1// Not needed on all platforms
2#![allow(dead_code)]
3
4use std::cmp;
5use std::num::NonZeroU32;
6
7use crate::Rect;
8use crate::SoftBufferError;
9
10/// Takes a mutable reference to a container and a function deriving a
11/// reference into it, and stores both, making it possible to get back the
12/// reference to the container once the other reference is no longer needed.
13///
14/// This should be consistent with stacked borrow rules, and miri seems to
15/// accept it at least in simple cases.
16pub struct BorrowStack<'a, T: 'static + ?Sized, U: 'static + ?Sized> {
17 container: *mut T,
18 member: *mut U,
19 _phantom: std::marker::PhantomData<&'a mut T>,
20}
21
22impl<'a, T: 'static + ?Sized, U: 'static + ?Sized> BorrowStack<'a, T, U> {
23 pub fn new<F>(container: &'a mut T, f: F) -> Result<Self, SoftBufferError>
24 where
25 F: for<'b> FnOnce(&'b mut T) -> Result<&'b mut U, SoftBufferError>,
26 {
27 let container = container as *mut T;
28 let member = f(unsafe { &mut *container })? as *mut U;
29 Ok(Self {
30 container,
31 member,
32 _phantom: std::marker::PhantomData,
33 })
34 }
35
36 pub fn member(&self) -> &U {
37 unsafe { &*self.member }
38 }
39
40 pub fn member_mut(&mut self) -> &mut U {
41 unsafe { &mut *self.member }
42 }
43
44 pub fn into_container(self) -> &'a mut T {
45 // SAFETY: Since we consume self and no longer reference member, this
46 // mutable reference is unique.
47 unsafe { &mut *self.container }
48 }
49}
50
51/// Calculates the smallest `Rect` necessary to represent all damaged `Rect`s.
52pub(crate) fn union_damage(damage: &[Rect]) -> Option<Rect> {
53 struct Region {
54 left: u32,
55 top: u32,
56 bottom: u32,
57 right: u32,
58 }
59
60 let region = damage
61 .iter()
62 .map(|rect| Region {
63 left: rect.x,
64 top: rect.y,
65 right: rect.x + rect.width.get(),
66 bottom: rect.y + rect.height.get(),
67 })
68 .reduce(|mut prev, next| {
69 prev.left = cmp::min(prev.left, next.left);
70 prev.top = cmp::min(prev.top, next.top);
71 prev.right = cmp::max(prev.right, next.right);
72 prev.bottom = cmp::max(prev.bottom, next.bottom);
73 prev
74 })?;
75
76 Some(Rect {
77 x: region.left,
78 y: region.top,
79 width: NonZeroU32::new(region.right - region.left)
80 .expect("`right` must always be bigger then `left`"),
81 height: NonZeroU32::new(region.bottom - region.top)
82 .expect("`bottom` must always be bigger then `top`"),
83 })
84}
85
86#[cfg(test)]
87mod tests {
88 use super::*;
89
90 #[test]
91 fn test_borrowstack_slice_int() {
92 fn f(mut stack: BorrowStack<[u32], u32>) {
93 assert_eq!(*stack.member(), 3);
94 *stack.member_mut() = 42;
95 assert_eq!(stack.into_container(), &[1, 2, 42, 4, 5]);
96 }
97
98 let mut v = vec![1, 2, 3, 4, 5];
99 f(BorrowStack::new(v.as_mut(), |v: &mut [u32]| Ok(&mut v[2])).unwrap());
100 assert_eq!(&v, &[1, 2, 42, 4, 5]);
101 }
102}
103