When a style change does not chang the structure of the box tree, it is
possible to skip box tree rebuilding for an element. This change adds
support for reusing old box trees when no element has that type of
damage. In order to make this happen, there needs to be a type of
"empty" `LayoutDamage` that just indicates that a fragment tree layout
is necessary.
This is the first step toward incremental fragment tree layout.
Testing: This should not change observable behavior and thus is covered
by
existing WPT tests. Performance numbers to follow.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
This change:
- Adds a new type of LayoutDamage that signifies that a box needs its
children recollected, because one or more of them need to be rebuilt.
- During restyle damage propagation, propagate this new damage upward in
the tree. Then box tree construction should be able to preserve any
still-valid box tree nodes from box slots.
- During BlockLevelBox job finalization, if a box slot is valid and
there is not LayoutDamage to the element, use the old box slot,
ensuring that its fragment cache is invalidated.
Testing: This should not change observable behavior and thus is covered
by existing WPT tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: coding-joedow <ibluegalaxy_taoj@163.com>
This will allow Servo to add custom types of damage in the near future
which correspond to minor phases layout. The damage exposed by Stylo
only corresponds to the major layout phses. In the future, both phases
will likely be managed by Servo itself and implementors will need to
provide their own damage system entirely.
Testing: This shouldn't change behavior and thus is covered by existing
tests.
Stylo PR: https://github.com/servo/stylo/pull/207
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
