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, 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> = &'a Style where
137        Self: 'a;
138
139    type CacheMut<'b> = &'b mut Cache where Self: 'b;
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 get_cache_mut(&mut self, node_id: NodeId) -> &mut Cache {
150        &mut self.node_from_id_mut(node_id).cache
151    }
152
153    fn compute_child_layout(&mut self, node_id: NodeId, inputs: taffy::tree::LayoutInput) -> taffy::tree::LayoutOutput {
154        compute_cached_layout(self, node_id, inputs, |parent, node_id, inputs| {
155            let node = parent.node_from_id_mut(node_id);
156            let font_metrics = FontMetrics { char_width: 10.0, char_height: 10.0 };
157
158            match node.kind {
159                NodeKind::Flexbox => compute_flexbox_layout(node, node_id, inputs),
160                NodeKind::Grid => compute_grid_layout(node, node_id, inputs),
161                NodeKind::Text => compute_leaf_layout(inputs, &node.style, |known_dimensions, available_space| {
162                    text_measure_function(
163                        known_dimensions,
164                        available_space,
165                        node.text_data.as_ref().unwrap(),
166                        &font_metrics,
167                    )
168                }),
169                NodeKind::Image => compute_leaf_layout(inputs, &node.style, |known_dimensions, _available_space| {
170                    image_measure_function(known_dimensions, node.image_data.as_ref().unwrap())
171                }),
172            }
173        })
174    }
175}
176
177impl taffy::LayoutFlexboxContainer for Node {
178    type FlexboxContainerStyle<'a> = &'a Style where
179        Self: 'a;
180
181    type FlexboxItemStyle<'a> = &'a Style where
182        Self: 'a;
183
184    fn get_flexbox_container_style(&self, node_id: NodeId) -> Self::FlexboxContainerStyle<'_> {
185        &self.node_from_id(node_id).style
186    }
187
188    fn get_flexbox_child_style(&self, child_node_id: NodeId) -> Self::FlexboxItemStyle<'_> {
189        &self.node_from_id(child_node_id).style
190    }
191}
192
193impl taffy::LayoutGridContainer for Node {
194    type GridContainerStyle<'a> = &'a Style where
195        Self: 'a;
196
197    type GridItemStyle<'a> = &'a Style where
198        Self: 'a;
199
200    fn get_grid_container_style(&self, node_id: NodeId) -> Self::GridContainerStyle<'_> {
201        &self.node_from_id(node_id).style
202    }
203
204    fn get_grid_child_style(&self, child_node_id: NodeId) -> Self::GridItemStyle<'_> {
205        &self.node_from_id(child_node_id).style
206    }
207}
208
209fn main() -> Result<(), taffy::TaffyError> {
210    let mut root = Node::new_column(Style::DEFAULT);
211
212    let text_node = Node::new_text(
213        Style::default(),
214        TextContext { text_content: LOREM_IPSUM.into(), writing_mode: WritingMode::Horizontal },
215    );
216    root.append_child(text_node);
217
218    let image_node = Node::new_image(Style::default(), ImageContext { width: 400.0, height: 300.0 });
219    root.append_child(image_node);
220
221    // Compute layout
222    root.compute_layout(Size::MAX_CONTENT);
223
224    Ok(())
225}