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gfx: Implement letter-spacing per CSS 2.1 § 16.4.

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The ligature disabling code has been manually verified, but I was unable
to reftest it. (The only way I could think of would be to create an
Ahem-like font with a ligature table, but that would be an awful lot of
work.)

Near as I can tell, the method used to apply the spacing (manually
inserting extra advance post-shaping) matches Gecko.
This commit is contained in:
Patrick Walton 2014-12-10 14:00:12 -08:00
parent 758d79fff4
commit 07bc97e3e2
11 changed files with 246 additions and 47 deletions
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22
components/layout/text.rs
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@ -9,7 +9,8 @@
use fragment::{Fragment, ScannedTextFragmentInfo, UnscannedTextFragment};
use inline::InlineFragments;
use gfx::font::{FontMetrics,RunMetrics};
use gfx::font::{FontMetrics, IGNORE_LIGATURES_SHAPING_FLAG, RunMetrics, ShapingFlags};
use gfx::font::{ShapingOptions};
use gfx::font_context::FontContext;
use gfx::text::glyph::CharIndex;
use gfx::text::text_run::TextRun;
@ -105,6 +106,7 @@ impl TextRunScanner {
let fontgroup;
let compression;
let text_transform;
let letter_spacing;
{
let in_fragment = self.clump.front().unwrap();
let font_style = in_fragment.style().get_font_arc();
@ -114,6 +116,7 @@ impl TextRunScanner {
white_space::pre => CompressNone,
};
text_transform = in_fragment.style().get_inheritedtext().text_transform;
letter_spacing = in_fragment.style().get_inheritedtext().letter_spacing;
}
// First, transform/compress text of all the nodes.
@ -150,7 +153,22 @@ impl TextRunScanner {
self.clump = DList::new();
return last_whitespace
}
Arc::new(box TextRun::new(&mut *fontgroup.fonts.get(0).borrow_mut(), run_text))
// Per CSS 2.1 § 16.4, "when the resultant space between two characters is not the same
// as the default space, user agents should not use ligatures." This ensures that, for
// example, `finally` with a wide `letter-spacing` renders as `f i n a l l y` and not
// `fi n a l l y`.
let options = ShapingOptions {
letter_spacing: letter_spacing,
flags: match letter_spacing {
Some(Au(0)) | None => ShapingFlags::empty(),
Some(_) => IGNORE_LIGATURES_SHAPING_FLAG,
},
};
Arc::new(box TextRun::new(&mut *fontgroup.fonts.get(0).borrow_mut(),
run_text,
&options))
};
// Make new fragments with the run and adjusted text indices.