text_layout

text-layout

text-layout provides algorithms for laying out text prior to rendering.

Features

• no_std support for constrained environments

Usage

Laying out a paragraph for display in a terminal:

fn layout_paragraph<'a, P: ParagraphLayout>(
    paragraph: &'a str,
    layout: &P,
    max_width: usize,
) -> Vec<&'a str> {
    // Process the paragraph into its items.
    let mut items = Vec::new();
    for c in paragraph.chars() {
        items.push(if c.is_whitespace() && items.len() != 0 {
            Item::Glue {
                width: 1.0,
                stretch: 1.0,
                shrink: 0.0,
                data: (),
            }
        } else {
            Item::Box {
                width: 1.0,
                data: (),
            }
        });
    }
    items.push(Item::Glue {
        width: 0.0,
        stretch: 100000.0,
        shrink: 0.0,
        data: (),
    });
    items.push(Item::Penalty {
        width: 0.0,
        cost: f32::NEG_INFINITY,
        flagged: true,
        data: (),
    });

    // Calculate the paragraph's breaks.
    let breaks = layout.layout_paragraph(&items, max_width as f32);

    // Render the laid-out paragraph using the break positions.
    let mut cursor = 0;
    let mut lines = Vec::new();
    let mut start = 0;
    for (i, _) in paragraph.chars().enumerate() {
        if i == breaks[cursor].break_at {
            lines.push(&paragraph[start..i]);
            start = i + 1;
            cursor += 1;
        }
    }
    lines.push(&paragraph[start..]);
    lines
}

fn layout_text() -> Result<String, fmt::Error> {
    let text = "  Far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy lies a small unregarded yellow sun. Orbiting this at a distance of roughly ninety-two million miles is an utterly insignificant little blue-green planet whose ape-descended life forms are so amazingly primitive that they still think digital watches are a pretty neat idea.";
    let knuth_plass = KnuthPlass::new().with_threshold(f32::INFINITY);
    let lines = layout_paragraph(&text, &knuth_plass, 80);
    let mut result = String::new();
    writeln!(&mut result, "┏{}┓", "━".repeat(80))?;
    for l in lines {
        let pad = 80 - l.chars().count();
        writeln!(&mut result, "┃{}{}┃", l, " ".repeat(pad))?;
    }
    writeln!(&mut result, "┗{}┛", "━".repeat(80))?;
    Ok(result)
}

fn main() -> Result<(), fmt::Error> {
    print!("{}", layout_text()?);
    Ok(())
}

This prints:

┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃  Far out in the uncharted backwaters of the unfashionable end of the western   ┃
┃spiral arm of the Galaxy lies a small unregarded yellow sun. Orbiting this at a ┃
┃distance of roughly ninety-two million miles is an utterly insignificant little ┃
┃blue-green planet whose ape-descended life forms are so amazingly primitive that┃
┃they still think digital watches are a pretty neat idea.                        ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛