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Make PSF code from bootproof into an independent library.

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James T. Martin 3 years ago
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root = true
[*]
charset = utf-8
indent_style = space
indent_size = 4
trim_trailing_whitespace = true
insert_final_newline = true
[*.yml]
indent_size = 2

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.github/workflows/rust.yml vendored
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name: Rust
on: [push]
jobs:
build:
runs-on: ubuntu-latest
steps:
- name: Checkout sources
uses: actions/checkout@v2
- name: Install latest stable
uses: actions-rs/toolchain@v1
with:
profile: minimal
toolchain: stable
override: true
- name: build
run: cargo build

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/target
Cargo.lock

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Cargo.toml
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[package]
name = "pc-screen-font"
version = "0.1.0"
authors = ["James Martin <james@jtmar.me>"]
edition = "2018"
repository = "https://github.com/jamestmartin/pc-screen-font"
license = "LGPL-3.0+"
publish = false
[dependencies.num-integer]
version = "0.1.43"
default-features = false

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LICENSE.txt
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GNU LESSER GENERAL PUBLIC LICENSE
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Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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README.md
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# PC Screen Font
A Rust library which can parses PSF version 2 fonts from their bytes.
It correctly handles fonts which contain extra pixels in their padding bits.
This library does not depend on the Rust standard library,
making it suitable for inclusion in bootloaders or kernels,
although it does require a working global allocator.
This library predates [the PSF crate](https://crates.io/crates/psf).
I have not investigated it at all, but you may wish to investigate using it instead
before choosing to use this library.
## Maintenance status
This library is only passively maintained, receiving updates as I need them.
I do not intend to publish this library to crates.io, but I will accept pull requests,
and if you wish to publish this library to crates.io and maintain it yourself,
you are welcome to do so.
## Limitations
Currently, this library does not support multi-codepoint spellings of characters.
Support may be added at some point, but I do not currently have any plans to do so.

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src/lib.rs
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#![no_std]
extern crate alloc;
use alloc::vec::Vec;
pub struct Font {
/// The width in pixels of this font's bounding box.
width: usize,
/// The height in pixels of this font's bounding box.
height: usize,
/// Every single glyph in the font.
glyphs: Vec<Glyph>,
// TODO: Replace this with a proper associative structure.
/// A map between unicode characters and indexes into the glyph vec.
unicode: Vec<UnicodeMap>,
}
/// Associates a unicode character and a glyph.
struct UnicodeMap {
c: char,
// The index of the glyph.
i: usize,
}
pub struct Glyph {
/// A set bit indicates that a pixel should be drawn for this glyph.
bitmap: Vec<u8>,
/// The number of bytes in the bitmap taken up by each line of pixels in this glyph.
line_size: usize,
/// See the docs for `Glyph::width`.
width: usize,
/// See the docs for `Glyph::height`.
height: usize,
}
impl Glyph {
/// The width in pixels of this individual glyph.
///
/// Although each PSF has a nominal width in pixels,
/// the length of each line of pixels stored in bits is actually rounded to the next byte.
/// Some fonts actually use this storage to make glyphs which are slightly wider
/// than the nominal width of the font, because it makes the glyph look better.
/// For example, Cozette does this for the unicode heart glyph.
pub fn width(&self) -> usize { self.width }
/// The height in pixels of this glyph. This will always be the same as the height of the font.
pub fn height(&self) -> usize { self.height }
/// Check whether an individual pixel of this glyph is set.
/// This will return `None` if `x` or `y` is outside the width or height of this glyph.
pub fn get(&self, x: usize, y: usize) -> Option<bool> {
if x > self.width || y > self.height {
return None
}
let (line_byte_index, bit_index) = num_integer::div_rem(x, 8);
let mask = 0b10000000 >> bit_index;
let byte = self.bitmap[(y * self.line_size + line_byte_index) as usize];
Some(byte & mask > 0)
}
}
impl Font {
/// The width in pixels of this font's bounding box.
pub fn width(&self) -> usize { self.width }
/// The height in pixels of this font's bounding box.
pub fn height(&self) -> usize { self.height }
/// The width and height in pixels of this font's bounding box.
pub fn bounding_box(&self) -> (usize, usize) {
(self.width, self.height)
}
/// Get the glyph associated with a particular unicode character,
/// or `None` if it is not present in this font.
pub fn lookup<'a>(&'a self, c: char) -> Option<&'a Glyph> {
self.index_of(c).map(|i| &self.glyphs[i])
}
/// The index of the glyph associated with a particular unicode character.
fn index_of(&self, c: char) -> Option<usize> {
for entry in &self.unicode {
if entry.c == c {
return Some(entry.i);
}
}
None
}
/// Parse a version 2 PC screen font from its bytes.
pub fn parse(font: &[u8]) -> Font {
use core::convert::TryInto;
// The number of glyphs in this font.
let length = u32::from_le_bytes(font[16..20].try_into().unwrap()) as usize;
// The size in bytes of a single glyph.
let charsize = u32::from_le_bytes(font[20..24].try_into().unwrap()) as usize;
// The height in pixels of this font's bounding box.
let height = u32::from_le_bytes(font[24..28].try_into().unwrap()) as usize;
// The width in pixels of this font's bounding box.
let width = u32::from_le_bytes(font[28..32].try_into().unwrap()) as usize;
// The size in bytes of a single row of pixels in a glyph.
let line_size = num_integer::div_ceil(width, 8);
let glyphs_offset = 32; // the size of the header
let glyphs_size = length * charsize;
let unicode_offset = glyphs_offset + glyphs_size;
let mut glyphs = Vec::with_capacity(length);
for i in 0..length {
let mut bitmap = Vec::with_capacity(charsize);
let bitmap_begin = glyphs_offset + charsize * i;
let bitmap_end = bitmap_begin + charsize;
bitmap.extend_from_slice(&font[bitmap_begin..bitmap_end]);
glyphs.push(Glyph {
bitmap,
line_size,
// Glyphs may overflow the font's nominal resolution in the padding bytes of the line!
// This trick only works for the width because there is no vertical padding.
// TODO: Pre-compute widths and bounding box offsets of individual glyphs.
width: line_size * 8,
height,
});
}
// HACK: This unicode map parser is still a mess.
let mut unicode_map = Vec::new();
let unicode_info = &font[unicode_offset..];
let mut glyph = 0;
let mut i = 0;
while i < unicode_info.len() {
let mut nc = unicode_info[i];
while nc != 0xFE && nc != 0xFF {
let ch_bytes = nc.leading_ones().max(1) as usize;
let st = core::str::from_utf8(&unicode_info[i..i + ch_bytes]).expect("Invalid character");
let ch = st.chars().next().unwrap();
unicode_map.push(UnicodeMap { c: ch, i: glyph });
i += ch_bytes;
nc = unicode_info[i];
}
// TODO: Support multi-codepoint spellings of characters.
while nc != 0xFF {
i += 1;
nc = unicode_info[i];
}
i += 1;
glyph += 1;
}
Font {
width,
height,
glyphs,
unicode: unicode_map,
}
}
}
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