < minimal_shadow_rect.height() {
+        minimal_shadow_rect.max.y = minimal_shadow_rect.min.y + shadow_rect_size.height;
+        stretch_mode_y = BoxShadowStretchMode::Simple;
+    }
+
+    // Expand the shadow rect by enough room for the blur to take effect.
+    let shadow_rect_alloc_size = LayoutSize::new(
+        2.0 * blur_region + minimal_shadow_rect.width().ceil(),
+        2.0 * blur_region + minimal_shadow_rect.height().ceil(),
+    );
+
+    BoxShadowClipSource {
+        original_alloc_size: shadow_rect_alloc_size,
+        shadow_rect_alloc_size,
+        shadow_radius,
+        prim_shadow_rect,
+        blur_radius,
+        clip_mode,
+        stretch_mode_x,
+        stretch_mode_y,
+        render_task: None,
+        cache_key: None,
+        minimal_shadow_rect,
+    }
+}
+
+impl ClipItemKind {
+    pub fn new_box_shadow(
+        shadow_rect_fract_offset: LayoutPoint,
+        shadow_rect_size: LayoutSize,
+        mut shadow_radius: BorderRadius,
+        prim_shadow_rect: LayoutRect,
+        blur_radius: f32,
+        clip_mode: BoxShadowClipMode,
+    ) -> Self {
+        let mut source = compute_box_shadow_parameters(
+            shadow_rect_fract_offset,
+            shadow_rect_size,
+            shadow_radius,
+            prim_shadow_rect,
+            blur_radius,
+            clip_mode,
+        );
+
+        fn needed_downscaling(source: &BoxShadowClipSource) -> Option<f32> {
+            // This size is fairly arbitrary, but it's the same as the size that
+            // we use to avoid caching big blurred stacking contexts.
+            //
+            // If you change it, ensure that the reftests
+            // box-shadow-large-blur-radius-* still hit the downscaling path,
+            // and that they render correctly.
+            const MAX_SIZE: f32 = 2048.;
+
+            let max_dimension =
+                source.shadow_rect_alloc_size.width.max(source.shadow_rect_alloc_size.height);
+
+            if max_dimension > MAX_SIZE {
+                Some(MAX_SIZE / max_dimension)
+            } else {
+                None
+            }
+        }
+
+        if let Some(downscale) = needed_downscaling(&source) {
+            shadow_radius.bottom_left.height *= downscale;
+            shadow_radius.bottom_left.width *= downscale;
+            shadow_radius.bottom_right.height *= downscale;
+            shadow_radius.bottom_right.width *= downscale;
+            shadow_radius.top_left.height *= downscale;
+            shadow_radius.top_left.width *= downscale;
+            shadow_radius.top_right.height *= downscale;
+            shadow_radius.top_right.width *= downscale;
+
+            let original_alloc_size = source.shadow_rect_alloc_size;
+
+            source = compute_box_shadow_parameters(
+                shadow_rect_fract_offset * downscale,
+                shadow_rect_size * downscale,
+                shadow_radius,
+                prim_shadow_rect,
+                blur_radius * downscale,
+                clip_mode,
+            );
+            source.original_alloc_size = original_alloc_size;
+        }
+        ClipItemKind::BoxShadow { source }
+    }
+
+    /// Returns true if this clip mask can run through the fast path
+    /// for the given clip item type.
+    ///
+    /// Note: this logic has to match `ClipBatcher::add` behavior.
+    fn supports_fast_path_rendering(&self) -> bool {
+        match *self {
+            ClipItemKind::Rectangle { .. } |
+            ClipItemKind::Image { .. } |
+            ClipItemKind::BoxShadow { .. } => {
+                false
+            }
+            ClipItemKind::RoundedRectangle { ref radius, .. } => {
+                // The rounded clip rect fast path shader can only work
+                // if the radii are uniform.
+                radius.is_uniform().is_some()
+            }
+        }
+    }
+
+    // Get an optional clip rect that a clip source can provide to
+    // reduce the size of a primitive region. This is typically
+    // used to eliminate redundant clips, and reduce the size of
+    // any clip mask that eventually gets drawn.
+    pub fn get_local_clip_rect(&self) -> Option<LayoutRect> {
+        match *self {
+            ClipItemKind::Rectangle { rect, mode: ClipMode::Clip } => Some(rect),
+            ClipItemKind::Rectangle { mode: ClipMode::ClipOut, .. } => None,
+            ClipItemKind::RoundedRectangle { rect, mode: ClipMode::Clip, .. } => Some(rect),
+            ClipItemKind::RoundedRectangle { mode: ClipMode::ClipOut, .. } => None,
+            ClipItemKind::Image { rect, .. } => {
+                Some(rect)
+            }
+            ClipItemKind::BoxShadow { .. } => None,
+        }
+    }
+
+    fn get_clip_result_complex(
+        &self,
+        transform: &LayoutToWorldTransform,
+        prim_world_rect: &WorldRect,
+        world_rect: &WorldRect,
+    ) -> ClipResult {
+        let visible_rect = match prim_world_rect.intersection(world_rect) {
+            Some(rect) => rect,
+            None => return ClipResult::Reject,
+        };
+
+        let (clip_rect, inner_rect, mode) = match *self {
+            ClipItemKind::Rectangle { rect, mode } => {
+                (rect, Some(rect), mode)
+            }
+            ClipItemKind::RoundedRectangle { rect, ref radius, mode } => {
+                let inner_clip_rect = extract_inner_rect_safe(&rect, radius);
+                (rect, inner_clip_rect, mode)
+            }
+            ClipItemKind::Image { rect, .. } => {
+                (rect, None, ClipMode::Clip)
+            }
+            ClipItemKind::BoxShadow { .. } => {
+                return ClipResult::Partial;
+            }
+        };
+
+        if let Some(ref inner_clip_rect) = inner_rect {
+            if let Some(()) = projected_rect_contains(inner_clip_rect, transform, &visible_rect) {
+                return match mode {
+                    ClipMode::Clip => ClipResult::Accept,
+                    ClipMode::ClipOut => ClipResult::Reject,
+                };
+            }
+        }
+
+        match mode {
+            ClipMode::Clip => {
+                let outer_clip_rect = match project_rect(
+                    transform,
+                    &clip_rect,
+                    &world_rect,
+                ) {
+                    Some(outer_clip_rect) => outer_clip_rect,
+                    None => return ClipResult::Partial,
+                };
+
+                match outer_clip_rect.intersection(prim_world_rect) {
+                    Some(..) => {
+                        ClipResult::Partial
+                    }
+                    None => {
+                        ClipResult::Reject
+                    }
+                }
+            }
+            ClipMode::ClipOut => ClipResult::Partial,
+        }
+    }
+
+    // Check how a given clip source affects a local primitive region.
+    fn get_clip_result(
+        &self,
+        prim_rect: &LayoutRect,
+    ) -> ClipResult {
+        match *self {
+            ClipItemKind::Rectangle { rect, mode: ClipMode::Clip } => {
+                if rect.contains_box(prim_rect) {
+                    return ClipResult::Accept;
+                }
+
+                match rect.intersection(prim_rect) {
+                    Some(..) => {
+                        ClipResult::Partial
+                    }
+                    None => {
+                        ClipResult::Reject
+                    }
+                }
+            }
+            ClipItemKind::Rectangle { rect, mode: ClipMode::ClipOut } => {
+                if rect.contains_box(prim_rect) {
+                    return ClipResult::Reject;
+                }
+
+                match rect.intersection(prim_rect) {
+                    Some(_) => {
+                        ClipResult::Partial
+                    }
+                    None => {
+                        ClipResult::Accept
+                    }
+                }
+            }
+            ClipItemKind::RoundedRectangle { rect, ref radius, mode: ClipMode::Clip } => {
+                // TODO(gw): Consider caching this in the ClipNode
+                //           if it ever shows in profiles.
+                if rounded_rectangle_contains_box_quick(&rect, radius, &prim_rect) {
+                    return ClipResult::Accept;
+                }
+
+                match rect.intersection(prim_rect) {
+                    Some(..) => {
+                        ClipResult::Partial
+                    }
+                    None => {
+                        ClipResult::Reject
+                    }
+                }
+            }
+            ClipItemKind::RoundedRectangle { rect, ref radius, mode: ClipMode::ClipOut } => {
+                // TODO(gw): Consider caching this in the ClipNode
+                //           if it ever shows in profiles.
+                if rounded_rectangle_contains_box_quick(&rect, radius, &prim_rect) {
+                    return ClipResult::Reject;
+                }
+
+                match rect.intersection(prim_rect) {
+                    Some(_) => {
+                        ClipResult::Partial
+                    }
+                    None => {
+                        ClipResult::Accept
+                    }
+                }
+            }
+            ClipItemKind::Image { rect, .. } => {
+                match rect.intersection(prim_rect) {
+                    Some(..) => {
+                        ClipResult::Partial
+                    }
+                    None => {
+                        ClipResult::Reject
+                    }
+                }
+            }
+            ClipItemKind::BoxShadow { .. } => {
+                ClipResult::Partial
+            }
+        }
+    }
+}
+
+/// Represents a local rect and a device space
+/// rectangles that are either outside or inside bounds.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Geometry {
+    pub local_rect: LayoutRect,
+    pub device_rect: DeviceIntRect,
+}
+
+impl From<LayoutRect> for Geometry {
+    fn from(local_rect: LayoutRect) -> Self {
+        Geometry {
+            local_rect,
+            device_rect: DeviceIntRect::zero(),
+        }
+    }
+}
+
+pub fn rounded_rectangle_contains_point(
+    point: &LayoutPoint,
+    rect: &LayoutRect,
+    radii: &BorderRadius
+) -> bool {
+    if !rect.contains(*point) {
+        return false;
+    }
+
+    let top_left_center = rect.min + radii.top_left.to_vector();
+    if top_left_center.x > point.x && top_left_center.y > point.y &&
+       !Ellipse::new(radii.top_left).contains(*point - top_left_center.to_vector()) {
+        return false;
+    }
+
+    let bottom_right_center = rect.bottom_right() - radii.bottom_right.to_vector();
+    if bottom_right_center.x < point.x && bottom_right_center.y < point.y &&
+       !Ellipse::new(radii.bottom_right).contains(*point - bottom_right_center.to_vector()) {
+        return false;
+    }
+
+    let top_right_center = rect.top_right() +
+                           LayoutVector2D::new(-radii.top_right.width, radii.top_right.height);
+    if top_right_center.x < point.x && top_right_center.y > point.y &&
+       !Ellipse::new(radii.top_right).contains(*point - top_right_center.to_vector()) {
+        return false;
+    }
+
+    let bottom_left_center = rect.bottom_left() +
+                             LayoutVector2D::new(radii.bottom_left.width, -radii.bottom_left.height);
+    if bottom_left_center.x > point.x && bottom_left_center.y < point.y &&
+       !Ellipse::new(radii.bottom_left).contains(*point - bottom_left_center.to_vector()) {
+        return false;
+    }
+
+    true
+}
+
+/// Return true if the rounded rectangle described by `container` and `radii`
+/// definitely contains `containee`. May return false negatives, but never false
+/// positives.
+fn rounded_rectangle_contains_box_quick(
+    container: &LayoutRect,
+    radii: &BorderRadius,
+    containee: &LayoutRect,
+) -> bool {
+    if !container.contains_box(containee) {
+        return false;
+    }
+
+    /// Return true if `point` falls within `corner`. This only covers the
+    /// upper-left case; we transform the other corners into that form.
+    fn foul(point: LayoutPoint, corner: LayoutPoint) -> bool {
+        point.x < corner.x && point.y < corner.y
+    }
+
+    /// Flip `pt` about the y axis (i.e. negate `x`).
+    fn flip_x(pt: LayoutPoint) -> LayoutPoint {
+        LayoutPoint { x: -pt.x, .. pt }
+    }
+
+    /// Flip `pt` about the x axis (i.e. negate `y`).
+    fn flip_y(pt: LayoutPoint) -> LayoutPoint {
+        LayoutPoint { y: -pt.y, .. pt }
+    }
+
+    if foul(containee.top_left(), container.top_left() + radii.top_left) ||
+        foul(flip_x(containee.top_right()), flip_x(container.top_right()) + radii.top_right) ||
+        foul(flip_y(containee.bottom_left()), flip_y(container.bottom_left()) + radii.bottom_left) ||
+        foul(-containee.bottom_right(), -container.bottom_right() + radii.bottom_right)
+    {
+        return false;
+    }
+
+    true
+}
+
+/// Test where point p is relative to the infinite line that passes through the segment
+/// defined by p0 and p1. Point p is on the "left" of the line if the triangle (p0, p1, p)
+/// forms a counter-clockwise triangle.
+/// > 0 is left of the line
+/// < 0 is right of the line
+/// == 0 is on the line
+pub fn is_left_of_line(
+    p_x: f32,
+    p_y: f32,
+    p0_x: f32,
+    p0_y: f32,
+    p1_x: f32,
+    p1_y: f32,
+) -> f32 {
+    (p1_x - p0_x) * (p_y - p0_y) - (p_x - p0_x) * (p1_y - p0_y)
+}
+
+pub fn polygon_contains_point(
+    point: &LayoutPoint,
+    rect: &LayoutRect,
+    polygon: &PolygonKey,
+) -> bool {
+    if !rect.contains(*point) {
+        return false;
+    }
+
+    // p is a LayoutPoint that we'll be comparing to dimensionless PointKeys,
+    // which were created from LayoutPoints, so it all works out.
+    let p = LayoutPoint::new(point.x - rect.min.x, point.y - rect.min.y);
+
+    // Calculate a winding number for this point.
+    let mut winding_number: i32 = 0;
+
+    let count = polygon.point_count as usize;
+
+    for i in 0..count {
+        let p0 = polygon.points[i];
+        let p1 = polygon.points[(i + 1) % count];
+
+        if p0.y <= p.y {
+            if p1.y > p.y {
+                if is_left_of_line(p.x, p.y, p0.x, p0.y, p1.x, p1.y) > 0.0 {
+                    winding_number = winding_number + 1;
+                }
+            }
+        } else if p1.y <= p.y {
+            if is_left_of_line(p.x, p.y, p0.x, p0.y, p1.x, p1.y) < 0.0 {
+                winding_number = winding_number - 1;
+            }
+        }
+    }
+
+    match polygon.fill_rule {
+        FillRule::Nonzero => winding_number != 0,
+        FillRule::Evenodd => winding_number.abs() % 2 == 1,
+    }
+}
+
+pub fn projected_rect_contains(
+    source_rect: &LayoutRect,
+    transform: &LayoutToWorldTransform,
+    target_rect: &WorldRect,
+) -> Option<()> {
+    let points = [
+        transform.transform_point2d(source_rect.top_left())?,
+        transform.transform_point2d(source_rect.top_right())?,
+        transform.transform_point2d(source_rect.bottom_right())?,
+        transform.transform_point2d(source_rect.bottom_left())?,
+    ];
+    let target_points = [
+        target_rect.top_left(),
+        target_rect.top_right(),
+        target_rect.bottom_right(),
+        target_rect.bottom_left(),
+    ];
+    // iterate the edges of the transformed polygon
+    for (a, b) in points
+        .iter()
+        .cloned()
+        .zip(points[1..].iter().cloned().chain(iter::once(points[0])))
+    {
+        // If this edge is redundant, it's a weird, case, and we shouldn't go
+        // length in trying to take the fast path (e.g. when the whole rectangle is a point).
+        // If any of edges of the target rectangle crosses the edge, it's not completely
+        // inside our transformed polygon either.
+        if a.approx_eq(&b) || target_points.iter().any(|&c| (b - a).cross(c - a) < 0.0) {
+            return None
+        }
+    }
+
+    Some(())
+}
+
+
+// Add a clip node into the list of clips to be processed
+// for the current clip chain. Returns false if the clip
+// results in the entire primitive being culled out.
+fn add_clip_node_to_current_chain(
+    handle: ClipDataHandle,
+    prim_spatial_node_index: SpatialNodeIndex,
+    pic_spatial_node_index: SpatialNodeIndex,
+    local_clip_rect: &mut LayoutRect,
+    clip_node_info: &mut Vec<ClipNodeInfo>,
+    pic_coverage_rect: &mut PictureRect,
+    clip_data_store: &ClipDataStore,
+    spatial_tree: &SpatialTree,
+) -> bool {
+    let clip_node = &clip_data_store[handle];
+
+    // Determine the most efficient way to convert between coordinate
+    // systems of the primitive and clip node.
+    let conversion = ClipSpaceConversion::new(
+        prim_spatial_node_index,
+        clip_node.item.spatial_node_index,
+        spatial_tree,
+    );
+
+    // If we can convert spaces, try to reduce the size of the region
+    // requested, and cache the conversion information for the next step.
+    if let Some(clip_rect) = clip_node.item.kind.get_local_clip_rect() {
+        match conversion {
+            ClipSpaceConversion::Local => {
+                *local_clip_rect = match local_clip_rect.intersection(&clip_rect) {
+                    Some(rect) => rect,
+                    None => return false,
+                };
+            }
+            ClipSpaceConversion::ScaleOffset(ref scale_offset) => {
+                let clip_rect = scale_offset.map_rect(&clip_rect);
+                *local_clip_rect = match local_clip_rect.intersection(&clip_rect) {
+                    Some(rect) => rect,
+                    None => return false,
+                };
+            }
+            ClipSpaceConversion::Transform(..) => {
+                // Map the local clip rect directly into the same space as the picture
+                // surface. This will often be the same space as the clip itself, which
+                // results in a reduction in allocated clip mask size.
+
+                // For simplicity, only apply this optimization if the clip is in the
+                // same coord system as the picture. There are some 'advanced' perspective
+                // clip tests in wrench that break without this check. Those cases are
+                // never used in Gecko, and we aim to remove support in WR for that
+                // in future to simplify the clipping pipeline.
+                let pic_coord_system = spatial_tree
+                    .get_spatial_node(pic_spatial_node_index)
+                    .coordinate_system_id;
+
+                let clip_coord_system = spatial_tree
+                    .get_spatial_node(clip_node.item.spatial_node_index)
+                    .coordinate_system_id;
+
+                if pic_coord_system == clip_coord_system {
+                    let mapper = SpaceMapper::new_with_target(
+                        pic_spatial_node_index,
+                        clip_node.item.spatial_node_index,
+                        PictureRect::max_rect(),
+                        spatial_tree,
+                    );
+
+                    if let Some(pic_clip_rect) = mapper.map(&clip_rect) {
+                        *pic_coverage_rect = pic_clip_rect
+                            .intersection(pic_coverage_rect)
+                            .unwrap_or(PictureRect::zero());
+                    }
+                }
+            }
+        }
+    }
+
+    clip_node_info.push(ClipNodeInfo {
+        conversion,
+        handle,
+    });
+
+    true
+}
+
+#[cfg(test)]
+mod tests {
+    use super::projected_rect_contains;
+    use euclid::{Transform3D, rect};
+
+    #[test]
+    fn test_empty_projected_rect() {
+        assert_eq!(
+            None,
+            projected_rect_contains(
+                &rect(10.0, 10.0, 0.0, 0.0).to_box2d(),
+                &Transform3D::identity(),
+                &rect(20.0, 20.0, 10.0, 10.0).to_box2d(),
+            ),
+            "Empty rectangle is considered to include a non-empty!"
+        );
+    }
+}
+
+/// PolygonKeys get interned, because it's a convenient way to move the data
+/// for the polygons out of the ClipItemKind and ClipItemKeyKind enums. The
+/// polygon data is both interned and retrieved by the scene builder, and not
+/// accessed at all by the frame builder. Another oddity is that the
+/// PolygonKey contains the totality of the information about the polygon, so
+/// the InternData and StoreData types are both PolygonKey.
+#[derive(Copy, Clone, Debug, Hash, MallocSizeOf, PartialEq, Eq)]
+#[cfg_attr(any(feature = "serde"), derive(Deserialize, Serialize))]
+pub enum PolygonIntern {}
+
+pub type PolygonDataHandle = intern::Handle<PolygonIntern>;
+
+impl intern::InternDebug for PolygonKey {}
+
+impl intern::Internable for PolygonIntern {
+    type Key = PolygonKey;
+    type StoreData = PolygonKey;
+    type InternData = PolygonKey;
+    const PROFILE_COUNTER: usize = crate::profiler::INTERNED_POLYGONS;
+}