This improves the quality of our font rendering, especially when
animations are involved. Relevant changes:
* Skia fonts have their subpixel flag set, which means that individual
glyphs are rendered at subpixel offsets causing glyph runs as a
whole to look better.
* Fragment offsets are no longer rounded to whole device pixels, and
instead the floating point offset is kept. This allows us to pass
through the floating point baseline position all the way to the Skia
calls, which already expected that to be a float position.
The `scrollable-contains-table.html` ref test needed different table
headings since they would slightly inflate the column size in the test
file, but not the reference.
This is a part of refactoring towards making the paintable tree
independent of the layout tree. Now, instead of transferring text
fragments from the layout tree to the paintable tree during the layout
commit phase, we allocate separate PaintableFragments that contain only
the information necessary for painting. Doing this also allows us to
get rid LineBoxes, as they are used only during layout.
This patch makes a few changes to the way we calculate line-height:
- `line-height: normal` is now resolved using metrics from the used
font (specifically, round(A + D + lineGap)).
- `line-height: calc(...)` is now resolved at style compute time.
- `line-height` values are now absolutized at style compute time.
As a consequence of the above, we no longer need to walk the DOM
ancestor chain looking for line-heights during style computation.
Instead, values are inherited, resolved and absolutized locally.
This is not only much faster, but also makes our line-height metrics
match those of other engines like Gecko and Blink.
This patch just adds the new root paintable and updates the tests
expectations. The next patch will move painting logic from the layout
viewport to the paint viewport.
Using fixed-point saturated arithmetics for CSSPixels allows to avoid
accumulating floating-point errors.
This implementation is not complete yet: currently saturated
arithmetics implemented only for addition. But it is enough to not
regress any of layout tests we have :)
See https://github.com/SerenityOS/serenity/issues/18566
The used width is already a content width, which doesn't include
borders. Border widths should be subtracted from the specified width
instead, since that initially specifies the total width including
borders, for consistent comparison. Also handle table box padding as an
additional fix.
Compute the contributions to a spanning cell width from each cell in the
span. This better handles uneven column widths, since each cell
contribution is proportional with its own width as opposed to the own
width of the first cell in the span.
This better matches the behavior of other browsers and further aligns
with the specification.
The specification isn't explicit about it, but the contribution we
compute should be distributed to all columns, not just the first one.
The first reason for it is symmetry, it doesn't make sense for the
increased width of the spanning column to only affect the first column
in the span.
The second reason is the formula for the cell contribution, which is
weighted by the non-spanning width of the cell relative to the total
width of the columns in the same row. This only covers a fraction of the
gap, in order to fully cover it we have to add it to all columns in the
span. For this to be exactly the case when the columns don't all have
the same width, we'd have to add additional weighting based on the width
ratios, but given that the specification doesn't suggest it at all we'll
leave it out for now.
