Stacking contexts are sorted after building a tree of them. They are
sorted by z-index first, DOM tree order second.
Sorting was previously *very* slow on pages with many stacking contexts.
That was because the sort() function used Node::is_before() in the
quick_sort comparator to see if one StackingContext was before another.
is_before() does tree traversal and can take quite a long time per call.
This patch avoids all that by letting StackingContext know its index
among all StackingContexts within the same document in tree order.
There's a noticeable snappiness increase on the CSS-FLEXBOX-1 spec page,
for instance. :^)
...and also for hit testing, which is involved in most of them.
Much of this is temporary conversions and other awkwardness, which
should resolve itself as the rest of LibWeb is converted to these new
types. Hopefully. :thousandyakstare:
When mousing over twitter, 17% of time was spent computing stacking
context transform origins. Since this never changes after the stacking
context is created, we can cache it and avoid all that work.
This is mainly so we can easily read that matrix later, but also has the
benefit of only calculating the matrix once, instead of every time we
paint. :^)
Since there is currently no easy way to handle rotations and skews
with LibGfx this only implements translation and scaling by first
constructing a general 4x4 transformation matrix like outlined in
the css-transforms-1 specification. This is then downgraded to a
Gfx::AffineTransform in order to transform the destination rectangle
used with draw_scaled_bitmap()
While rotation would be nice this already looks pretty good :^)
Instead of calling quick_sort() every time a StackingContext child
is added to a parent, we now do a single pass of sorting work after the
full StackingContext tree has been built.
Before this change, the quick_sort() was ~13.5% of the profile while
hovering links on GitHub in the Browser. After the change, it's down to
~0.6%. Pretty good! :^)
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
