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>
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