1 files changed, 100 insertions, 0 deletions
diff --git a/components/layout_2020/fragment_tree/positioning_fragment.rs b/components/layout_2020/fragment_tree/positioning_fragment.rs
new file mode 100644
index 00000000000..4a629b31698
--- /dev/null
+++ b/components/layout_2020/fragment_tree/positioning_fragment.rs
@@ -0,0 +1,100 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use gfx_traits::print_tree::PrintTree;
+use serde::Serialize;
+use servo_arc::Arc as ServoArc;
+use style::logical_geometry::WritingMode;
+use style::properties::ComputedValues;
+use style::values::computed::Length;
+
+use super::{BaseFragment, BaseFragmentInfo, Fragment};
+use crate::cell::ArcRefCell;
+use crate::geom::{LogicalRect, PhysicalRect};
+
+/// Can contain child fragments with relative coordinates, but does not contribute to painting
+/// itself. [`PositioningFragments`] may be completely anonymous, or just non-painting Fragments
+/// generated by boxes.
+#[derive(Serialize)]
+pub(crate) struct PositioningFragment {
+    pub base: BaseFragment,
+    pub rect: LogicalRect<Length>,
+    pub children: Vec<ArcRefCell<Fragment>>,
+    pub writing_mode: WritingMode,
+
+    /// The scrollable overflow of this anonymous fragment's children.
+    pub scrollable_overflow: PhysicalRect<Length>,
+
+    /// If this fragment was created with a style, the style of the fragment.
+    #[serde(skip_serializing)]
+    pub style: Option<ServoArc<ComputedValues>>,
+}
+
+impl PositioningFragment {
+    pub fn new_anonymous(
+        rect: LogicalRect<Length>,
+        children: Vec<Fragment>,
+        mode: WritingMode,
+    ) -> Self {
+        Self::new_with_base_fragment(BaseFragment::anonymous(), None, rect, children, mode)
+    }
+
+    pub fn new_empty(
+        base_fragment_info: BaseFragmentInfo,
+        rect: LogicalRect<Length>,
+        style: ServoArc<ComputedValues>,
+    ) -> Self {
+        let writing_mode = style.writing_mode;
+        Self::new_with_base_fragment(
+            base_fragment_info.into(),
+            Some(style),
+            rect,
+            Vec::new(),
+            writing_mode,
+        )
+    }
+
+    fn new_with_base_fragment(
+        base: BaseFragment,
+        style: Option<ServoArc<ComputedValues>>,
+        rect: LogicalRect<Length>,
+        children: Vec<Fragment>,
+        mode: WritingMode,
+    ) -> Self {
+        // FIXME(mrobinson, bug 25564): We should be using the containing block
+        // here to properly convert scrollable overflow to physical geometry.
+        let containing_block = PhysicalRect::zero();
+        let content_origin = rect.start_corner.to_physical(mode);
+        let scrollable_overflow = children.iter().fold(PhysicalRect::zero(), |acc, child| {
+            acc.union(
+                &child
+                    .scrollable_overflow(&containing_block)
+                    .translate(content_origin.to_vector()),
+            )
+        });
+        PositioningFragment {
+            base,
+            style,
+            rect,
+            children: children.into_iter().map(ArcRefCell::new).collect(),
+            writing_mode: mode,
+            scrollable_overflow,
+        }
+    }
+
+    pub fn print(&self, tree: &mut PrintTree) {
+        tree.new_level(format!(
+            "PositioningFragment\
+                \nbase={:?}\
+                \nrect={:?}\
+                \nscrollable_overflow={:?}",
+            self.base, self.rect, self.scrollable_overflow
+        ));
+
+        for child in &self.children {
+            child.borrow().print(tree);
+        }
+        tree.end_level();
+    }
+}