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
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
mod utils;
use std::f64::consts::PI;
use wasm_bindgen::prelude::*;
#[cfg(feature = "wee_alloc")]
#[global_allocator]
static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Error {
LengthInvalid,
LengthMismatch,
}
#[wasm_bindgen(js_name = "decode")]
pub fn wasm_decode(blur_hash: &str, width: usize, height: usize) -> Option<Vec<u8>> {
match decode(blur_hash, width, height) {
Ok(img) => Some(img),
Err(_err) => None,
}
}
pub fn decode(blur_hash: &str, width: usize, height: usize) -> Result<Vec<u8>, Error> {
if blur_hash.len() < 6 {
return Err(Error::LengthInvalid);
}
let size_flag = decode_base83_string(blur_hash.get(0..1).unwrap());
let num_y = (size_flag / 9) + 1;
let num_x = (size_flag % 9) + 1;
let expected_digits = 4 + 2 * num_x * num_y;
if blur_hash.len() != expected_digits {
return Err(Error::LengthMismatch);
}
let quantised_maximum_value = decode_base83_string(blur_hash.get(1..2).unwrap());
let maximum_value = ((quantised_maximum_value + 1) as f64) / 166f64;
let mut colours: Vec<[f64; 3]> = Vec::new();
for i in 0..(num_x * num_y) {
if i == 0 {
let value = decode_base83_string(blur_hash.get(2..6).unwrap());
colours.push(decode_dc(value));
} else {
let value = decode_base83_string(blur_hash.get((4 + i * 2)..(4 + i * 2 + 2)).unwrap());
colours.push(decode_ac(value, maximum_value * 1.0));
}
}
let bytes_per_row = width * 4;
let mut pixels = vec![0; bytes_per_row * height];
for y in 0..height {
for x in 0..width {
let mut r = 0f64;
let mut g = 0f64;
let mut b = 0f64;
for j in 0..num_y {
for i in 0..num_x {
let basis = f64::cos(PI * (x as f64) * (i as f64) / (width as f64))
* f64::cos(PI * (y as f64) * (j as f64) / (height as f64));
let colour = colours[i + j * num_x];
r += colour[0] * basis;
g += colour[1] * basis;
b += colour[2] * basis;
}
}
let int_r = linear_to_srgb(r);
let int_g = linear_to_srgb(g);
let int_b = linear_to_srgb(b);
pixels[4 * x + 0 + y * bytes_per_row] = int_r;
pixels[4 * x + 1 + y * bytes_per_row] = int_g;
pixels[4 * x + 2 + y * bytes_per_row] = int_b;
pixels[4 * x + 3 + y * bytes_per_row] = 255;
}
}
Ok(pixels)
}
fn decode_dc(value: usize) -> [f64; 3] {
let int_r = value >> 16;
let int_g = (value >> 8) & 255;
let int_b = value & 255;
[
srgb_to_linear(int_r),
srgb_to_linear(int_g),
srgb_to_linear(int_b),
]
}
fn decode_ac(value: usize, maximum_value: f64) -> [f64; 3] {
let quant_r = f64::floor((value / (19 * 19)) as f64);
let quant_g = f64::floor(((value / 19) as f64) % 19f64);
let quant_b = (value as f64) % 19f64;
let rgb = [
sign_pow((quant_r - 9f64) / 9f64, 2f64) * maximum_value,
sign_pow((quant_g - 9f64) / 9f64, 2f64) * maximum_value,
sign_pow((quant_b - 9f64) / 9f64, 2f64) * maximum_value,
];
rgb
}
fn sign_pow(value: f64, exp: f64) -> f64 {
get_sign(value) * f64::powf(f64::abs(value), exp)
}
fn get_sign(n: f64) -> f64 {
if n < 0f64 {
-1f64
} else {
1f64
}
}
fn linear_to_srgb(value: f64) -> u8 {
let v = f64::max(0f64, f64::min(1f64, value));
if v <= 0.0031308 {
return (v * 12.92 * 255f64 + 0.5) as u8;
} else {
return ((1.055 * f64::powf(v, 1f64 / 2.4) - 0.055) * 255f64 + 0.5) as u8;
}
}
fn srgb_to_linear(value: usize) -> f64 {
let v = (value as f64) / 255f64;
if v <= 0.04045 {
return v / 12.92;
} else {
return ((v + 0.055) / 1.055).powf(2.4);
}
}
const ENCODE_CHARACTERS: &str =
"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~";
fn decode_base83_string(string: &str) -> usize {
let mut value: usize = 0;
for character in string.chars() {
match ENCODE_CHARACTERS.find(character) {
Some(digit) => value = value * 83 + digit,
None => (),
}
}
value
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn it_decodes_size_flag() {
assert_eq!(21, decode_base83_string("L"));
assert_eq!(0, decode_base83_string("0"));
}
#[test]
fn decodes_size_0_out_of_range() {
let res = decode_base83_string("/");
assert_eq!(
0, res,
"Did not expect to decode size for input out of range (expected 0), but got {}",
res
);
}
}