Resolved style is a spec concept that refers to the weird mix of
computed style and used style reflected by getComputedStyle().
The purpose of this class is to produce the *computed* style for a given
element, so let's call it StyleComputer.
Once we've performed the cascade on a set of values for an element,
we should have enough information to resolve/absolutize some lengths.
Basically, any CSS length that isn't "auto" or a percentage can be
turned into an absolute length (in pixels) as long as we have the
following information:
- The viewport rect
- The parent element's font
- The document element's font
- The element's own font
To ensure that we can absolutize lengths relative to the element's own
font, we now do a separate first pass where font-related properties are
defaulted (in the cascade spec sense of the word) and become usable.
There's a lot more work to do here, but this should open up a lot of
simplification in layout code, since it will no longer need to care
about relative lengths. Layout still needs to resolve percentages, since
we can't do that for some properties until the containing block
dimensions are known.
The 'C' in "CSS" is for Cascade, so let's actually implement the cascade
in LibWeb. :^)
StyleResolver::resolve_style() now begins by collecting all the matching
CSS rules for the given DOM::Element. Rules are then processed in the
spec's cascade order (instead of in the order we encounter them.)
With this, "!important" is now honored on CSS properties.
After performing the cascade, we do another pass of what the spec calls
"defaulting" where we resolve "inherit" and "initial" values.
I've left a FIXME about supporting correct "initial" values for every
property, since we're currently lacking some coverage there.
Note that this mechanism now resolves every known CSS property. This is
*not* space-efficient and we'll eventually need to come up with some
strategies to reduce memory usage around this. However, this will do
fine until we have more of the engine working correctly. :^)
We already include the inheritance for each property in Properties.json,
so made sense to use that instead of a list in StyleResolver.
Added `inherited: true` to a couple of properties to match the previous
code's behavior. One of those had a FIXME which I've moved to the JSON
file, which is hacky, but it works.
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 *
