taffy/compute/
leaf.rs

1//! Computes size using styles and measure functions
2
3#[cfg(feature = "content_size")]
4use crate::geometry::Rect;
5use crate::geometry::Size;
6use crate::style::{AvailableSpace, Overflow, Position};
7use crate::tree::{Baselines, CollapsibleMarginSet, RunMode};
8use crate::tree::{LayoutInput, LayoutOutput, SizingMode};
9use crate::util::debug::debug_log;
10use crate::util::sys::f32_max;
11use crate::util::MaybeMath;
12use crate::util::{MaybeResolve, ResolveOrZero};
13use crate::{BoxSizing, CoreStyle};
14use core::unreachable;
15
16/// Compute the size of a leaf node (node with no children)
17pub fn compute_leaf_layout<MeasureFunction>(
18    inputs: LayoutInput,
19    style: &impl CoreStyle,
20    resolve_calc_value: impl Fn(*const (), f32) -> f32,
21    measure_function: MeasureFunction,
22) -> LayoutOutput
23where
24    MeasureFunction: FnOnce(Size<Option<f32>>, Size<AvailableSpace>) -> Size<f32>,
25{
26    let LayoutInput { known_dimensions, parent_size, available_space, sizing_mode, run_mode, .. } = inputs;
27
28    // Note: both horizontal and vertical percentage padding/borders are resolved against the container's inline size (i.e. width).
29    // This is not a bug, but is how CSS is specified (see: https://developer.mozilla.org/en-US/docs/Web/CSS/padding#values)
30    let margin = style.margin().resolve_or_zero(parent_size.width, &resolve_calc_value);
31    let padding = style.padding().resolve_or_zero(parent_size.width, &resolve_calc_value);
32    let border = style.border().resolve_or_zero(parent_size.width, &resolve_calc_value);
33    let padding_border = padding + border;
34    let pb_sum = padding_border.sum_axes();
35    let box_sizing_adjustment = if style.box_sizing() == BoxSizing::ContentBox { pb_sum } else { Size::ZERO };
36
37    // Resolve node's preferred/min/max sizes (width/heights) against the available space (percentages resolve to pixel values)
38    // For ContentSize mode, we pretend that the node has no size styles as these should be ignored.
39    let (node_size, node_min_size, node_max_size, aspect_ratio) = match sizing_mode {
40        SizingMode::ContentSize => {
41            let node_size = known_dimensions;
42            let node_min_size = Size::NONE;
43            let node_max_size = Size::NONE;
44            (node_size, node_min_size, node_max_size, None)
45        }
46        SizingMode::InherentSize => {
47            let aspect_ratio = style.aspect_ratio();
48            let style_size = style
49                .size()
50                .maybe_resolve(parent_size, &resolve_calc_value)
51                .maybe_apply_aspect_ratio(aspect_ratio)
52                .maybe_add(box_sizing_adjustment);
53            let style_min_size = style
54                .min_size()
55                .maybe_resolve(parent_size, &resolve_calc_value)
56                .maybe_apply_aspect_ratio(aspect_ratio)
57                .maybe_add(box_sizing_adjustment);
58            let style_max_size =
59                style.max_size().maybe_resolve(parent_size, &resolve_calc_value).maybe_add(box_sizing_adjustment);
60
61            let node_size = known_dimensions.or(style_size);
62            (node_size, style_min_size, style_max_size, aspect_ratio)
63        }
64    };
65
66    // Scrollbar gutters are reserved when the `overflow` property is set to `Overflow::Scroll`.
67    // However, the axis are switched (transposed) because a node that scrolls vertically needs
68    // *horizontal* space to be reserved for a scrollbar
69    let scrollbar_gutter = style.overflow().transpose().map(|overflow| match overflow {
70        Overflow::Scroll => style.scrollbar_width(),
71        _ => 0.0,
72    });
73    // TODO: make side configurable based on the `direction` property
74    let mut content_box_inset = padding_border;
75    content_box_inset.right += scrollbar_gutter.x;
76    content_box_inset.bottom += scrollbar_gutter.y;
77
78    let has_styles_preventing_being_collapsed_through = !style.is_block()
79        || style.overflow().x.is_scroll_container()
80        || style.overflow().y.is_scroll_container()
81        || style.position() == Position::Absolute
82        || style.contain().establishes_independent_formatting_context()
83        || padding.top > 0.0
84        || padding.bottom > 0.0
85        || border.top > 0.0
86        || border.bottom > 0.0
87        || matches!(node_size.height, Some(h) if h > 0.0)
88        || matches!(node_min_size.height, Some(h) if h > 0.0);
89
90    debug_log!("LEAF");
91    debug_log!("node_size", dbg:node_size);
92    debug_log!("min_size ", dbg:node_min_size);
93    debug_log!("max_size ", dbg:node_max_size);
94
95    // Return early if both width and height are known
96    if run_mode == RunMode::ComputeSize && has_styles_preventing_being_collapsed_through {
97        if let Size { width: Some(width), height: Some(height) } = node_size {
98            let size = Size { width, height }
99                .maybe_clamp(node_min_size, node_max_size)
100                .maybe_max(padding_border.sum_axes().map(Some));
101            return LayoutOutput {
102                size,
103                #[cfg(feature = "content_size")]
104                scrollable_overflow_rect: Rect::ZERO,
105                baselines: Baselines::NONE,
106                top_margin: CollapsibleMarginSet::ZERO,
107                bottom_margin: CollapsibleMarginSet::ZERO,
108                margins_can_collapse_through: false,
109            };
110        };
111    }
112
113    // Compute available space
114    let available_space = Size {
115        width: known_dimensions
116            .width
117            .map(AvailableSpace::from)
118            .unwrap_or(available_space.width)
119            .maybe_sub(margin.horizontal_axis_sum())
120            .maybe_set(known_dimensions.width)
121            .maybe_set(node_size.width)
122            .map_definite_value(|size| {
123                size.maybe_clamp(node_min_size.width, node_max_size.width) - content_box_inset.horizontal_axis_sum()
124            }),
125        height: known_dimensions
126            .height
127            .map(AvailableSpace::from)
128            .unwrap_or(available_space.height)
129            .maybe_sub(margin.vertical_axis_sum())
130            .maybe_set(known_dimensions.height)
131            .maybe_set(node_size.height)
132            .map_definite_value(|size| {
133                size.maybe_clamp(node_min_size.height, node_max_size.height) - content_box_inset.vertical_axis_sum()
134            }),
135    };
136
137    // Measure node
138    let measured_size = measure_function(
139        match run_mode {
140            RunMode::ComputeSize => known_dimensions,
141            RunMode::PerformLayout => Size::NONE,
142            RunMode::PerformHiddenLayout => unreachable!(),
143        },
144        available_space,
145    );
146    let clamped_size = known_dimensions
147        .or(node_size)
148        .unwrap_or(measured_size + content_box_inset.sum_axes())
149        .maybe_clamp(node_min_size, node_max_size);
150    let size = Size {
151        width: clamped_size.width,
152        height: f32_max(clamped_size.height, aspect_ratio.map(|ratio| clamped_size.width / ratio).unwrap_or(0.0)),
153    };
154    let size = size.maybe_max(padding_border.sum_axes().map(Some));
155
156    // A scroll container's own padding at the end of the content is part of its scrollable
157    // overflow region, so it is included in the overflow rect. Boxes that are not scroll
158    // containers do not extend their overflow region by their own padding.
159    #[cfg(feature = "content_size")]
160    let scrollable_overflow_rect = {
161        let is_scroll_container = style.overflow().x.is_scroll_container() || style.overflow().y.is_scroll_container();
162        let is_rtl = style.direction().is_rtl();
163        let start_padding = if is_rtl { padding.right } else { padding.left };
164        let end_padding = if is_rtl { padding.left } else { padding.right };
165        Rect {
166            left: 0.0,
167            right: start_padding + measured_size.width + if is_scroll_container { end_padding } else { 0.0 },
168            top: 0.0,
169            bottom: padding.top + measured_size.height + if is_scroll_container { padding.bottom } else { 0.0 },
170        }
171    };
172
173    LayoutOutput {
174        size,
175        #[cfg(feature = "content_size")]
176        scrollable_overflow_rect,
177        baselines: Baselines::NONE,
178        top_margin: CollapsibleMarginSet::ZERO,
179        bottom_margin: CollapsibleMarginSet::ZERO,
180        margins_can_collapse_through: !has_styles_preventing_being_collapsed_through
181            && size.height == 0.0
182            && measured_size.height == 0.0,
183    }
184}
taffy/compute/leaf.rs

taffy/compute/
leaf.rs
