taffy/compute/
leaf.rs

1//! Computes size using styles and measure functions
2
3use crate::geometry::{Point, Size};
4use crate::style::{AvailableSpace, Overflow, Position};
5use crate::tree::{CollapsibleMarginSet, RunMode};
6use crate::tree::{LayoutInput, LayoutOutput, SizingMode};
7use crate::util::debug::debug_log;
8use crate::util::sys::f32_max;
9use crate::util::MaybeMath;
10use crate::util::{MaybeResolve, ResolveOrZero};
11use crate::{BoxSizing, CoreStyle};
12use core::unreachable;
13
14/// Compute the size of a leaf node (node with no children)
15pub fn compute_leaf_layout<MeasureFunction>(
16    inputs: LayoutInput,
17    style: &impl CoreStyle,
18    measure_function: MeasureFunction,
19) -> LayoutOutput
20where
21    MeasureFunction: FnOnce(Size<Option<f32>>, Size<AvailableSpace>) -> Size<f32>,
22{
23    let LayoutInput { known_dimensions, parent_size, available_space, sizing_mode, run_mode, .. } = inputs;
24
25    // Note: both horizontal and vertical percentage padding/borders are resolved against the container's inline size (i.e. width).
26    // This is not a bug, but is how CSS is specified (see: https://developer.mozilla.org/en-US/docs/Web/CSS/padding#values)
27    let margin = style.margin().resolve_or_zero(parent_size.width);
28    let padding = style.padding().resolve_or_zero(parent_size.width);
29    let border = style.border().resolve_or_zero(parent_size.width);
30    let padding_border = padding + border;
31    let pb_sum = padding_border.sum_axes();
32    let box_sizing_adjustment = if style.box_sizing() == BoxSizing::ContentBox { pb_sum } else { Size::ZERO };
33
34    // Resolve node's preferred/min/max sizes (width/heights) against the available space (percentages resolve to pixel values)
35    // For ContentSize mode, we pretend that the node has no size styles as these should be ignored.
36    let (node_size, node_min_size, node_max_size, aspect_ratio) = match sizing_mode {
37        SizingMode::ContentSize => {
38            let node_size = known_dimensions;
39            let node_min_size = Size::NONE;
40            let node_max_size = Size::NONE;
41            (node_size, node_min_size, node_max_size, None)
42        }
43        SizingMode::InherentSize => {
44            let aspect_ratio = style.aspect_ratio();
45            let style_size = style
46                .size()
47                .maybe_resolve(parent_size)
48                .maybe_apply_aspect_ratio(aspect_ratio)
49                .maybe_add(box_sizing_adjustment);
50            let style_min_size = style
51                .min_size()
52                .maybe_resolve(parent_size)
53                .maybe_apply_aspect_ratio(aspect_ratio)
54                .maybe_add(box_sizing_adjustment);
55            let style_max_size = style.max_size().maybe_resolve(parent_size).maybe_add(box_sizing_adjustment);
56
57            let node_size = known_dimensions.or(style_size);
58            (node_size, style_min_size, style_max_size, aspect_ratio)
59        }
60    };
61
62    // Scrollbar gutters are reserved when the `overflow` property is set to `Overflow::Scroll`.
63    // However, the axis are switched (transposed) because a node that scrolls vertically needs
64    // *horizontal* space to be reserved for a scrollbar
65    let scrollbar_gutter = style.overflow().transpose().map(|overflow| match overflow {
66        Overflow::Scroll => style.scrollbar_width(),
67        _ => 0.0,
68    });
69    // TODO: make side configurable based on the `direction` property
70    let mut content_box_inset = padding_border;
71    content_box_inset.right += scrollbar_gutter.x;
72    content_box_inset.bottom += scrollbar_gutter.y;
73
74    let has_styles_preventing_being_collapsed_through = !style.is_block()
75        || style.overflow().x.is_scroll_container()
76        || style.overflow().y.is_scroll_container()
77        || style.position() == Position::Absolute
78        || padding.top > 0.0
79        || padding.bottom > 0.0
80        || border.top > 0.0
81        || border.bottom > 0.0
82        || matches!(node_size.height, Some(h) if h > 0.0)
83        || matches!(node_min_size.height, Some(h) if h > 0.0);
84
85    debug_log!("LEAF");
86    debug_log!("node_size", dbg:node_size);
87    debug_log!("min_size ", dbg:node_min_size);
88    debug_log!("max_size ", dbg:node_max_size);
89
90    // Return early if both width and height are known
91    if run_mode == RunMode::ComputeSize && has_styles_preventing_being_collapsed_through {
92        if let Size { width: Some(width), height: Some(height) } = node_size {
93            let size = Size { width, height }
94                .maybe_clamp(node_min_size, node_max_size)
95                .maybe_max(padding_border.sum_axes().map(Some));
96            return LayoutOutput {
97                size,
98                #[cfg(feature = "content_size")]
99                content_size: Size::ZERO,
100                first_baselines: Point::NONE,
101                top_margin: CollapsibleMarginSet::ZERO,
102                bottom_margin: CollapsibleMarginSet::ZERO,
103                margins_can_collapse_through: false,
104            };
105        };
106    }
107
108    // Compute available space
109    let available_space = Size {
110        width: known_dimensions
111            .width
112            .map(AvailableSpace::from)
113            .unwrap_or(available_space.width)
114            .maybe_sub(margin.horizontal_axis_sum())
115            .maybe_set(known_dimensions.width)
116            .maybe_set(node_size.width)
117            .maybe_set(node_max_size.width)
118            .map_definite_value(|size| {
119                size.maybe_clamp(node_min_size.width, node_max_size.width) - content_box_inset.horizontal_axis_sum()
120            }),
121        height: known_dimensions
122            .height
123            .map(AvailableSpace::from)
124            .unwrap_or(available_space.height)
125            .maybe_sub(margin.vertical_axis_sum())
126            .maybe_set(known_dimensions.height)
127            .maybe_set(node_size.height)
128            .maybe_set(node_max_size.height)
129            .map_definite_value(|size| {
130                size.maybe_clamp(node_min_size.height, node_max_size.height) - content_box_inset.vertical_axis_sum()
131            }),
132    };
133
134    // Measure node
135    let measured_size = measure_function(
136        match run_mode {
137            RunMode::ComputeSize => known_dimensions,
138            RunMode::PerformLayout => Size::NONE,
139            RunMode::PerformHiddenLayout => unreachable!(),
140        },
141        available_space,
142    );
143    let clamped_size = known_dimensions
144        .or(node_size)
145        .unwrap_or(measured_size + content_box_inset.sum_axes())
146        .maybe_clamp(node_min_size, node_max_size);
147    let size = Size {
148        width: clamped_size.width,
149        height: f32_max(clamped_size.height, aspect_ratio.map(|ratio| clamped_size.width / ratio).unwrap_or(0.0)),
150    };
151    let size = size.maybe_max(padding_border.sum_axes().map(Some));
152
153    LayoutOutput {
154        size,
155        #[cfg(feature = "content_size")]
156        content_size: measured_size + padding.sum_axes(),
157        first_baselines: Point::NONE,
158        top_margin: CollapsibleMarginSet::ZERO,
159        bottom_margin: CollapsibleMarginSet::ZERO,
160        margins_can_collapse_through: !has_styles_preventing_being_collapsed_through
161            && size.height == 0.0
162            && measured_size.height == 0.0,
163    }
164}
taffy/compute/leaf.rs

taffy/compute/
leaf.rs
