⎇ 325413cd16d8e81598b36d2129c717d4c53baaa9
src/compute/grid/track_sizing.rs
Historia
Quién tocó qué
crudo
Trampoline child measurement/layout through the `LayoutTree` trait (#427)
1//! Implements the track sizing algorithm
2//! <https://www.w3.org/TR/css-grid-1/#layout-algorithm>
3use super::types::{GridItem, GridTrack, TrackCounts};
4use crate::axis::AbstractAxis;
5use crate::geometry::Size;
6use crate::layout::SizingMode;
7use crate::math::MaybeMath;
8use crate::prelude::{LayoutTree, TaffyMinContent};
9use crate::resolve::ResolveOrZero;
10use crate::style::{
11 AlignContent, AlignSelf, AvailableSpace, LengthPercentage, MaxTrackSizingFunction, MinTrackSizingFunction,
12};
13use crate::sys::{f32_max, f32_min, Vec};
14use core::cmp::Ordering;
15
16/// Takes an axis, and a list of grid items sorted firstly by whether they cross a flex track
17/// in the specified axis (items that don't cross a flex track first) and then by the number
18/// of tracks they cross in specified axis (ascending order).
19struct ItemBatcher {
20 /// The axis in which the ItemBatcher is operating. Used when querying properties from items.
21 axis: AbstractAxis,
22 /// The starting index of the current batch
23 index_offset: usize,
24 /// The span of the items in the current batch
25 current_span: u16,
26 /// Whether the current batch of items cross a flexible track
27 current_is_flex: bool,
28}
29
30impl ItemBatcher {
31 /// Create a new ItemBatcher for the specified axis
32 #[inline(always)]
33 fn new(axis: AbstractAxis) -> Self {
34 ItemBatcher { index_offset: 0, axis, current_span: 1, current_is_flex: false }
35 }
36
37 /// This is basically a manual version of Iterator::next which passes `items`
38 /// in as a parameter on each iteration to work around borrow checker rules
39 #[inline]
40 fn next<'items>(&mut self, items: &'items mut [GridItem]) -> Option<(&'items mut [GridItem], bool)> {
41 if self.current_is_flex || self.index_offset >= items.len() {
42 return None;
43 }
44
45 let item = &items[self.index_offset];
46 self.current_span = item.span(self.axis);
47 self.current_is_flex = item.crosses_flexible_track(self.axis);
48
49 let next_index_offset = if self.current_is_flex {
50 items.len()
51 } else {
52 items
53 .iter()
54 .position(|item: &GridItem| {
55 item.crosses_flexible_track(self.axis) || item.span(self.axis) > self.current_span
56 })
57 .unwrap_or(items.len())
58 };
59
60 let batch_range = self.index_offset..next_index_offset;
61 self.index_offset = next_index_offset;
62
63 let batch = &mut items[batch_range];
64 Some((batch, self.current_is_flex))
65 }
66}
67
68/// This struct captures a bunch of variables which are used to compute the intrinsic sizes of children so that those variables
69/// don't have to be passed around all over the place below. It then has methods that implement the intrinsic sizing computations
70struct IntrisicSizeMeasurer<'tree, 'oat, Tree, EstimateFunction>
71where
72 Tree: LayoutTree,
73 EstimateFunction: Fn(&GridTrack, Option<f32>) -> Option<f32>,
74{
75 /// The layout tree
76 tree: &'tree mut Tree,
77 /// The tracks in the opposite axis to the one we are currently sizing
78 other_axis_tracks: &'oat [GridTrack],
79 /// A function that computes an estimate of an other-axis track's size which is passed to
80 /// the child size measurement functions
81 get_track_size_estimate: EstimateFunction,
82 /// The axis we are currently sizing
83 axis: AbstractAxis,
84 /// The available grid space
85 inner_node_size: Size<Option<f32>>,
86}
87
88impl<'tree, 'oat, Tree, EstimateFunction> IntrisicSizeMeasurer<'tree, 'oat, Tree, EstimateFunction>
89where
90 Tree: LayoutTree,
91 EstimateFunction: Fn(&GridTrack, Option<f32>) -> Option<f32>,
92{
93 /// Compute the available_space to be passed to the child sizing functions
94 /// These are estimates based on either the max track sizing function or the provisional base size in the opposite
95 /// axis to the one currently being sized.
96 /// https://www.w3.org/TR/css-grid-1/#algo-overview
97 #[inline(always)]
98 fn available_space(&self, item: &mut GridItem) -> Size<Option<f32>> {
99 item.available_space_cached(
100 self.axis,
101 self.other_axis_tracks,
102 self.inner_node_size.get(self.axis.other()),
103 &self.get_track_size_estimate,
104 )
105 }
106
107 /// Compute the item's resolved margins for size contributions. Horizontal percentage margins always resolve
108 /// to zero if the container size is indefinite as otherwise this would introduce a cyclic dependency.
109 #[inline(always)]
110 fn margins_axis_sums_with_baseline_shims(&self, item: &mut GridItem) -> Size<f32> {
111 item.margins_axis_sums_with_baseline_shims(self.inner_node_size.width)
112 }
113
114 /// Retrieve the item's min content contribution from the cache or compute it using the provided parameters
115 #[inline(always)]
116 fn min_content_contribution(&mut self, item: &mut GridItem) -> f32 {
117 let available_space = self.available_space(item);
118 let margin_axis_sums = self.margins_axis_sums_with_baseline_shims(item);
119 let contribution =
120 item.min_content_contribution_cached(self.axis, self.tree, available_space, self.inner_node_size);
121 contribution + margin_axis_sums.get(self.axis)
122 }
123
124 /// Retrieve the item's max content contribution from the cache or compute it using the provided parameters
125 #[inline(always)]
126 fn max_content_contribution(&mut self, item: &mut GridItem) -> f32 {
127 let available_space = self.available_space(item);
128 let margin_axis_sums = self.margins_axis_sums_with_baseline_shims(item);
129 let contribution =
130 item.max_content_contribution_cached(self.axis, self.tree, available_space, self.inner_node_size);
131 contribution + margin_axis_sums.get(self.axis)
132 }
133
134 /// The minimum contribution of an item is the smallest outer size it can have.
135 /// Specifically:
136 /// - If the item’s computed preferred size behaves as auto or depends on the size of its containing block in the relevant axis:
137 /// Its minimum contribution is the outer size that would result from assuming the item’s used minimum size as its preferred size;
138 /// - Else the item’s minimum contribution is its min-content contribution.
139 /// Because the minimum contribution often depends on the size of the item’s content, it is considered a type of intrinsic size contribution.
140 #[inline(always)]
141 fn minimum_contribution(&mut self, item: &mut GridItem, axis_tracks: &[GridTrack]) -> f32 {
142 let available_space = self.available_space(item);
143 let margin_axis_sums = self.margins_axis_sums_with_baseline_shims(item);
144 let contribution =
145 item.minimum_contribution_cached(self.tree, self.axis, axis_tracks, available_space, self.inner_node_size);
146 contribution + margin_axis_sums.get(self.axis)
147 }
148}
149
150/// To make track sizing efficient we want to order tracks
151/// Here a placement is either a Line<i16> representing a row-start/row-end or a column-start/column-end
152#[inline(always)]
153pub(super) fn cmp_by_cross_flex_then_span_then_start(
154 axis: AbstractAxis,
155) -> impl FnMut(&GridItem, &GridItem) -> Ordering {
156 move |item_a: &GridItem, item_b: &GridItem| -> Ordering {
157 match (item_a.crosses_flexible_track(axis), item_b.crosses_flexible_track(axis)) {
158 (false, true) => Ordering::Less,
159 (true, false) => Ordering::Greater,
160 _ => {
161 let placement_a = item_a.placement(axis);
162 let placement_b = item_b.placement(axis);
163 match placement_a.span().cmp(&placement_b.span()) {
164 Ordering::Less => Ordering::Less,
165 Ordering::Greater => Ordering::Greater,
166 Ordering::Equal => placement_a.start.cmp(&placement_b.start),
167 }
168 }
169 }
170 }
171}
172
173/// When applying the track sizing algorithm and estimating the size in the other axis for content sizing items
174/// we should take into account align-content/justify-content if both the grid container and all items in the
175/// other axis have definite sizes. This function computes such a per-gutter additional size adjustment.
176#[inline(always)]
177pub(super) fn compute_alignment_gutter_adjustment(
178 alignment: AlignContent,
179 axis_inner_node_size: Option<f32>,
180 get_track_size_estimate: impl Fn(&GridTrack, Option<f32>) -> Option<f32>,
181 tracks: &[GridTrack],
182) -> f32 {
183 if tracks.len() <= 1 {
184 return 0.0;
185 }
186
187 // As items never cross the outermost gutters in a grid, we can simplify our calculations by treating
188 // AlignContent::Start and AlignContent::End the same
189 let outer_gutter_weight = match alignment {
190 AlignContent::Start => 1,
191 AlignContent::FlexStart => 1,
192 AlignContent::End => 1,
193 AlignContent::FlexEnd => 1,
194 AlignContent::Center => 1,
195 AlignContent::Stretch => 0,
196 AlignContent::SpaceBetween => 0,
197 AlignContent::SpaceAround => 1,
198 AlignContent::SpaceEvenly => 1,
199 };
200
201 let inner_gutter_weight = match alignment {
202 AlignContent::FlexStart => 0,
203 AlignContent::Start => 0,
204 AlignContent::FlexEnd => 0,
205 AlignContent::End => 0,
206 AlignContent::Center => 0,
207 AlignContent::Stretch => 0,
208 AlignContent::SpaceBetween => 1,
209 AlignContent::SpaceAround => 2,
210 AlignContent::SpaceEvenly => 1,
211 };
212
213 if inner_gutter_weight == 0 {
214 return 0.0;
215 }
216
217 if let Some(axis_inner_node_size) = axis_inner_node_size {
218 let free_space = tracks
219 .iter()
220 .map(|track| get_track_size_estimate(track, Some(axis_inner_node_size)))
221 .sum::<Option<f32>>()
222 .map(|track_size_sum| f32_max(0.0, axis_inner_node_size - track_size_sum))
223 .unwrap_or(0.0);
224
225 let weighted_track_count =
226 (((tracks.len() - 3) / 2) * inner_gutter_weight as usize) + (2 * outer_gutter_weight as usize);
227
228 return (free_space / weighted_track_count as f32) * inner_gutter_weight as f32;
229 }
230
231 0.0
232}
233
234/// Convert origin-zero coordinates track placement in grid track vector indexes
235#[inline(always)]
236pub(super) fn resolve_item_track_indexes(items: &mut [GridItem], column_counts: TrackCounts, row_counts: TrackCounts) {
237 for item in items {
238 item.column_indexes = item.column.map(|line| line.into_track_vec_index(column_counts) as u16);
239 item.row_indexes = item.row.map(|line| line.into_track_vec_index(row_counts) as u16);
240 }
241}
242
243/// Determine (in each axis) whether the item crosses any flexible tracks
244#[inline(always)]
245pub(super) fn determine_if_item_crosses_flexible_or_intrinsic_tracks(
246 items: &mut Vec<GridItem>,
247 columns: &[GridTrack],
248 rows: &[GridTrack],
249) {
250 for item in items {
251 item.crosses_flexible_column =
252 item.track_range_excluding_lines(AbstractAxis::Inline).any(|i| columns[i].is_flexible());
253 item.crosses_intrinsic_column =
254 item.track_range_excluding_lines(AbstractAxis::Inline).any(|i| columns[i].has_intrinsic_sizing_function());
255 item.crosses_flexible_row =
256 item.track_range_excluding_lines(AbstractAxis::Block).any(|i| rows[i].is_flexible());
257 item.crosses_intrinsic_row =
258 item.track_range_excluding_lines(AbstractAxis::Block).any(|i| rows[i].has_intrinsic_sizing_function());
259 }
260}
261
262/// Track sizing algorithm
263/// Note: Gutters are treated as empty fixed-size tracks for the purpose of the track sizing algorithm.
264#[allow(clippy::too_many_arguments)]
265#[inline(always)]
266pub(super) fn track_sizing_algorithm<Tree: LayoutTree>(
267 tree: &mut Tree,
268 axis: AbstractAxis,
269 axis_min_size: Option<f32>,
270 axis_max_size: Option<f32>,
271 other_axis_alignment: AlignContent,
272 available_grid_space: Size<AvailableSpace>,
273 inner_node_size: Size<Option<f32>>,
274 axis_tracks: &mut [GridTrack],
275 other_axis_tracks: &mut [GridTrack],
276 items: &mut [GridItem],
277 get_track_size_estimate: impl Fn(&GridTrack, Option<f32>) -> Option<f32>,
278 has_baseline_aligned_item: bool,
279) {
280 // 11.4 Initialise Track sizes
281 // Initialize each track’s base size and growth limit.
282 initialize_track_sizes(axis_tracks, inner_node_size.get(axis));
283
284 // 11.5.1 Shim item baselines
285 if has_baseline_aligned_item {
286 resolve_item_baselines(tree, axis, items, inner_node_size);
287 }
288
289 // If all tracks have base_size = growth_limit, then skip the rest of this function.
290 // Note: this can only happen both track sizing function have the same fixed track sizing function
291 if axis_tracks.iter().all(|track| track.base_size == track.growth_limit) {
292 return;
293 }
294
295 // Pre-computations for 11.5 Resolve Intrinsic Track Sizes
296
297 // Compute an additional amount to add to each spanned gutter when computing item's estimated size in the
298 // in the opposite axis based on the alignment, container size, and estimated track sizes in that axis
299 let gutter_alignment_adjustment = compute_alignment_gutter_adjustment(
300 other_axis_alignment,
301 inner_node_size.get(axis.other()),
302 &get_track_size_estimate,
303 other_axis_tracks,
304 );
305 if other_axis_tracks.len() > 3 {
306 let len = other_axis_tracks.len();
307 let inner_gutter_tracks = other_axis_tracks[2..len].iter_mut().step_by(2);
308 for track in inner_gutter_tracks {
309 track.content_alignment_adjustment = gutter_alignment_adjustment;
310 }
311 }
312
313 // 11.5 Resolve Intrinsic Track Sizes
314 resolve_intrinsic_track_sizes(
315 tree,
316 axis,
317 axis_tracks,
318 other_axis_tracks,
319 items,
320 available_grid_space.get(axis),
321 inner_node_size,
322 get_track_size_estimate,
323 );
324
325 // 11.6. Maximise Tracks
326 // Distributes free space (if any) to tracks with FINITE growth limits, up to their limits.
327 maximise_tracks(axis_tracks, inner_node_size.get(axis), available_grid_space.get(axis));
328
329 // 11.7. Expand Flexible Tracks
330 // This step sizes flexible tracks using the largest value it can assign to an fr without exceeding the available space.
331 expand_flexible_tracks(
332 tree,
333 axis,
334 axis_tracks,
335 items,
336 axis_min_size,
337 axis_max_size,
338 available_grid_space,
339 inner_node_size,
340 );
341
342 // 11.8. Stretch auto Tracks
343 // This step expands tracks that have an auto max track sizing function by dividing any remaining positive, definite free space equally amongst them.
344 stretch_auto_tracks(axis, axis_tracks, axis_min_size, available_grid_space);
345}
346
347/// Whether it is a minimum or maximum size's space being distributed
348/// This controls behaviour of the space distribution algorithm when distributing beyond limits
349/// See "distributing space beyond limits" at https://www.w3.org/TR/css-grid-1/#extra-space
350#[derive(Copy, Clone, Debug, PartialEq, Eq)]
351enum IntrinsicContributionType {
352 /// It's a minimum size's space being distributed
353 Minimum,
354 /// It's a maximum size's space being distributed
355 Maximum,
356}
357
358/// Add any planned base size increases to the base size after a round of distributing space to base sizes
359/// Reset the planed base size increase to zero ready for the next round.
360#[inline(always)]
361fn flush_planned_base_size_increases(tracks: &mut [GridTrack]) {
362 for track in tracks {
363 track.base_size += track.base_size_planned_increase;
364 track.base_size_planned_increase = 0.0;
365 }
366}
367
368/// Add any planned growth limit increases to the growth limit after a round of distributing space to growth limits
369/// Reset the planed growth limit increase to zero ready for the next round.
370#[inline(always)]
371fn flush_planned_growth_limit_increases(tracks: &mut [GridTrack], set_infinitely_growable: bool) {
372 for track in tracks {
373 if track.growth_limit_planned_increase > 0.0 {
374 track.growth_limit = if track.growth_limit == f32::INFINITY {
375 track.base_size + track.growth_limit_planned_increase
376 } else {
377 track.growth_limit + track.growth_limit_planned_increase
378 };
379 track.infinitely_growable = set_infinitely_growable;
380 } else {
381 track.infinitely_growable = false;
382 }
383 track.growth_limit_planned_increase = 0.0
384 }
385}
386
387/// 11.4 Initialise Track sizes
388/// Initialize each track’s base size and growth limit.
389#[inline(always)]
390fn initialize_track_sizes(axis_tracks: &mut [GridTrack], axis_inner_node_size: Option<f32>) {
391 let last_track_idx = axis_tracks.len() - 1;
392
393 // First and last grid lines are always zero-sized.
394 axis_tracks[0].base_size = 0.0;
395 axis_tracks[0].growth_limit = 0.0;
396 axis_tracks[last_track_idx].base_size = 0.0;
397 axis_tracks[last_track_idx].growth_limit = 0.0;
398
399 let all_but_first_and_last = 1..last_track_idx;
400 for track in axis_tracks[all_but_first_and_last].iter_mut() {
401 // For each track, if the track’s min track sizing function is:
402 // - A fixed sizing function
403 // Resolve to an absolute length and use that size as the track’s initial base size.
404 // Note: Indefinite lengths cannot occur, as they’re treated as auto.
405 // - An intrinsic sizing function
406 // Use an initial base size of zero.
407 track.base_size = track.min_track_sizing_function.definite_value(axis_inner_node_size).unwrap_or(0.0);
408
409 // For each track, if the track’s max track sizing function is:
410 // - A fixed sizing function
411 // Resolve to an absolute length and use that size as the track’s initial growth limit.
412 // - An intrinsic sizing function
413 // Use an initial growth limit of infinity.
414 // - A flexible sizing function
415 // Use an initial growth limit of infinity.
416 track.growth_limit =
417 track.max_track_sizing_function.definite_value(axis_inner_node_size).unwrap_or(f32::INFINITY);
418
419 // In all cases, if the growth limit is less than the base size, increase the growth limit to match the base size.
420 if track.growth_limit < track.base_size {
421 track.growth_limit = track.base_size;
422 }
423 }
424}
425
426/// 11.5.1 Shim baseline-aligned items so their intrinsic size contributions reflect their baseline alignment.
427fn resolve_item_baselines(
428 tree: &mut impl LayoutTree,
429 axis: AbstractAxis,
430 items: &mut [GridItem],
431 inner_node_size: Size<Option<f32>>,
432) {
433 // Sort items by track in the other axis (row) start position so that we can iterate items in groups which
434 // are in the same track in the other axis (row)
435 let other_axis = axis.other();
436 items.sort_by_key(|item| item.placement(other_axis).start);
437
438 // Iterate over grid rows
439 let mut remaining_items = &mut items[0..];
440 while !remaining_items.is_empty() {
441 // Get the row index of the current row
442 let current_row = remaining_items[0].placement(other_axis).start;
443
444 // Find the item index of the first item that is in a different row (or None if we've reached the end of the list)
445 let next_row_first_item =
446 remaining_items.iter().position(|item| item.placement(other_axis).start != current_row);
447
448 // Use this index to split the `remaining_items` slice in two slices:
449 // - A `row_items` slice containing the items (that start) in the current row
450 // - A new `remaining_items` consisting of the remainder of the `remaining_items` slice
451 // that hasn't been split off into `row_items
452 let row_items = if let Some(index) = next_row_first_item {
453 let (row_items, tail) = remaining_items.split_at_mut(index);
454 remaining_items = tail;
455 row_items
456 } else {
457 let row_items = remaining_items;
458 remaining_items = &mut [];
459 row_items
460 };
461
462 // Count how many items in *this row* are baseline aligned
463 // If a row has one or zero items participating in baseline alignment then baseline alignment is a no-op
464 // for those items and we skip further computations for that row
465 let row_baseline_item_count = row_items.iter().filter(|item| item.align_self == AlignSelf::Baseline).count();
466 if row_baseline_item_count <= 1 {
467 continue;
468 }
469
470 // Compute the baselines of all items in the row
471 for item in row_items.iter_mut() {
472 let measured_size_and_baselines = tree.perform_child_layout(
473 item.node,
474 Size::NONE,
475 inner_node_size,
476 Size::MIN_CONTENT,
477 SizingMode::InherentSize,
478 );
479
480 let baseline = measured_size_and_baselines.first_baselines.y;
481 let height = measured_size_and_baselines.size.height;
482
483 item.baseline = Some(baseline.unwrap_or(height) + item.margin.top.resolve_or_zero(inner_node_size.width));
484 }
485
486 // Compute the max baseline of all items in the row
487 let row_max_baseline =
488 row_items.iter().map(|item| item.baseline.unwrap_or(0.0)).max_by(|a, b| a.total_cmp(b)).unwrap();
489
490 // Compute the baseline shim for each item in the row
491 for item in row_items.iter_mut() {
492 item.baseline_shim = row_max_baseline - item.baseline.unwrap_or(0.0);
493 }
494 }
495}
496
497/// 11.5 Resolve Intrinsic Track Sizes
498#[allow(clippy::too_many_arguments)]
499fn resolve_intrinsic_track_sizes(
500 tree: &mut impl LayoutTree,
501 axis: AbstractAxis,
502 axis_tracks: &mut [GridTrack],
503 other_axis_tracks: &mut [GridTrack],
504 items: &mut [GridItem],
505 axis_available_grid_space: AvailableSpace,
506 inner_node_size: Size<Option<f32>>,
507 get_track_size_estimate: impl Fn(&GridTrack, Option<f32>) -> Option<f32>,
508) {
509 // Step 1. Shim baseline-aligned items so their intrinsic size contributions reflect their baseline alignment.
510
511 // Already done at this point. See resolve_item_baselines function.
512
513 // Step 2.
514
515 // The track sizing algorithm requires us to iterate through the items in ascendeding order of the number of
516 // tracks they span (first items that span 1 track, then items that span 2 tracks, etc).
517 // To avoid having to do multiple iterations of the items, we pre-sort them into this order.
518 items.sort_by(cmp_by_cross_flex_then_span_then_start(axis));
519
520 // Step 2, Step 3 and Step 4
521 // 2 & 3. Iterate over items that don't cross a flex track. Items should have already been sorted in ascending order
522 // of the number of tracks they span. Step 2 is the 1 track case and has an optimised implementation
523 // 4. Next, repeat the previous step instead considering (together, rather than grouped by span size) all items
524 // that do span a track with a flexible sizing function while
525
526 // Compute item's intrinsic (content-based) sizes
527 // Note: For items with a specified minimum size of auto (the initial value), the minimum contribution is usually equivalent
528 // to the min-content contribution—but can differ in some cases, see §6.6 Automatic Minimum Size of Grid Items.
529 // Also, minimum contribution <= min-content contribution <= max-content contribution.
530
531 let axis_inner_node_size = inner_node_size.get(axis);
532 let flex_factor_sum = axis_tracks.iter().map(|track| track.flex_factor()).sum::<f32>();
533 let mut item_sizer =
534 IntrisicSizeMeasurer { tree, other_axis_tracks, axis, inner_node_size, get_track_size_estimate };
535
536 let mut batched_item_iterator = ItemBatcher::new(axis);
537 while let Some((batch, is_flex)) = batched_item_iterator.next(items) {
538 // 2. Size tracks to fit non-spanning items: For each track with an intrinsic track sizing function and not a flexible sizing function,
539 // consider the items in it with a span of 1:
540 let batch_span = batch[0].placement(axis).span();
541 if !is_flex && batch_span == 1 {
542 for item in batch.iter_mut() {
543 let track_index = item.placement_indexes(axis).start + 1;
544 let track = &axis_tracks[track_index as usize];
545
546 // Handle base sizes
547 let new_base_size = match track.min_track_sizing_function {
548 MinTrackSizingFunction::MinContent => {
549 f32_max(track.base_size, item_sizer.min_content_contribution(item))
550 }
551 // If the container size is indefinite and has not yet been resolved then percentage sized
552 // tracks should be treated as min-content (this matches Chrome's behaviour and seems sensible)
553 MinTrackSizingFunction::Fixed(LengthPercentage::Percent(_)) => {
554 if axis_inner_node_size.is_none() {
555 f32_max(track.base_size, item_sizer.min_content_contribution(item))
556 } else {
557 track.base_size
558 }
559 }
560 MinTrackSizingFunction::MaxContent => {
561 f32_max(track.base_size, item_sizer.max_content_contribution(item))
562 }
563 MinTrackSizingFunction::Auto => {
564 let space = match axis_available_grid_space {
565 AvailableSpace::MinContent | AvailableSpace::MaxContent => {
566 let axis_minimum_size = item_sizer.minimum_contribution(item, axis_tracks);
567 let axis_min_content_size = item_sizer.min_content_contribution(item);
568 let limit = track.max_track_sizing_function.definite_limit(axis_inner_node_size);
569 axis_min_content_size.maybe_min(limit).max(axis_minimum_size)
570 }
571 AvailableSpace::Definite(_) => item_sizer.minimum_contribution(item, axis_tracks),
572 };
573 f32_max(track.base_size, space)
574 }
575 MinTrackSizingFunction::Fixed(_) => {
576 // Do nothing as it's not an intrinsic track sizing function
577 track.base_size
578 }
579 };
580 let track = &mut axis_tracks[track_index as usize];
581 track.base_size = new_base_size;
582
583 // Handle growth limits
584 if let MaxTrackSizingFunction::FitContent(_) = track.max_track_sizing_function {
585 let fit_content_limit = track.fit_content_limit(axis_inner_node_size);
586 let min_content_contribution = item_sizer.min_content_contribution(item);
587 let max_content_contribution =
588 f32_min(item_sizer.max_content_contribution(item), fit_content_limit);
589 track.growth_limit_planned_increase =
590 f32_max(track.growth_limit_planned_increase, min_content_contribution);
591 track.growth_limit_planned_increase =
592 f32_max(track.growth_limit_planned_increase, max_content_contribution);
593 } else if track.max_track_sizing_function.is_max_content_alike()
594 || track.max_track_sizing_function.uses_percentage() && axis_inner_node_size.is_none()
595 {
596 // If the container size is indefinite and has not yet been resolved then percentage sized
597 // tracks should be treated as auto (this matches Chrome's behaviour and seems sensible)
598 track.growth_limit_planned_increase =
599 f32_max(track.growth_limit_planned_increase, item_sizer.max_content_contribution(item));
600 } else if track.max_track_sizing_function.is_intrinsic() {
601 track.growth_limit_planned_increase =
602 f32_max(track.growth_limit_planned_increase, item_sizer.min_content_contribution(item));
603 }
604 }
605
606 for track in axis_tracks.iter_mut() {
607 if track.growth_limit_planned_increase > 0.0 {
608 track.growth_limit = if track.growth_limit == f32::INFINITY {
609 track.growth_limit_planned_increase
610 } else {
611 f32_max(track.growth_limit, track.growth_limit_planned_increase)
612 };
613 }
614 track.infinitely_growable = false;
615 track.growth_limit_planned_increase = 0.0;
616 if track.growth_limit < track.base_size {
617 track.growth_limit = track.base_size;
618 }
619 }
620
621 continue;
622 }
623
624 let use_flex_factor_for_distribution = is_flex && flex_factor_sum != 0.0;
625
626 // 1. For intrinsic minimums:
627 // First increase the base size of tracks with an intrinsic min track sizing function
628 let has_intrinsic_min_track_sizing_function =
629 move |track: &GridTrack| track.min_track_sizing_function.definite_value(axis_inner_node_size).is_none();
630 for item in batch.iter_mut().filter(|item| item.crosses_intrinsic_track(axis)) {
631 // ...by distributing extra space as needed to accommodate these items’ minimum contributions.
632 // If the grid container is being sized under a min- or max-content constraint, use the items’ limited min-content contributions
633 // in place of their minimum contributions here.
634 let space = match axis_available_grid_space {
635 AvailableSpace::MinContent | AvailableSpace::MaxContent => {
636 let axis_minimum_size = item_sizer.minimum_contribution(item, axis_tracks);
637 let axis_min_content_size = item_sizer.min_content_contribution(item);
638 let limit = item.spanned_track_limit(axis, axis_tracks, axis_inner_node_size);
639 axis_min_content_size.maybe_min(limit).max(axis_minimum_size)
640 }
641 AvailableSpace::Definite(_) => item_sizer.minimum_contribution(item, axis_tracks),
642 };
643 let tracks = &mut axis_tracks[item.track_range_excluding_lines(axis)];
644 if space > 0.0 {
645 distribute_item_space_to_base_size(
646 is_flex,
647 use_flex_factor_for_distribution,
648 space,
649 tracks,
650 has_intrinsic_min_track_sizing_function,
651 |_| f32::INFINITY,
652 IntrinsicContributionType::Minimum,
653 );
654 }
655 }
656 flush_planned_base_size_increases(axis_tracks);
657
658 // 2. For content-based minimums:
659 // Next continue to increase the base size of tracks with a min track sizing function of min-content or max-content
660 // by distributing extra space as needed to account for these items' min-content contributions.
661 let has_min_or_max_content_min_track_sizing_function = move |track: &GridTrack| {
662 use MinTrackSizingFunction::{MaxContent, MinContent};
663 matches!(track.min_track_sizing_function, MinContent | MaxContent)
664 };
665 for item in batch.iter_mut() {
666 let space = item_sizer.min_content_contribution(item);
667 let tracks = &mut axis_tracks[item.track_range_excluding_lines(axis)];
668 if space > 0.0 {
669 distribute_item_space_to_base_size(
670 is_flex,
671 use_flex_factor_for_distribution,
672 space,
673 tracks,
674 has_min_or_max_content_min_track_sizing_function,
675 |_| f32::INFINITY,
676 IntrinsicContributionType::Minimum,
677 );
678 }
679 }
680 flush_planned_base_size_increases(axis_tracks);
681
682 // 3. For max-content minimums:
683
684 // If the grid container is being sized under a max-content constraint, continue to increase the base size of tracks with
685 // a min track sizing function of auto or max-content by distributing extra space as needed to account for these items'
686 // limited max-content contributions.
687
688 // Define fit_content_limited_growth_limit function. This is passed to the distribute_space_up_to_limits
689 // helper function, and is used to compute the limit to distribute up to for each track.
690 // Wrapping the method on GridTrack is necessary in order to resolve percentage fit-content arguments.
691 if axis_available_grid_space == AvailableSpace::MaxContent {
692 /// Whether a track:
693 /// - has an Auto MIN track sizing function
694 /// - Does not have a MinContent MAX track sizing function
695 ///
696 /// The latter condition was added in order to match Chrome. But I believe it is due to the provision
697 /// under minmax here https://www.w3.org/TR/css-grid-1/#track-sizes which states that:
698 ///
699 /// "If the max is less than the min, then the max will be floored by the min (essentially yielding minmax(min, min))"
700 #[inline(always)]
701 fn has_auto_min_track_sizing_function(track: &GridTrack) -> bool {
702 track.min_track_sizing_function == MinTrackSizingFunction::Auto
703 && track.max_track_sizing_function != MaxTrackSizingFunction::MinContent
704 }
705
706 /// Whether a track has a MaxContent min track sizing function
707 #[inline(always)]
708 fn has_max_content_min_track_sizing_function(track: &GridTrack) -> bool {
709 track.min_track_sizing_function == MinTrackSizingFunction::MaxContent
710 }
711
712 for item in batch.iter_mut() {
713 let axis_max_content_size = item_sizer.max_content_contribution(item);
714 let limit = item.spanned_track_limit(axis, axis_tracks, axis_inner_node_size);
715 let space = axis_max_content_size.maybe_min(limit);
716 let tracks = &mut axis_tracks[item.track_range_excluding_lines(axis)];
717 if space > 0.0 {
718 // If any of the tracks spanned by the item have a MaxContent min track sizing function then
719 // distribute space only to those tracks. Otherwise distribute space to tracks with an Auto min
720 // track sizing function.
721 //
722 // Note: this prioritisation of MaxContent over Auto is not mentioned in the spec (which suggests that
723 // we ought to distribute space evenly between MaxContent and Auto tracks). But it is implemented like
724 // this in both Chrome and Firefox (and it does have a certain logic to it), so we implement it too for
725 // compatibility.
726 //
727 // See: https://www.w3.org/TR/css-grid-1/#track-size-max-content-min
728 if tracks.iter().any(has_max_content_min_track_sizing_function) {
729 distribute_item_space_to_base_size(
730 is_flex,
731 use_flex_factor_for_distribution,
732 space,
733 tracks,
734 has_max_content_min_track_sizing_function,
735 |_| f32::INFINITY,
736 IntrinsicContributionType::Maximum,
737 );
738 } else {
739 let fit_content_limited_growth_limit =
740 move |track: &GridTrack| track.fit_content_limited_growth_limit(axis_inner_node_size);
741 distribute_item_space_to_base_size(
742 is_flex,
743 use_flex_factor_for_distribution,
744 space,
745 tracks,
746 has_auto_min_track_sizing_function,
747 fit_content_limited_growth_limit,
748 IntrinsicContributionType::Maximum,
749 );
750 }
751 }
752 }
753 flush_planned_base_size_increases(axis_tracks);
754 }
755
756 // In all cases, continue to increase the base size of tracks with a min track sizing function of max-content by distributing
757 // extra space as needed to account for these items' max-content contributions.
758 let has_max_content_min_track_sizing_function =
759 move |track: &GridTrack| matches!(track.min_track_sizing_function, MinTrackSizingFunction::MaxContent);
760 for item in batch.iter_mut() {
761 let axis_max_content_size = item_sizer.max_content_contribution(item);
762 let space = axis_max_content_size;
763 let tracks = &mut axis_tracks[item.track_range_excluding_lines(axis)];
764 if space > 0.0 {
765 distribute_item_space_to_base_size(
766 is_flex,
767 use_flex_factor_for_distribution,
768 space,
769 tracks,
770 has_max_content_min_track_sizing_function,
771 |_| f32::INFINITY,
772 IntrinsicContributionType::Maximum,
773 );
774 }
775 }
776 flush_planned_base_size_increases(axis_tracks);
777
778 // 4. If at this point any track’s growth limit is now less than its base size, increase its growth limit to match its base size.
779 for track in axis_tracks.iter_mut() {
780 if track.growth_limit < track.base_size {
781 track.growth_limit = track.base_size;
782 }
783 }
784
785 // If a track is a flexible track, then it has flexible max track sizing function
786 // It cannot also have an intrinsic max track sizing function, so these steps do not apply.
787 if !is_flex {
788 // 5. For intrinsic maximums: Next increase the growth limit of tracks with an intrinsic max track sizing function by
789 // distributing extra space as needed to account for these items' min-content contributions.
790 let has_intrinsic_max_track_sizing_function =
791 move |track: &GridTrack| track.max_track_sizing_function.definite_value(axis_inner_node_size).is_none();
792 for item in batch.iter_mut() {
793 let axis_min_content_size = item_sizer.min_content_contribution(item);
794 let space = axis_min_content_size;
795 let tracks = &mut axis_tracks[item.track_range_excluding_lines(axis)];
796 if space > 0.0 {
797 distribute_item_space_to_growth_limit(
798 space,
799 tracks,
800 has_intrinsic_max_track_sizing_function,
801 inner_node_size.get(axis),
802 );
803 }
804 }
805 // Mark any tracks whose growth limit changed from infinite to finite in this step as infinitely growable for the next step.
806 flush_planned_growth_limit_increases(axis_tracks, true);
807
808 // 6. For max-content maximums: Lastly continue to increase the growth limit of tracks with a max track sizing function of max-content
809 // by distributing extra space as needed to account for these items' max-content contributions. However, limit the growth of any
810 // fit-content() tracks by their fit-content() argument.
811 let has_max_content_max_track_sizing_function = |track: &GridTrack| {
812 track.max_track_sizing_function.is_max_content_alike()
813 || (track.max_track_sizing_function.uses_percentage() && axis_inner_node_size.is_none())
814 };
815 for item in batch.iter_mut() {
816 let axis_max_content_size = item_sizer.max_content_contribution(item);
817 let space = axis_max_content_size;
818 let tracks = &mut axis_tracks[item.track_range_excluding_lines(axis)];
819 if space > 0.0 {
820 distribute_item_space_to_growth_limit(
821 space,
822 tracks,
823 has_max_content_max_track_sizing_function,
824 inner_node_size.get(axis),
825 );
826 }
827 }
828 // Mark any tracks whose growth limit changed from infinite to finite in this step as infinitely growable for the next step.
829 flush_planned_growth_limit_increases(axis_tracks, false);
830 }
831 }
832
833 // Step 5. If any track still has an infinite growth limit (because, for example, it had no items placed
834 // in it or it is a flexible track), set its growth limit to its base size.
835 // NOTE: this step is super-important to ensure that the "Maximise Tracks" step doesn't affect flexible tracks
836 axis_tracks
837 .iter_mut()
838 .filter(|track| track.growth_limit == f32::INFINITY)
839 .for_each(|track| track.growth_limit = track.base_size);
840}
841
842/// 11.5.1. Distributing Extra Space Across Spanned Tracks
843/// https://www.w3.org/TR/css-grid-1/#extra-space
844#[inline(always)]
845fn distribute_item_space_to_base_size(
846 is_flex: bool,
847 use_flex_factor_for_distribution: bool,
848 space: f32,
849 tracks: &mut [GridTrack],
850 track_is_affected: impl Fn(&GridTrack) -> bool,
851 track_limit: impl Fn(&GridTrack) -> f32,
852 intrinsic_contribution_type: IntrinsicContributionType,
853) {
854 if is_flex {
855 let filter = |track: &GridTrack| track.is_flexible() && track_is_affected(track);
856 if use_flex_factor_for_distribution {
857 distribute_item_space_to_base_size_inner(
858 space,
859 tracks,
860 filter,
861 |track| track.flex_factor(),
862 track_limit,
863 intrinsic_contribution_type,
864 )
865 } else {
866 distribute_item_space_to_base_size_inner(
867 space,
868 tracks,
869 filter,
870 |_| 1.0,
871 track_limit,
872 intrinsic_contribution_type,
873 )
874 }
875 } else {
876 distribute_item_space_to_base_size_inner(
877 space,
878 tracks,
879 track_is_affected,
880 |_| 1.0,
881 track_limit,
882 intrinsic_contribution_type,
883 )
884 }
885
886 /// Inner function that doesn't account for differences due to distributing to flex items
887 /// This difference is handled by the closure passed in above
888 fn distribute_item_space_to_base_size_inner(
889 space: f32,
890 tracks: &mut [GridTrack],
891 track_is_affected: impl Fn(&GridTrack) -> bool,
892 track_distribution_proportion: impl Fn(&GridTrack) -> f32,
893 track_limit: impl Fn(&GridTrack) -> f32,
894 intrinsic_contribution_type: IntrinsicContributionType,
895 ) {
896 // Skip this distribution if there is either
897 // - no space to distribute
898 // - no affected tracks to distribute space to
899 if space == 0.0 || !tracks.iter().any(&track_is_affected) {
900 return;
901 }
902
903 // Define get_base_size function. This is passed to the distribute_space_up_to_limits helper function
904 // to indicate that it is the base size that is being distributed to.
905 let get_base_size = |track: &GridTrack| track.base_size;
906
907 // 1. Find the space to distribute
908 let track_sizes: f32 = tracks.iter().map(|track| track.base_size).sum();
909 let extra_space: f32 = f32_max(0.0, space - track_sizes);
910
911 // 2. Distribute space up to limits:
912 // Note: there are two exit conditions to this loop:
913 // - We run out of space to distribute (extra_space falls below THRESHOLD)
914 // - We run out of growable tracks to distribute to
915
916 /// Define a small constant to avoid infinite loops due to rounding errors. Rather than stopping distributing
917 /// extra space when it gets to exactly zero, we will stop when it falls below this amount
918 const THRESHOLD: f32 = 0.000001;
919
920 let extra_space = distribute_space_up_to_limits(
921 extra_space,
922 tracks,
923 &track_is_affected,
924 &track_distribution_proportion,
925 get_base_size,
926 &track_limit,
927 );
928
929 // 3. Distribute remaining span beyond limits (if any)
930 if extra_space > THRESHOLD {
931 // When accommodating minimum contributions or accommodating min-content contributions:
932 // - any affected track that happens to also have an intrinsic max track sizing function;
933 // When accommodating max-content contributions:
934 // - any affected track that happens to also have a max-content max track sizing function
935 let mut filter = match intrinsic_contribution_type {
936 IntrinsicContributionType::Minimum => {
937 (|track: &GridTrack| track.max_track_sizing_function.is_intrinsic()) as fn(&GridTrack) -> bool
938 }
939 IntrinsicContributionType::Maximum => {
940 use MaxTrackSizingFunction::{FitContent, MaxContent};
941 (|track: &GridTrack| {
942 matches!(track.max_track_sizing_function, MaxContent | FitContent(_))
943 || track.min_track_sizing_function == MinTrackSizingFunction::MaxContent
944 }) as fn(&GridTrack) -> bool
945 }
946 };
947
948 // If there are no such tracks (matching filter above), then use all affected tracks.
949 let number_of_tracks =
950 tracks.iter().filter(|track| track_is_affected(track)).filter(|track| filter(track)).count();
951 if number_of_tracks == 0 {
952 filter = (|_| true) as fn(&GridTrack) -> bool;
953 }
954
955 distribute_space_up_to_limits(
956 extra_space,
957 tracks,
958 filter,
959 &track_distribution_proportion,
960 get_base_size,
961 &track_limit, // Should apply only fit-content limit here?
962 );
963 }
964
965 // 4. For each affected track, if the track’s item-incurred increase is larger than the track’s planned increase
966 // set the track’s planned increase to that value.
967 for track in tracks.iter_mut() {
968 if track.item_incurred_increase > track.base_size_planned_increase {
969 track.base_size_planned_increase = track.item_incurred_increase;
970 }
971
972 // Reset the item_incurresed increase ready for the next space distribution
973 track.item_incurred_increase = 0.0;
974 }
975 }
976}
977
978/// 11.5.1. Distributing Extra Space Across Spanned Tracks
979/// This is simplified (and faster) version of the algorithm for growth limits
980/// https://www.w3.org/TR/css-grid-1/#extra-space
981fn distribute_item_space_to_growth_limit(
982 space: f32,
983 tracks: &mut [GridTrack],
984 track_is_affected: impl Fn(&GridTrack) -> bool,
985 axis_inner_node_size: Option<f32>,
986) {
987 // Skip this distribution if there is either
988 // - no space to distribute
989 // - no affected tracks to distribute space to
990 if space == 0.0 || tracks.iter().filter(|track| track_is_affected(track)).count() == 0 {
991 return;
992 }
993
994 // 1. Find the space to distribute
995 let track_sizes: f32 = tracks
996 .iter()
997 .map(|track| if track.growth_limit == f32::INFINITY { track.base_size } else { track.growth_limit })
998 .sum();
999 let extra_space: f32 = f32_max(0.0, space - track_sizes);
1000
1001 // 2. Distribute space up to limits:
1002 // For growth limits the limit is either Infinity, or the growth limit itself. Which means that:
1003 // - If there are any tracks with infinite limits then all space will be distributed to those track(s).
1004 // - Otherwise no space will be distributed as part of this step
1005 let number_of_growable_tracks = tracks
1006 .iter()
1007 .filter(|track| track_is_affected(track))
1008 .filter(|track| {
1009 track.infinitely_growable || track.fit_content_limited_growth_limit(axis_inner_node_size) == f32::INFINITY
1010 })
1011 .count();
1012 if number_of_growable_tracks > 0 {
1013 let item_incurred_increase = extra_space / number_of_growable_tracks as f32;
1014 for track in tracks.iter_mut().filter(|track| track_is_affected(track)).filter(|track| {
1015 track.infinitely_growable || track.fit_content_limited_growth_limit(axis_inner_node_size) == f32::INFINITY
1016 }) {
1017 track.item_incurred_increase = item_incurred_increase;
1018 }
1019 } else {
1020 // 3. Distribute space beyond limits
1021 // If space remains after all tracks are frozen, unfreeze and continue to distribute space to the item-incurred increase
1022 // ...when handling any intrinsic growth limit: all affected tracks.
1023 distribute_space_up_to_limits(
1024 extra_space,
1025 tracks,
1026 track_is_affected,
1027 |_| 1.0,
1028 |track| if track.growth_limit == f32::INFINITY { track.base_size } else { track.growth_limit },
1029 move |track| track.fit_content_limit(axis_inner_node_size),
1030 );
1031 };
1032
1033 // 4. For each affected track, if the track’s item-incurred increase is larger than the track’s planned increase
1034 // set the track’s planned increase to that value.
1035 for track in tracks.iter_mut() {
1036 if track.item_incurred_increase > track.growth_limit_planned_increase {
1037 track.growth_limit_planned_increase = track.item_incurred_increase;
1038 }
1039
1040 // Reset the item_incurresed increase ready for the next space distribution
1041 track.item_incurred_increase = 0.0;
1042 }
1043}
1044
1045/// 11.6 Maximise Tracks
1046/// Distributes free space (if any) to tracks with FINITE growth limits, up to their limits.
1047#[inline(always)]
1048fn maximise_tracks(
1049 axis_tracks: &mut [GridTrack],
1050 axis_inner_node_size: Option<f32>,
1051 axis_available_grid_space: AvailableSpace,
1052) {
1053 let used_space: f32 = axis_tracks.iter().map(|track| track.base_size).sum();
1054 let free_space = axis_available_grid_space.compute_free_space(used_space);
1055 if free_space == f32::INFINITY {
1056 axis_tracks.iter_mut().for_each(|track| track.base_size = track.growth_limit);
1057 } else if free_space > 0.0 {
1058 distribute_space_up_to_limits(
1059 free_space,
1060 axis_tracks,
1061 |_| true,
1062 |_| 1.0,
1063 |track| track.base_size,
1064 move |track: &GridTrack| track.fit_content_limited_growth_limit(axis_inner_node_size),
1065 );
1066 for track in axis_tracks.iter_mut() {
1067 track.base_size += track.item_incurred_increase;
1068 track.item_incurred_increase = 0.0;
1069 }
1070 }
1071}
1072
1073/// 11.7. Expand Flexible Tracks
1074/// This step sizes flexible tracks using the largest value it can assign to an fr without exceeding the available space.
1075#[allow(clippy::too_many_arguments)]
1076#[inline(always)]
1077fn expand_flexible_tracks(
1078 tree: &mut impl LayoutTree,
1079 axis: AbstractAxis,
1080 axis_tracks: &mut [GridTrack],
1081 items: &mut [GridItem],
1082 axis_min_size: Option<f32>,
1083 axis_max_size: Option<f32>,
1084 available_grid_space: Size<AvailableSpace>,
1085 inner_node_size: Size<Option<f32>>,
1086) {
1087 // First, find the grid’s used flex fraction:
1088 let flex_fraction = match available_grid_space.get(axis) {
1089 // If the free space is zero:
1090 // The used flex fraction is zero.
1091 // Otherwise, if the free space is a definite length:
1092 // The used flex fraction is the result of finding the size of an fr using all of the grid tracks and
1093 // a space to fill of the available grid space.
1094 AvailableSpace::Definite(available_space) => {
1095 let used_space: f32 = axis_tracks.iter().map(|track| track.base_size).sum();
1096 let free_space = available_space - used_space;
1097 if free_space <= 0.0 {
1098 0.0
1099 } else {
1100 find_size_of_fr(axis_tracks, available_space)
1101 }
1102 }
1103 // If ... sizing the grid container under a min-content constraint the used flex fraction is zero.
1104 AvailableSpace::MinContent => 0.0,
1105 // Otherwise, if the free space is an indefinite length:
1106 AvailableSpace::MaxContent => {
1107 // The used flex fraction is the maximum of:
1108 let flex_fraction = f32_max(
1109 // For each flexible track, if the flexible track’s flex factor is greater than one,
1110 // the result of dividing the track’s base size by its flex factor; otherwise, the track’s base size.
1111 axis_tracks
1112 .iter()
1113 .filter(|track| track.max_track_sizing_function.is_flexible())
1114 .map(|track| {
1115 let flex_factor = track.flex_factor();
1116 if flex_factor > 1.0 {
1117 track.base_size / flex_factor
1118 } else {
1119 track.base_size
1120 }
1121 })
1122 .max_by(|a, b| a.total_cmp(b))
1123 .unwrap_or(0.0),
1124 // For each grid item that crosses a flexible track, the result of finding the size of an fr using all the grid tracks
1125 // that the item crosses and a space to fill of the item’s max-content contribution.
1126 items
1127 .iter_mut()
1128 .filter(|item| item.crosses_flexible_track(axis))
1129 .map(|item| {
1130 let tracks = &axis_tracks[item.track_range_excluding_lines(axis)];
1131 // TODO: plumb estimate of other axis size (known_dimensions) in here rather than just passing Size::NONE?
1132 let max_content_contribution =
1133 item.max_content_contribution_cached(axis, tree, Size::NONE, inner_node_size);
1134 find_size_of_fr(tracks, max_content_contribution)
1135 })
1136 .max_by(|a, b| a.total_cmp(b))
1137 .unwrap_or(0.0),
1138 );
1139
1140 // If using this flex fraction would cause the grid to be smaller than the grid container’s min-width/height (or larger than the
1141 // grid container’s max-width/height), then redo this step, treating the free space as definite and the available grid space as equal
1142 // to the grid container’s inner size when it’s sized to its min-width/height (max-width/height).
1143 // (Note: min_size takes precedence over max_size)
1144 let hypothetical_grid_size: f32 = axis_tracks
1145 .iter()
1146 .map(|track| match track.max_track_sizing_function {
1147 MaxTrackSizingFunction::Fraction(track_flex_factor) => {
1148 f32_max(track.base_size, track_flex_factor * flex_fraction)
1149 }
1150 _ => track.base_size,
1151 })
1152 .sum();
1153 let axis_min_size = axis_min_size.unwrap_or(0.0);
1154 let axis_max_size = axis_max_size.unwrap_or(f32::INFINITY);
1155 if hypothetical_grid_size < axis_min_size {
1156 find_size_of_fr(axis_tracks, axis_min_size)
1157 } else if hypothetical_grid_size > axis_max_size {
1158 find_size_of_fr(axis_tracks, axis_max_size)
1159 } else {
1160 flex_fraction
1161 }
1162 }
1163 };
1164
1165 // For each flexible track, if the product of the used flex fraction and the track’s flex factor is greater
1166 // than the track’s base size, set its base size to that product.
1167 for track in axis_tracks.iter_mut() {
1168 if let MaxTrackSizingFunction::Fraction(track_flex_factor) = track.max_track_sizing_function {
1169 track.base_size = f32_max(track.base_size, track_flex_factor * flex_fraction);
1170 }
1171 }
1172}
1173
1174/// 11.7.1. Find the Size of an fr
1175/// This algorithm finds the largest size that an fr unit can be without exceeding the target size.
1176/// It must be called with a set of grid tracks and some quantity of space to fill.
1177#[inline(always)]
1178fn find_size_of_fr(tracks: &[GridTrack], space_to_fill: f32) -> f32 {
1179 // Handle the trivial case where there is no space to fill
1180 // Do not remove as otherwise the loop below will loop infinitely
1181 if space_to_fill == 0.0 {
1182 return 0.0;
1183 }
1184
1185 // If the product of the hypothetical fr size (computed below) and any flexible track’s flex factor
1186 // is less than the track’s base size, then we must restart this algorithm treating all such tracks as inflexible.
1187 // We therefore wrap the entire algorithm in a loop, with an hypotherical_fr_size of INFINITY such that the above
1188 // condition can never be true for the first iteration.
1189 let mut hypothetical_fr_size = f32::INFINITY;
1190 let mut previous_iter_hypothetical_fr_size;
1191 loop {
1192 // Let leftover space be the space to fill minus the base sizes of the non-flexible grid tracks.
1193 // Let flex factor sum be the sum of the flex factors of the flexible tracks. If this value is less than 1, set it to 1 instead.
1194 // We compute both of these in a single loop to avoid iterating over the data twice
1195 let mut used_space = 0.0;
1196 let mut naive_flex_factor_sum = 0.0;
1197 for track in tracks.iter() {
1198 match track.max_track_sizing_function {
1199 // Tracks for which flex_factor * hypothetical_fr_size < track.base_size are treated as inflexible
1200 MaxTrackSizingFunction::Fraction(flex_factor)
1201 if flex_factor * hypothetical_fr_size >= track.base_size =>
1202 {
1203 naive_flex_factor_sum += flex_factor;
1204 }
1205 _ => used_space += track.base_size,
1206 };
1207 }
1208 let leftover_space = space_to_fill - used_space;
1209 let flex_factor = f32_max(naive_flex_factor_sum, 1.0);
1210
1211 // Let the hypothetical fr size be the leftover space divided by the flex factor sum.
1212 previous_iter_hypothetical_fr_size = hypothetical_fr_size;
1213 hypothetical_fr_size = leftover_space / flex_factor;
1214
1215 // If the product of the hypothetical fr size and a flexible track’s flex factor is less than the track’s base size,
1216 // restart this algorithm treating all such tracks as inflexible.
1217 // We keep track of the hypothetical_fr_size
1218 let hypotherical_fr_size_is_valid = tracks.iter().all(|track| match track.max_track_sizing_function {
1219 MaxTrackSizingFunction::Fraction(flex_factor) => {
1220 flex_factor * hypothetical_fr_size >= track.base_size
1221 || flex_factor * previous_iter_hypothetical_fr_size < track.base_size
1222 }
1223 _ => true,
1224 });
1225 if hypotherical_fr_size_is_valid {
1226 break;
1227 }
1228 }
1229
1230 // Return the hypothetical fr size.
1231 hypothetical_fr_size
1232}
1233
1234/// 11.8. Stretch auto Tracks
1235/// This step expands tracks that have an auto max track sizing function by dividing any remaining positive, definite free space equally amongst them.
1236#[inline(always)]
1237fn stretch_auto_tracks(
1238 axis: AbstractAxis,
1239 axis_tracks: &mut [GridTrack],
1240 axis_min_size: Option<f32>,
1241 available_grid_space: Size<AvailableSpace>,
1242) {
1243 let num_auto_tracks =
1244 axis_tracks.iter().filter(|track| track.max_track_sizing_function == MaxTrackSizingFunction::Auto).count();
1245 if num_auto_tracks > 0 {
1246 let used_space: f32 = axis_tracks.iter().map(|track| track.base_size).sum();
1247
1248 // If the free space is indefinite, but the grid container has a definite min-width/height
1249 // use that size to calculate the free space for this step instead.
1250 let free_space = if available_grid_space.get(axis).is_definite() {
1251 available_grid_space.get(axis).compute_free_space(used_space)
1252 } else {
1253 match axis_min_size {
1254 Some(size) => size - used_space,
1255 None => 0.0,
1256 }
1257 };
1258 if free_space > 0.0 {
1259 let extra_space_per_auto_track = free_space / num_auto_tracks as f32;
1260 axis_tracks
1261 .iter_mut()
1262 .filter(|track| track.max_track_sizing_function == MaxTrackSizingFunction::Auto)
1263 .for_each(|track| track.base_size += extra_space_per_auto_track);
1264 }
1265 }
1266}
1267
1268/// Helper function for distributing space to tracks evenly
1269/// Used by both distribute_item_space_to_base_size and maximise_tracks steps
1270#[inline(always)]
1271fn distribute_space_up_to_limits(
1272 space_to_distribute: f32,
1273 tracks: &mut [GridTrack],
1274 track_is_affected: impl Fn(&GridTrack) -> bool,
1275 track_distribution_proportion: impl Fn(&GridTrack) -> f32,
1276 track_affected_property: impl Fn(&GridTrack) -> f32,
1277 track_limit: impl Fn(&GridTrack) -> f32,
1278) -> f32 {
1279 /// Define a small constant to avoid infinite loops due to rounding errors. Rather than stopping distributing
1280 /// extra space when it gets to exactly zero, we will stop when it falls below this amount
1281 const THRESHOLD: f32 = 0.000001;
1282
1283 let mut space_to_distribute = space_to_distribute;
1284 while space_to_distribute > THRESHOLD {
1285 let track_distribution_proportion_sum: f32 = tracks
1286 .iter()
1287 .filter(|track| track_affected_property(track) + track.item_incurred_increase < track_limit(track))
1288 .filter(|track| track_is_affected(track))
1289 .map(&track_distribution_proportion)
1290 .sum();
1291
1292 if track_distribution_proportion_sum == 0.0 {
1293 break;
1294 }
1295
1296 // Compute item-incurred increase for this iteration
1297 let min_increase_limit = tracks
1298 .iter()
1299 .filter(|track| track_affected_property(track) + track.item_incurred_increase < track_limit(track))
1300 .filter(|track| track_is_affected(track))
1301 .map(|track| (track_limit(track) - track_affected_property(track)) / track_distribution_proportion(track))
1302 .min_by(|a, b| a.total_cmp(b))
1303 .unwrap(); // We will never pass an empty track list to this function
1304 let iteration_item_incurred_increase =
1305 f32_min(min_increase_limit, space_to_distribute / track_distribution_proportion_sum);
1306
1307 for track in tracks.iter_mut().filter(|track| track_is_affected(track)) {
1308 let increase = iteration_item_incurred_increase * track_distribution_proportion(track);
1309 if increase > 0.0 && track_affected_property(track) + increase <= track_limit(track) {
1310 track.item_incurred_increase += increase;
1311 space_to_distribute -= increase;
1312 }
1313 }
1314 }
1315
1316 space_to_distribute
1317}