After speaking with fantasai at CSSWG about this, it turns out I had
misunderstood intrinsic heights. I originally believed all intrinsic
sizes had to be computed with no influence from the surrounding context.
As it turns out, intrinsic heights *are* influenced by the available
width, since it's needed to determine where lines break.
The APIs for calculating min-content and max-content heights now take
the available width as inputs. This instantly improves layout in many
cases where we'd previously make things way too wide.
This is a big and messy change, and here's the gist:
- AvaliableSpace is now 2x AvailableSize (width and height)
- Layout algorithms are redesigned around the idea of available space
- When doing layout across nested formatting contexts, the parent
context tells the child context how much space is available for the
child's root box in both axes.
- "Available space" replaces "containing block width" in most places.
- The width and height in a box's UsedValues are considered to be
definite after they're assigned to. Marking something as having
definite size is no longer a separate step,
This probably introduces various regressions, but the big win here is
that our layout system now works with available space, just like the
specs are written. Fixing issues will be much easier going forward,
since you don't need to do nearly as much conversion from "spec logic"
to "LibWeb logic" as you previously did.
I couldn't find anything in the specs about this, but GMail uses
empty generated boxes (`::before` and `::after` with `content: ""`)
inside a flexbox container in order to vertically center things.
The flexbox spec tells us to not generate flex items for empty
*anonymous* boxes, so we continue not doing that, but generated boxes
(any pseudo-element box) now always produce a flex item. This probably
isn't perfect either, and we'll have to revisit it for stuff like
`::first-letter`.
Instead of formatting contexts flailing around to figure out from the
"inside" how much space is available on the "outside", we should
provide the amount of available space in both axes as an input to run().
This basically means that when something creates a nested formatting
context, the parent context is responsible for telling the nested context
how much space is available for layout. This information is provided
immediately when invoking run().
Note that this commit doesn't pass accurate values in all cases yet.
This first step just makes it build, and passes available values in some
cases where getting them was trivial.
This patch changes the *computed* representation of the following CSS
properties to use CSS::Size:
- width, min-width, max-width
- height, min-height, max-height
A few things had to change in order for things to keep working,
but I tried to keep the diff to a minimum.
The main trouble was that `min-width` and `max-width` can't actually be
`auto`, but they *can* be `none`. We previously treated `auto` as a
valid value (and it behaved mostly like `none`).
This ends up having a big impact on performance, as we now correctly
treat a used flex-basis of `content` as `max-content` which means
we can use cacheable intrinsic sizes for flex items in the majority
of cases.
This function should return the automatic height of the formatting
context's root box.
Until now, we've been relying on some magical handshakes between parent
and child context, when negotiating the height of child context root
boxes. This is a step towards something more reasonable.
The flex line cross size includes the margin boxes of items, so when
we're taking the flex line's cross size to use as an item cross size,
we have to subtract the margin, border padding from both sides.
Previous we only subtracted the cross margins, which led to oversized
items in some cases.
This remained undetected for a long time as HeaderCheck is disabled by
default. This commit makes the following file compile again:
// file: compile_me.cpp
#include <LibWeb/CSS/GridTrackSize.h>
// That's it, this was enough to cause a compilation error.
This is rather subtle and points to our architecture around definite
sizes not being exactly right, but...
At some points during flexbox layout, the spec tells us that the sizes
of certain flex items are considered definite from this point on.
We implement this by marking each item's associated UsedValues as
"has-definite-width/height".
However, this breaks code that tries to resolve computed "auto" sizes
by taking the corresponding size from the containing block. The end
result was that the 1st sizing pass in flexbox would find the right size
for an "auto" sized item, but the 2nd pass would override the correct
size with the containing block's content size in that axis instead.
To work around the issue, FFC now remembers when it "definitizes" an
item, and future attempts to resolve an "auto" computed size for that
value will bypass the computed-auto-is-resolved-against-containing-block
step of the algorithm. It's not perfect, and we'll need to think more
about how to really represent these intermediate states relating to
box sizes being definite..
By asking if the value *contains* a percentage rather than whether it
*is* one, we cover many more cases where e.g `width: calc(100% - 10px)`
should be "treated as auto" etc.
This is a basic attempt at trying to handle parent container case
justify-content: flex-end.
Test-scenario:
Head to https://ryanwatkins.me and note that now the header nav is on
the right as opposed to the left in-line with how Chrome/Firefox would
respectively handle it also, i.e. 'flex-end'
Implementation:
Move cursor to the end and render in reverse backwards shifting the
cursor leftwards.
Percentage sizes of flex items are relative to the flex container, but
even when the flex container is automatically sized, we still have to
support them.
To make this work, we first do a pass where percentage sizes are ignored
(treated as "auto", basically) in order to get a "reference" value.
Then we do a second pass where percentages can be resolved against this
reference value.
We were neglecting to clamp flex items when calculating the intrinsic
main size of the flex container. This was covered by a FIXME, which we
can now remove. :^)
We had an older incomplete implementation of flex container max-content
sizing that we used for unconstrained main size determination.
This patch replaces the old implementation with a call to the new
max-content sizing code.
Note that this isn't a complete implementation of flex container sizing
still, but at least we've deduplicated some code.
The CSS-FLEXBOX-1 spec gives us two situations in which flex item cross
sizes should be considered definite. Both of them happen *during* flex
layout, which is super finicky but it is what it is.
Previously, we considered all LengthPercentage values for used flex
basis to be definite. This is not accurate, as percentages should only
be considered definite if the reference value they resolve against is
a definite size.
Fix this by checking the flex container's main definite size flag.
There's no need to override the sizes before calculating the cross size.
Besides, by the time we're calculating the hypothetical cross size of
flex items, we may already have established a definite main size anyway,
so overriding it would be wrong.
This state is less static than we originally assumed, and there are
special formatting context-specific rules that say certain sizes are
definite in special circumstances.
To be able to support this, we move the has-definite-size flags from
the layout node to the UsedValues struct instead.
If we wait until after the parent context has laid out the flex
container, abspos children are able to use the final results of the
parent sizing the flex container.
This makes `height:auto` work on abspos children of a flex container.
`min-width: auto` and `min-height: auto` have special behavior on flex
items. We already handled it in many cases but there were two places
where it was incorrectly treated as 0. This fixes that.
This was a leftover from when ComputedValues stored sizes in Optionals.
Now that we've gotten rid of the "undefined" state, there's no need for
this helper, we can just access the size values directly.
