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//! Core typesetting engine.
use crate::syntax::{SyntaxTree, Node};
use crate::doc::{Document, Page, Text, TextCommand};
use crate::font::{Font, FontFamily, FontConfig, FontError};
use crate::Context;
mod size;
pub use size::Size;
/// The core typesetting engine, transforming an abstract syntax tree into a document.
pub(crate) struct Engine<'a> {
// Immutable
tree: &'a SyntaxTree<'a>,
ctx: &'a Context<'a>,
// Mutable
fonts: Vec<Font>,
active_font: usize,
text_commands: Vec<TextCommand>,
current_line: String,
current_width: Size,
}
impl<'a> Engine<'a> {
/// Create a new generator from a syntax tree.
pub fn new(tree: &'a SyntaxTree<'a>, context: &'a Context<'a>) -> Engine<'a> {
Engine {
tree,
ctx: context,
fonts: Vec::new(),
active_font: 0,
text_commands: Vec::new(),
current_line: String::new(),
current_width: Size::zero(),
}
}
/// Generate the abstract document.
pub fn typeset(mut self) -> TypeResult<Document> {
// Load font defined by style
let mut font = None;
let config = FontConfig::new(self.ctx.style.font_families.clone());
for provider in &self.ctx.font_providers {
if let Some(mut source) = provider.provide(&config) {
let mut program = Vec::new();
source.read_to_end(&mut program)?;
font = Some(Font::new(program)?);
break;
}
}
let font = match font {
Some(font) => font,
None => return Err(TypesetError::MissingFont),
};
self.fonts.push(font);
self.active_font = 0;
// Move cursor to top-left position
self.text_commands.push(TextCommand::Move(
self.ctx.style.margin_left,
self.ctx.style.height - self.ctx.style.margin_top
));
// Set the current font
self.text_commands.push(TextCommand::SetFont(0, self.ctx.style.font_size));
// Iterate through the documents nodes.
for node in &self.tree.nodes {
match node {
Node::Word(word) => self.write_word(word),
Node::Space => self.write_space(),
Node::Newline => (),
Node::ToggleItalics | Node::ToggleBold | Node::ToggleMath => unimplemented!(),
Node::Func(_) => unimplemented!(),
}
}
// Create a page from the contents.
let page = Page {
width: self.ctx.style.width,
height: self.ctx.style.height,
text: vec![Text {
commands: self.text_commands,
}],
};
Ok(Document {
pages: vec![page],
fonts: self.fonts,
})
}
fn write_word(&mut self, word: &str) {
let font = &self.fonts[self.active_font];
let width = self.width(word);
if self.would_overflow(width) {
let vertical_move = - self.ctx.style.font_size
* self.ctx.style.line_spacing
* font.metrics.ascender;
self.text_commands.push(TextCommand::Move(Size::zero(), vertical_move));
self.current_line.clear();
self.current_width = Size::zero();
}
self.text_commands.push(TextCommand::Text(word.to_owned()));
self.current_line.push_str(word);
self.current_width += width;
}
fn write_space(&mut self) {
let space_width = self.width(" ");
if !self.would_overflow(space_width) && !self.current_line.is_empty() {
self.text_commands.push(TextCommand::Text(" ".to_owned()));
self.current_line.push_str(" ");
self.current_width += space_width;
}
}
fn width(&self, word: &str) -> Size {
let font = &self.fonts[self.active_font];
word.chars()
.map(|c| font.widths[font.map(c) as usize] * self.ctx.style.font_size)
.sum()
}
fn would_overflow(&self, width: Size) -> bool {
let max_width = self.ctx.style.width
- self.ctx.style.margin_left
- self.ctx.style.margin_right;
self.current_width + width > max_width
}
}
/// Default styles for a document.
#[derive(Debug, Clone, PartialEq)]
pub struct Style {
/// The width of the paper.
pub width: Size,
/// The height of the paper.
pub height: Size,
/// The left margin of the paper.
pub margin_left: Size,
/// The top margin of the paper.
pub margin_top: Size,
/// The right margin of the paper.
pub margin_right: Size,
/// The bottom margin of the paper.
pub margin_bottom: Size,
/// A fallback list of font families to use.
pub font_families: Vec<FontFamily>,
/// The font size.
pub font_size: f32,
/// The line spacing (as a multiple of the font size).
pub line_spacing: f32,
}
impl Default for Style {
fn default() -> Style {
use FontFamily::*;
Style {
// A4 paper.
width: Size::from_mm(210.0),
height: Size::from_mm(297.0),
// Margins. A bit more on top and bottom.
margin_left: Size::from_cm(2.5),
margin_top: Size::from_cm(3.0),
margin_right: Size::from_cm(2.5),
margin_bottom: Size::from_cm(3.0),
// Default font family, font size and line spacing.
font_families: vec![SansSerif, Serif, Monospace],
font_size: 12.0,
line_spacing: 1.25,
}
}
}
/// The error type for typesetting.
pub enum TypesetError {
/// There was no suitable font.
MissingFont,
/// An error occured while gathering font data.
Font(FontError),
}
error_type! {
err: TypesetError,
res: TypeResult,
show: f => match err {
TypesetError::MissingFont => write!(f, "missing font"),
TypesetError::Font(err) => write!(f, "font error: {}", err),
},
source: match err {
TypesetError::Font(err) => Some(err),
_ => None,
},
from: (std::io::Error, TypesetError::Font(FontError::Io(err))),
from: (FontError, TypesetError::Font(err)),
}
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