loop9/
lib.rs

1use core::ops::Deref;
2use imgref::ImgRef;
3
4/// Previous, current, and next pixel or row
5#[derive(Copy,Clone,Debug,Eq,PartialEq)]
6#[repr(C)]
7pub struct Triple<T> {
8    pub prev: T,
9    pub curr: T,
10    pub next: T,
11}
12
13impl<T> Triple<T> {
14    #[must_use]
15    #[inline(always)]
16    pub fn new(prev: T, curr: T, next: T) -> Self {
17        Triple { prev, curr, next }
18    }
19}
20
21impl<T> AsRef<[T]> for Triple<T> {
22    #[inline(always)]
23    fn as_ref(&self) -> &[T] {
24        unsafe {
25            std::slice::from_raw_parts(self as *const Triple<T> as *const T, 3)
26        }
27    }
28}
29
30impl<T> Deref for Triple<T> {
31    type Target = [T];
32
33    #[inline(always)]
34    fn deref(&self) -> &Self::Target {
35        self.as_ref()
36    }
37}
38
39impl<T: Copy> Triple<T> {
40    /// Add the next item, and shift others (prev is gone, prev = current)
41    /// If the item is `None`, it'll copy the last one instead.
42    #[must_use]
43    #[inline(always)]
44    pub fn advance(self, next: Option<T>) -> Self {
45        Triple {
46            prev: self.curr,
47            curr: self.next,
48            next: next.unwrap_or(self.next),
49        }
50    }
51}
52
53/// Loop over 9 neighboring pixels in the image described by [`ImgRef`] (`Img.as_ref()`)
54///
55/// The callback is: (`x`, `y`, `previous_row`, `current_row`, `next_row`)
56///
57/// This function will never panic, if your callback doesn't panic.
58#[inline(always)]
59pub fn loop9_img<Pixel, Callback>(img: ImgRef<'_, Pixel>, cb: Callback)
60    where Pixel: Copy, Callback: FnMut(usize, usize, Triple<Pixel>,Triple<Pixel>,Triple<Pixel>)
61{
62    loop9(img, 0, 0, img.width(), img.height(), cb);
63}
64
65/// Loop over 9 neighboring pixels in the left/top/width/height fragment of the image described by [`ImgRef`] (`Img.as_ref()`)
66///
67/// The callback is: (`x`, `y`, `previous_row`, `current_row`, `next_row`)
68///
69/// This function will never panic, if your callback doesn't panic.
70pub fn loop9<Pixel, Callback>(img: ImgRef<'_, Pixel>, left: usize, top: usize, width: usize, height: usize, mut cb: Callback)
71    where Pixel: Copy, Callback: FnMut(usize, usize, Triple<Pixel>,Triple<Pixel>,Triple<Pixel>)
72{
73    let max_width = img.width();
74    let max_height = img.height();
75    let stride = img.stride();
76    if stride == 0 || max_height == 0 || max_width == 0 {
77        return;
78    }
79    let data = img.buf();
80    let t = top.min(max_height-1) * stride;
81    let start_row = if let Some(r) = data.get(t..t+max_width) { r } else { return };
82    if start_row.is_empty() { return; }
83    let mut row = Triple {
84        prev: start_row,
85        curr: start_row,
86        next: start_row,
87    };
88    for y in top..top+height {
89        row = row.advance({
90            let t = (y+1) * stride;
91            data.get(t..t+max_width)
92        });
93        if row.prev.is_empty() || row.curr.is_empty() || row.next.is_empty() {
94            return;
95        }
96        let mut tp;
97        let mut tn = row.prev[left.min(row.prev.len()-1)];
98        let mut tc = row.prev[left.saturating_sub(1).min(row.prev.len()-1)];
99        let mut mp;
100        let mut mn = row.curr[left.min(row.curr.len()-1)];
101        let mut mc = row.curr[left.saturating_sub(1).min(row.curr.len()-1)];
102        let mut bp;
103        let mut bn = row.next[left.min(row.next.len()-1)];
104        let mut bc = row.next[left.saturating_sub(1).min(row.next.len()-1)];
105        for x in left..left+width {
106            tp = tc;
107            tc = tn;
108            tn = row.prev.get(x+1).copied().unwrap_or(tc);
109            mp = mc;
110            mc = mn;
111            mn = row.curr.get(x+1).copied().unwrap_or(mc);
112            bp = bc;
113            bc = bn;
114            bn = row.next.get(x+1).copied().unwrap_or(bc);
115            cb(x-left, y-top, Triple::new(tp, tc, tn), Triple::new(mp, mc, mn), Triple::new(bp, bc, bn));
116        }
117    }
118}
119
120
121#[test]
122fn test_oob() {
123    use imgref::Img;
124    let img = Img::new(vec![0; 5*4], 5, 4);
125    for w in 1..8 {
126        for h in 1..8 {
127            for x in 0..8 {
128                for y in 0..8 {
129                    let mut n = 0;
130                    loop9(img.as_ref(), x,y,w,h, |_x,_y,_top,_mid,_bot| { n += 1 });
131                    assert_eq!(n, w*h, "{x},{y},{w},{h}");
132                }
133            }
134        }
135    }
136}
137
138#[test]
139fn test_loop9() {
140    use imgref::Img;
141
142    let src = vec![
143         1, 2, 3, 4, 0,
144         5, 6, 7, 8, 0,
145         9,10,11,12, 0,
146        13,14,15,16, 0,
147    ];
148    let img = Img::new_stride(src.clone(), 4, 4, 5);
149    assert_eq!(4, img.width());
150    assert_eq!(5, img.stride());
151    assert_eq!(4, img.height());
152
153    let check = |l,t,w,h,exp: &[_]|{
154        let mut res = Vec::new();
155        loop9(img.as_ref(), l,t,w,h, |_x,_y,_top,mid,_bot| res.push(mid.curr));
156        assert_eq!(exp, res);
157    };
158
159    check(0,0,4,4, &[
160         1, 2, 3, 4,
161         5, 6, 7, 8,
162         9,10,11,12,
163        13,14,15,16,
164    ]);
165
166    check(0,0,4,1, &[1, 2, 3, 4]);
167
168    check(0,3,4,1, &[13,14,15,16]);
169
170    check(0,0,3,3, &[
171         1, 2, 3,
172         5, 6, 7,
173         9,10,11,
174    ]);
175
176    check(0,0,1,1, &[1]);
177    check(1,0,1,1, &[2]);
178    check(2,0,1,1, &[3]);
179    check(3,0,1,1, &[4]);
180
181    check(1,0,3,4,&[
182         2, 3, 4,
183         6, 7, 8,
184        10,11,12,
185        14,15,16,
186    ]);
187}
loop9/lib.rs

loop9/
lib.rs
