egui/emigui/src/font.rs

use std::{collections::BTreeMap, sync::Arc};

use parking_lot::Mutex;
use rusttype::{point, Scale};

use crate::{
    math::{vec2, Vec2},
    texture_atlas::TextureAtlas,
};

/// A typeset piece of text on a single line.
#[derive(Clone, Debug)]
pub struct Line {
    /// The start of each character, probably starting at zero.
    /// The last element is the end of the last character.
    /// x_offsets.len() == text.chars().count() + 1
    /// This is never empty.
    /// Unit: points.
    pub x_offsets: Vec<f32>,

    /// Top y offset of this line. 0.0 for the first line, n * line_spacing for the rest.
    /// Unit: points.
    pub y_offset: f32,
}

impl Line {
    pub fn sanity_check(&self) {
        assert!(!self.x_offsets.is_empty());
    }

    pub fn char_count(&self) -> usize {
        assert!(!self.x_offsets.is_empty());
        self.x_offsets.len() - 1
    }

    pub fn min_x(&self) -> f32 {
        *self.x_offsets.first().unwrap()
    }

    pub fn max_x(&self) -> f32 {
        *self.x_offsets.last().unwrap()
    }
}

/// A collection of text locked into place.
#[derive(Clone, Debug, Default)]
pub struct Galley {
    /// The full text
    pub text: String,

    /// Lines of text, from top to bottom.
    /// The number of chars in all lines sum up to text.chars().count()
    pub lines: Vec<Line>,

    // We need size here to keep track of extra newline at the end. Hacky. Should fix.
    // Newlines should probably be part of the start of the line?
    pub size: Vec2,
}

impl Galley {
    pub fn sanity_check(&self) {
        let mut char_count = 0;
        for line in &self.lines {
            line.sanity_check();
            char_count += line.char_count();
        }
        assert_eq!(char_count, self.text.chars().count());
    }

    /// If given a char index after the first line, the end of the last character is returned instead.
    /// Returns a Vec2 rather than a Pos2 as this is an offset into the galley. *shrug*
    pub fn char_start_pos(&self, char_idx: usize) -> Vec2 {
        let mut char_count = 0;
        for line in &self.lines {
            let line_char_count = line.char_count();
            if char_count <= char_idx && char_idx < char_count + line_char_count {
                let line_char_offset = char_idx - char_count;
                return vec2(line.x_offsets[line_char_offset], line.y_offset);
            }
            char_count += line_char_count;
        }

        if let Some(last) = self.lines.last() {
            if self.text.ends_with('\n') {
                // The position of the next character will be here:
                vec2(0.0, 0.5 * (self.size.y + last.y_offset)) // TODO: fix this hack
            } else {
                vec2(last.max_x(), last.y_offset)
            }
        } else {
            // Empty galley
            vec2(0.0, 0.0)
        }
    }
}

// ----------------------------------------------------------------------------

// const REPLACEMENT_CHAR: char = '\u{25A1}'; // □ white square Replaces a missing or unsupported Unicode character.
// const REPLACEMENT_CHAR: char = '\u{FFFD}'; // <20> REPLACEMENT CHARACTER
const REPLACEMENT_CHAR: char = '?';

#[derive(Clone, Copy, Debug)]
pub struct UvRect {
    /// X/Y offset for nice rendering (unit: points).
    pub offset: Vec2,
    pub size: Vec2,

    /// Top left corner UV in texture.
    pub min: (u16, u16),

    /// Bottom right corner (exclusive).
    pub max: (u16, u16),
}

#[derive(Clone, Copy, Debug)]
pub struct GlyphInfo {
    id: rusttype::GlyphId,

    /// Unit: points.
    pub advance_width: f32,

    /// Texture coordinates. None for space.
    pub uv_rect: Option<UvRect>,
}

/// The interface uses points as the unit for everything.
#[derive(Clone)]
pub struct Font {
    font: rusttype::Font<'static>,
    /// Maximum character height
    scale_in_pixels: f32,
    pixels_per_point: f32,
    glyph_infos: BTreeMap<char, GlyphInfo>,
    atlas: Arc<Mutex<TextureAtlas>>,
}

impl Font {
    pub fn new(
        atlas: Arc<Mutex<TextureAtlas>>,
        font_data: &'static [u8],
        scale_in_points: f32,
        pixels_per_point: f32,
    ) -> Font {
        let font = rusttype::Font::try_from_bytes(font_data).expect("Error constructing Font");
        let scale_in_pixels = pixels_per_point * scale_in_points;

        let mut font = Font {
            font,
            scale_in_pixels,
            pixels_per_point,
            glyph_infos: Default::default(),
            atlas,
        };

        /// Printable ASCII characters [32, 126], which excludes control codes.
        const FIRST_ASCII: usize = 32; // 32 == space
        const LAST_ASCII: usize = 126;
        for c in (FIRST_ASCII..=LAST_ASCII).map(|c| c as u8 as char) {
            font.add_char(c);
        }
        font.add_char(REPLACEMENT_CHAR);

        font
    }

    pub fn round_to_pixel(&self, point: f32) -> f32 {
        (point * self.pixels_per_point).round() / self.pixels_per_point
    }

    /// Height of one line of text. In points
    /// TODO: rename height ?
    pub fn line_spacing(&self) -> f32 {
        self.scale_in_pixels / self.pixels_per_point
    }
    pub fn height(&self) -> f32 {
        self.scale_in_pixels / self.pixels_per_point
    }

    pub fn uv_rect(&self, c: char) -> Option<UvRect> {
        self.glyph_infos.get(&c).and_then(|gi| gi.uv_rect)
    }

    fn glyph_info_or_none(&self, c: char) -> Option<&GlyphInfo> {
        self.glyph_infos.get(&c)
    }

    fn glyph_info_or_replacemnet(&self, c: char) -> &GlyphInfo {
        self.glyph_info_or_none(c)
            .unwrap_or_else(|| self.glyph_info_or_none(REPLACEMENT_CHAR).unwrap())
    }

    fn add_char(&mut self, c: char) {
        if self.glyph_infos.contains_key(&c) {
            return;
        }

        let glyph = self.font.glyph(c);
        assert_ne!(
            glyph.id().0,
            0,
            "Failed to find a glyph for the character '{}'",
            c
        );
        let glyph = glyph.scaled(Scale::uniform(self.scale_in_pixels));
        let glyph = glyph.positioned(point(0.0, 0.0));

        let uv_rect = if let Some(bb) = glyph.pixel_bounding_box() {
            let glyph_width = bb.width() as usize;
            let glyph_height = bb.height() as usize;
            assert!(glyph_width >= 1);
            assert!(glyph_height >= 1);

            let mut atlas_lock = self.atlas.lock();
            let glyph_pos = atlas_lock.allocate((glyph_width, glyph_height));

            let texture = atlas_lock.texture_mut();
            glyph.draw(|x, y, v| {
                if v > 0.0 {
                    let px = glyph_pos.0 + x as usize;
                    let py = glyph_pos.1 + y as usize;
                    texture[(px, py)] = (v * 255.0).round() as u8;
                }
            });

            let offset_y_in_pixels =
                self.scale_in_pixels as f32 + bb.min.y as f32 - 4.0 * self.pixels_per_point; // TODO: use font.v_metrics
            Some(UvRect {
                offset: vec2(
                    bb.min.x as f32 / self.pixels_per_point,
                    offset_y_in_pixels / self.pixels_per_point,
                ),
                size: vec2(glyph_width as f32, glyph_height as f32) / self.pixels_per_point,
                min: (glyph_pos.0 as u16, glyph_pos.1 as u16),
                max: (
                    (glyph_pos.0 + glyph_width) as u16,
                    (glyph_pos.1 + glyph_height) as u16,
                ),
            })
        } else {
            // No bounding box. Maybe a space?
            None
        };

        let advance_width_in_points =
            glyph.unpositioned().h_metrics().advance_width / self.pixels_per_point;

        self.glyph_infos.insert(
            c,
            GlyphInfo {
                id: glyph.id(),
                advance_width: advance_width_in_points,
                uv_rect,
            },
        );
    }

    /// Typeset the given text onto one line.
    /// Assumes there are no \n in the text.
    /// Return x_offsets, one longer than the number of characters in the text.
    fn layout_single_line_fragment(&self, text: &str) -> Vec<f32> {
        let scale_in_pixels = Scale::uniform(self.scale_in_pixels);

        let mut x_offsets = vec![0.0];
        let mut cursor_x_in_points = 0.0f32;
        let mut last_glyph_id = None;

        for c in text.chars() {
            let glyph = self.glyph_info_or_replacemnet(c);

            if let Some(last_glyph_id) = last_glyph_id {
                cursor_x_in_points +=
                    self.font
                        .pair_kerning(scale_in_pixels, last_glyph_id, glyph.id)
                        / self.pixels_per_point
            }
            cursor_x_in_points += glyph.advance_width;
            cursor_x_in_points = self.round_to_pixel(cursor_x_in_points);
            last_glyph_id = Some(glyph.id);

            x_offsets.push(cursor_x_in_points);
        }

        x_offsets
    }

    /// Typeset the given text onto one line.
    /// Assumes there are no \n in the text.
    /// Always returns exactly one frament.
    pub fn layout_single_line(&self, text: &str) -> Galley {
        let x_offsets = self.layout_single_line_fragment(text);
        let line = Line {
            x_offsets,
            y_offset: 0.0,
        };
        let width = line.max_x();
        let size = vec2(width, self.height());
        let galley = Galley {
            text: text.to_owned(),
            lines: vec![line],
            size,
        };
        galley.sanity_check();
        galley
    }

    /// A paragraph is text with no line break character in it.
    /// The text will be linebreaked by the given `max_width_in_points`.
    pub fn layout_paragraph_max_width(&self, text: &str, max_width_in_points: f32) -> Vec<Line> {
        let full_x_offsets = self.layout_single_line_fragment(text);

        let mut line_start_x = full_x_offsets[0];
        assert_eq!(line_start_x, 0.0);
        let mut cursor_y = 0.0;
        let mut line_start_idx = 0;

        // start index of the last space. A candidate for a new line.
        let mut last_space = None;

        let mut out_lines = vec![];

        for (i, (x, chr)) in full_x_offsets.iter().skip(1).zip(text.chars()).enumerate() {
            let line_width = x - line_start_x;

            if line_width > max_width_in_points {
                if let Some(last_space_idx) = last_space {
                    let include_trailing_space = true;
                    let line = if include_trailing_space {
                        Line {
                            x_offsets: full_x_offsets[line_start_idx..=last_space_idx + 1]
                                .iter()
                                .map(|x| x - line_start_x)
                                .collect(),
                            y_offset: cursor_y,
                        }
                    } else {
                        Line {
                            x_offsets: full_x_offsets[line_start_idx..=last_space_idx]
                                .iter()
                                .map(|x| x - line_start_x)
                                .collect(),
                            y_offset: cursor_y,
                        }
                    };
                    line.sanity_check();
                    out_lines.push(line);

                    line_start_idx = last_space_idx + 1;
                    line_start_x = full_x_offsets[line_start_idx];
                    last_space = None;
                    cursor_y += self.line_spacing();
                    cursor_y = self.round_to_pixel(cursor_y);
                }
            }

            const NON_BREAKING_SPACE: char = '\u{A0}';
            if chr.is_whitespace() && chr != NON_BREAKING_SPACE {
                last_space = Some(i);
            }
        }

        if line_start_idx + 1 < full_x_offsets.len() {
            let line = Line {
                x_offsets: full_x_offsets[line_start_idx..]
                    .iter()
                    .map(|x| x - line_start_x)
                    .collect(),
                y_offset: cursor_y,
            };
            line.sanity_check();
            out_lines.push(line);
        }

        out_lines
    }

    pub fn layout_multiline(&self, text: &str, max_width_in_points: f32) -> Galley {
        let line_spacing = self.line_spacing();
        let mut cursor_y = 0.0;
        let mut lines = Vec::new();

        let mut paragraph_start = 0;

        while paragraph_start < text.len() {
            let next_newline = text[paragraph_start..].find('\n');
            let paragraph_end = next_newline
                .map(|newline| paragraph_start + newline + 1)
                .unwrap_or_else(|| text.len());

            assert!(paragraph_start < paragraph_end);
            let paragraph_text = &text[paragraph_start..paragraph_end];
            let mut paragraph_lines =
                self.layout_paragraph_max_width(paragraph_text, max_width_in_points);
            assert!(!paragraph_lines.is_empty());

            let paragraph_height = paragraph_lines.last().unwrap().y_offset + line_spacing;
            for line in &mut paragraph_lines {
                line.y_offset += cursor_y;
            }
            lines.append(&mut paragraph_lines);
            cursor_y += paragraph_height; // TODO: add extra spacing between paragraphs

            paragraph_start = paragraph_end;
        }

        if text.ends_with('\n') {
            cursor_y += line_spacing;
        }

        let mut widest_line = 0.0;
        for line in &lines {
            widest_line = line.max_x().max(widest_line);
        }

        let galley = Galley {
            text: text.to_owned(),
            lines,
            size: vec2(widest_line, cursor_y),
        };
        galley.sanity_check();
        galley
    }
}