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::{GenericAlgorithm, 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 .map(|size| size.map(AvailableSpace::Definite))
153 .unwrap_or(available_space)
154 .maybe_clamp(min_size, max_size)
155 .maybe_max(padding_border_size);
156
157 let available_grid_space = Size {
158 width: constrained_available_space
159 .width
160 .map_definite_value(|space| space - padding.horizontal_axis_sum() - border.horizontal_axis_sum()),
161 height: constrained_available_space
162 .height
163 .map_definite_value(|space| space - padding.vertical_axis_sum() - border.vertical_axis_sum()),
164 };
165
166 let outer_node_size = known_dimensions.or(size).maybe_clamp(min_size, max_size).maybe_max(padding_border_size);
167 let mut inner_node_size = Size {
168 width: outer_node_size.width.map(|space| space - padding.horizontal_axis_sum() - border.horizontal_axis_sum()),
169 height: outer_node_size.height.map(|space| space - padding.vertical_axis_sum() - border.vertical_axis_sum()),
170 };
171
172 #[cfg(feature = "debug")]
173 NODE_LOGGER.labelled_debug_log("parent_size", parent_size);
174 #[cfg(feature = "debug")]
175 NODE_LOGGER.labelled_debug_log("outer_node_size", outer_node_size);
176 #[cfg(feature = "debug")]
177 NODE_LOGGER.labelled_debug_log("inner_node_size", inner_node_size);
178
179 // 5. Track Sizing
180
181 // Convert grid placements in origin-zero coordinates to indexes into the GridTrack (rows and columns) vectors
182 // This computation is relatively trivial, but it requires the final number of negative (implicit) tracks in
183 // each axis, and doing it up-front here means we don't have to keep repeating that calculation
184 resolve_item_track_indexes(&mut items, final_col_counts, final_row_counts);
185
186 // For each item, and in each axis, determine whether the item crosses any flexible (fr) tracks
187 // Record this as a boolean (per-axis) on each item for later use in the track-sizing algorithm
188 determine_if_item_crosses_flexible_or_intrinsic_tracks(&mut items, &columns, &rows);
189
190 // Determine if the grid has any baseline aligned items
191 let has_baseline_aligned_item = items.iter().any(|item| item.align_self == AlignSelf::Baseline);
192
193 // Run track sizing algorithm for Inline axis
194 track_sizing_algorithm(
195 tree,
196 AbstractAxis::Inline,
197 min_size.get(AbstractAxis::Inline),
198 max_size.get(AbstractAxis::Inline),
199 style.grid_align_content(AbstractAxis::Block),
200 available_grid_space,
201 inner_node_size,
202 &mut columns,
203 &mut rows,
204 &mut items,
205 |track: &GridTrack, parent_size: Option<f32>| track.max_track_sizing_function.definite_value(parent_size),
206 has_baseline_aligned_item,
207 );
208 let initial_column_sum = columns.iter().map(|track| track.base_size).sum::<f32>();
209 inner_node_size.width = inner_node_size.width.or_else(|| initial_column_sum.into());
210
211 items.iter_mut().for_each(|item| item.available_space_cache = None);
212
213 // Run track sizing algorithm for Block axis
214 track_sizing_algorithm(
215 tree,
216 AbstractAxis::Block,
217 min_size.get(AbstractAxis::Block),
218 max_size.get(AbstractAxis::Block),
219 style.grid_align_content(AbstractAxis::Inline),
220 available_grid_space,
221 inner_node_size,
222 &mut rows,
223 &mut columns,
224 &mut items,
225 |track: &GridTrack, _| Some(track.base_size),
226 false, // TODO: Support baseline alignment in the vertical axis
227 );
228 let initial_row_sum = rows.iter().map(|track| track.base_size).sum::<f32>();
229 inner_node_size.height = inner_node_size.height.or_else(|| initial_row_sum.into());
230
231 #[cfg(feature = "debug")]
232 NODE_LOGGER.labelled_debug_log("initial_column_sum", initial_column_sum);
233 #[cfg(feature = "debug")]
234 NODE_LOGGER.labelled_debug_log("initial_row_sum", initial_row_sum);
235
236 // 6. Compute container size
237 let resolved_style_size = known_dimensions.or(style.size.maybe_resolve(parent_size));
238 let container_border_box = Size {
239 width: resolved_style_size
240 .get(AbstractAxis::Inline)
241 .unwrap_or_else(|| initial_column_sum + padding.horizontal_axis_sum() + border.horizontal_axis_sum())
242 .maybe_clamp(min_size.width, max_size.width)
243 .max(padding_border_size.width),
244 height: resolved_style_size
245 .get(AbstractAxis::Block)
246 .unwrap_or_else(|| initial_row_sum + padding.vertical_axis_sum() + border.vertical_axis_sum())
247 .maybe_clamp(min_size.height, max_size.height)
248 .max(padding_border_size.height),
249 };
250 let container_content_box = Size {
251 width: container_border_box.width - padding.horizontal_axis_sum() - border.horizontal_axis_sum(),
252 height: container_border_box.height - padding.vertical_axis_sum() - border.vertical_axis_sum(),
253 };
254
255 // If only the container's size has been requested
256 if run_mode == RunMode::ComputeSize {
257 return container_border_box.into();
258 }
259
260 // 7. Resolve percentage track base sizes
261 // In the case of an indefinitely sized container these resolve to zero during the "Initialise Tracks" step
262 // and therefore need to be re-resolved here based on the content-sized content box of the container
263 if !available_grid_space.width.is_definite() {
264 for column in &mut columns {
265 let min: Option<f32> =
266 column.min_track_sizing_function.resolved_percentage_size(container_content_box.width);
267 let max: Option<f32> =
268 column.max_track_sizing_function.resolved_percentage_size(container_content_box.width);
269 column.base_size = column.base_size.maybe_clamp(min, max);
270 }
271 }
272 if !available_grid_space.height.is_definite() {
273 for row in &mut rows {
274 let min: Option<f32> = row.min_track_sizing_function.resolved_percentage_size(container_content_box.height);
275 let max: Option<f32> = row.max_track_sizing_function.resolved_percentage_size(container_content_box.height);
276 row.base_size = row.base_size.maybe_clamp(min, max);
277 }
278 }
279
280 // Column sizing must be re-run (once) if:
281 // - The grid container's width was initially indefinite and there are any columns with percentage track sizing functions
282 // - Any grid item crossing an intrinsically sized track's min content contribution width has changed
283 // TODO: Only rerun sizing for tracks that actually require it rather than for all tracks if any need it.
284 let mut rerun_column_sizing;
285
286 let has_percentage_column = columns.iter().any(|track| track.uses_percentage());
287 let parent_width_indefinite = !available_space.width.is_definite();
288 rerun_column_sizing = parent_width_indefinite && has_percentage_column;
289
290 if !rerun_column_sizing {
291 let min_content_contribution_changed = items
292 .iter_mut()
293 .filter(|item| item.crosses_intrinsic_column)
294 .map(|item| {
295 let available_space = item.available_space(
296 AbstractAxis::Inline,
297 &rows,
298 inner_node_size.height,
299 |track: &GridTrack, _| Some(track.base_size),
300 );
301 let new_min_content_contribution =
302 item.min_content_contribution(AbstractAxis::Inline, tree, available_space, inner_node_size);
303
304 let has_changed = Some(new_min_content_contribution) != item.min_content_contribution_cache.width;
305
306 item.available_space_cache = Some(available_space);
307 item.min_content_contribution_cache.width = Some(new_min_content_contribution);
308 item.max_content_contribution_cache.width = None;
309 item.minimum_contribution_cache.width = None;
310
311 has_changed
312 })
313 .any(|has_changed| has_changed);
314 rerun_column_sizing = min_content_contribution_changed;
315 } else {
316 // Clear intrisic width caches
317 items.iter_mut().for_each(|item| {
318 item.available_space_cache = None;
319 item.min_content_contribution_cache.width = None;
320 item.max_content_contribution_cache.width = None;
321 item.minimum_contribution_cache.width = None;
322 });
323 }
324
325 if rerun_column_sizing {
326 // Re-run track sizing algorithm for Inline axis
327 track_sizing_algorithm(
328 tree,
329 AbstractAxis::Inline,
330 min_size.get(AbstractAxis::Inline),
331 max_size.get(AbstractAxis::Inline),
332 style.grid_align_content(AbstractAxis::Block),
333 available_grid_space,
334 inner_node_size,
335 &mut columns,
336 &mut rows,
337 &mut items,
338 |track: &GridTrack, _| Some(track.base_size),
339 has_baseline_aligned_item,
340 );
341
342 // Row sizing must be re-run (once) if:
343 // - The grid container's height was initially indefinite and there are any rows with percentage track sizing functions
344 // - Any grid item crossing an intrinsically sized track's min content contribution height has changed
345 // TODO: Only rerun sizing for tracks that actually require it rather than for all tracks if any need it.
346 let mut rerun_row_sizing;
347
348 let has_percentage_row = rows.iter().any(|track| track.uses_percentage());
349 let parent_height_indefinite = !available_space.height.is_definite();
350 rerun_row_sizing = parent_height_indefinite && has_percentage_row;
351
352 if !rerun_row_sizing {
353 let min_content_contribution_changed = items
354 .iter_mut()
355 .filter(|item| item.crosses_intrinsic_column)
356 .map(|item| {
357 let available_space = item.available_space(
358 AbstractAxis::Block,
359 &columns,
360 inner_node_size.width,
361 |track: &GridTrack, _| Some(track.base_size),
362 );
363 let new_min_content_contribution =
364 item.min_content_contribution(AbstractAxis::Block, tree, available_space, inner_node_size);
365
366 let has_changed = Some(new_min_content_contribution) != item.min_content_contribution_cache.height;
367
368 item.available_space_cache = Some(available_space);
369 item.min_content_contribution_cache.height = Some(new_min_content_contribution);
370 item.max_content_contribution_cache.height = None;
371 item.minimum_contribution_cache.height = None;
372
373 has_changed
374 })
375 .any(|has_changed| has_changed);
376 rerun_row_sizing = min_content_contribution_changed;
377 } else {
378 items.iter_mut().for_each(|item| {
379 // Clear intrisic height caches
380 item.available_space_cache = None;
381 item.min_content_contribution_cache.height = None;
382 item.max_content_contribution_cache.height = None;
383 item.minimum_contribution_cache.height = None;
384 });
385 }
386
387 if rerun_row_sizing {
388 // Re-run track sizing algorithm for Block axis
389 track_sizing_algorithm(
390 tree,
391 AbstractAxis::Block,
392 min_size.get(AbstractAxis::Block),
393 max_size.get(AbstractAxis::Block),
394 style.grid_align_content(AbstractAxis::Inline),
395 available_grid_space,
396 inner_node_size,
397 &mut rows,
398 &mut columns,
399 &mut items,
400 |track: &GridTrack, _| Some(track.base_size),
401 false, // TODO: Support baseline alignment in the vertical axis
402 );
403 }
404 }
405
406 // 8. Track Alignment
407
408 // Align columns
409 align_tracks(
410 container_content_box.get(AbstractAxis::Inline),
411 Line { start: padding.left, end: padding.right },
412 Line { start: border.left, end: border.right },
413 &mut columns,
414 style.justify_content.unwrap_or(AlignContent::Stretch),
415 );
416 // Align rows
417 align_tracks(
418 container_content_box.get(AbstractAxis::Block),
419 Line { start: padding.top, end: padding.bottom },
420 Line { start: border.top, end: border.bottom },
421 &mut rows,
422 style.align_content.unwrap_or(AlignContent::Stretch),
423 );
424
425 // 9. Size, Align, and Position Grid Items
426
427 // Sort items back into original order to allow them to be matched up with styles
428 items.sort_by_key(|item| item.source_order);
429
430 let container_alignment_styles = InBothAbsAxis { horizontal: style.justify_items, vertical: style.align_items };
431
432 // Position in-flow children (stored in items vector)
433 for (index, item) in items.iter().enumerate() {
434 let grid_area = Rect {
435 top: rows[item.row_indexes.start as usize + 1].offset,
436 bottom: rows[item.row_indexes.end as usize].offset,
437 left: columns[item.column_indexes.start as usize + 1].offset,
438 right: columns[item.column_indexes.end as usize].offset,
439 };
440 align_and_position_item(
441 tree,
442 item.node,
443 index as u32,
444 grid_area,
445 container_alignment_styles,
446 item.baseline_shim,
447 );
448 }
449
450 // Position hidden and absolutely positioned children
451 let mut order = items.len() as u32;
452 (0..tree.child_count(node)).for_each(|index| {
453 let child = tree.child(node, index);
454 let child_style = tree.style(child);
455
456 // Position hidden child
457 if child_style.display == Display::None {
458 *tree.layout_mut(child) = Layout::with_order(order);
459 GenericAlgorithm::perform_layout(
460 tree,
461 child,
462 Size::NONE,
463 Size::NONE,
464 Size::MAX_CONTENT,
465 SizingMode::InherentSize,
466 );
467 order += 1;
468 return;
469 }
470
471 // Position absolutely positioned child
472 if child_style.position == Position::Absolute {
473 // Convert grid-col-{start/end} into Option's of indexes into the columns vector
474 // The Option is None if the style property is Auto and an unresolvable Span
475 let maybe_col_indexes = child_style
476 .grid_column
477 .into_origin_zero(final_col_counts.explicit)
478 .resolve_absolutely_positioned_grid_tracks()
479 .map(|maybe_grid_line| {
480 maybe_grid_line.map(|line: OriginZeroLine| line.into_track_vec_index(final_col_counts))
481 });
482 // Convert grid-row-{start/end} into Option's of indexes into the row vector
483 // The Option is None if the style property is Auto and an unresolvable Span
484 let maybe_row_indexes = child_style
485 .grid_row
486 .into_origin_zero(final_row_counts.explicit)
487 .resolve_absolutely_positioned_grid_tracks()
488 .map(|maybe_grid_line| {
489 maybe_grid_line.map(|line: OriginZeroLine| line.into_track_vec_index(final_row_counts))
490 });
491
492 let grid_area = Rect {
493 top: maybe_row_indexes.start.map(|index| rows[index].offset).unwrap_or(border.top),
494 bottom: maybe_row_indexes
495 .end
496 .map(|index| rows[index].offset)
497 .unwrap_or(container_border_box.height - border.bottom),
498 left: maybe_col_indexes.start.map(|index| columns[index].offset).unwrap_or(border.left),
499 right: maybe_col_indexes
500 .end
501 .map(|index| columns[index].offset)
502 .unwrap_or(container_border_box.width - border.right),
503 };
504 // TODO: Baseline alignment support for absolutely positioned items (should check if is actuallty specified)
505 align_and_position_item(tree, child, order, grid_area, container_alignment_styles, 0.0);
506 order += 1;
507 }
508 });
509
510 // If there are not items then return just the container size (no baseline)
511 if items.is_empty() {
512 return SizeAndBaselines { size: container_border_box, first_baselines: Point::NONE };
513 }
514
515 // Determine the grid container baseline(s) (currently we only compute the first baseline)
516 let grid_container_baseline: f32 = {
517 // Sort items by row start position so that we can iterate items in groups which are in the same row
518 items.sort_by_key(|item| item.row_indexes.start);
519
520 // Get the row index of the first row containing items
521 let first_row = items[0].row_indexes.start;
522
523 // Create a slice of all of the items start in this row (taking advantage of the fact that we have just sorted the array)
524 let first_row_items = &items[0..].split(|item| item.row_indexes.start != first_row).next().unwrap();
525
526 // Check if any items in *this row* are baseline aligned
527 let row_has_baseline_item = first_row_items.iter().any(|item| item.align_self == AlignSelf::Baseline);
528
529 let item = if row_has_baseline_item {
530 first_row_items.iter().find(|item| item.align_self == AlignSelf::Baseline).unwrap()
531 } else {
532 &first_row_items[0]
533 };
534
535 let layout = tree.layout_mut(item.node);
536 layout.location.y + item.baseline.unwrap_or(layout.size.height)
537 };
538
539 SizeAndBaselines {
540 size: container_border_box,
541 first_baselines: Point { x: None, y: Some(grid_container_baseline) },
542 }
543}