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use typst_library::diag::SourceResult;
use typst_library::foundations::{Packed, StyleChain};
use typst_library::layout::{Em, Frame, Point, Size};
use typst_library::math::{Accent, AccentElem};
use super::{style_cramped, FrameFragment, GlyphFragment, MathContext, MathFragment};
/// How much the accent can be shorter than the base.
const ACCENT_SHORT_FALL: Em = Em::new(0.5);
/// Lays out an [`AccentElem`].
#[typst_macros::time(name = "math.accent", span = elem.span())]
pub fn layout_accent(
elem: &Packed<AccentElem>,
ctx: &mut MathContext,
styles: StyleChain,
) -> SourceResult<()> {
let cramped = style_cramped();
let mut base = ctx.layout_into_fragment(elem.base(), styles.chain(&cramped))?;
// Try to replace a glyph with its dotless variant.
if let MathFragment::Glyph(glyph) = &mut base {
glyph.make_dotless_form(ctx);
}
// Preserve class to preserve automatic spacing.
let base_class = base.class();
let base_attach = base.accent_attach();
let width = elem.size(styles).relative_to(base.width());
let Accent(c) = elem.accent();
let mut glyph = GlyphFragment::new(ctx, styles, *c, elem.span());
// Try to replace accent glyph with flattened variant.
let flattened_base_height = scaled!(ctx, styles, flattened_accent_base_height);
if base.height() > flattened_base_height {
glyph.make_flattened_accent_form(ctx);
}
// Forcing the accent to be at least as large as the base makes it too
// wide in many case.
let short_fall = ACCENT_SHORT_FALL.at(glyph.font_size);
let variant = glyph.stretch_horizontal(ctx, width, short_fall);
let accent = variant.frame;
let accent_attach = variant.accent_attach;
// Descent is negative because the accent's ink bottom is above the
// baseline. Therefore, the default gap is the accent's negated descent
// minus the accent base height. Only if the base is very small, we need
// a larger gap so that the accent doesn't move too low.
let accent_base_height = scaled!(ctx, styles, accent_base_height);
let gap = -accent.descent() - base.height().min(accent_base_height);
let size = Size::new(base.width(), accent.height() + gap + base.height());
let accent_pos = Point::with_x(base_attach - accent_attach);
let base_pos = Point::with_y(accent.height() + gap);
let baseline = base_pos.y + base.ascent();
let base_italics_correction = base.italics_correction();
let base_text_like = base.is_text_like();
let base_ascent = match &base {
MathFragment::Frame(frame) => frame.base_ascent,
_ => base.ascent(),
};
let mut frame = Frame::soft(size);
frame.set_baseline(baseline);
frame.push_frame(accent_pos, accent);
frame.push_frame(base_pos, base.into_frame());
ctx.push(
FrameFragment::new(styles, frame)
.with_class(base_class)
.with_base_ascent(base_ascent)
.with_italics_correction(base_italics_correction)
.with_accent_attach(base_attach)
.with_text_like(base_text_like),
);
Ok(())
}
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