tawasuyu/taffy

1//! Alignment of tracks and final positioning of items
2use super::types::GridTrack;
3use crate::compute::common::alignment::{apply_alignment_fallback, compute_alignment_offset};
4use crate::geometry::{InBothAbsAxis, Line, Point, Rect, Size};
5use crate::style::{AlignContent, AlignItems, AlignSelf, AvailableSpace, CoreStyle, GridItemStyle, Overflow, Position};
6use crate::tree::{Layout, LayoutPartialTreeExt, NodeId, SizingMode};
7use crate::util::sys::f32_max;
8use crate::util::{MaybeMath, MaybeResolve, ResolveOrZero};
9
10#[cfg(feature = "content_size")]
11use crate::compute::common::content_size::compute_content_size_contribution;
12use crate::{BoxSizing, LayoutGridContainer};
13
14/// Align the grid tracks within the grid according to the align-content (rows) or
15/// justify-content (columns) property. This only does anything if the size of the
16/// grid is not equal to the size of the grid container in the axis being aligned.
17pub(super) fn align_tracks(
18    grid_container_content_box_size: f32,
19    padding: Line<f32>,
20    border: Line<f32>,
21    tracks: &mut [GridTrack],
22    track_alignment_style: AlignContent,
23) {
24    let used_size: f32 = tracks.iter().map(|track| track.base_size).sum();
25    let free_space = grid_container_content_box_size - used_size;
26    let origin = padding.start + border.start;
27
28    // Count the number of non-collapsed tracks (not counting gutters)
29    let num_tracks = tracks.iter().skip(1).step_by(2).filter(|track| !track.is_collapsed).count();
30
31    // Grid layout treats gaps as full tracks rather than applying them at alignment so we
32    // simply pass zero here. Grid layout is never reversed.
33    let gap = 0.0;
34    let layout_is_reversed = false;
35    let is_safe = false; // TODO: Implement safe alignment
36    let track_alignment = apply_alignment_fallback(free_space, num_tracks, track_alignment_style, is_safe);
37
38    // Compute offsets
39    let mut total_offset = origin;
40    tracks.iter_mut().enumerate().for_each(|(i, track)| {
41        // Odd tracks are gutters (but slices are zero-indexed, so odd tracks have even indices)
42        let is_gutter = i % 2 == 0;
43
44        // The first non-gutter track is index 1
45        let is_first = i == 1;
46
47        let offset = if is_gutter {
48            0.0
49        } else {
50            compute_alignment_offset(free_space, num_tracks, gap, track_alignment, layout_is_reversed, is_first)
51        };
52
53        track.offset = total_offset + offset;
54        total_offset = total_offset + offset + track.base_size;
55    });
56}
57
58/// Align and size a grid item into it's final position
59pub(super) fn align_and_position_item(
60    tree: &mut impl LayoutGridContainer,
61    node: NodeId,
62    order: u32,
63    grid_area: Rect<f32>,
64    container_alignment_styles: InBothAbsAxis<Option<AlignItems>>,
65    baseline_shim: f32,
66) -> (Size<f32>, f32, f32) {
67    let grid_area_size = Size { width: grid_area.right - grid_area.left, height: grid_area.bottom - grid_area.top };
68
69    let style = tree.get_grid_child_style(node);
70
71    let overflow = style.overflow();
72    let scrollbar_width = style.scrollbar_width();
73    let aspect_ratio = style.aspect_ratio();
74    let justify_self = style.justify_self();
75    let align_self = style.align_self();
76
77    let position = style.position();
78    let inset_horizontal =
79        style.inset().horizontal_components().map(|size| size.resolve_to_option(grid_area_size.width));
80    let inset_vertical = style.inset().vertical_components().map(|size| size.resolve_to_option(grid_area_size.height));
81    let padding = style.padding().map(|p| p.resolve_or_zero(Some(grid_area_size.width)));
82    let border = style.border().map(|p| p.resolve_or_zero(Some(grid_area_size.width)));
83    let padding_border_size = (padding + border).sum_axes();
84
85    let box_sizing_adjustment =
86        if style.box_sizing() == BoxSizing::ContentBox { padding_border_size } else { Size::ZERO };
87
88    let inherent_size = style
89        .size()
90        .maybe_resolve(grid_area_size)
91        .maybe_apply_aspect_ratio(aspect_ratio)
92        .maybe_add(box_sizing_adjustment);
93    let min_size = style
94        .min_size()
95        .maybe_resolve(grid_area_size)
96        .maybe_add(box_sizing_adjustment)
97        .or(padding_border_size.map(Some))
98        .maybe_max(padding_border_size)
99        .maybe_apply_aspect_ratio(aspect_ratio);
100    let max_size = style
101        .max_size()
102        .maybe_resolve(grid_area_size)
103        .maybe_apply_aspect_ratio(aspect_ratio)
104        .maybe_add(box_sizing_adjustment);
105
106    // Resolve default alignment styles if they are set on neither the parent or the node itself
107    // Note: if the child has a preferred aspect ratio but neither width or height are set, then the width is stretched
108    // and the then height is calculated from the width according the aspect ratio
109    // See: https://www.w3.org/TR/css-grid-1/#grid-item-sizing
110    let alignment_styles = InBothAbsAxis {
111        horizontal: justify_self.or(container_alignment_styles.horizontal).unwrap_or_else(|| {
112            if inherent_size.width.is_some() {
113                AlignSelf::Start
114            } else {
115                AlignSelf::Stretch
116            }
117        }),
118        vertical: align_self.or(container_alignment_styles.vertical).unwrap_or_else(|| {
119            if inherent_size.height.is_some() || aspect_ratio.is_some() {
120                AlignSelf::Start
121            } else {
122                AlignSelf::Stretch
123            }
124        }),
125    };
126
127    // Note: This is not a bug. It is part of the CSS spec that both horizontal and vertical margins
128    // resolve against the WIDTH of the grid area.
129    let margin = style.margin().map(|margin| margin.resolve_to_option(grid_area_size.width));
130
131    let grid_area_minus_item_margins_size = Size {
132        width: grid_area_size.width.maybe_sub(margin.left).maybe_sub(margin.right),
133        height: grid_area_size.height.maybe_sub(margin.top).maybe_sub(margin.bottom) - baseline_shim,
134    };
135
136    // If node is absolutely positioned and width is not set explicitly, then deduce it
137    // from left, right and container_content_box if both are set.
138    let width = inherent_size.width.or_else(|| {
139        // Apply width derived from both the left and right properties of an absolutely
140        // positioned element being set
141        if position == Position::Absolute {
142            if let (Some(left), Some(right)) = (inset_horizontal.start, inset_horizontal.end) {
143                return Some(f32_max(grid_area_minus_item_margins_size.width - left - right, 0.0));
144            }
145        }
146
147        // Apply width based on stretch alignment if:
148        //  - Alignment style is "stretch"
149        //  - The node is not absolutely positioned
150        //  - The node does not have auto margins in this axis.
151        if margin.left.is_some()
152            && margin.right.is_some()
153            && alignment_styles.horizontal == AlignSelf::Stretch
154            && position != Position::Absolute
155        {
156            return Some(grid_area_minus_item_margins_size.width);
157        }
158
159        None
160    });
161
162    // Reapply aspect ratio after stretch and absolute position width adjustments
163    let Size { width, height } = Size { width, height: inherent_size.height }.maybe_apply_aspect_ratio(aspect_ratio);
164
165    let height = height.or_else(|| {
166        if position == Position::Absolute {
167            if let (Some(top), Some(bottom)) = (inset_vertical.start, inset_vertical.end) {
168                return Some(f32_max(grid_area_minus_item_margins_size.height - top - bottom, 0.0));
169            }
170        }
171
172        // Apply height based on stretch alignment if:
173        //  - Alignment style is "stretch"
174        //  - The node is not absolutely positioned
175        //  - The node does not have auto margins in this axis.
176        if margin.top.is_some()
177            && margin.bottom.is_some()
178            && alignment_styles.vertical == AlignSelf::Stretch
179            && position != Position::Absolute
180        {
181            return Some(grid_area_minus_item_margins_size.height);
182        }
183
184        None
185    });
186    // Reapply aspect ratio after stretch and absolute position height adjustments
187    let Size { width, height } = Size { width, height }.maybe_apply_aspect_ratio(aspect_ratio);
188
189    // Clamp size by min and max width/height
190    let Size { width, height } = Size { width, height }.maybe_clamp(min_size, max_size);
191
192    // Layout node
193    drop(style);
194    let layout_output = tree.perform_child_layout(
195        node,
196        Size { width, height },
197        grid_area_size.map(Option::Some),
198        grid_area_minus_item_margins_size.map(AvailableSpace::Definite),
199        SizingMode::InherentSize,
200        Line::FALSE,
201    );
202
203    // Resolve final size
204    let Size { width, height } = Size { width, height }.unwrap_or(layout_output.size).maybe_clamp(min_size, max_size);
205
206    let (x, x_margin) = align_item_within_area(
207        Line { start: grid_area.left, end: grid_area.right },
208        justify_self.unwrap_or(alignment_styles.horizontal),
209        width,
210        position,
211        inset_horizontal,
212        margin.horizontal_components(),
213        0.0,
214    );
215    let (y, y_margin) = align_item_within_area(
216        Line { start: grid_area.top, end: grid_area.bottom },
217        align_self.unwrap_or(alignment_styles.vertical),
218        height,
219        position,
220        inset_vertical,
221        margin.vertical_components(),
222        baseline_shim,
223    );
224
225    let scrollbar_size = Size {
226        width: if overflow.y == Overflow::Scroll { scrollbar_width } else { 0.0 },
227        height: if overflow.x == Overflow::Scroll { scrollbar_width } else { 0.0 },
228    };
229
230    let resolved_margin = Rect { left: x_margin.start, right: x_margin.end, top: y_margin.start, bottom: y_margin.end };
231
232    tree.set_unrounded_layout(
233        node,
234        &Layout {
235            order,
236            location: Point { x, y },
237            size: Size { width, height },
238            #[cfg(feature = "content_size")]
239            content_size: layout_output.content_size,
240            scrollbar_size,
241            padding,
242            border,
243            margin: resolved_margin,
244        },
245    );
246
247    #[cfg(feature = "content_size")]
248    let contribution =
249        compute_content_size_contribution(Point { x, y }, Size { width, height }, layout_output.content_size, overflow);
250    #[cfg(not(feature = "content_size"))]
251    let contribution = Size::ZERO;
252
253    (contribution, y, height)
254}
255
256/// Align and size a grid item along a single axis
257pub(super) fn align_item_within_area(
258    grid_area: Line<f32>,
259    alignment_style: AlignSelf,
260    resolved_size: f32,
261    position: Position,
262    inset: Line<Option<f32>>,
263    margin: Line<Option<f32>>,
264    baseline_shim: f32,
265) -> (f32, Line<f32>) {
266    // Calculate grid area dimension in the axis
267    let non_auto_margin = Line { start: margin.start.unwrap_or(0.0) + baseline_shim, end: margin.end.unwrap_or(0.0) };
268    let grid_area_size = f32_max(grid_area.end - grid_area.start, 0.0);
269    let free_space = f32_max(grid_area_size - resolved_size - non_auto_margin.sum(), 0.0);
270
271    // Expand auto margins to fill available space
272    let auto_margin_count = margin.start.is_none() as u8 + margin.end.is_none() as u8;
273    let auto_margin_size = if auto_margin_count > 0 { free_space / auto_margin_count as f32 } else { 0.0 };
274    let resolved_margin = Line {
275        start: margin.start.unwrap_or(auto_margin_size) + baseline_shim,
276        end: margin.end.unwrap_or(auto_margin_size),
277    };
278
279    // Compute offset in the axis
280    let alignment_based_offset = match alignment_style {
281        AlignSelf::Start | AlignSelf::FlexStart => resolved_margin.start,
282        AlignSelf::End | AlignSelf::FlexEnd => grid_area_size - resolved_size - resolved_margin.end,
283        AlignSelf::Center => (grid_area_size - resolved_size + resolved_margin.start - resolved_margin.end) / 2.0,
284        // TODO: Add support for baseline alignment. For now we treat it as "start".
285        AlignSelf::Baseline => resolved_margin.start,
286        AlignSelf::Stretch => resolved_margin.start,
287    };
288
289    let offset_within_area = if position == Position::Absolute {
290        if let Some(start) = inset.start {
291            start + non_auto_margin.start
292        } else if let Some(end) = inset.end {
293            grid_area_size - end - resolved_size - non_auto_margin.end
294        } else {
295            alignment_based_offset
296        }
297    } else {
298        alignment_based_offset
299    };
300
301    let mut start = grid_area.start + offset_within_area;
302    if position == Position::Relative {
303        start += inset.start.or(inset.end.map(|pos| -pos)).unwrap_or(0.0);
304    }
305
306    (start, resolved_margin)
307}