Given a selector like `.foo .bar #baz`, we know that elements with
the class names `foo` and `bar` must be present in the ancestor chain of
the candidate element, or the selector cannot match.
By keeping track of the current ancestor chain during style computation,
and which strings are used in tag names and attribute names, we can do
a quick check before evaluating the selector itself, to see if all the
required ancestors are present.
The way this works:
1. CSS::Selector now has a cache of up to 8 strings that must be present
in the ancestor chain of a matching element. Note that we actually
store string *hashes*, not the strings themselves.
2. When Document performs a recursive style update, we now push and pop
elements to the ancestor chain stack as they are entered and exited.
3. When entering/exiting an ancestor, StyleComputer collects all the
relevant string hashes from that ancestor element and updates a
counting bloom filter.
4. Before evaluating a selector, we first check if any of the hashes
required by the selector are definitely missing from the ancestor
filter. If so, it cannot be a match, and we reject it immediately.
5. Otherwise, we carry on and evaluate the selector as usual.
I originally tried doing this with a HashMap, but we ended up losing
a huge chunk of the time saved to HashMap instead. As it turns out,
a simple counting bloom filter is way better at handling this.
The cost is a flat 8KB per StyleComputer, and since it's a bloom filter,
false positives are a thing.
This is extremely efficient, and allows us to quickly reject the
majority of selectors on many huge websites.
Some example rejection rates:
- https://amazon.com: 77%
- https://github.com/SerenityOS/serenity: 61%
- https://nytimes.com: 57%
- https://store.steampowered.com: 55%
- https://en.wikipedia.org: 45%
- https://youtube.com: 32%
- https://shopify.com: 25%
This also yields a chunky 37% speedup on StyleBench. :^)
When iterating through a @keyframes rule, it isn't possible to resolve
unresolved style properties since there are no elements. This change
allows those properties to simply pass through this helper function.
These will need to store unresolved styles as well, since they may be
built during parsing of a @keyframes rule. In that case there is no
target element or pseudo-element, and thus the value cannot be resolved.
If we determine that a selector is simple enough, we now run it using a
special matching loop that traverses up the DOM ancestor chain without
recursion.
The criteria for this fast path are:
- All combinators involved must be either descendant or child.
- Only tag name, class, ID and attribute selectors allowed.
It's definitely possible to increase the coverage of this fast path,
but this first version already provides a substantial reduction in time
spent evaluating selectors.
48% of the selectors evaluated when loading our GitHub repo are now
using this fast path.
18% speed-up on the "Descendant and child combinators" subtest of
StyleBench. :^)
This URL library ends up being a relatively fundamental base library of
the system, as LibCore depends on LibURL.
This change has two main benefits:
* Moving AK back more towards being an agnostic library that can
be used between the kernel and userspace. URL has never really fit
that description - and is not used in the kernel.
* URL _should_ depend on LibUnicode, as it needs punnycode support.
However, it's not really possible to do this inside of AK as it can't
depend on any external library. This change brings us a little closer
to being able to do that, but unfortunately we aren't there quite
yet, as the code generators depend on LibCore.
Instead of wrapping every entry in Optional, use the null state of the
style pointer for the same purpose.
This shrinks StyleProperties by 1752 bytes per instance.
This allows us to skip evaluating selectors like "[foo=bar]" for any
element that doesn't have a "foo" attribute.
Note that the bucket is case-insensitively keyed on the attribute name
since case sensitivity is depending on evaluation context. This ensures
we may get some false positives but no false negatives.
Reduces the number of selectors evaluated by 36% when loading our GitHub
repo at https://github.com/SerenityOS/serenity
We already grow the "rules to run" vector before appending to it, so we
can actually use unchecked_append() here and avoid the "needs to grow"
checks every time we append to it.
This takes appending from 3% to <1% when loading our GitHub repo.
Patch up existing style properties instead of using the regular style
invalidation path, which requires rule matching for each element in the
invalidated subtree.
- !important properties: this change introduces a flag used to skip the
update of animated properties overridden by !important.
- inherited animated properties: for now, these are invalidated by
traversing animated element's subtree to propagate the update.
- StyleProperties has a separate array for animated properties that
allows the removal animated properties after animation has ended,
without requiring full style invalidation.
If a selector must match a pseudo element, or must match the root
element, we now cache that information in the MatchingRule struct.
We also introduce separate buckets for these rules, so we can avoid
running them altogether if the current element can't possibly match.
This cuts the number of selectors evaluated by 32% when loading our
GitHub repo page https://github.com/SerenityOS/serenity
We frequently end up matching hundreds or even thousands of rules. By
giving this vector some inline capacity, we avoid a lot of the
repetitive churn from dynamically growing it all the way from 0
capacity.
Now, if an element belongs to a shadow tree, we use only the style
sheets from the corresponding shadow root during style computation,
instead of using all available style sheets as was the case
previously.
The only exception is the user agent style sheets, which are still
taken into account for all elements.
Tests/LibWeb/Layout/input/input-element-with-display-inline.html
is affected because style of document no longer affects shadow tree
of input element, like it is supposed to be.
Co-authored-by: Simon Wanner <simon+git@skyrising.xyz>
Animation::play_state() does not consider the fill state, and thus will
not return "Playing" for a fill-forward animation in the after phase.
It is still valid for paused, as pausing is not affected by the fill
mode.
All of this error propogation came from a single call to
HashMap::try_ensure_capacity! As part of the ongoing effort to ignore
small allocation failures, lets just assert this works. This has the
nice side-effect of propogating out to a few other classes.
The property values here will always be StyleValueLists and not
TransformationStyleValues. The handling of interpolation in this case
gets quite a bit more complex, so let's just remove the dead code for
now and attempt this optimization again in the future if it's needed.
This can be perfectly valid, and depends on the property being animated.
For example, interpolating between the StyleValue "none" (an identifier)
and a TransformationStyleValue is perfectly defined.
In the upcoming commits where we properly handle transformation
interpolation, it actually becomes easier to change this back to custom,
so lets do that since its more correct anyways.
If a DOM::Element has an animation-name property, then in addition to
remembering where it came from, it will also remember the
Animations::Animation object that was created for it. This allows
StyleComputer to cancel that animation if the animation-name property
changes as well as to apply any changes required (for example, if
animation-play-state changes from "running" to "paused", it needs to
call .pause() on the animation).
This also changes transform's animation-type to by-computed-value. It is
far easier to handle since we switch on StyleValue::type(), and it might
be the case that this applies to all custom animated properties and we
don't need "custom" at all, but let's wait until we get to those
properties to make that decision.
This is now handled by Web Animations, so if the animation was ever
running backwards, this logic would re-reverse it so that it played
forwards again.
