This patch also makes Servo not crash when
`generated_containing_block_rect()` is called on a list item (as, for
example, GitHub does), and for good measure I added the fix to other
flows as well.
through display list building.
The old `flow_origin` concept was ill-defined (sometimes the border box
plus the flow origin, sometimes including horizontal margins and
sometimes not, sometimes including relative position and sometimes not),
leading to brittleness and test failures. This commit reworks the logic
to always pass border box origins in during display list building.
Instead of looking at the display tree, have ContentBox(es)Query consult
the flow tree. This allow optimizing away parts of the display tree
later. To do this we need to be more careful about how we send reflow
requests, only querying the flow tree when possible.
Fixes#3790.
matching, and use it for `<input size>` and `<td width>`.
This implements a general framework for legacy presentational attributes
to the DOM and style calculation, so that adding more of them later will
be straightforward.
absolutely-positioned elements declared with `display: inline`.
Although the computed `display` property of elements with `position:
absolute` is `block`, `position: absolute; display: inline` can still
behave differently from `position: absolute; display: block`. This is
because the hypothetical box for `position: absolute` can be at the
position it would have been if it had `display: inline`. CSS 2.1 §
10.3.7 describes this case in a parenthetical:
"The static-position containing block is the containing block of a
hypothetical box that would have been the first box of the element if
its specified 'position' value had been 'static' and its specified
'float' had been 'none'. (Note that due to the rules in section 9.7 this
hypothetical calculation might require also assuming a different
computed value for 'display'.)"
To handle this, I had to change both style computation and layout. For
the former, I added an internal property
`-servo-display-for-hypothetical-box`, which stores the `display` value
supplied by the author, before the computed value is calculated. Flow
construction now uses this value.
As for layout, implementing the proper behavior is tricky because the
position of an inline fragment in the inline direction cannot be
determined until height assignment, which is a parallelism hazard
because in parallel layout widths are computed before heights. However,
in this particular case we can avoid the parallelism hazard because the
inline direction of a hypothetical box only affects the layout if an
absolutely-positioned element is unconstrained in the inline direction.
Therefore, we can just lay out such absolutely-positioned elements with
a bogus inline position and fix it up once the true inline position of
the hypothetical box is computed. The name for this fix-up process is
"late computation of inline position" (and the corresponding fix-up for
the block position is called "late computation of block position").
This improves the header on /r/rust.
