Trampoline child measurement/layout through the `LayoutTree` trait (#427)
1//! This module is a partial implementation of the CSS Grid Level 1 specification
2//! <https://www.w3.org/TR/css-grid-1>
3use crate::axis::{AbsoluteAxis, AbstractAxis, InBothAbsAxis};
4use crate::geometry::{Line, Point, Rect, Size};
5use crate::layout::{Layout, RunMode, SizeAndBaselines, SizingMode};
6use crate::math::MaybeMath;
7use crate::node::Node;
8use crate::resolve::{MaybeResolve, ResolveOrZero};
9use crate::style::{AlignContent, AlignItems, AlignSelf, AvailableSpace, Display, Position};
10use crate::style_helpers::*;
11use crate::sys::{GridTrackVec, Vec};
12use crate::tree::LayoutTree;
13use alignment::{align_and_position_item, align_tracks};
14use explicit_grid::{compute_explicit_grid_size_in_axis, initialize_grid_tracks};
15use implicit_grid::compute_grid_size_estimate;
16use placement::place_grid_items;
17use track_sizing::{
18 determine_if_item_crosses_flexible_or_intrinsic_tracks, resolve_item_track_indexes, track_sizing_algorithm,
19};
20use types::{CellOccupancyMatrix, GridTrack};
21
22pub(crate) use types::{GridCoordinate, GridLine, OriginZeroLine};
23
24#[cfg(feature = "debug")]
25use crate::debug::NODE_LOGGER;
26
27use super::LayoutAlgorithm;
28
29mod alignment;
30mod explicit_grid;
31mod implicit_grid;
32mod placement;
33mod track_sizing;
34mod types;
35mod util;
36
37/// The public interface to Taffy's CSS Grid algorithm implementation
38pub(crate) struct CssGridAlgorithm;
39impl LayoutAlgorithm for CssGridAlgorithm {
40 const NAME: &'static str = "CSS GRID";
41
42 fn perform_layout(
43 tree: &mut impl LayoutTree,
44 node: Node,
45 known_dimensions: Size<Option<f32>>,
46 parent_size: Size<Option<f32>>,
47 available_space: Size<AvailableSpace>,
48 _sizing_mode: SizingMode,
49 ) -> SizeAndBaselines {
50 compute(tree, node, known_dimensions, parent_size, available_space, RunMode::PeformLayout)
51 }
52
53 fn measure_size(
54 tree: &mut impl LayoutTree,
55 node: Node,
56 known_dimensions: Size<Option<f32>>,
57 parent_size: Size<Option<f32>>,
58 available_space: Size<AvailableSpace>,
59 _sizing_mode: SizingMode,
60 ) -> Size<f32> {
61 compute(tree, node, known_dimensions, parent_size, available_space, RunMode::ComputeSize).size
62 }
63}
64
65/// Grid layout algorithm
66/// This consists of a few phases:
67/// - Resolving the explicit grid
68/// - Placing items (which also resolves the implicit grid)
69/// - Track (row/column) sizing
70/// - Alignment & Final item placement
71pub fn compute(
72 tree: &mut impl LayoutTree,
73 node: Node,
74 known_dimensions: Size<Option<f32>>,
75 parent_size: Size<Option<f32>>,
76 available_space: Size<AvailableSpace>,
77 run_mode: RunMode,
78) -> SizeAndBaselines {
79 let get_child_styles_iter = |node| tree.children(node).map(|child_node: &Node| tree.style(*child_node));
80 let style = tree.style(node).clone();
81 let child_styles_iter = get_child_styles_iter(node);
82
83 // 1. Resolve the explicit grid
84 // Exactly compute the number of rows and columns in the explicit grid.
85 let explicit_col_count = compute_explicit_grid_size_in_axis(&style, AbsoluteAxis::Horizontal);
86 let explicit_row_count = compute_explicit_grid_size_in_axis(&style, AbsoluteAxis::Vertical);
87
88 // 2. Implicit Grid: Estimate Track Counts
89 // Estimate the number of rows and columns in the implicit grid (= the entire grid)
90 // This is necessary as part of placement. Doing it early here is a perf optimisation to reduce allocations.
91 let (est_col_counts, est_row_counts) =
92 compute_grid_size_estimate(explicit_col_count, explicit_row_count, child_styles_iter);
93
94 // 2. Grid Item Placement
95 // Match items (children) to a definite grid position (row start/end and column start/end position)
96 let mut items = Vec::with_capacity(tree.child_count(node));
97 let mut cell_occupancy_matrix = CellOccupancyMatrix::with_track_counts(est_col_counts, est_row_counts);
98 let in_flow_children_iter = || {
99 tree.children(node)
100 .copied()
101 .enumerate()
102 .map(|(index, child_node)| (index, child_node, tree.style(child_node)))
103 .filter(|(_, _, style)| style.display != Display::None && style.position != Position::Absolute)
104 };
105 place_grid_items(
106 &mut cell_occupancy_matrix,
107 &mut items,
108 in_flow_children_iter,
109 style.grid_auto_flow,
110 style.align_items.unwrap_or(AlignItems::Stretch),
111 style.justify_items.unwrap_or(AlignItems::Stretch),
112 );
113
114 // Extract track counts from previous step (auto-placement can expand the number of tracks)
115 let final_col_counts = *cell_occupancy_matrix.track_counts(AbsoluteAxis::Horizontal);
116 let final_row_counts = *cell_occupancy_matrix.track_counts(AbsoluteAxis::Vertical);
117
118 // 3. Initialize Tracks
119 // Initialize (explicit and implicit) grid tracks (and gutters)
120 // This resolves the min and max track sizing functions for all tracks and gutters
121 let mut columns = GridTrackVec::new();
122 let mut rows = GridTrackVec::new();
123 initialize_grid_tracks(
124 &mut columns,
125 final_col_counts,
126 &style.grid_template_columns,
127 &style.grid_auto_columns,
128 style.gap.width,
129 |column_index| cell_occupancy_matrix.column_is_occupied(column_index),
130 );
131 initialize_grid_tracks(
132 &mut rows,
133 final_row_counts,
134 &style.grid_template_rows,
135 &style.grid_auto_rows,
136 style.gap.height,
137 |row_index| cell_occupancy_matrix.row_is_occupied(row_index),
138 );
139
140 // 4. Compute "available grid space"
141 // https://www.w3.org/TR/css-grid-1/#available-grid-space
142 let padding = style.padding.resolve_or_zero(parent_size.width);
143 let border = style.border.resolve_or_zero(parent_size.width);
144 let padding_border_size = (padding + border).sum_axes();
145 let aspect_ratio = style.aspect_ratio;
146 let min_size = style.min_size.maybe_resolve(parent_size).maybe_apply_aspect_ratio(aspect_ratio);
147 let max_size = style.max_size.maybe_resolve(parent_size).maybe_apply_aspect_ratio(aspect_ratio);
148 let size = style.size.maybe_resolve(parent_size).maybe_apply_aspect_ratio(aspect_ratio);
149
150 let constrained_available_space = known_dimensions
151 .or(size)
152 .maybe_clamp(min_size, max_size)
153 .map(|size| size.map(AvailableSpace::Definite))
154 .unwrap_or(available_space.map(|space| match space {
155 // Available grid space should not depend on Definite available space as a grid is allowed
156 // to expand beyond it's available space
157 AvailableSpace::Definite(_) => AvailableSpace::MaxContent,
158 _ => space,
159 }));
160
161 let available_grid_space = Size {
162 width: constrained_available_space
163 .width
164 .map_definite_value(|space| space - padding.horizontal_axis_sum() - border.horizontal_axis_sum()),
165 height: constrained_available_space
166 .height
167 .map_definite_value(|space| space - padding.vertical_axis_sum() - border.vertical_axis_sum()),
168 };
169
170 let outer_node_size = known_dimensions.or(size.maybe_clamp(min_size, max_size).or(min_size));
171 let mut inner_node_size = Size {
172 width: outer_node_size.width.map(|space| space - padding.horizontal_axis_sum() - border.horizontal_axis_sum()),
173 height: outer_node_size.height.map(|space| space - padding.vertical_axis_sum() - border.vertical_axis_sum()),
174 };
175
176 #[cfg(feature = "debug")]
177 NODE_LOGGER.labelled_debug_log("parent_size", parent_size);
178 #[cfg(feature = "debug")]
179 NODE_LOGGER.labelled_debug_log("outer_node_size", outer_node_size);
180 #[cfg(feature = "debug")]
181 NODE_LOGGER.labelled_debug_log("inner_node_size", inner_node_size);
182
183 // 5. Track Sizing
184
185 // Convert grid placements in origin-zero coordinates to indexes into the GridTrack (rows and columns) vectors
186 // This computation is relatively trivial, but it requires the final number of negative (implicit) tracks in
187 // each axis, and doing it up-front here means we don't have to keep repeating that calculation
188 resolve_item_track_indexes(&mut items, final_col_counts, final_row_counts);
189
190 // For each item, and in each axis, determine whether the item crosses any flexible (fr) tracks
191 // Record this as a boolean (per-axis) on each item for later use in the track-sizing algorithm
192 determine_if_item_crosses_flexible_or_intrinsic_tracks(&mut items, &columns, &rows);
193
194 // Determine if the grid has any baseline aligned items
195 let has_baseline_aligned_item = items.iter().any(|item| item.align_self == AlignSelf::Baseline);
196
197 // Run track sizing algorithm for Inline axis
198 track_sizing_algorithm(
199 tree,
200 AbstractAxis::Inline,
201 min_size.get(AbstractAxis::Inline),
202 max_size.get(AbstractAxis::Inline),
203 style.grid_align_content(AbstractAxis::Block),
204 available_grid_space,
205 inner_node_size,
206 &mut columns,
207 &mut rows,
208 &mut items,
209 |track: &GridTrack, parent_size: Option<f32>| track.max_track_sizing_function.definite_value(parent_size),
210 has_baseline_aligned_item,
211 );
212 let initial_column_sum = columns.iter().map(|track| track.base_size).sum::<f32>();
213 inner_node_size.width = inner_node_size.width.or_else(|| initial_column_sum.into());
214
215 items.iter_mut().for_each(|item| item.available_space_cache = None);
216
217 // Run track sizing algorithm for Block axis
218 track_sizing_algorithm(
219 tree,
220 AbstractAxis::Block,
221 min_size.get(AbstractAxis::Block),
222 max_size.get(AbstractAxis::Block),
223 style.grid_align_content(AbstractAxis::Inline),
224 available_grid_space,
225 inner_node_size,
226 &mut rows,
227 &mut columns,
228 &mut items,
229 |track: &GridTrack, _| Some(track.base_size),
230 false, // TODO: Support baseline alignment in the vertical axis
231 );
232 let initial_row_sum = rows.iter().map(|track| track.base_size).sum::<f32>();
233 inner_node_size.height = inner_node_size.height.or_else(|| initial_row_sum.into());
234
235 // 6. Compute container size
236 let resolved_style_size = known_dimensions.or(style.size.maybe_resolve(parent_size));
237 let container_border_box = Size {
238 width: resolved_style_size
239 .get(AbstractAxis::Inline)
240 .unwrap_or_else(|| initial_column_sum + padding.horizontal_axis_sum() + border.horizontal_axis_sum())
241 .max(padding_border_size.width),
242 height: resolved_style_size
243 .get(AbstractAxis::Block)
244 .unwrap_or_else(|| initial_row_sum + padding.vertical_axis_sum() + border.vertical_axis_sum())
245 .max(padding_border_size.height),
246 };
247 let container_content_box = Size {
248 width: container_border_box.width - padding.horizontal_axis_sum() - border.horizontal_axis_sum(),
249 height: container_border_box.height - padding.vertical_axis_sum() - border.vertical_axis_sum(),
250 };
251
252 // If only the container's size has been requested
253 if run_mode == RunMode::ComputeSize {
254 return container_border_box.into();
255 }
256
257 // 7. Resolve percentage track base sizes
258 // In the case of an indefinitely sized container these resolve to zero during the "Initialise Tracks" step
259 // and therefore need to be re-resolved here based on the content-sized content box of the container
260 if !available_grid_space.width.is_definite() {
261 for column in &mut columns {
262 let min: Option<f32> =
263 column.min_track_sizing_function.resolved_percentage_size(container_content_box.width);
264 let max: Option<f32> =
265 column.max_track_sizing_function.resolved_percentage_size(container_content_box.width);
266 column.base_size = column.base_size.maybe_clamp(min, max);
267 }
268 }
269 if !available_grid_space.height.is_definite() {
270 for row in &mut rows {
271 let min: Option<f32> = row.min_track_sizing_function.resolved_percentage_size(container_content_box.height);
272 let max: Option<f32> = row.max_track_sizing_function.resolved_percentage_size(container_content_box.height);
273 row.base_size = row.base_size.maybe_clamp(min, max);
274 }
275 }
276
277 // Column sizing must be re-run (once) if:
278 // - The grid container's width was initially indefinite and there are any columns with percentage track sizing functions
279 // - Any grid item crossing an intrinsically sized track's min content contribution width has changed
280 // TODO: Only rerun sizing for tracks that actually require it rather than for all tracks if any need it.
281 let mut rerun_column_sizing;
282
283 let has_percentage_column = columns.iter().any(|track| track.uses_percentage());
284 let parent_width_indefinite = !available_space.width.is_definite();
285 rerun_column_sizing = parent_width_indefinite && has_percentage_column;
286
287 if !rerun_column_sizing {
288 let min_content_contribution_changed = items
289 .iter_mut()
290 .filter(|item| item.crosses_intrinsic_column)
291 .map(|item| {
292 let available_space = item.available_space(
293 AbstractAxis::Inline,
294 &rows,
295 inner_node_size.height,
296 |track: &GridTrack, _| Some(track.base_size),
297 );
298 let new_min_content_contribution =
299 item.min_content_contribution(AbstractAxis::Inline, tree, available_space, inner_node_size);
300
301 let has_changed = Some(new_min_content_contribution) != item.min_content_contribution_cache.width;
302
303 item.available_space_cache = Some(available_space);
304 item.min_content_contribution_cache.width = Some(new_min_content_contribution);
305 item.max_content_contribution_cache.width = None;
306 item.minimum_contribution_cache.width = None;
307
308 has_changed
309 })
310 .any(|has_changed| has_changed);
311 rerun_column_sizing = min_content_contribution_changed;
312 } else {
313 // Clear intrisic width caches
314 items.iter_mut().for_each(|item| {
315 item.available_space_cache = None;
316 item.min_content_contribution_cache.width = None;
317 item.max_content_contribution_cache.width = None;
318 item.minimum_contribution_cache.width = None;
319 });
320 }
321
322 if rerun_column_sizing {
323 // Re-run track sizing algorithm for Inline axis
324 track_sizing_algorithm(
325 tree,
326 AbstractAxis::Inline,
327 min_size.get(AbstractAxis::Inline),
328 max_size.get(AbstractAxis::Inline),
329 style.grid_align_content(AbstractAxis::Block),
330 available_grid_space,
331 inner_node_size,
332 &mut columns,
333 &mut rows,
334 &mut items,
335 |track: &GridTrack, _| Some(track.base_size),
336 has_baseline_aligned_item,
337 );
338
339 // Row sizing must be re-run (once) if:
340 // - The grid container's height was initially indefinite and there are any rows with percentage track sizing functions
341 // - Any grid item crossing an intrinsically sized track's min content contribution height has changed
342 // TODO: Only rerun sizing for tracks that actually require it rather than for all tracks if any need it.
343 let mut rerun_row_sizing;
344
345 let has_percentage_row = rows.iter().any(|track| track.uses_percentage());
346 let parent_height_indefinite = !available_space.height.is_definite();
347 rerun_row_sizing = parent_height_indefinite && has_percentage_row;
348
349 if !rerun_row_sizing {
350 let min_content_contribution_changed = items
351 .iter_mut()
352 .filter(|item| item.crosses_intrinsic_column)
353 .map(|item| {
354 let available_space = item.available_space(
355 AbstractAxis::Block,
356 &columns,
357 inner_node_size.width,
358 |track: &GridTrack, _| Some(track.base_size),
359 );
360 let new_min_content_contribution =
361 item.min_content_contribution(AbstractAxis::Block, tree, available_space, inner_node_size);
362
363 let has_changed = Some(new_min_content_contribution) != item.min_content_contribution_cache.height;
364
365 item.available_space_cache = Some(available_space);
366 item.min_content_contribution_cache.height = Some(new_min_content_contribution);
367 item.max_content_contribution_cache.height = None;
368 item.minimum_contribution_cache.height = None;
369
370 has_changed
371 })
372 .any(|has_changed| has_changed);
373 rerun_row_sizing = min_content_contribution_changed;
374 } else {
375 items.iter_mut().for_each(|item| {
376 // Clear intrisic height caches
377 item.available_space_cache = None;
378 item.min_content_contribution_cache.height = None;
379 item.max_content_contribution_cache.height = None;
380 item.minimum_contribution_cache.height = None;
381 });
382 }
383
384 if rerun_row_sizing {
385 // Re-run track sizing algorithm for Block axis
386 track_sizing_algorithm(
387 tree,
388 AbstractAxis::Block,
389 min_size.get(AbstractAxis::Block),
390 max_size.get(AbstractAxis::Block),
391 style.grid_align_content(AbstractAxis::Inline),
392 available_grid_space,
393 inner_node_size,
394 &mut rows,
395 &mut columns,
396 &mut items,
397 |track: &GridTrack, _| Some(track.base_size),
398 false, // TODO: Support baseline alignment in the vertical axis
399 );
400 }
401 }
402
403 // 8. Track Alignment
404
405 // Align columns
406 align_tracks(
407 container_content_box.get(AbstractAxis::Inline),
408 Line { start: padding.left, end: padding.right },
409 Line { start: border.left, end: border.right },
410 &mut columns,
411 style.justify_content.unwrap_or(AlignContent::Stretch),
412 );
413 // Align rows
414 align_tracks(
415 container_content_box.get(AbstractAxis::Block),
416 Line { start: padding.top, end: padding.bottom },
417 Line { start: border.top, end: border.bottom },
418 &mut rows,
419 style.align_content.unwrap_or(AlignContent::Stretch),
420 );
421
422 // 9. Size, Align, and Position Grid Items
423
424 // Sort items back into original order to allow them to be matched up with styles
425 items.sort_by_key(|item| item.source_order);
426
427 let container_alignment_styles = InBothAbsAxis { horizontal: style.justify_items, vertical: style.align_items };
428
429 // Position in-flow children (stored in items vector)
430 for (index, item) in items.iter().enumerate() {
431 let grid_area = Rect {
432 top: rows[item.row_indexes.start as usize + 1].offset,
433 bottom: rows[item.row_indexes.end as usize].offset,
434 left: columns[item.column_indexes.start as usize + 1].offset,
435 right: columns[item.column_indexes.end as usize].offset,
436 };
437 align_and_position_item(
438 tree,
439 item.node,
440 index as u32,
441 grid_area,
442 container_alignment_styles,
443 item.baseline_shim,
444 );
445 }
446
447 // Position hidden and absolutely positioned children
448 let mut order = items.len() as u32;
449 (0..tree.child_count(node)).for_each(|index| {
450 let child = tree.child(node, index);
451 let child_style = tree.style(child);
452
453 // Position hidden child
454 if child_style.display == Display::None {
455 *tree.layout_mut(child) = Layout::with_order(order);
456 tree.perform_child_layout(child, Size::NONE, Size::NONE, Size::MAX_CONTENT, SizingMode::InherentSize);
457 order += 1;
458 return;
459 }
460
461 // Position absolutely positioned child
462 if child_style.position == Position::Absolute {
463 // Convert grid-col-{start/end} into Option's of indexes into the columns vector
464 // The Option is None if the style property is Auto and an unresolvable Span
465 let maybe_col_indexes = child_style
466 .grid_column
467 .into_origin_zero(final_col_counts.explicit)
468 .resolve_absolutely_positioned_grid_tracks()
469 .map(|maybe_grid_line| {
470 maybe_grid_line.map(|line: OriginZeroLine| line.into_track_vec_index(final_col_counts))
471 });
472 // Convert grid-row-{start/end} into Option's of indexes into the row vector
473 // The Option is None if the style property is Auto and an unresolvable Span
474 let maybe_row_indexes = child_style
475 .grid_row
476 .into_origin_zero(final_row_counts.explicit)
477 .resolve_absolutely_positioned_grid_tracks()
478 .map(|maybe_grid_line| {
479 maybe_grid_line.map(|line: OriginZeroLine| line.into_track_vec_index(final_row_counts))
480 });
481
482 let grid_area = Rect {
483 top: maybe_row_indexes.start.map(|index| rows[index].offset).unwrap_or(border.top),
484 bottom: maybe_row_indexes
485 .end
486 .map(|index| rows[index].offset)
487 .unwrap_or(container_border_box.height - border.bottom),
488 left: maybe_col_indexes.start.map(|index| columns[index].offset).unwrap_or(border.left),
489 right: maybe_col_indexes
490 .end
491 .map(|index| columns[index].offset)
492 .unwrap_or(container_border_box.width - border.right),
493 };
494 // TODO: Baseline alignment support for absolutely positioned items (should check if is actuallty specified)
495 align_and_position_item(tree, child, order, grid_area, container_alignment_styles, 0.0);
496 order += 1;
497 }
498 });
499
500 // If there are not items then return just the container size (no baseline)
501 if items.is_empty() {
502 return SizeAndBaselines { size: container_border_box, first_baselines: Point::NONE };
503 }
504
505 // Determine the grid container baseline(s) (currently we only compute the first baseline)
506 let grid_container_baseline: f32 = {
507 // Sort items by row start position so that we can iterate items in groups which are in the same row
508 items.sort_by_key(|item| item.row_indexes.start);
509
510 // Get the row index of the first row containing items
511 let first_row = items[0].row_indexes.start;
512
513 // Create a slice of all of the items start in this row (taking advantage of the fact that we have just sorted the array)
514 let first_row_items = &items[0..].split(|item| item.row_indexes.start != first_row).next().unwrap();
515
516 // Check if any items in *this row* are baseline aligned
517 let row_has_baseline_item = first_row_items.iter().any(|item| item.align_self == AlignSelf::Baseline);
518
519 let item = if row_has_baseline_item {
520 first_row_items.iter().find(|item| item.align_self == AlignSelf::Baseline).unwrap()
521 } else {
522 &first_row_items[0]
523 };
524
525 let layout = tree.layout_mut(item.node);
526 layout.location.y + item.baseline.unwrap_or(layout.size.height)
527 };
528
529 SizeAndBaselines {
530 size: container_border_box,
531 first_baselines: Point { x: None, y: Some(grid_container_baseline) },
532 }
533}