tawasuyu/taffy

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    type CustomIdent = String;
142
143    fn get_core_container_style(&self, node_id: NodeId) -> Self::CoreContainerStyle<'_> {
144        &self.node_from_id(node_id).style
145    }
146
147    fn set_unrounded_layout(&mut self, node_id: NodeId, layout: &Layout) {
148        self.node_from_id_mut(node_id).layout = *layout
149    }
150
151    fn resolve_calc_value(&self, _val: *const (), _basis: f32) -> f32 {
152        0.0
153    }
154
155    fn compute_child_layout(&mut self, node_id: NodeId, inputs: taffy::tree::LayoutInput) -> taffy::tree::LayoutOutput {
156        compute_cached_layout(self, node_id, inputs, |parent, node_id, inputs| {
157            let node = parent.node_from_id_mut(node_id);
158            let font_metrics = FontMetrics { char_width: 10.0, char_height: 10.0 };
159
160            match node.kind {
161                NodeKind::Flexbox => compute_flexbox_layout(node, node_id, inputs),
162                NodeKind::Grid => compute_grid_layout(node, node_id, inputs),
163                NodeKind::Text => compute_leaf_layout(
164                    inputs,
165                    &node.style,
166                    |_val, _basis| 0.0,
167                    |known_dimensions, available_space| {
168                        text_measure_function(
169                            known_dimensions,
170                            available_space,
171                            node.text_data.as_ref().unwrap(),
172                            &font_metrics,
173                        )
174                    },
175                ),
176                NodeKind::Image => compute_leaf_layout(
177                    inputs,
178                    &node.style,
179                    |_val, _basis| 0.0,
180                    |known_dimensions, _available_space| {
181                        image_measure_function(known_dimensions, node.image_data.as_ref().unwrap())
182                    },
183                ),
184            }
185        })
186    }
187}
188
189impl CacheTree for Node {
190    fn cache_get(&self, node_id: NodeId, inputs: &taffy::LayoutInput) -> Option<taffy::LayoutOutput> {
191        self.node_from_id(node_id).cache.get(inputs)
192    }
193
194    fn cache_store(&mut self, node_id: NodeId, inputs: &taffy::LayoutInput, layout_output: taffy::LayoutOutput) {
195        self.node_from_id_mut(node_id).cache.store(inputs, layout_output)
196    }
197
198    fn cache_clear(&mut self, node_id: NodeId) {
199        self.node_from_id_mut(node_id).cache.clear();
200    }
201}
202
203impl taffy::LayoutFlexboxContainer for Node {
204    type FlexboxContainerStyle<'a>
205        = &'a Style
206    where
207        Self: 'a;
208
209    type FlexboxItemStyle<'a>
210        = &'a Style
211    where
212        Self: 'a;
213
214    fn get_flexbox_container_style(&self, node_id: NodeId) -> Self::FlexboxContainerStyle<'_> {
215        &self.node_from_id(node_id).style
216    }
217
218    fn get_flexbox_child_style(&self, child_node_id: NodeId) -> Self::FlexboxItemStyle<'_> {
219        &self.node_from_id(child_node_id).style
220    }
221}
222
223impl taffy::LayoutGridContainer for Node {
224    type GridContainerStyle<'a>
225        = &'a Style
226    where
227        Self: 'a;
228
229    type GridItemStyle<'a>
230        = &'a Style
231    where
232        Self: 'a;
233
234    fn get_grid_container_style(&self, node_id: NodeId) -> Self::GridContainerStyle<'_> {
235        &self.node_from_id(node_id).style
236    }
237
238    fn get_grid_child_style(&self, child_node_id: NodeId) -> Self::GridItemStyle<'_> {
239        &self.node_from_id(child_node_id).style
240    }
241}
242
243fn main() -> Result<(), taffy::TaffyError> {
244    let mut root = Node::new_column(Style::DEFAULT);
245
246    let text_node = Node::new_text(
247        Style::default(),
248        TextContext { text_content: LOREM_IPSUM.into(), writing_mode: WritingMode::Horizontal },
249    );
250    root.append_child(text_node);
251
252    let image_node = Node::new_image(Style::default(), ImageContext { width: 400.0, height: 300.0 });
253    root.append_child(image_node);
254
255    // Compute layout
256    root.compute_layout(Size::MAX_CONTENT);
257
258    Ok(())
259}