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//! Construct bitmap font using FreeType library.
//! Generates raw texture data for the given font and collects information
//! about available font characters to map them into texture.
use std::cmp::max;
use std::iter::{repeat, FromIterator};
use std::collections::{HashMap, HashSet};
use std::char::from_u32;
use ::freetype as ft;
use ::freetype::Error as FreetypeError;
use ::freetype::Face;
#[derive(Debug)]
pub struct BitmapFont {
width: u16,
height: u16,
chars: HashMap<char, BitmapChar>,
image: Vec<u8>,
}
#[derive(Debug)]
pub struct BitmapChar {
// Real glyph's coordinates in pixels.
pub x_offset: i32,
pub y_offset: i32,
pub x_advance: i32,
pub width: i32,
pub height: i32,
// Precalculated scaled positions in texture.
pub tex: [f32; 2],
pub tex_width: f32,
pub tex_height: f32,
// This field is used only while building the texture.
data: Option<Vec<u8>>,
}
/// Represents possible errors which may occur during the font loading.
#[derive(Debug)]
pub enum FontError {
/// No font was specified
NoFont,
/// Character set is empty
EmptyFont,
/// FreeType library error
FreetypeError(FreetypeError),
}
impl From<FreetypeError> for FontError {
fn from(e: FreetypeError) -> FontError { FontError::FreetypeError(e) }
}
pub type FontResult = Result<BitmapFont, FontError>;
impl BitmapFont {
pub fn from_path(path: &str, font_size: u8, chars: Option<&[char]>) -> FontResult {
let library = try!(ft::Library::init());
let face = try!(library.new_face(path, 0));
Self::new(face, font_size, chars)
}
pub fn from_bytes(data: &[u8], font_size: u8, chars: Option<&[char]>) -> FontResult {
let library = try!(ft::Library::init());
let face = try!(library.new_memory_face(data, 0));
Self::new(face, font_size, chars)
}
fn get_all_face_chars<'a>(face: &mut Face<'a>) -> HashSet<char> {
let mut result = HashSet::new();
let mut index = 0;
let face_ptr = face.raw_mut();
unsafe {
let mut code = ft::ffi::FT_Get_First_Char(face_ptr, &mut index);
while index != 0 {
from_u32(code as u32).map(|ch| result.insert(ch));
code = ft::ffi::FT_Get_Next_Char(face_ptr, code, &mut index);
}
}
result
}
// FIXME(Kagami): Profile and optimize this function!
// TODO(Kagami): Limit too huge textures? We should keep it less than
// 8k X 8k in general.
// TODO(Kagami): Add bunch of asserts to check for negative values and
// overflows.
/// Construct new BitMap font using provided parameters (this is general
/// method, called via `from_` helpers).
fn new<'a>(mut face: ft::Face<'a>, font_size: u8, chars: Option<&[char]>) -> FontResult {
let needed_chars = chars
.map(|sl| HashSet::from_iter(sl.iter().cloned()))
.unwrap_or_else(|| Self::get_all_face_chars(&mut face));
if needed_chars.is_empty() {
return Err(FontError::EmptyFont);
}
try!(face.set_pixel_sizes(0, font_size as u32));
// FreeType representation of rendered glyph 'j':
//
// b_left w
// +-----+-----+-----+
// | | | | font_size - bitmap_top()
// +-----+-----+-----+
// | | x | |
// | | | |
// | | x | | bitmap_top()
// | | x | |
// | | x | |
// | | x | |
// +-----+--x--+-----+
// | | x | | rows() - bitmap_top()
// | |x | |
// +-----------+-----+
// advance.x
//
// (Read <http://www.freetype.org/freetype2/docs/glyphs/glyphs-3.html>
// for more details.)
//
// Notes:
// * Width/height of the rendered glyph generally smaller than the the
// specified font size
// * But if we add x/y offsets to the real glyph's dimensions it might
// go beyound that limits (e.g. chars like 'j', 'q')
// * `bottom_left()` may be less than zero for some tight characters
// (too push it to the previous one)
// * Theoretically `bitmap_top()` may be bigger than the `font_size`
//
// For simplicity we use fixed box height to store characters in the
// texture (extended with blank pixels downwards), but width may vary:
//
// width()
// +-----+-------+
// | x | x |
// | | |
// | x | x |
// | x | x | rows()
// | x | x |
// | x | x |
// +-----+ x |
// | | x |
// | +-------+
// | | | ch_box_height - rows()
// +-----+-------+
//
// To construct the optimal texture (i.e. square enought and with box
// height of the highest character) we need to do several passes.
// In first pass we collect information about the chars and store their
// raw bitmap data. It gives us max character height and summary width
// of all characters.
let chars_len = needed_chars.len();
let mut chars_info = HashMap::with_capacity(chars_len);
let mut sum_image_width = 0;
let mut max_ch_width = 0;
let mut ch_box_height = 0;
// debug!("Start building the bitmap (chars: {})", chars_len);
for ch in needed_chars {
try!(face.load_char(ch as usize, ft::face::LoadFlag::RENDER));
let glyph = face.glyph();
let bitmap = glyph.bitmap();
let ch_width = bitmap.width();
let ch_height = bitmap.rows();
let ch_x_offset = glyph.bitmap_left();
let ch_y_offset = font_size as i32 - glyph.bitmap_top();
let ch_x_advance = (glyph.advance().x >> 6) as i32;
let buffer = bitmap.buffer();
let ch_data = Vec::from(buffer);
chars_info.insert(ch, BitmapChar {
x_offset: ch_x_offset,
y_offset: ch_y_offset,
x_advance: ch_x_advance,
width: ch_width,
height: ch_height,
// We'll need to fix that fields later:
tex: [0.0, 0.0],
tex_width: 0.0,
tex_height: 0.0,
data: Some(ch_data),
});
sum_image_width += ch_width;
max_ch_width = max(max_ch_width, ch_width);
ch_box_height = max(ch_box_height, ch_height);
}
// In second pass we map character boxes with varying width onto the
// fixed quad texture image and build the final texture image.
//
// We start with optimist (square) assumption about texture dimensions
// and adjust the image's height and size while filling the rows.
//
// TODO(Kagami): We may try some cool CS algorithm to fit char boxes
// into the quad texture space with the best level of compression.
// Though current level of inefficiency is good enough.
let ideal_image_size = sum_image_width * ch_box_height;
let ideal_image_width = (ideal_image_size as f32).sqrt() as i32;
let image_width = max(max_ch_width, ideal_image_width);
let assumed_size = ideal_image_size as f32 * 1.5;
let assumed_ch_in_row = image_width as f32 / max_ch_width as f32;
let mut image = Vec::with_capacity(assumed_size as usize);
let mut chars_row = Vec::with_capacity(assumed_ch_in_row as usize);
let mut cursor_x = 0;
let mut image_height = 0;
let dump_row = |image: &mut Vec<u8>, chars_row: &Vec<(i32, i32, Vec<u8>)>| {
// Copy character data into the image row by row:
//
// image_width
// +-------+---------+---+
// | x | x | |
// | | | |
// | x | x | | ch_box_height
// | x | x | |
// | x | x | |
// | x | x | |
// | | x | |
// +-------+---------+---+
// ^--- image_width - width_ch_i - width_ch_j
for i in 0..ch_box_height {
let mut x = 0;
for &(width, height, ref data) in chars_row {
if i >= height {
image.extend(repeat(0).take(width as usize));
} else {
let skip = i * width;
debug_assert!(data.len() >= (skip + width) as usize);
let line = data.iter().skip(skip as usize).take(width as usize);
image.extend(line.cloned());
};
x += width;
}
let cols_to_fill = image_width - x;
image.extend(repeat(0).take(cols_to_fill as usize));
}
};
// debug!("Placing chars onto a plane");
// Hashmap doesn't preserve the order but we don't need it anyway.
for (_, ch_info) in chars_info.iter_mut() {
if cursor_x + ch_info.width > image_width {
dump_row(&mut image, &chars_row);
chars_row.clear();
cursor_x = 0;
image_height += ch_box_height;
}
let ch_data = ch_info.data.take().unwrap();
chars_row.push((ch_info.width, ch_info.height, ch_data));
ch_info.tex = [cursor_x as f32, image_height as f32];
cursor_x += ch_info.width;
}
dump_row(&mut image, &chars_row);
image_height += ch_box_height;
// Finally, we just precalculate some fields to make it easier to use
// our font.
for (_, ch_info) in chars_info.iter_mut() {
ch_info.tex[0] /= image_width as f32;
ch_info.tex[1] /= image_height as f32;
ch_info.tex_width = ch_info.width as f32 / image_width as f32;
ch_info.tex_height = ch_info.height as f32 / image_height as f32;
}
// info!("Image width: {}, image height: {}, total size: {}",
// image_width, image_height, image.len());
Ok(BitmapFont {
width: image_width as u16,
height: image_height as u16,
chars: chars_info,
image: image,
})
}
pub fn get_width(&self) -> u16 {
self.width
}
pub fn get_height(&self) -> u16 {
self.height
}
/// Return 8-bit texture raw data (grayscale).
pub fn get_image(&self) -> &[u8] {
&self.image
}
pub fn find_char(&self, ch: char) -> Option<&BitmapChar> {
self.chars.get(&ch)
}
}