mirror of
https://github.com/typst/typst
synced 2025-05-15 01:25:28 +08:00
138 lines
4.3 KiB
Rust
138 lines
4.3 KiB
Rust
use super::*;
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/// A square root.
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///
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/// ```example
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/// $ sqrt(3 - 2 sqrt(2)) = sqrt(2) - 1 $
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/// ```
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#[func(title = "Square Root")]
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pub fn sqrt(
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/// The expression to take the square root of.
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radicand: Content,
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) -> Content {
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RootElem::new(radicand).pack()
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}
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/// A general root.
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///
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/// ```example
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/// $ root(3, x) $
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/// ```
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#[elem(LayoutMath)]
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pub struct RootElem {
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/// Which root of the radicand to take.
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#[positional]
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pub index: Option<Content>,
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/// The expression to take the root of.
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#[required]
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pub radicand: Content,
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}
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impl LayoutMath for RootElem {
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#[tracing::instrument(skip(ctx))]
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fn layout_math(&self, ctx: &mut MathContext) -> SourceResult<()> {
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layout(ctx, self.index(ctx.styles()).as_ref(), &self.radicand(), self.span())
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}
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}
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/// Layout a root.
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///
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/// TeXbook page 443, page 360
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/// See also: https://www.w3.org/TR/mathml-core/#radicals-msqrt-mroot
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fn layout(
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ctx: &mut MathContext,
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index: Option<&Content>,
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radicand: &Content,
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span: Span,
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) -> SourceResult<()> {
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let gap = scaled!(
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ctx,
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text: radical_vertical_gap,
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display: radical_display_style_vertical_gap,
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);
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let thickness = scaled!(ctx, radical_rule_thickness);
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let extra_ascender = scaled!(ctx, radical_extra_ascender);
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let kern_before = scaled!(ctx, radical_kern_before_degree);
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let kern_after = scaled!(ctx, radical_kern_after_degree);
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let raise_factor = percent!(ctx, radical_degree_bottom_raise_percent);
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// Layout radicand.
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ctx.style(ctx.style.with_cramped(true));
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let radicand = ctx.layout_frame(radicand)?;
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ctx.unstyle();
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// Layout root symbol.
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let target = radicand.height() + thickness + gap;
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let sqrt = GlyphFragment::new(ctx, '√', span)
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.stretch_vertical(ctx, target, Abs::zero())
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.frame;
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// Layout the index.
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ctx.style(ctx.style.with_size(MathSize::ScriptScript));
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let index = index.map(|elem| ctx.layout_frame(elem)).transpose()?;
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ctx.unstyle();
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// TeXbook, page 443, item 11
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// Keep original gap, and then distribute any remaining free space
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// equally above and below.
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let gap = gap.max((sqrt.height() - thickness - radicand.height() + gap) / 2.0);
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let sqrt_ascent = radicand.ascent() + gap + thickness;
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let descent = sqrt.height() - sqrt_ascent;
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let inner_ascent = sqrt_ascent + extra_ascender;
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let mut sqrt_offset = Abs::zero();
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let mut shift_up = Abs::zero();
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let mut ascent = inner_ascent;
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if let Some(index) = &index {
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sqrt_offset = kern_before + index.width() + kern_after;
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// The formula below for how much raise the index by comes from
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// the TeXbook, page 360, in the definition of `\root`.
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// However, the `+ index.descent()` part is different from TeX.
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// Without it, descenders can collide with the surd, a rarity
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// in practice, but possible. MS Word also adjusts index positions
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// for descenders.
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shift_up = raise_factor * (inner_ascent - descent) + index.descent();
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ascent.set_max(shift_up + index.ascent());
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}
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let radicand_x = sqrt_offset + sqrt.width();
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let radicand_y = ascent - radicand.ascent();
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let width = radicand_x + radicand.width();
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let size = Size::new(width, ascent + descent);
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// The extra "- thickness" comes from the fact that the sqrt is placed
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// in `push_frame` with respect to its top, not its baseline.
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let sqrt_pos = Point::new(sqrt_offset, radicand_y - gap - thickness);
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let line_pos = Point::new(radicand_x, radicand_y - gap - (thickness / 2.0));
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let radicand_pos = Point::new(radicand_x, radicand_y);
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let mut frame = Frame::soft(size);
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frame.set_baseline(ascent);
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if let Some(index) = index {
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let index_pos = Point::new(kern_before, ascent - index.ascent() - shift_up);
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frame.push_frame(index_pos, index);
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}
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frame.push_frame(sqrt_pos, sqrt);
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frame.push(
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line_pos,
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FrameItem::Shape(
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Geometry::Line(Point::with_x(radicand.width())).stroked(FixedStroke {
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paint: TextElem::fill_in(ctx.styles()),
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thickness,
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..FixedStroke::default()
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}),
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span,
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),
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);
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frame.push_frame(radicand_pos, radicand);
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ctx.push(FrameFragment::new(ctx, frame));
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Ok(())
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}
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