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//! Layouting of text into boxes.
use toddle::query::{FontQuery, SharedFontLoader};
use toddle::tables::{Header, CharMap, HorizontalMetrics};
use crate::doc::LayoutAction;
use crate::size::{Size, Size2D};
use super::*;
/// The context for text layouting.
#[derive(Copy, Clone)]
pub struct TextContext<'a, 'p> {
/// Loads fonts matching queries.
pub loader: &'a SharedFontLoader<'p>,
/// Base style to set text with.
pub style: &'a TextStyle,
}
/// Layout one piece of text without any breaks as one continous box.
pub fn layout(text: &str, ctx: TextContext) -> LayoutResult<BoxLayout> {
let mut loader = ctx.loader.borrow_mut();
let mut actions = Vec::new();
let mut active_font = std::usize::MAX;
let mut buffer = String::new();
let mut width = Size::zero();
// Walk the characters.
for character in text.chars() {
// Retrieve the best font for this character.
let mut font = None;
let mut classes = ctx.style.classes.clone();
for class in &ctx.style.fallback {
classes.push(class.clone());
font = loader.get(FontQuery {
chars: &[character],
classes: &classes,
});
if font.is_some() {
break;
}
classes.pop();
}
let (font, index) = match font {
Some(f) => f,
None => return Err(LayoutError::NoSuitableFont(character)),
};
// Create a conversion function between font units and sizes.
let font_unit_ratio = 1.0 / (font.read_table::<Header>()?.units_per_em as f32);
let font_unit_to_size = |x| Size::pt(font_unit_ratio * x);
// Add the char width to the total box width.
let glyph = font.read_table::<CharMap>()?
.get(character)
.expect("layout text: font should have char");
let glyph_width = font_unit_to_size(
font.read_table::<HorizontalMetrics>()?
.get(glyph)
.expect("layout text: font should have glyph")
.advance_width as f32
);
let char_width = glyph_width * ctx.style.font_size;
width += char_width;
// Change the font if necessary.
if active_font != index {
if !buffer.is_empty() {
actions.push(LayoutAction::WriteText(buffer));
buffer = String::new();
}
actions.push(LayoutAction::SetFont(index, ctx.style.font_size));
active_font = index;
}
buffer.push(character);
}
// Write the remaining characters.
if !buffer.is_empty() {
actions.push(LayoutAction::WriteText(buffer));
}
Ok(BoxLayout {
dimensions: Size2D::new(width, Size::pt(ctx.style.font_size)),
actions,
})
}
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