lopdf 0.40.0

A Rust library for PDF document manipulation.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152

use std::convert::{TryFrom, TryInto};
use std::io::{Error, ErrorKind, Read, Result, Write};
use std::mem;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum FilterType {
    None,
    Sub,
    Up,
    Avg,
    Paeth,
}

impl TryFrom<u8> for FilterType {
    type Error = ();

    fn try_from(n: u8) -> std::result::Result<FilterType, ()> {
        match n {
            0 => Ok(FilterType::None),
            1 => Ok(FilterType::Sub),
            2 => Ok(FilterType::Up),
            3 => Ok(FilterType::Avg),
            4 => Ok(FilterType::Paeth),
            _ => Err(()),
        }
    }
}

fn paeth_predict(left: u8, above: u8, upperleft: u8) -> u8 {
    let expand_left = i16::from(left);
    let expand_above = i16::from(above);
    let expand_upperleft = i16::from(upperleft);

    let initial_estimate = expand_left + expand_above - expand_upperleft;

    let dist_left = (initial_estimate - expand_left).abs();
    let dist_above = (initial_estimate - expand_above).abs();
    let dist_upperleft = (initial_estimate - expand_upperleft).abs();

    if dist_left <= dist_above && dist_left <= dist_upperleft {
        left
    } else if dist_above <= dist_upperleft {
        above
    } else {
        upperleft
    }
}

pub fn decode_row(filter: FilterType, bpp: usize, previous: &[u8], current: &mut [u8]) {
    use self::FilterType::*;
    let len = current.len();
    let bpp = bpp.min(len);

    match filter {
        None => (),
        Sub => {
            for i in bpp..len {
                current[i] = current[i].wrapping_add(current[i - bpp]);
            }
        }
        Up => {
            for i in 0..len {
                current[i] = current[i].wrapping_add(previous[i]);
            }
        }
        Avg => {
            for i in 0..bpp {
                current[i] = current[i].wrapping_add(previous[i] / 2);
            }

            for i in bpp..len {
                current[i] = current[i].wrapping_add((i16::from(current[i - bpp]) + i16::from(previous[i]) / 2) as u8);
            }
        }
        Paeth => {
            for i in 0..bpp {
                current[i] = current[i].wrapping_add(paeth_predict(0, previous[i], 0));
            }

            for i in bpp..len {
                current[i] = current[i].wrapping_add(paeth_predict(current[i - bpp], previous[i], previous[i - bpp]));
            }
        }
    }
}

pub fn decode_frame(content: &[u8], bytes_per_pixel: usize, pixels_per_row: usize) -> Result<Vec<u8>> {
    let bytes_per_row = bytes_per_pixel * pixels_per_row;
    let mut previous = Vec::new();
    previous.try_reserve(bytes_per_row)?;
    previous.resize(bytes_per_row, 0_u8);
    let mut current = Vec::new();
    current.try_reserve(bytes_per_row)?;
    current.resize(bytes_per_row, 0_u8);
    let mut decoded = Vec::new();
    let mut pos = 0;
    while pos < content.len() {
        if let Ok(filter) = content[pos].try_into() {
            pos += 1;
            (&content[pos..]).read_exact(current.as_mut_slice())?;
            pos += bytes_per_row;

            decode_row(filter, bytes_per_pixel, previous.as_slice(), current.as_mut_slice());
            decoded.write_all(current.as_slice())?;
            mem::swap(&mut previous, &mut current);
        } else {
            return Err(Error::new(
                ErrorKind::InvalidData,
                format!("invalid PNG filter type ({})", content[pos]),
            ));
        }
    }
    Ok(decoded)
}

pub fn encode_row(method: FilterType, bpp: usize, previous: &[u8], current: &mut [u8]) {
    use self::FilterType::*;
    let len = current.len();
    let bpp = bpp.min(len);

    match method {
        None => (),
        Sub => {
            for i in (bpp..len).rev() {
                current[i] = current[i].wrapping_sub(current[i - bpp]);
            }
        }
        Up => {
            for i in 0..len {
                current[i] = current[i].wrapping_sub(previous[i]);
            }
        }
        Avg => {
            for i in (bpp..len).rev() {
                current[i] = current[i].wrapping_sub(current[i - bpp].wrapping_add(previous[i]) / 2);
            }

            for i in 0..bpp {
                current[i] = current[i].wrapping_sub(previous[i] / 2);
            }
        }
        Paeth => {
            for i in (bpp..len).rev() {
                current[i] = current[i].wrapping_sub(paeth_predict(current[i - bpp], previous[i], previous[i - bpp]));
            }

            for i in 0..bpp {
                current[i] = current[i].wrapping_sub(paeth_predict(0, previous[i], 0));
            }
        }
    }
}