Increase coverage of serde derives
1//! A cache for storing the results of layout computation
2use crate::geometry::Size;
3use crate::style::AvailableSpace;
4use crate::tree::{LayoutOutput, RunMode};
5
6/// The number of cache entries for each node in the tree
7const CACHE_SIZE: usize = 9;
8
9/// Cached intermediate layout results
10#[derive(Debug, Clone, Copy)]
11#[cfg_attr(feature = "serde", derive(Serialize))]
12pub(crate) struct CacheEntry<T> {
13 /// The initial cached size of the node itself
14 known_dimensions: Size<Option<f32>>,
15 /// The initial cached size of the parent's node
16 available_space: Size<AvailableSpace>,
17 /// The cached size and baselines of the item
18 content: T,
19}
20
21/// A cache for caching the results of a sizing a Grid Item or Flexbox Item
22#[cfg_attr(feature = "serde", derive(Serialize))]
23pub struct Cache {
24 /// The cache entry for the node's final layout
25 final_layout_entry: Option<CacheEntry<LayoutOutput>>,
26 /// The cache entries for the node's preliminary size measurements
27 measure_entries: [Option<CacheEntry<Size<f32>>>; CACHE_SIZE],
28}
29
30impl Default for Cache {
31 fn default() -> Self {
32 Self::new()
33 }
34}
35
36impl Cache {
37 /// Create a new empty cache
38 pub const fn new() -> Self {
39 Self { final_layout_entry: None, measure_entries: [None; CACHE_SIZE] }
40 }
41
42 /// Return the cache slot to cache the current computed result in
43 ///
44 /// ## Caching Strategy
45 ///
46 /// We need multiple cache slots, because a node's size is often queried by it's parent multiple times in the course of the layout
47 /// process, and we don't want later results to clobber earlier ones.
48 ///
49 /// The two variables that we care about when determining cache slot are:
50 ///
51 /// - How many "known_dimensions" are set. In the worst case, a node may be called first with neither dimension known, then with one
52 /// dimension known (either width of height - which doesn't matter for our purposes here), and then with both dimensions known.
53 /// - Whether unknown dimensions are being sized under a min-content or a max-content available space constraint (definite available space
54 /// shares a cache slot with max-content because a node will generally be sized under one or the other but not both).
55 ///
56 /// ## Cache slots:
57 ///
58 /// - Slot 0: Both known_dimensions were set
59 /// - Slots 1-4: 1 of 2 known_dimensions were set and:
60 /// - Slot 1: width but not height known_dimension was set and the other dimension was either a MaxContent or Definite available space constraintraint
61 /// - Slot 2: width but not height known_dimension was set and the other dimension was a MinContent constraint
62 /// - Slot 3: height but not width known_dimension was set and the other dimension was either a MaxContent or Definite available space constraintable space constraint
63 /// - Slot 4: height but not width known_dimension was set and the other dimension was a MinContent constraint
64 /// - Slots 5-8: Neither known_dimensions were set and:
65 /// - Slot 5: x-axis available space is MaxContent or Definite and y-axis available space is MaxContent or Definite
66 /// - Slot 6: x-axis available space is MaxContent or Definite and y-axis available space is MinContent
67 /// - Slot 7: x-axis available space is MinContent and y-axis available space is MaxContent or Definite
68 /// - Slot 8: x-axis available space is MinContent and y-axis available space is MinContent
69 #[inline]
70 fn compute_cache_slot(known_dimensions: Size<Option<f32>>, available_space: Size<AvailableSpace>) -> usize {
71 use AvailableSpace::{Definite, MaxContent, MinContent};
72
73 let has_known_width = known_dimensions.width.is_some();
74 let has_known_height = known_dimensions.height.is_some();
75
76 // Slot 0: Both known_dimensions were set
77 if has_known_width && has_known_height {
78 return 0;
79 }
80
81 // Slot 1: width but not height known_dimension was set and the other dimension was either a MaxContent or Definite available space constraint
82 // Slot 2: width but not height known_dimension was set and the other dimension was a MinContent constraint
83 if has_known_width && !has_known_height {
84 return 1 + (available_space.height == MinContent) as usize;
85 }
86
87 // Slot 3: height but not width known_dimension was set and the other dimension was either a MaxContent or Definite available space constraint
88 // Slot 4: height but not width known_dimension was set and the other dimension was a MinContent constraint
89 if has_known_height && !has_known_width {
90 return 3 + (available_space.width == MinContent) as usize;
91 }
92
93 // Slots 5-8: Neither known_dimensions were set and:
94 match (available_space.width, available_space.height) {
95 // Slot 5: x-axis available space is MaxContent or Definite and y-axis available space is MaxContent or Definite
96 (MaxContent | Definite(_), MaxContent | Definite(_)) => 5,
97 // Slot 6: x-axis available space is MaxContent or Definite and y-axis available space is MinContent
98 (MaxContent | Definite(_), MinContent) => 6,
99 // Slot 7: x-axis available space is MinContent and y-axis available space is MaxContent or Definite
100 (MinContent, MaxContent | Definite(_)) => 7,
101 // Slot 8: x-axis available space is MinContent and y-axis available space is MinContent
102 (MinContent, MinContent) => 8,
103 }
104 }
105
106 /// Try to retrieve a cached result from the cache
107 #[inline]
108 pub fn get(
109 &self,
110 known_dimensions: Size<Option<f32>>,
111 available_space: Size<AvailableSpace>,
112 run_mode: RunMode,
113 ) -> Option<LayoutOutput> {
114 match run_mode {
115 RunMode::PerformLayout => self
116 .final_layout_entry
117 .filter(|entry| {
118 let cached_size = entry.content.size;
119 (known_dimensions.width == entry.known_dimensions.width
120 || known_dimensions.width == Some(cached_size.width))
121 && (known_dimensions.height == entry.known_dimensions.height
122 || known_dimensions.height == Some(cached_size.height))
123 && (known_dimensions.width.is_some()
124 || entry.available_space.width.is_roughly_equal(available_space.width))
125 && (known_dimensions.height.is_some()
126 || entry.available_space.height.is_roughly_equal(available_space.height))
127 })
128 .map(|e| e.content),
129 RunMode::ComputeSize => {
130 for entry in self.measure_entries.iter().flatten() {
131 let cached_size = entry.content;
132
133 if (known_dimensions.width == entry.known_dimensions.width
134 || known_dimensions.width == Some(cached_size.width))
135 && (known_dimensions.height == entry.known_dimensions.height
136 || known_dimensions.height == Some(cached_size.height))
137 && (known_dimensions.width.is_some()
138 || entry.available_space.width.is_roughly_equal(available_space.width))
139 && (known_dimensions.height.is_some()
140 || entry.available_space.height.is_roughly_equal(available_space.height))
141 {
142 return Some(LayoutOutput::from_outer_size(cached_size));
143 }
144 }
145
146 None
147 }
148 RunMode::PerformHiddenLayout => None,
149 }
150 }
151
152 /// Store a computed size in the cache
153 pub fn store(
154 &mut self,
155 known_dimensions: Size<Option<f32>>,
156 available_space: Size<AvailableSpace>,
157 run_mode: RunMode,
158 layout_output: LayoutOutput,
159 ) {
160 match run_mode {
161 RunMode::PerformLayout => {
162 self.final_layout_entry = Some(CacheEntry { known_dimensions, available_space, content: layout_output })
163 }
164 RunMode::ComputeSize => {
165 let cache_slot = Self::compute_cache_slot(known_dimensions, available_space);
166 self.measure_entries[cache_slot] =
167 Some(CacheEntry { known_dimensions, available_space, content: layout_output.size });
168 }
169 RunMode::PerformHiddenLayout => {}
170 }
171 }
172
173 /// Clear all cache entries
174 pub fn clear(&mut self) {
175 self.final_layout_entry = None;
176 self.measure_entries = [None; CACHE_SIZE];
177 }
178
179 /// Returns true if all cache entries are None, else false
180 pub fn is_empty(&self) -> bool {
181 self.final_layout_entry.is_none() && !self.measure_entries.iter().any(|entry| entry.is_some())
182 }
183}