Split out caching into separate `CacheTree` trait (#758)
1//! ## Example: Partial Tree with Directly Owned Children
2//!
3//! The following example demonstrate an implementation of Taffy's Partial trait and usage of the low-level compute APIs.
4//! This example uses directly owned children with NodeId's being index's into vec on parent node.
5//! Since an iterator created from a node can't access grandchildren, we are limited to only implement `TraversePartialTree`.
6//! See the [`crate::tree::traits`] module for more details about the low-level traits.
7
8mod common {
9 pub mod image;
10 pub mod text;
11}
12use common::image::{image_measure_function, ImageContext};
13use common::text::{text_measure_function, FontMetrics, TextContext, WritingMode, LOREM_IPSUM};
14use taffy::{
15 compute_cached_layout, compute_flexbox_layout, compute_grid_layout, compute_leaf_layout, compute_root_layout,
16 prelude::*, Cache, CacheTree, Layout, Style,
17};
18
19#[derive(Debug, Copy, Clone)]
20#[allow(dead_code)]
21enum NodeKind {
22 Flexbox,
23 Grid,
24 Text,
25 Image,
26}
27
28struct Node {
29 kind: NodeKind,
30 style: Style,
31 text_data: Option<TextContext>,
32 image_data: Option<ImageContext>,
33 cache: Cache,
34 layout: Layout,
35 children: Vec<Node>,
36}
37
38impl Default for Node {
39 fn default() -> Self {
40 Node {
41 kind: NodeKind::Flexbox,
42 style: Style::default(),
43 text_data: None,
44 image_data: None,
45 cache: Cache::new(),
46 layout: Layout::with_order(0),
47 children: Vec::new(),
48 }
49 }
50}
51
52#[allow(dead_code)]
53impl Node {
54 pub fn new_row(style: Style) -> Node {
55 Node {
56 kind: NodeKind::Flexbox,
57 style: Style { display: Display::Flex, flex_direction: FlexDirection::Row, ..style },
58 ..Node::default()
59 }
60 }
61 pub fn new_column(style: Style) -> Node {
62 Node {
63 kind: NodeKind::Flexbox,
64 style: Style { display: Display::Flex, flex_direction: FlexDirection::Column, ..style },
65 ..Node::default()
66 }
67 }
68 pub fn new_grid(style: Style) -> Node {
69 Node { kind: NodeKind::Grid, style: Style { display: Display::Grid, ..style }, ..Node::default() }
70 }
71 pub fn new_text(style: Style, text_data: TextContext) -> Node {
72 Node { kind: NodeKind::Text, style, text_data: Some(text_data), ..Node::default() }
73 }
74 pub fn new_image(style: Style, image_data: ImageContext) -> Node {
75 Node { kind: NodeKind::Image, style, image_data: Some(image_data), ..Node::default() }
76 }
77 pub fn append_child(&mut self, node: Node) {
78 self.children.push(node);
79 }
80
81 pub fn compute_layout(&mut self, available_space: Size<AvailableSpace>) {
82 compute_root_layout(self, NodeId::from(usize::MAX), available_space);
83 }
84
85 /// The methods on LayoutPartialTree need to be able to access:
86 ///
87 /// - The node being laid out
88 /// - Direct children of the node being laid out
89 ///
90 /// Each must have an ID. For children we simply use it's index. For the node itself
91 /// we use usize::MAX on the assumption that there will never be that many children.
92 fn node_from_id(&self, node_id: NodeId) -> &Node {
93 let idx = usize::from(node_id);
94 if idx == usize::MAX {
95 self
96 } else {
97 &self.children[idx]
98 }
99 }
100
101 fn node_from_id_mut(&mut self, node_id: NodeId) -> &mut Node {
102 let idx = usize::from(node_id);
103 if idx == usize::MAX {
104 self
105 } else {
106 &mut self.children[idx]
107 }
108 }
109}
110
111struct ChildIter(std::ops::Range<usize>);
112impl Iterator for ChildIter {
113 type Item = NodeId;
114 fn next(&mut self) -> Option<Self::Item> {
115 self.0.next().map(NodeId::from)
116 }
117}
118
119impl taffy::TraversePartialTree for Node {
120 type ChildIter<'a> = ChildIter;
121
122 fn child_ids(&self, _node_id: NodeId) -> Self::ChildIter<'_> {
123 ChildIter(0..self.children.len())
124 }
125
126 fn child_count(&self, _node_id: NodeId) -> usize {
127 self.children.len()
128 }
129
130 fn get_child_id(&self, _node_id: NodeId, index: usize) -> NodeId {
131 NodeId::from(index)
132 }
133}
134
135impl taffy::LayoutPartialTree for Node {
136 type CoreContainerStyle<'a>
137 = &'a Style
138 where
139 Self: 'a;
140
141 fn get_core_container_style(&self, node_id: NodeId) -> Self::CoreContainerStyle<'_> {
142 &self.node_from_id(node_id).style
143 }
144
145 fn set_unrounded_layout(&mut self, node_id: NodeId, layout: &Layout) {
146 self.node_from_id_mut(node_id).layout = *layout
147 }
148
149 fn compute_child_layout(&mut self, node_id: NodeId, inputs: taffy::tree::LayoutInput) -> taffy::tree::LayoutOutput {
150 compute_cached_layout(self, node_id, inputs, |parent, node_id, inputs| {
151 let node = parent.node_from_id_mut(node_id);
152 let font_metrics = FontMetrics { char_width: 10.0, char_height: 10.0 };
153
154 match node.kind {
155 NodeKind::Flexbox => compute_flexbox_layout(node, node_id, inputs),
156 NodeKind::Grid => compute_grid_layout(node, node_id, inputs),
157 NodeKind::Text => compute_leaf_layout(inputs, &node.style, |known_dimensions, available_space| {
158 text_measure_function(
159 known_dimensions,
160 available_space,
161 node.text_data.as_ref().unwrap(),
162 &font_metrics,
163 )
164 }),
165 NodeKind::Image => compute_leaf_layout(inputs, &node.style, |known_dimensions, _available_space| {
166 image_measure_function(known_dimensions, node.image_data.as_ref().unwrap())
167 }),
168 }
169 })
170 }
171}
172
173impl CacheTree for Node {
174 fn cache_get(
175 &self,
176 node_id: NodeId,
177 known_dimensions: Size<Option<f32>>,
178 available_space: Size<AvailableSpace>,
179 run_mode: taffy::RunMode,
180 ) -> Option<taffy::LayoutOutput> {
181 self.node_from_id(node_id).cache.get(known_dimensions, available_space, run_mode)
182 }
183
184 fn cache_store(
185 &mut self,
186 node_id: NodeId,
187 known_dimensions: Size<Option<f32>>,
188 available_space: Size<AvailableSpace>,
189 run_mode: taffy::RunMode,
190 layout_output: taffy::LayoutOutput,
191 ) {
192 self.node_from_id_mut(node_id).cache.store(known_dimensions, available_space, run_mode, layout_output)
193 }
194
195 fn cache_clear(&mut self, node_id: NodeId) {
196 self.node_from_id_mut(node_id).cache.clear()
197 }
198}
199
200impl taffy::LayoutFlexboxContainer for Node {
201 type FlexboxContainerStyle<'a>
202 = &'a Style
203 where
204 Self: 'a;
205
206 type FlexboxItemStyle<'a>
207 = &'a Style
208 where
209 Self: 'a;
210
211 fn get_flexbox_container_style(&self, node_id: NodeId) -> Self::FlexboxContainerStyle<'_> {
212 &self.node_from_id(node_id).style
213 }
214
215 fn get_flexbox_child_style(&self, child_node_id: NodeId) -> Self::FlexboxItemStyle<'_> {
216 &self.node_from_id(child_node_id).style
217 }
218}
219
220impl taffy::LayoutGridContainer for Node {
221 type GridContainerStyle<'a>
222 = &'a Style
223 where
224 Self: 'a;
225
226 type GridItemStyle<'a>
227 = &'a Style
228 where
229 Self: 'a;
230
231 fn get_grid_container_style(&self, node_id: NodeId) -> Self::GridContainerStyle<'_> {
232 &self.node_from_id(node_id).style
233 }
234
235 fn get_grid_child_style(&self, child_node_id: NodeId) -> Self::GridItemStyle<'_> {
236 &self.node_from_id(child_node_id).style
237 }
238}
239
240fn main() -> Result<(), taffy::TaffyError> {
241 let mut root = Node::new_column(Style::DEFAULT);
242
243 let text_node = Node::new_text(
244 Style::default(),
245 TextContext { text_content: LOREM_IPSUM.into(), writing_mode: WritingMode::Horizontal },
246 );
247 root.append_child(text_node);
248
249 let image_node = Node::new_image(Style::default(), ImageContext { width: 400.0, height: 300.0 });
250 root.append_child(image_node);
251
252 // Compute layout
253 root.compute_layout(Size::MAX_CONTENT);
254
255 Ok(())
256}