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
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
use std::iter::Iterator;
use std::time::Duration;

use num_rational::Ratio;

use crate::error::ImageResult;
use crate::RgbaImage;

/// An implementation dependent iterator, reading the frames as requested
pub struct Frames<'a> {
    iterator: Box<dyn Iterator<Item = ImageResult<Frame>> + 'a>,
}

impl<'a> Frames<'a> {
    /// Creates a new `Frames` from an implementation specific iterator.
    pub fn new(iterator: Box<dyn Iterator<Item = ImageResult<Frame>> + 'a>) -> Self {
        Frames { iterator }
    }

    /// Steps through the iterator from the current frame until the end and pushes each frame into
    /// a `Vec`.
    /// If en error is encountered that error is returned instead.
    ///
    /// Note: This is equivalent to `Frames::collect::<ImageResult<Vec<Frame>>>()`
    pub fn collect_frames(self) -> ImageResult<Vec<Frame>> {
        self.collect()
    }
}

impl<'a> Iterator for Frames<'a> {
    type Item = ImageResult<Frame>;
    fn next(&mut self) -> Option<ImageResult<Frame>> {
        self.iterator.next()
    }
}

/// A single animation frame
#[derive(Clone)]
pub struct Frame {
    /// Delay between the frames in milliseconds
    delay: Delay,
    /// x offset
    left: u32,
    /// y offset
    top: u32,
    buffer: RgbaImage,
}

/// The delay of a frame relative to the previous one.
#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd)]
pub struct Delay {
    ratio: Ratio<u32>,
}

impl Frame {
    /// Constructs a new frame without any delay.
    pub fn new(buffer: RgbaImage) -> Frame {
        Frame {
            delay: Delay::from_ratio(Ratio::from_integer(0)),
            left: 0,
            top: 0,
            buffer,
        }
    }

    /// Constructs a new frame
    pub fn from_parts(buffer: RgbaImage, left: u32, top: u32, delay: Delay) -> Frame {
        Frame {
            delay,
            left,
            top,
            buffer,
        }
    }

    /// Delay of this frame
    pub fn delay(&self) -> Delay {
        self.delay
    }

    /// Returns the image buffer
    pub fn buffer(&self) -> &RgbaImage {
        &self.buffer
    }

    /// Returns a mutable image buffer
    pub fn buffer_mut(&mut self) -> &mut RgbaImage {
        &mut self.buffer
    }

    /// Returns the image buffer
    pub fn into_buffer(self) -> RgbaImage {
        self.buffer
    }

    /// Returns the x offset
    pub fn left(&self) -> u32 {
        self.left
    }

    /// Returns the y offset
    pub fn top(&self) -> u32 {
        self.top
    }
}

impl Delay {
    /// Create a delay from a ratio of milliseconds.
    ///
    /// # Examples
    ///
    /// ```
    /// use image::Delay;
    /// let delay_10ms = Delay::from_numer_denom_ms(10, 1);
    /// ```
    pub fn from_numer_denom_ms(numerator: u32, denominator: u32) -> Self {
        Delay {
            ratio: Ratio::new_raw(numerator, denominator),
        }
    }

    /// Convert from a duration, clamped between 0 and an implemented defined maximum.
    ///
    /// The maximum is *at least* `i32::MAX` milliseconds. It should be noted that the accuracy of
    /// the result may be relative and very large delays have a coarse resolution.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::time::Duration;
    /// use image::Delay;
    ///
    /// let duration = Duration::from_millis(20);
    /// let delay = Delay::from_saturating_duration(duration);
    /// ```
    pub fn from_saturating_duration(duration: Duration) -> Self {
        // A few notes: The largest number we can represent as a ratio is u32::MAX but we can
        // sometimes represent much smaller numbers.
        //
        // We can represent duration as `millis+a/b` (where a < b, b > 0).
        // We must thus bound b with `b·millis + (b-1) <= u32::MAX` or
        // > `0 < b <= (u32::MAX + 1)/(millis + 1)`
        // Corollary: millis <= u32::MAX

        const MILLIS_BOUND: u128 = u32::max_value() as u128;

        let millis = duration.as_millis().min(MILLIS_BOUND);
        let submillis = (duration.as_nanos() % 1_000_000) as u32;

        let max_b = if millis > 0 {
            ((MILLIS_BOUND + 1) / (millis + 1)) as u32
        } else {
            MILLIS_BOUND as u32
        };
        let millis = millis as u32;

        let (a, b) = Self::closest_bounded_fraction(max_b, submillis, 1_000_000);
        Self::from_numer_denom_ms(a + b * millis, b)
    }

    /// The numerator and denominator of the delay in milliseconds.
    ///
    /// This is guaranteed to be an exact conversion if the `Delay` was previously created with the
    /// `from_numer_denom_ms` constructor.
    pub fn numer_denom_ms(self) -> (u32, u32) {
        (*self.ratio.numer(), *self.ratio.denom())
    }

    pub(crate) fn from_ratio(ratio: Ratio<u32>) -> Self {
        Delay { ratio }
    }

    pub(crate) fn into_ratio(self) -> Ratio<u32> {
        self.ratio
    }

    /// Given some fraction, compute an approximation with denominator bounded.
    ///
    /// Note that `denom_bound` bounds nominator and denominator of all intermediate
    /// approximations and the end result.
    fn closest_bounded_fraction(denom_bound: u32, nom: u32, denom: u32) -> (u32, u32) {
        use std::cmp::Ordering::{self, *};
        assert!(0 < denom);
        assert!(0 < denom_bound);
        assert!(nom < denom);

        // Avoid a few type troubles. All intermediate results are bounded by `denom_bound` which
        // is in turn bounded by u32::MAX. Representing with u64 allows multiplication of any two
        // values without fears of overflow.

        // Compare two fractions whose parts fit into a u32.
        fn compare_fraction((an, ad): (u64, u64), (bn, bd): (u64, u64)) -> Ordering {
            (an * bd).cmp(&(bn * ad))
        }

        // Computes the nominator of the absolute difference between two such fractions.
        fn abs_diff_nom((an, ad): (u64, u64), (bn, bd): (u64, u64)) -> u64 {
            let c0 = an * bd;
            let c1 = ad * bn;

            let d0 = c0.max(c1);
            let d1 = c0.min(c1);
            d0 - d1
        }

        let exact = (u64::from(nom), u64::from(denom));
        // The lower bound fraction, numerator and denominator.
        let mut lower = (0u64, 1u64);
        // The upper bound fraction, numerator and denominator.
        let mut upper = (1u64, 1u64);
        // The closest approximation for now.
        let mut guess = (u64::from(nom * 2 > denom), 1u64);

        // loop invariant: ad, bd <= denom_bound
        // iterates the Farey sequence.
        loop {
            // Break if we are done.
            if compare_fraction(guess, exact) == Equal {
                break;
            }

            // Break if next Farey number is out-of-range.
            if u64::from(denom_bound) - lower.1 < upper.1 {
                break;
            }

            // Next Farey approximation n between a and b
            let next = (lower.0 + upper.0, lower.1 + upper.1);
            // if F < n then replace the upper bound, else replace lower.
            if compare_fraction(exact, next) == Less {
                upper = next;
            } else {
                lower = next;
            }

            // Now correct the closest guess.
            // In other words, if |c - f| > |n - f| then replace it with the new guess.
            // This favors the guess with smaller denominator on equality.

            // |g - f| = |g_diff_nom|/(gd*fd);
            let g_diff_nom = abs_diff_nom(guess, exact);
            // |n - f| = |n_diff_nom|/(nd*fd);
            let n_diff_nom = abs_diff_nom(next, exact);

            // The difference |n - f| is smaller than |g - f| if either the integral part of the
            // fraction |n_diff_nom|/nd is smaller than the one of |g_diff_nom|/gd or if they are
            // the same but the fractional part is larger.
            if match (n_diff_nom / next.1).cmp(&(g_diff_nom / guess.1)) {
                Less => true,
                Greater => false,
                // Note that the nominator for the fractional part is smaller than its denominator
                // which is smaller than u32 and can't overflow the multiplication with the other
                // denominator, that is we can compare these fractions by multiplication with the
                // respective other denominator.
                Equal => {
                    compare_fraction(
                        (n_diff_nom % next.1, next.1),
                        (g_diff_nom % guess.1, guess.1),
                    ) == Less
                }
            } {
                guess = next;
            }
        }

        (guess.0 as u32, guess.1 as u32)
    }
}

impl From<Delay> for Duration {
    fn from(delay: Delay) -> Self {
        let ratio = delay.into_ratio();
        let ms = ratio.to_integer();
        let rest = ratio.numer() % ratio.denom();
        let nanos = (u64::from(rest) * 1_000_000) / u64::from(*ratio.denom());
        Duration::from_millis(ms.into()) + Duration::from_nanos(nanos)
    }
}

#[cfg(test)]
mod tests {
    use super::{Delay, Duration, Ratio};

    #[test]
    fn simple() {
        let second = Delay::from_numer_denom_ms(1000, 1);
        assert_eq!(Duration::from(second), Duration::from_secs(1));
    }

    #[test]
    fn fps_30() {
        let thirtieth = Delay::from_numer_denom_ms(1000, 30);
        let duration = Duration::from(thirtieth);
        assert_eq!(duration.as_secs(), 0);
        assert_eq!(duration.subsec_millis(), 33);
        assert_eq!(duration.subsec_nanos(), 33_333_333);
    }

    #[test]
    fn duration_outlier() {
        let oob = Duration::from_secs(0xFFFF_FFFF);
        let delay = Delay::from_saturating_duration(oob);
        assert_eq!(delay.numer_denom_ms(), (0xFFFF_FFFF, 1));
    }

    #[test]
    fn duration_approx() {
        let oob = Duration::from_millis(0xFFFF_FFFF) + Duration::from_micros(1);
        let delay = Delay::from_saturating_duration(oob);
        assert_eq!(delay.numer_denom_ms(), (0xFFFF_FFFF, 1));

        let inbounds = Duration::from_millis(0xFFFF_FFFF) - Duration::from_micros(1);
        let delay = Delay::from_saturating_duration(inbounds);
        assert_eq!(delay.numer_denom_ms(), (0xFFFF_FFFF, 1));

        let fine =
            Duration::from_millis(0xFFFF_FFFF / 1000) + Duration::from_micros(0xFFFF_FFFF % 1000);
        let delay = Delay::from_saturating_duration(fine);
        // Funnily, 0xFFFF_FFFF is divisble by 5, thus we compare with a `Ratio`.
        assert_eq!(delay.into_ratio(), Ratio::new(0xFFFF_FFFF, 1000));
    }

    #[test]
    fn precise() {
        // The ratio has only 32 bits in the numerator, too imprecise to get more than 11 digits
        // correct. But it may be expressed as 1_000_000/3 instead.
        let exceed = Duration::from_secs(333) + Duration::from_nanos(333_333_333);
        let delay = Delay::from_saturating_duration(exceed);
        assert_eq!(Duration::from(delay), exceed);
    }

    #[test]
    fn small() {
        // Not quite a delay of `1 ms`.
        let delay = Delay::from_numer_denom_ms(1 << 16, (1 << 16) + 1);
        let duration = Duration::from(delay);
        assert_eq!(duration.as_millis(), 0);
        // Not precisely the original but should be smaller than 0.
        let delay = Delay::from_saturating_duration(duration);
        assert_eq!(delay.into_ratio().to_integer(), 0);
    }
}