This is a step towards fixing #17267. To fix that, we need to be able to
try various different fallback fonts in turn, which would become
unweildy with the prior eager-loading strategy.
Prior to this change, FontGroup loaded up all Font instances, including
the fallback font, before any of them were checked for the presence of
the glyphs we're trying to render.
So for the following CSS:
font-family: Helvetica, Arial;
The FontGroup would contain a Font instance for Helvetica, and a Font
instance for Arial, and a Font instance for the fallback font.
It may be that Helvetica contains glyphs for every character in the
document, and therefore Arial and the fallback font are not needed at
all.
This change makes the strategy lazy, so that we'll only create a Font
for Arial if we cannot find a glyph within Helvetica. I've also
substantially refactored the existing code in the process and added
some documentation along the way.
First, we define computed::CSSPixelLength which contains a CSSFloat, a
pixel value, and then we replace computed::Length with CSSPixelLength.
Therefore, the |ComputedValue| of NoCalcLength, AbsoluteLength,
FontRelativeLength, ViewportPercentageLength, CharacterWidth, and
PhysicalLength is CSSPixelLength.
Besides, we drop NonNegativeAu, and replace computed::NonNegativeLength
with NonNegative<computed::Length>. (i.e. NonNegative<CSSPixelLength>)
The alias is left there temporarilly and will be removed completely in a later commit where
also components/style/gecko/generated/structs_{debug|release}.rs are re-generated (they still
use the old alias).
Remove incomplete and buggy support for text-orientation in Servo.
Make the property values align with Gecko and the latest draft of CSS
Writing Modes Level 3.
This was making us fall in a loop where the start split was empty, but we didn't
ignore it because the current fragment had this flag, but then we treated it
differently depending on the white_space property.
Not totally sure this is the proper fix, but it makes sense to me. In case it
is:
Fixes#12369.
Replace character indices with UTF-8 byte offsets throughout the code dealing
with text shaping and breaking. This eliminates a lot of complexity when
converting from one to the other, and interoperates better with the rest of
the Rust ecosystem.
Empty fragments may need to be layed out to draw borders, padding/background,
and insertion points. (Fragments that consist of discardable whitespace and
control characters, on the other hand, can still be discarded.)
This ends up preserving some useless empty fragments. It's possible we could
avoid this by storing some sort of flag on "important" empty fragments, so we
can discard the rest.
This fixes two problems that could cause scanned text fragments to end up with
incorrect LAST_FRAGMENT_OF_ELEMENT or FIRST_FRAGMENT_OF_ELEMENT flags:
1. If a single unscanned fragment was split into multiple scanned fragments,
then all of them would inherit its flags. We need to clear these flags,
except for the first and last scanned fragment.
2. When an unscanned fragment generated zero scanned fragments, we correctly
called `meld_with_next_inline_fragment` to transfer LAST_FRAGMENT flags to
the preceding fragment, but we didn't do anything to transfer
FIRST_FRAGMENT flags to the following fragment. We can fix this by calling
`meld_with_prev_inline_fragment` on the following fragment.
Before this fix, if a TextRun containing an insertion point was split into
multiple ScannedText fragments, text layout would draw an insertion point
inside of each of the fragments. This patch records the insertion point
position at most once per TextRun, and copies it only into the appropriate
ScannedText fragment.
Reduce size of layout::fragment::Fragment struct
This reduces the size of the SpecificFragmentInfo enum from 48 to 24.
r? @pcwalton
<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="35" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/10255)
<!-- Reviewable:end -->
This is the first part of #10185. More to follow. I have built this locally with both servo and geckolib without errors; let's see if it succeeds on all platforms as well.
