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layout: Store scroll offsets in the ScrollTree (#37428)

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There are currently five places that scroll offsets are stored:

 - DOM: A set of scroll offsets used for script.
 - Layout: An array of scroll offsets that is used for tracking
   layout-side scroll offsets.
 - Layout: The scroll offsets stored in the `ScrollTree`. These are
   currently unset and unused.
 - Compositor: The scroll offsets stored in the `ScrollTree` mirrored
   from layout.
 - WebRender: The scrolled offsets stored in the WebRender spatial tree.

This change is the first step in combining the first three into the
layout `ScrollTree`. It eliminates the extra array of scroll offsets
stored in layout in favor of the storing them in the `ScrollTree`. A
followup change will eliminate the ones stored in the DOM.

- In addition the `ScrollState` data structure is eliminated as these
are
now stored in a `HashMap` everywhere when passing them via IPC.
- The offsests stored in layout can now never scroll past the boundaries
of the scrolled content.

Testing: This should not change behavior and is thus covered by existing
WPT tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: stevennovaryo <steven.novaryo@gmail.com>
This commit is contained in:
Martin Robinson 2025-06-13 14:01:27 +02:00 • committed by GitHub
parent 6cac782fb1
commit f451dccd0b
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11 changed files with 182 additions and 122 deletions
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27
components/shared/compositing/display_list.rs
View file

@ -4,6 +4,8 @@
//! Defines data structures which are consumed by the Compositor.
use std::collections::HashMap;
use base::id::ScrollTreeNodeId;
use bitflags::bitflags;
use embedder_traits::Cursor;
@ -338,7 +340,7 @@ impl ScrollTree {
/// Given an [`ExternalScrollId`] and an offset, update the scroll offset of the scroll node
/// with the given id.
pub fn set_scroll_offsets_for_node_with_external_scroll_id(
pub fn set_scroll_offset_for_node_with_external_scroll_id(
&mut self,
external_scroll_id: ExternalScrollId,
offset: LayoutVector2D,
@ -353,6 +355,29 @@ impl ScrollTree {
_ => None,
})
}
/// Given a set of all scroll offsets coming from the Servo renderer, update all of the offsets
/// for nodes that actually exist in this tree.
pub fn set_all_scroll_offsets(&mut self, offsets: &HashMap<ExternalScrollId, LayoutVector2D>) {
for node in self.nodes.iter_mut() {
if let SpatialTreeNodeInfo::Scroll(ref mut scroll_info) = node.info {
if let Some(offset) = offsets.get(&scroll_info.external_id) {
scroll_info.offset = *offset;
}
}
}
}
/// Collect all of the scroll offsets of the scrolling nodes of this tree into a
/// [`HashMap`] which can be applied to another tree.
pub fn scroll_offsets(&self) -> HashMap<ExternalScrollId, LayoutVector2D> {
HashMap::from_iter(self.nodes.iter().filter_map(|node| match node.info {
SpatialTreeNodeInfo::Scroll(ref scroll_info) => {
Some((scroll_info.external_id, scroll_info.offset))
},
_ => None,
}))
}
}
/// A data structure which stores compositor-side information about