1//! Computes the [flexbox](https://css-tricks.com/snippets/css/a-guide-to-flexbox/) layout algorithm on [`Taffy`](crate::Taffy) according to the [spec](https://www.w3.org/TR/css-flexbox-1/)
2use core::f32;
3
4use crate::compute::common::alignment::compute_alignment_offset;
5use crate::compute::{GenericAlgorithm, LayoutAlgorithm};
6use crate::geometry::{Point, Rect, Size};
7use crate::layout::{Layout, RunMode, SizeAndBaselines, SizingMode};
8use crate::math::MaybeMath;
9use crate::node::Node;
10use crate::prelude::{TaffyMaxContent, TaffyMinContent};
11use crate::resolve::{MaybeResolve, ResolveOrZero};
12use crate::style::{
13 AlignContent, AlignItems, AlignSelf, AvailableSpace, Dimension, Display, FlexWrap, JustifyContent,
14 LengthPercentageAuto, Position,
15};
16use crate::style::{FlexDirection, Style};
17use crate::sys::Vec;
18use crate::sys::{f32_max, new_vec_with_capacity};
19use crate::tree::LayoutTree;
20
21#[cfg(feature = "debug")]
22use crate::debug::NODE_LOGGER;
23
24/// The public interface to Taffy's Flexbox algorithm implementation
25pub(crate) struct FlexboxAlgorithm;
26impl LayoutAlgorithm for FlexboxAlgorithm {
27 const NAME: &'static str = "FLEXBOX";
28
29 fn perform_layout(
30 tree: &mut impl LayoutTree,
31 node: Node,
32 known_dimensions: Size<Option<f32>>,
33 parent_size: Size<Option<f32>>,
34 available_space: Size<AvailableSpace>,
35 _sizing_mode: SizingMode,
36 ) -> SizeAndBaselines {
37 compute(tree, node, known_dimensions, parent_size, available_space, RunMode::PeformLayout)
38 }
39
40 fn measure_size(
41 tree: &mut impl LayoutTree,
42 node: Node,
43 known_dimensions: Size<Option<f32>>,
44 parent_size: Size<Option<f32>>,
45 available_space: Size<AvailableSpace>,
46 _sizing_mode: SizingMode,
47 ) -> Size<f32> {
48 compute(tree, node, known_dimensions, parent_size, available_space, RunMode::ComputeSize).size
49 }
50}
51
52/// The intermediate results of a flexbox calculation for a single item
53struct FlexItem {
54 /// The identifier for the associated [`Node`](crate::node::Node)
55 node: Node,
56
57 /// The base size of this item
58 size: Size<Option<f32>>,
59 /// The minimum allowable size of this item
60 min_size: Size<Option<f32>>,
61 /// The maximum allowable size of this item
62 max_size: Size<Option<f32>>,
63 /// The cross-alignment of this item
64 align_self: AlignSelf,
65
66 /// The flex shrink style of the item
67 flex_shrink: f32,
68 /// The flex grow style of the item
69 flex_grow: f32,
70
71 /// The minimum size of the item. This differs from min_size above because it also
72 /// takes into account content based automatic minimum sizes
73 resolved_minimum_size: Size<f32>,
74
75 /// The final offset of this item
76 inset: Rect<Option<f32>>,
77 /// The margin of this item
78 margin: Rect<f32>,
79 /// Whether each margin is an auto margin or not
80 margin_is_auto: Rect<bool>,
81 /// The padding of this item
82 padding: Rect<f32>,
83 /// The border of this item
84 border: Rect<f32>,
85
86 /// The default size of this item
87 flex_basis: f32,
88 /// The default size of this item, minus padding and border
89 inner_flex_basis: f32,
90 /// The amount by which this item has deviated from its target size
91 violation: f32,
92 /// Is the size of this item locked
93 frozen: bool,
94
95 /// Either the max- or min- content flex fraction
96 /// See https://www.w3.org/TR/css-flexbox-1/#intrinsic-main-sizes
97 content_flex_fraction: f32,
98
99 /// The proposed inner size of this item
100 hypothetical_inner_size: Size<f32>,
101 /// The proposed outer size of this item
102 hypothetical_outer_size: Size<f32>,
103 /// The size that this item wants to be
104 target_size: Size<f32>,
105 /// The size that this item wants to be, plus any padding and border
106 outer_target_size: Size<f32>,
107
108 /// The position of the bottom edge of this item
109 baseline: f32,
110
111 /// A temporary value for the main offset
112 ///
113 /// Offset is the relative position from the item's natural flow position based on
114 /// relative position values, alignment, and justification. Does not include margin/padding/border.
115 offset_main: f32,
116 /// A temporary value for the cross offset
117 ///
118 /// Offset is the relative position from the item's natural flow position based on
119 /// relative position values, alignment, and justification. Does not include margin/padding/border.
120 offset_cross: f32,
121}
122
123/// A line of [`FlexItem`] used for intermediate computation
124struct FlexLine<'a> {
125 /// The slice of items to iterate over during computation of this line
126 items: &'a mut [FlexItem],
127 /// The dimensions of the cross-axis
128 cross_size: f32,
129 /// The relative offset of the cross-axis
130 offset_cross: f32,
131}
132
133/// Values that can be cached during the flexbox algorithm
134struct AlgoConstants {
135 /// The direction of the current segment being laid out
136 dir: FlexDirection,
137 /// Is this segment a row
138 is_row: bool,
139 /// Is this segment a column
140 is_column: bool,
141 /// Is wrapping enabled (in either direction)
142 is_wrap: bool,
143 /// Is the wrap direction inverted
144 is_wrap_reverse: bool,
145
146 /// The item's min_size style
147 min_size: Size<Option<f32>>,
148 /// The item's max_size style
149 max_size: Size<Option<f32>>,
150 /// The margin of this section
151 margin: Rect<f32>,
152 /// The border of this section
153 border: Rect<f32>,
154 /// The padding of this section
155 padding_border: Rect<f32>,
156 /// The gap of this section
157 gap: Size<f32>,
158 /// The align_items property of this node
159 align_items: AlignItems,
160 /// The align_content property of this node
161 align_content: AlignContent,
162 /// The justify_content property of this node
163 justify_content: Option<JustifyContent>,
164
165 /// The border-box size of the node being laid out (if known)
166 node_outer_size: Size<Option<f32>>,
167 /// The content-box size of the node being laid out (if known)
168 node_inner_size: Size<Option<f32>>,
169
170 /// The size of the virtual container containing the flex items.
171 container_size: Size<f32>,
172 /// The size of the internal container
173 inner_container_size: Size<f32>,
174}
175
176/// Computes the layout of [`LayoutTree`] according to the flexbox algorithm
177pub fn compute(
178 tree: &mut impl LayoutTree,
179 node: Node,
180 known_dimensions: Size<Option<f32>>,
181 parent_size: Size<Option<f32>>,
182 available_space: Size<AvailableSpace>,
183 run_mode: RunMode,
184) -> SizeAndBaselines {
185 let style = tree.style(node);
186
187 // Pull these out earlier to avoid borrowing issues
188 let aspect_ratio = style.aspect_ratio;
189 let min_size = style.min_size.maybe_resolve(parent_size).maybe_apply_aspect_ratio(aspect_ratio);
190 let max_size = style.max_size.maybe_resolve(parent_size).maybe_apply_aspect_ratio(aspect_ratio);
191 let clamped_style_size =
192 style.size.maybe_resolve(parent_size).maybe_apply_aspect_ratio(aspect_ratio).maybe_clamp(min_size, max_size);
193
194 // If both min and max in a given axis are set and max <= min then this determines the size in that axis
195 let min_max_definite_size = min_size.zip_map(max_size, |min, max| match (min, max) {
196 (Some(min), Some(max)) if max <= min => Some(min),
197 _ => None,
198 });
199 let styled_based_known_dimensions = known_dimensions.or(min_max_definite_size).or(clamped_style_size);
200
201 // Short-circuit layout if the container's size is fully determined by the container's size and the run mode
202 // is ComputeSize (and thus the container's size is all that we're interested in)
203 if run_mode == RunMode::ComputeSize {
204 if let Size { width: Some(width), height: Some(height) } = styled_based_known_dimensions {
205 return Size { width, height }.into();
206 }
207 }
208
209 #[cfg(feature = "debug")]
210 NODE_LOGGER.log("FLEX: single-pass");
211 compute_preliminary(tree, node, styled_based_known_dimensions, parent_size, available_space, run_mode)
212}
213
214/// Compute a preliminary size for an item
215fn compute_preliminary(
216 tree: &mut impl LayoutTree,
217 node: Node,
218 known_dimensions: Size<Option<f32>>,
219 parent_size: Size<Option<f32>>,
220 available_space: Size<AvailableSpace>,
221 run_mode: RunMode,
222) -> SizeAndBaselines {
223 // Define some general constants we will need for the remainder of the algorithm.
224 let mut constants = compute_constants(tree.style(node), known_dimensions, parent_size);
225
226 // 9. Flex Layout Algorithm
227
228 // 9.1. Initial Setup
229
230 // 1. Generate anonymous flex items as described in §4 Flex Items.
231 #[cfg(feature = "debug")]
232 NODE_LOGGER.log("generate_anonymous_flex_items");
233 let mut flex_items = generate_anonymous_flex_items(tree, node, &constants);
234
235 // 9.2. Line Length Determination
236
237 // 2. Determine the available main and cross space for the flex items
238 #[cfg(feature = "debug")]
239 NODE_LOGGER.log("determine_available_space");
240 let available_space = determine_available_space(known_dimensions, available_space, &constants);
241
242 // 3. Determine the flex base size and hypothetical main size of each item.
243 #[cfg(feature = "debug")]
244 NODE_LOGGER.log("determine_flex_base_size");
245 determine_flex_base_size(tree, &constants, available_space, &mut flex_items);
246
247 #[cfg(feature = "debug")]
248 for item in flex_items.iter() {
249 NODE_LOGGER.labelled_log("item.flex_basis", item.flex_basis);
250 NODE_LOGGER.labelled_log("item.inner_flex_basis", item.inner_flex_basis);
251 NODE_LOGGER.labelled_debug_log("item.hypothetical_outer_size", item.hypothetical_outer_size);
252 NODE_LOGGER.labelled_debug_log("item.hypothetical_inner_size", item.hypothetical_inner_size);
253 NODE_LOGGER.labelled_debug_log("item.resolved_minimum_size", item.resolved_minimum_size);
254 }
255
256 // 4. Determine the main size of the flex container
257 // This has already been done as part of compute_constants. The inner size is exposed as constants.node_inner_size.
258
259 // 9.3. Main Size Determination
260
261 // 5. Collect flex items into flex lines.
262 #[cfg(feature = "debug")]
263 NODE_LOGGER.log("collect_flex_lines");
264 let mut flex_lines = collect_flex_lines(&constants, available_space, &mut flex_items);
265
266 // If container size is undefined, determine the container's main size
267 // and then re-resolve gaps based on newly determined size
268 #[cfg(feature = "debug")]
269 NODE_LOGGER.log("determine_container_main_size");
270 let original_gap = constants.gap;
271 if let Some(inner_main_size) = constants.node_inner_size.main(constants.dir) {
272 let outer_main_size = inner_main_size + constants.padding_border.main_axis_sum(constants.dir);
273 constants.inner_container_size.set_main(constants.dir, inner_main_size);
274 constants.container_size.set_main(constants.dir, outer_main_size);
275 } else {
276 // Sets constants.container_size and constants.outer_container_size
277 determine_container_main_size(tree, available_space, &mut flex_lines, &mut constants);
278 constants.node_inner_size.set_main(constants.dir, Some(constants.inner_container_size.main(constants.dir)));
279 constants.node_outer_size.set_main(constants.dir, Some(constants.container_size.main(constants.dir)));
280
281 #[cfg(feature = "debug")]
282 NODE_LOGGER.labelled_debug_log("constants.node_outer_size", constants.node_outer_size);
283 #[cfg(feature = "debug")]
284 NODE_LOGGER.labelled_debug_log("constants.node_inner_size", constants.node_inner_size);
285
286 // Re-resolve percentage gaps
287 let style = tree.style(node);
288 let inner_container_size = constants.inner_container_size.main(constants.dir);
289 let new_gap = style.gap.main(constants.dir).maybe_resolve(inner_container_size).unwrap_or(0.0);
290 constants.gap.set_main(constants.dir, new_gap);
291 }
292
293 // 6. Resolve the flexible lengths of all the flex items to find their used main size.
294 #[cfg(feature = "debug")]
295 NODE_LOGGER.log("resolve_flexible_lengths");
296 for line in &mut flex_lines {
297 resolve_flexible_lengths(line, &constants, original_gap);
298 }
299
300 // 9.4. Cross Size Determination
301
302 // 7. Determine the hypothetical cross size of each item.
303 #[cfg(feature = "debug")]
304 NODE_LOGGER.log("determine_hypothetical_cross_size");
305 for line in &mut flex_lines {
306 determine_hypothetical_cross_size(tree, line, &constants, available_space);
307 }
308
309 // Calculate child baselines. This function is internally smart and only computes child baselines
310 // if they are necessary.
311 #[cfg(feature = "debug")]
312 NODE_LOGGER.log("calculate_children_base_lines");
313 calculate_children_base_lines(tree, known_dimensions, available_space, &mut flex_lines, &constants);
314
315 // 8. Calculate the cross size of each flex line.
316 #[cfg(feature = "debug")]
317 NODE_LOGGER.log("calculate_cross_size");
318 calculate_cross_size(&mut flex_lines, known_dimensions, &constants);
319
320 // 9. Handle 'align-content: stretch'.
321 #[cfg(feature = "debug")]
322 NODE_LOGGER.log("handle_align_content_stretch");
323 handle_align_content_stretch(&mut flex_lines, known_dimensions, &constants);
324
325 // 10. Collapse visibility:collapse items. If any flex items have visibility: collapse,
326 // note the cross size of the line they’re in as the item’s strut size, and restart
327 // layout from the beginning.
328 //
329 // In this second layout round, when collecting items into lines, treat the collapsed
330 // items as having zero main size. For the rest of the algorithm following that step,
331 // ignore the collapsed items entirely (as if they were display:none) except that after
332 // calculating the cross size of the lines, if any line’s cross size is less than the
333 // largest strut size among all the collapsed items in the line, set its cross size to
334 // that strut size.
335 //
336 // Skip this step in the second layout round.
337
338 // TODO implement once (if ever) we support visibility:collapse
339
340 // 11. Determine the used cross size of each flex item.
341 #[cfg(feature = "debug")]
342 NODE_LOGGER.log("determine_used_cross_size");
343 determine_used_cross_size(tree, &mut flex_lines, &constants);
344
345 // 9.5. Main-Axis Alignment
346
347 // 12. Distribute any remaining free space.
348 #[cfg(feature = "debug")]
349 NODE_LOGGER.log("distribute_remaining_free_space");
350 distribute_remaining_free_space(&mut flex_lines, &constants);
351
352 // 9.6. Cross-Axis Alignment
353
354 // 13. Resolve cross-axis auto margins (also includes 14).
355 #[cfg(feature = "debug")]
356 NODE_LOGGER.log("resolve_cross_axis_auto_margins");
357 resolve_cross_axis_auto_margins(&mut flex_lines, &constants);
358
359 // 15. Determine the flex container’s used cross size.
360 #[cfg(feature = "debug")]
361 NODE_LOGGER.log("determine_container_cross_size");
362 let total_line_cross_size = determine_container_cross_size(&flex_lines, known_dimensions, &mut constants);
363
364 // We have the container size.
365 // If our caller does not care about performing layout we are done now.
366 if run_mode == RunMode::ComputeSize {
367 return constants.container_size.into();
368 }
369
370 // 16. Align all flex lines per align-content.
371 #[cfg(feature = "debug")]
372 NODE_LOGGER.log("align_flex_lines_per_align_content");
373 align_flex_lines_per_align_content(&mut flex_lines, &constants, total_line_cross_size);
374
375 // Do a final layout pass and gather the resulting layouts
376 #[cfg(feature = "debug")]
377 NODE_LOGGER.log("final_layout_pass");
378 final_layout_pass(tree, node, &mut flex_lines, &constants);
379
380 // Before returning we perform absolute layout on all absolutely positioned children
381 #[cfg(feature = "debug")]
382 NODE_LOGGER.log("perform_absolute_layout_on_absolute_children");
383 perform_absolute_layout_on_absolute_children(tree, node, &constants);
384
385 #[cfg(feature = "debug")]
386 NODE_LOGGER.log("hidden_layout");
387 let len = tree.child_count(node);
388 for order in 0..len {
389 let child = tree.child(node, order);
390 if tree.style(child).display == Display::None {
391 *tree.layout_mut(child) = Layout::with_order(order as u32);
392 GenericAlgorithm::perform_layout(
393 tree,
394 child,
395 Size::NONE,
396 Size::NONE,
397 Size::MAX_CONTENT,
398 SizingMode::InherentSize,
399 );
400 }
401 }
402
403 // 8.5. Flex Container Baselines: calculate the flex container's first baseline
404 // See https://www.w3.org/TR/css-flexbox-1/#flex-baselines
405 let first_vertical_baseline = if flex_lines.is_empty() {
406 None
407 } else {
408 flex_lines[0]
409 .items
410 .iter()
411 .find(|item| constants.is_column || item.align_self == AlignSelf::Baseline)
412 .or_else(|| flex_lines[0].items.iter().next())
413 .map(|child| {
414 let offset_vertical = if constants.is_row { child.offset_cross } else { child.offset_main };
415 offset_vertical + child.baseline
416 })
417 };
418
419 SizeAndBaselines { size: constants.container_size, first_baselines: Point { x: None, y: first_vertical_baseline } }
420}
421
422/// Compute constants that can be reused during the flexbox algorithm.
423#[inline]
424fn compute_constants(
425 style: &Style,
426 known_dimensions: Size<Option<f32>>,
427 parent_size: Size<Option<f32>>,
428) -> AlgoConstants {
429 let dir = style.flex_direction;
430 let is_row = dir.is_row();
431 let is_column = dir.is_column();
432 let is_wrap = matches!(style.flex_wrap, FlexWrap::Wrap | FlexWrap::WrapReverse);
433 let is_wrap_reverse = style.flex_wrap == FlexWrap::WrapReverse;
434
435 let aspect_ratio = style.aspect_ratio;
436 let margin = style.margin.resolve_or_zero(parent_size.width);
437 let padding = style.padding.resolve_or_zero(parent_size.width);
438 let border = style.border.resolve_or_zero(parent_size.width);
439 let align_items = style.align_items.unwrap_or(AlignItems::Stretch);
440 let align_content = style.align_content.unwrap_or(AlignContent::Stretch);
441 let justify_content = style.justify_content;
442
443 let padding_border = padding + border;
444
445 let node_outer_size = known_dimensions;
446 let node_inner_size = node_outer_size.maybe_sub(padding_border.sum_axes());
447 let gap = style.gap.resolve_or_zero(node_inner_size.or(Size::zero()));
448
449 let container_size = Size::zero();
450 let inner_container_size = Size::zero();
451
452 AlgoConstants {
453 dir,
454 is_row,
455 is_column,
456 is_wrap,
457 is_wrap_reverse,
458 min_size: style.min_size.maybe_resolve(parent_size).maybe_apply_aspect_ratio(aspect_ratio),
459 max_size: style.max_size.maybe_resolve(parent_size).maybe_apply_aspect_ratio(aspect_ratio),
460 margin,
461 border,
462 gap,
463 padding_border,
464 align_items,
465 align_content,
466 justify_content,
467 node_outer_size,
468 node_inner_size,
469 container_size,
470 inner_container_size,
471 }
472}
473
474/// Generate anonymous flex items.
475///
476/// # [9.1. Initial Setup](https://www.w3.org/TR/css-flexbox-1/#box-manip)
477///
478/// - [**Generate anonymous flex items**](https://www.w3.org/TR/css-flexbox-1/#algo-anon-box) as described in [§4 Flex Items](https://www.w3.org/TR/css-flexbox-1/#flex-items).
479#[inline]
480fn generate_anonymous_flex_items(tree: &impl LayoutTree, node: Node, constants: &AlgoConstants) -> Vec<FlexItem> {
481 tree.children(node)
482 .map(|child| (child, tree.style(*child)))
483 .filter(|(_, style)| style.position != Position::Absolute)
484 .filter(|(_, style)| style.display != Display::None)
485 .map(|(child, child_style)| {
486 let aspect_ratio = child_style.aspect_ratio;
487 FlexItem {
488 node: *child,
489 size: child_style.size.maybe_resolve(constants.node_inner_size).maybe_apply_aspect_ratio(aspect_ratio),
490 min_size: child_style
491 .min_size
492 .maybe_resolve(constants.node_inner_size)
493 .maybe_apply_aspect_ratio(aspect_ratio),
494 max_size: child_style
495 .max_size
496 .maybe_resolve(constants.node_inner_size)
497 .maybe_apply_aspect_ratio(aspect_ratio),
498
499 inset: child_style.inset.zip_size(constants.node_inner_size, |p, s| p.maybe_resolve(s)),
500 margin: child_style.margin.resolve_or_zero(constants.node_inner_size.width),
501 margin_is_auto: child_style.margin.map(|m| m == LengthPercentageAuto::Auto),
502 padding: child_style.padding.resolve_or_zero(constants.node_inner_size.width),
503 border: child_style.border.resolve_or_zero(constants.node_inner_size.width),
504 align_self: child_style.align_self.unwrap_or(constants.align_items),
505 flex_grow: child_style.flex_grow,
506 flex_shrink: child_style.flex_shrink,
507 flex_basis: 0.0,
508 inner_flex_basis: 0.0,
509 violation: 0.0,
510 frozen: false,
511
512 resolved_minimum_size: Size::zero(),
513 hypothetical_inner_size: Size::zero(),
514 hypothetical_outer_size: Size::zero(),
515 target_size: Size::zero(),
516 outer_target_size: Size::zero(),
517 content_flex_fraction: 0.0,
518
519 baseline: 0.0,
520
521 offset_main: 0.0,
522 offset_cross: 0.0,
523 }
524 })
525 .collect()
526}
527
528/// Determine the available main and cross space for the flex items.
529///
530/// # [9.2. Line Length Determination](https://www.w3.org/TR/css-flexbox-1/#line-sizing)
531///
532/// - [**Determine the available main and cross space for the flex items**](https://www.w3.org/TR/css-flexbox-1/#algo-available).
533/// For each dimension, if that dimension of the flex container’s content box is a definite size, use that;
534/// if that dimension of the flex container is being sized under a min or max-content constraint, the available space in that dimension is that constraint;
535/// otherwise, subtract the flex container’s margin, border, and padding from the space available to the flex container in that dimension and use that value.
536/// **This might result in an infinite value**.
537#[inline]
538#[must_use]
539fn determine_available_space(
540 known_dimensions: Size<Option<f32>>,
541 outer_available_space: Size<AvailableSpace>,
542 constants: &AlgoConstants,
543) -> Size<AvailableSpace> {
544 // Note: min/max/preferred size styles have already been applied to known_dimensions in the `compute` function above
545 let width = match known_dimensions.width {
546 Some(node_width) => AvailableSpace::Definite(node_width - constants.padding_border.horizontal_axis_sum()),
547 None => outer_available_space
548 .width
549 .maybe_sub(constants.margin.horizontal_axis_sum())
550 .maybe_sub(constants.padding_border.horizontal_axis_sum()),
551 };
552
553 let height = match known_dimensions.height {
554 Some(node_height) => AvailableSpace::Definite(node_height - constants.padding_border.vertical_axis_sum()),
555 None => outer_available_space
556 .height
557 .maybe_sub(constants.margin.vertical_axis_sum())
558 .maybe_sub(constants.padding_border.vertical_axis_sum()),
559 };
560
561 Size { width, height }
562}
563
564/// Determine the flex base size and hypothetical main size of each item.
565///
566/// # [9.2. Line Length Determination](https://www.w3.org/TR/css-flexbox-1/#line-sizing)
567///
568/// - [**Determine the flex base size and hypothetical main size of each item:**](https://www.w3.org/TR/css-flexbox-1/#algo-main-item)
569///
570/// - A. If the item has a definite used flex basis, that’s the flex base size.
571///
572/// - B. If the flex item has ...
573///
574/// - an intrinsic aspect ratio,
575/// - a used flex basis of content, and
576/// - a definite cross size,
577///
578/// then the flex base size is calculated from its inner cross size and the flex item’s intrinsic aspect ratio.
579///
580/// - C. If the used flex basis is content or depends on its available space, and the flex container is being sized under a min-content
581/// or max-content constraint (e.g. when performing automatic table layout \[CSS21\]), size the item under that constraint.
582/// The flex base size is the item’s resulting main size.
583///
584/// - E. Otherwise, size the item into the available space using its used flex basis in place of its main size, treating a value of content as max-content.
585/// If a cross size is needed to determine the main size (e.g. when the flex item’s main size is in its block axis) and the flex item’s cross size is auto and not definite,
586/// in this calculation use fit-content as the flex item’s cross size. The flex base size is the item’s resulting main size.
587///
588/// When determining the flex base size, the item’s min and max main sizes are ignored (no clamping occurs).
589/// Furthermore, the sizing calculations that floor the content box size at zero when applying box-sizing are also ignored.
590/// (For example, an item with a specified size of zero, positive padding, and box-sizing: border-box will have an outer flex base size of zero—and hence a negative inner flex base size.)
591#[inline]
592fn determine_flex_base_size(
593 tree: &mut impl LayoutTree,
594 constants: &AlgoConstants,
595 available_space: Size<AvailableSpace>,
596 flex_items: &mut [FlexItem],
597) {
598 let dir = constants.dir;
599
600 for child in flex_items.iter_mut() {
601 let child_style = tree.style(child.node);
602
603 // Parent size for child sizing
604 let cross_axis_parent_size = constants.node_inner_size.cross(dir);
605
606 // Available space for child sizing
607 let cross_axis_margin_sum = constants.margin.cross_axis_sum(dir);
608 let child_min_cross = child.min_size.cross(dir).maybe_add(cross_axis_margin_sum);
609 let child_max_cross = child.max_size.cross(dir).maybe_add(cross_axis_margin_sum);
610 let cross_axis_available_space = cross_axis_parent_size.maybe_clamp(child_min_cross, child_max_cross).into();
611
612 child.flex_basis = 'flex_basis: {
613 // A. If the item has a definite used flex basis, that’s the flex base size.
614
615 // B. If the flex item has an intrinsic aspect ratio,
616 // a used flex basis of content, and a definite cross size,
617 // then the flex base size is calculated from its inner
618 // cross size and the flex item’s intrinsic aspect ratio.
619
620 // Note: `child.size` has already been resolved against aspect_ratio in generate_anonymous_flex_items
621 // So B will just work here by using main_size without special handling for aspect_ratio
622
623 let flex_basis = child_style.flex_basis.maybe_resolve(constants.node_inner_size.main(dir));
624 let main_size = child.size.main(dir);
625 if let Some(flex_basis) = flex_basis.or(main_size) {
626 break 'flex_basis flex_basis;
627 };
628
629 // C. If the used flex basis is content or depends on its available space,
630 // and the flex container is being sized under a min-content or max-content
631 // constraint (e.g. when performing automatic table layout [CSS21]),
632 // size the item under that constraint. The flex base size is the item’s
633 // resulting main size.
634
635 // This is covered by the implementation of E below, which passes the available_space constraint
636 // through to the child size computation. It may need a separate implementation if/when D is implemented.
637
638 // D. Otherwise, if the used flex basis is content or depends on its
639 // available space, the available main size is infinite, and the flex item’s
640 // inline axis is parallel to the main axis, lay the item out using the rules
641 // for a box in an orthogonal flow [CSS3-WRITING-MODES]. The flex base size
642 // is the item’s max-content main size.
643
644 // TODO if/when vertical writing modes are supported
645
646 // E. Otherwise, size the item into the available space using its used flex basis
647 // in place of its main size, treating a value of content as max-content.
648 // If a cross size is needed to determine the main size (e.g. when the
649 // flex item’s main size is in its block axis) and the flex item’s cross size
650 // is auto and not definite, in this calculation use fit-content as the
651 // flex item’s cross size. The flex base size is the item’s resulting main size.
652
653 let child_parent_size = Size::NONE.with_cross(dir, cross_axis_parent_size);
654 let child_available_space = available_space.with_cross(dir, cross_axis_available_space);
655
656 let child_known_dimensions = {
657 let mut ckd = child.size;
658 if child.align_self == AlignSelf::Stretch && ckd.cross(dir).is_none() {
659 ckd.set_cross(
660 dir,
661 child_available_space
662 .cross(dir)
663 .into_option()
664 .maybe_clamp(child_min_cross, child_max_cross)
665 .maybe_sub(child.margin.cross_axis_sum(dir)),
666 );
667 }
668 ckd
669 };
670
671 break 'flex_basis GenericAlgorithm::measure_size(
672 tree,
673 child.node,
674 child_known_dimensions,
675 child_parent_size,
676 child_available_space,
677 SizingMode::ContentSize,
678 )
679 .main(dir);
680 };
681
682 // Floor flex-basis by the padding_border_sum (floors inner_flex_basis at zero)
683 // This seems to be in violation of the spec which explicitly states that the content box should not be floored at zero
684 // (like it usually is) when calculating the flex-basis. But including this matches both Chrome and Firefox's behaviour.
685 //
686 // TODO: resolve spec violation
687 // Spec: https://www.w3.org/TR/css-flexbox-1/#intrinsic-item-contributions
688 // Spec: https://www.w3.org/TR/css-flexbox-1/#change-2016-max-contribution
689 let padding_border_sum = child.padding.main_axis_sum(constants.dir) + child.border.main_axis_sum(constants.dir);
690 child.flex_basis = child.flex_basis.max(padding_border_sum);
691
692 // The hypothetical main size is the item’s flex base size clamped according to its
693 // used min and max main sizes (and flooring the content box size at zero).
694
695 child.inner_flex_basis =
696 child.flex_basis - child.padding.main_axis_sum(constants.dir) - child.border.main_axis_sum(constants.dir);
697
698 let padding_border_axes_sums = (child.padding + child.border).sum_axes().map(Some);
699 let hypothetical_inner_min_main =
700 child.min_size.main(constants.dir).maybe_max(padding_border_axes_sums.main(constants.dir));
701 let hypothetical_inner_size =
702 child.flex_basis.maybe_clamp(hypothetical_inner_min_main, child.max_size.main(constants.dir));
703 let hypothetical_outer_size = hypothetical_inner_size + child.margin.main_axis_sum(constants.dir);
704
705 child.hypothetical_inner_size.set_main(constants.dir, hypothetical_inner_size);
706 child.hypothetical_outer_size.set_main(constants.dir, hypothetical_outer_size);
707
708 // Note that it is important that the `parent_size` parameter in the main axis is not set for this
709 // function call as it used for resolving percentages, and percentage size in an axis should not contribute
710 // to a min-content contribution in that same axis. However the `parent_size` and `available_space` *should*
711 // be set to their usual values in the cross axis so that wrapping content can wrap correctly.
712 //
713 // See https://drafts.csswg.org/css-sizing-3/#min-percentage-contribution
714 let min_content_size = {
715 let child_parent_size = Size::NONE.with_cross(dir, cross_axis_parent_size);
716 let child_available_space = Size::MIN_CONTENT.with_cross(dir, cross_axis_available_space);
717
718 GenericAlgorithm::measure_size(
719 tree,
720 child.node,
721 Size::NONE,
722 child_parent_size,
723 child_available_space,
724 SizingMode::ContentSize,
725 )
726 };
727
728 // 4.5. Automatic Minimum Size of Flex Items
729 // https://www.w3.org/TR/css-flexbox-1/#min-size-auto
730 let clamped_min_content_size = min_content_size.maybe_min(child.size).maybe_min(child.max_size);
731 child.resolved_minimum_size =
732 child.min_size.unwrap_or(clamped_min_content_size).maybe_max(padding_border_axes_sums);
733 }
734}
735
736/// Collect flex items into flex lines.
737///
738/// # [9.3. Main Size Determination](https://www.w3.org/TR/css-flexbox-1/#main-sizing)
739///
740/// - [**Collect flex items into flex lines**](https://www.w3.org/TR/css-flexbox-1/#algo-line-break):
741///
742/// - If the flex container is single-line, collect all the flex items into a single flex line.
743///
744/// - Otherwise, starting from the first uncollected item, collect consecutive items one by one until the first time that the next collected item would not fit into the flex container’s inner main size
745/// (or until a forced break is encountered, see [§10 Fragmenting Flex Layout](https://www.w3.org/TR/css-flexbox-1/#pagination)).
746/// If the very first uncollected item wouldn't fit, collect just it into the line.
747///
748/// For this step, the size of a flex item is its outer hypothetical main size. (**Note: This can be negative**.)
749///
750/// Repeat until all flex items have been collected into flex lines.
751///
752/// **Note that the "collect as many" line will collect zero-sized flex items onto the end of the previous line even if the last non-zero item exactly "filled up" the line**.
753#[inline]
754fn collect_flex_lines<'a>(
755 constants: &AlgoConstants,
756 available_space: Size<AvailableSpace>,
757 flex_items: &'a mut Vec<FlexItem>,
758) -> Vec<FlexLine<'a>> {
759 if !constants.is_wrap {
760 let mut lines = new_vec_with_capacity(1);
761 lines.push(FlexLine { items: flex_items.as_mut_slice(), cross_size: 0.0, offset_cross: 0.0 });
762 lines
763 } else {
764 match available_space.main(constants.dir) {
765 // If we're sizing under a max-content constraint then the flex items will never wrap
766 // (at least for now - future extensions to the CSS spec may add provisions for forced wrap points)
767 AvailableSpace::MaxContent => {
768 let mut lines = new_vec_with_capacity(1);
769 lines.push(FlexLine { items: flex_items.as_mut_slice(), cross_size: 0.0, offset_cross: 0.0 });
770 lines
771 }
772 // If flex-wrap is Wrap and we're sizing under a min-content constraint, then we take every possible wrapping opportunity
773 // and place each item in it's own line
774 AvailableSpace::MinContent => {
775 let mut lines = new_vec_with_capacity(flex_items.len());
776 let mut items = &mut flex_items[..];
777 while !items.is_empty() {
778 let (line_items, rest) = items.split_at_mut(1);
779 lines.push(FlexLine { items: line_items, cross_size: 0.0, offset_cross: 0.0 });
780 items = rest;
781 }
782 lines
783 }
784 AvailableSpace::Definite(main_axis_available_space) => {
785 let mut lines = new_vec_with_capacity(1);
786 let mut flex_items = &mut flex_items[..];
787 let main_axis_gap = constants.gap.main(constants.dir);
788
789 while !flex_items.is_empty() {
790 // Find index of the first item in the next line
791 // (or the last item if all remaining items are in the current line)
792 let mut line_length = 0.0;
793 let index = flex_items
794 .iter()
795 .enumerate()
796 .find(|&(idx, child)| {
797 // Gaps only occur between items (not before the first one or after the last one)
798 // So first item in the line does not contribute a gap to the line length
799 let gap_contribution = if idx == 0 { 0.0 } else { main_axis_gap };
800 line_length += child.hypothetical_outer_size.main(constants.dir) + gap_contribution;
801 line_length > main_axis_available_space && idx != 0
802 })
803 .map(|(idx, _)| idx)
804 .unwrap_or(flex_items.len());
805
806 let (items, rest) = flex_items.split_at_mut(index);
807 lines.push(FlexLine { items, cross_size: 0.0, offset_cross: 0.0 });
808 flex_items = rest;
809 }
810 lines
811 }
812 }
813 }
814}
815
816/// Determine the container's main size (if not already known)
817fn determine_container_main_size(
818 tree: &mut impl LayoutTree,
819 available_space: Size<AvailableSpace>,
820 lines: &mut Vec<FlexLine<'_>>,
821 constants: &mut AlgoConstants,
822) {
823 let dir = constants.dir;
824 let main_padding_border = constants.padding_border.main_axis_sum(constants.dir);
825
826 let outer_main_size: f32 = constants.node_outer_size.main(constants.dir).unwrap_or_else(|| {
827 match available_space.main(dir) {
828 AvailableSpace::Definite(main_axis_available_space) => {
829 let longest_line_length: f32 = lines
830 .iter()
831 .map(|line| {
832 let line_main_axis_gap = sum_axis_gaps(constants.gap.main(constants.dir), line.items.len());
833 let total_target_size = line
834 .items
835 .iter()
836 .map(|child| {
837 let padding_border_sum = (child.padding + child.border).main_axis_sum(constants.dir);
838 (child.flex_basis + child.margin.main_axis_sum(constants.dir)).max(padding_border_sum)
839 })
840 .sum::<f32>();
841 total_target_size + line_main_axis_gap
842 })
843 .max_by(|a, b| a.total_cmp(b))
844 .unwrap_or(0.0);
845 let size = longest_line_length + main_padding_border;
846 if lines.len() > 1 {
847 f32_max(size, main_axis_available_space)
848 } else {
849 size
850 }
851 }
852 AvailableSpace::MinContent if constants.is_wrap => {
853 let longest_line_length: f32 = lines
854 .iter()
855 .map(|line| {
856 let line_main_axis_gap = sum_axis_gaps(constants.gap.main(constants.dir), line.items.len());
857 let total_target_size = line
858 .items
859 .iter()
860 .map(|child| {
861 let padding_border_sum = (child.padding + child.border).main_axis_sum(constants.dir);
862 (child.flex_basis + child.margin.main_axis_sum(constants.dir)).max(padding_border_sum)
863 })
864 .sum::<f32>();
865 total_target_size + line_main_axis_gap
866 })
867 .max_by(|a, b| a.total_cmp(b))
868 .unwrap_or(0.0);
869 longest_line_length + main_padding_border
870 }
871 AvailableSpace::MinContent | AvailableSpace::MaxContent => {
872 // Define a base main_size variable. This is mutated once for iteration over the outer
873 // loop over the flex lines as:
874 // "The flex container’s max-content size is the largest sum of the afore-calculated sizes of all items within a single line."
875 let mut main_size = 0.0;
876
877 for line in lines.iter_mut() {
878 for item in line.items.iter_mut() {
879 let style_min = item.min_size.main(constants.dir);
880 let style_preferred = item.size.main(constants.dir);
881 let style_max = item.max_size.main(constants.dir);
882
883 // The spec seems a bit unclear on this point (my initial reading was that the `.maybe_max(style_preferred)` should
884 // not be included here), however this matches both Chrome and Firefox as of 9th March 2023.
885 //
886 // Spec: https://www.w3.org/TR/css-flexbox-1/#intrinsic-item-contributions
887 // Spec modifcation: https://www.w3.org/TR/css-flexbox-1/#change-2016-max-contribution
888 // Issue: https://github.com/w3c/csswg-drafts/issues/1435
889 // Gentest: padding_border_overrides_size_flex_basis_0.html
890 let clamping_basis = Some(item.flex_basis).maybe_max(style_preferred);
891 let flex_basis_min = clamping_basis.filter(|_| item.flex_shrink == 0.0);
892 let flex_basis_max = clamping_basis.filter(|_| item.flex_grow == 0.0);
893
894 let resolved_min = item.resolved_minimum_size.main(constants.dir);
895 let min_main_size = style_min
896 .maybe_max(flex_basis_min)
897 .or(flex_basis_min)
898 .unwrap_or(resolved_min)
899 .max(resolved_min);
900 let max_main_size =
901 style_max.maybe_min(flex_basis_max).or(flex_basis_max).unwrap_or(f32::INFINITY);
902
903 let content_contribution = match (min_main_size, style_preferred, max_main_size) {
904 // If the clamping values are such that max <= min, then we can avoid the expensive step of computing the content size
905 // as we know that the clamping values will override it anyway
906 (min, Some(pref), max) if max <= min || max <= pref => {
907 pref.min(max).max(min) + item.margin.main_axis_sum(constants.dir)
908 }
909 (min, _, max) if max <= min => min + item.margin.main_axis_sum(constants.dir),
910 // Else compute the min- or -max content size and apply the full formula for computing the
911 // min- or max- content contributuon
912 _ => {
913 // Parent size for child sizing
914 let cross_axis_parent_size = constants.node_inner_size.cross(dir);
915
916 // Available space for child sizing
917 let cross_axis_margin_sum = constants.margin.cross_axis_sum(dir);
918 let child_min_cross = item.min_size.cross(dir).maybe_add(cross_axis_margin_sum);
919 let child_max_cross = item.max_size.cross(dir).maybe_add(cross_axis_margin_sum);
920 let cross_axis_available_space: AvailableSpace = available_space
921 .cross(dir)
922 .map_definite_value(|val| cross_axis_parent_size.unwrap_or(val))
923 .maybe_clamp(child_min_cross, child_max_cross);
924
925 let child_available_space = available_space.with_cross(dir, cross_axis_available_space);
926
927 // Either the min- or max- content size depending on which constraint we are sizing under.
928 // TODO: Optimise by using already computed values where available
929 let content_main_size = GenericAlgorithm::measure_size(
930 tree,
931 item.node,
932 Size::NONE,
933 constants.node_inner_size,
934 child_available_space,
935 SizingMode::InherentSize,
936 )
937 .main(constants.dir)
938 + item.margin.main_axis_sum(constants.dir);
939
940 // This is somewhat bizarre in that it's asymetrical depending whether the flex container is a column or a row.
941 //
942 // I *think* this might relate to https://drafts.csswg.org/css-flexbox-1/#algo-main-container:
943 //
944 // "The automatic block size of a block-level flex container is its max-content size."
945 //
946 // Which could suggest that flex-basis defining a vertical size does not shrink because it is in the block axis, and the automatic size
947 // in the block axis is a MAX content size. Whereas a flex-basis defining a horizontal size does shrink because the automatic size in
948 // inline axis is MIN content size (although I don't have a reference for that).
949 //
950 // Ultimately, this was not found by reading the spec, but by trial and error fixing tests to align with Webkit/Firefox output.
951 // (see the `flex_basis_unconstraint_row` and `flex_basis_uncontraint_column` generated tests which demonstrate this)
952 if constants.is_row {
953 content_main_size.maybe_clamp(style_min, style_max).max(main_padding_border)
954 } else {
955 content_main_size
956 .max(item.flex_basis)
957 .maybe_clamp(style_min, style_max)
958 .max(main_padding_border)
959 }
960 }
961 };
962 item.content_flex_fraction = {
963 let diff = content_contribution - item.flex_basis;
964 if diff > 0.0 {
965 diff / f32_max(1.0, item.flex_grow)
966 } else if diff < 0.0 {
967 let scaled_shrink_factor = f32_max(1.0, item.flex_shrink * item.inner_flex_basis);
968 diff / scaled_shrink_factor
969 } else {
970 // We are assuming that diff is 0.0 here and that we haven't accidentally introduced a NaN
971 0.0
972 }
973 };
974 }
975
976 // TODO Spec says to scale everything by the line's max flex fraction. But neither Chrome nor firefox implement this
977 // so we don't either. But if we did want to, we'd need this computation here (and to use it below):
978 //
979 // Within each line, find the largest max-content flex fraction among all the flex items.
980 // let line_flex_fraction = line
981 // .items
982 // .iter()
983 // .map(|item| item.content_flex_fraction)
984 // .max_by(|a, b| a.total_cmp(b))
985 // .unwrap_or(0.0); // Unwrap case never gets hit because there is always at least one item a line
986
987 // Add each item’s flex base size to the product of:
988 // - its flex grow factor (or scaled flex shrink factor,if the chosen max-content flex fraction was negative)
989 // - the chosen max-content flex fraction
990 // then clamp that result by the max main size floored by the min main size.
991 //
992 // The flex container’s max-content size is the largest sum of the afore-calculated sizes of all items within a single line.
993 let item_main_size_sum = line
994 .items
995 .iter_mut()
996 .map(|item| {
997 let flex_fraction = item.content_flex_fraction;
998 // let flex_fraction = line_flex_fraction;
999
1000 let flex_contribution = if item.content_flex_fraction > 0.0 {
1001 f32_max(1.0, item.flex_grow) * flex_fraction
1002 } else if item.content_flex_fraction < 0.0 {
1003 let scaled_shrink_factor = f32_max(1.0, item.flex_shrink) * item.inner_flex_basis;
1004 scaled_shrink_factor * flex_fraction
1005 } else {
1006 0.0
1007 };
1008 let size = item.flex_basis + flex_contribution;
1009 item.outer_target_size.set_main(constants.dir, size);
1010 item.target_size.set_main(constants.dir, size);
1011 size
1012 })
1013 .sum::<f32>();
1014
1015 let gap_sum = sum_axis_gaps(constants.gap.main(constants.dir), line.items.len());
1016 main_size = f32_max(main_size, item_main_size_sum + gap_sum)
1017 }
1018
1019 main_size + main_padding_border
1020 }
1021 }
1022 });
1023
1024 let outer_main_size = outer_main_size
1025 .maybe_clamp(constants.min_size.main(constants.dir), constants.max_size.main(constants.dir))
1026 .max(main_padding_border);
1027
1028 // let outer_main_size = inner_main_size + constants.padding_border.main_axis_sum(constants.dir);
1029 let inner_main_size = outer_main_size - constants.padding_border.main_axis_sum(constants.dir);
1030 constants.container_size.set_main(constants.dir, outer_main_size);
1031 constants.inner_container_size.set_main(constants.dir, inner_main_size);
1032 constants.node_inner_size.set_main(constants.dir, Some(inner_main_size));
1033}
1034
1035/// Resolve the flexible lengths of the items within a flex line.
1036/// Sets the `main` component of each item's `target_size` and `outer_target_size`
1037///
1038/// # [9.7. Resolving Flexible Lengths](https://www.w3.org/TR/css-flexbox-1/#resolve-flexible-lengths)
1039#[inline]
1040fn resolve_flexible_lengths(line: &mut FlexLine, constants: &AlgoConstants, original_gap: Size<f32>) {
1041 let total_original_main_axis_gap = sum_axis_gaps(original_gap.main(constants.dir), line.items.len());
1042 let total_main_axis_gap = sum_axis_gaps(constants.gap.main(constants.dir), line.items.len());
1043
1044 // 1. Determine the used flex factor. Sum the outer hypothetical main sizes of all
1045 // items on the line. If the sum is less than the flex container’s inner main size,
1046 // use the flex grow factor for the rest of this algorithm; otherwise, use the
1047 // flex shrink factor.
1048
1049 let total_hypothetical_outer_main_size =
1050 line.items.iter().map(|child| child.hypothetical_outer_size.main(constants.dir)).sum::<f32>();
1051 let used_flex_factor: f32 = total_original_main_axis_gap + total_hypothetical_outer_main_size;
1052 let growing = used_flex_factor < constants.node_inner_size.main(constants.dir).unwrap_or(0.0);
1053 let shrinking = !growing;
1054
1055 // 2. Size inflexible items. Freeze, setting its target main size to its hypothetical main size
1056 // - Any item that has a flex factor of zero
1057 // - If using the flex grow factor: any item that has a flex base size
1058 // greater than its hypothetical main size
1059 // - If using the flex shrink factor: any item that has a flex base size
1060 // smaller than its hypothetical main size
1061
1062 for child in line.items.iter_mut() {
1063 let inner_target_size = child.hypothetical_inner_size.main(constants.dir);
1064 child.target_size.set_main(constants.dir, inner_target_size);
1065
1066 if (child.flex_grow == 0.0 && child.flex_shrink == 0.0)
1067 || (growing && child.flex_basis > child.hypothetical_inner_size.main(constants.dir))
1068 || (shrinking && child.flex_basis < child.hypothetical_inner_size.main(constants.dir))
1069 {
1070 child.frozen = true;
1071 let outer_target_size = inner_target_size + child.margin.main_axis_sum(constants.dir);
1072 child.outer_target_size.set_main(constants.dir, outer_target_size);
1073 }
1074 }
1075
1076 // 3. Calculate initial free space. Sum the outer sizes of all items on the line,
1077 // and subtract this from the flex container’s inner main size. For frozen items,
1078 // use their outer target main size; for other items, use their outer flex base size.
1079
1080 let used_space: f32 = total_main_axis_gap
1081 + line
1082 .items
1083 .iter()
1084 .map(|child| {
1085 child.margin.main_axis_sum(constants.dir)
1086 + if child.frozen { child.outer_target_size.main(constants.dir) } else { child.flex_basis }
1087 })
1088 .sum::<f32>();
1089
1090 let initial_free_space = constants.node_inner_size.main(constants.dir).maybe_sub(used_space).unwrap_or(0.0);
1091
1092 // 4. Loop
1093
1094 loop {
1095 // a. Check for flexible items. If all the flex items on the line are frozen,
1096 // free space has been distributed; exit this loop.
1097
1098 if line.items.iter().all(|child| child.frozen) {
1099 break;
1100 }
1101
1102 // b. Calculate the remaining free space as for initial free space, above.
1103 // If the sum of the unfrozen flex items’ flex factors is less than one,
1104 // multiply the initial free space by this sum. If the magnitude of this
1105 // value is less than the magnitude of the remaining free space, use this
1106 // as the remaining free space.
1107
1108 let used_space: f32 = total_main_axis_gap
1109 + line
1110 .items
1111 .iter()
1112 .map(|child| {
1113 child.margin.main_axis_sum(constants.dir)
1114 + if child.frozen { child.outer_target_size.main(constants.dir) } else { child.flex_basis }
1115 })
1116 .sum::<f32>();
1117
1118 let mut unfrozen: Vec<&mut FlexItem> = line.items.iter_mut().filter(|child| !child.frozen).collect();
1119
1120 let (sum_flex_grow, sum_flex_shrink): (f32, f32) =
1121 unfrozen.iter().fold((0.0, 0.0), |(flex_grow, flex_shrink), item| {
1122 (flex_grow + item.flex_grow, flex_shrink + item.flex_shrink)
1123 });
1124
1125 let free_space = if growing && sum_flex_grow < 1.0 {
1126 (initial_free_space * sum_flex_grow - total_main_axis_gap)
1127 .maybe_min(constants.node_inner_size.main(constants.dir).maybe_sub(used_space))
1128 } else if shrinking && sum_flex_shrink < 1.0 {
1129 (initial_free_space * sum_flex_shrink - total_main_axis_gap)
1130 .maybe_max(constants.node_inner_size.main(constants.dir).maybe_sub(used_space))
1131 } else {
1132 (constants.node_inner_size.main(constants.dir).maybe_sub(used_space))
1133 .unwrap_or(used_flex_factor - used_space)
1134 };
1135
1136 // c. Distribute free space proportional to the flex factors.
1137 // - If the remaining free space is zero
1138 // Do Nothing
1139 // - If using the flex grow factor
1140 // Find the ratio of the item’s flex grow factor to the sum of the
1141 // flex grow factors of all unfrozen items on the line. Set the item’s
1142 // target main size to its flex base size plus a fraction of the remaining
1143 // free space proportional to the ratio.
1144 // - If using the flex shrink factor
1145 // For every unfrozen item on the line, multiply its flex shrink factor by
1146 // its inner flex base size, and note this as its scaled flex shrink factor.
1147 // Find the ratio of the item’s scaled flex shrink factor to the sum of the
1148 // scaled flex shrink factors of all unfrozen items on the line. Set the item’s
1149 // target main size to its flex base size minus a fraction of the absolute value
1150 // of the remaining free space proportional to the ratio. Note this may result
1151 // in a negative inner main size; it will be corrected in the next step.
1152 // - Otherwise
1153 // Do Nothing
1154
1155 if free_space.is_normal() {
1156 if growing && sum_flex_grow > 0.0 {
1157 for child in &mut unfrozen {
1158 child
1159 .target_size
1160 .set_main(constants.dir, child.flex_basis + free_space * (child.flex_grow / sum_flex_grow));
1161 }
1162 } else if shrinking && sum_flex_shrink > 0.0 {
1163 let sum_scaled_shrink_factor: f32 =
1164 unfrozen.iter().map(|child| child.inner_flex_basis * child.flex_shrink).sum();
1165
1166 if sum_scaled_shrink_factor > 0.0 {
1167 for child in &mut unfrozen {
1168 let scaled_shrink_factor = child.inner_flex_basis * child.flex_shrink;
1169 child.target_size.set_main(
1170 constants.dir,
1171 child.flex_basis + free_space * (scaled_shrink_factor / sum_scaled_shrink_factor),
1172 )
1173 }
1174 }
1175 }
1176 }
1177
1178 // d. Fix min/max violations. Clamp each non-frozen item’s target main size by its
1179 // used min and max main sizes and floor its content-box size at zero. If the
1180 // item’s target main size was made smaller by this, it’s a max violation.
1181 // If the item’s target main size was made larger by this, it’s a min violation.
1182
1183 let total_violation = unfrozen.iter_mut().fold(0.0, |acc, child| -> f32 {
1184 let resolved_min_main: Option<f32> = child.resolved_minimum_size.main(constants.dir).into();
1185 let max_main = child.max_size.main(constants.dir);
1186 let clamped = child.target_size.main(constants.dir).maybe_clamp(resolved_min_main, max_main).max(0.0);
1187 child.violation = clamped - child.target_size.main(constants.dir);
1188 child.target_size.set_main(constants.dir, clamped);
1189 child.outer_target_size.set_main(
1190 constants.dir,
1191 child.target_size.main(constants.dir) + child.margin.main_axis_sum(constants.dir),
1192 );
1193
1194 acc + child.violation
1195 });
1196
1197 // e. Freeze over-flexed items. The total violation is the sum of the adjustments
1198 // from the previous step ∑(clamped size - unclamped size). If the total violation is:
1199 // - Zero
1200 // Freeze all items.
1201 // - Positive
1202 // Freeze all the items with min violations.
1203 // - Negative
1204 // Freeze all the items with max violations.
1205
1206 for child in &mut unfrozen {
1207 match total_violation {
1208 v if v > 0.0 => child.frozen = child.violation > 0.0,
1209 v if v < 0.0 => child.frozen = child.violation < 0.0,
1210 _ => child.frozen = true,
1211 }
1212 }
1213
1214 // f. Return to the start of this loop.
1215 }
1216}
1217
1218/// Determine the hypothetical cross size of each item.
1219///
1220/// # [9.4. Cross Size Determination](https://www.w3.org/TR/css-flexbox-1/#cross-sizing)
1221///
1222/// - [**Determine the hypothetical cross size of each item**](https://www.w3.org/TR/css-flexbox-1/#algo-cross-item)
1223/// by performing layout with the used main size and the available space, treating auto as fit-content.
1224#[inline]
1225fn determine_hypothetical_cross_size(
1226 tree: &mut impl LayoutTree,
1227 line: &mut FlexLine,
1228 constants: &AlgoConstants,
1229 available_space: Size<AvailableSpace>,
1230) {
1231 for child in line.items.iter_mut() {
1232 let padding_border_sum = (child.padding + child.border).cross_axis_sum(constants.dir);
1233
1234 let child_known_main = constants.container_size.main(constants.dir).into();
1235
1236 let child_cross = child
1237 .size
1238 .cross(constants.dir)
1239 .maybe_clamp(child.min_size.cross(constants.dir), child.max_size.cross(constants.dir))
1240 .maybe_max(padding_border_sum);
1241
1242 let child_available_cross = available_space
1243 .cross(constants.dir)
1244 .maybe_clamp(child.min_size.cross(constants.dir), child.max_size.cross(constants.dir))
1245 .maybe_max(padding_border_sum);
1246
1247 let child_inner_cross = child_cross.unwrap_or_else(|| {
1248 GenericAlgorithm::measure_size(
1249 tree,
1250 child.node,
1251 Size {
1252 width: if constants.is_row { child.target_size.width.into() } else { child_cross },
1253 height: if constants.is_row { child_cross } else { child.target_size.height.into() },
1254 },
1255 constants.node_inner_size,
1256 Size {
1257 width: if constants.is_row { child_known_main } else { child_available_cross },
1258 height: if constants.is_row { child_available_cross } else { child_known_main },
1259 },
1260 SizingMode::ContentSize,
1261 )
1262 .cross(constants.dir)
1263 .maybe_clamp(child.min_size.cross(constants.dir), child.max_size.cross(constants.dir))
1264 .max(padding_border_sum)
1265 });
1266 let child_outer_cross = child_inner_cross + child.margin.cross_axis_sum(constants.dir);
1267
1268 child.hypothetical_inner_size.set_cross(constants.dir, child_inner_cross);
1269 child.hypothetical_outer_size.set_cross(constants.dir, child_outer_cross);
1270 }
1271}
1272
1273/// Calculate the base lines of the children.
1274#[inline]
1275fn calculate_children_base_lines(
1276 tree: &mut impl LayoutTree,
1277 node_size: Size<Option<f32>>,
1278 available_space: Size<AvailableSpace>,
1279 flex_lines: &mut [FlexLine],
1280 constants: &AlgoConstants,
1281) {
1282 // Only compute baselines for flex rows because we only support baseline alignment in the cross axis
1283 // where that axis is also the inline axis
1284 // TODO: this may need revisiting if/when we support vertical writing modes
1285 if !constants.is_row {
1286 return;
1287 }
1288
1289 for line in flex_lines {
1290 // If a flex line has one or zero items participating in baseline alignment then baseline alignment is a no-op so we skip
1291 let line_baseline_child_count =
1292 line.items.iter().filter(|child| child.align_self == AlignSelf::Baseline).count();
1293 if line_baseline_child_count <= 1 {
1294 continue;
1295 }
1296
1297 for child in line.items.iter_mut() {
1298 // Only calculate baselines for children participating in baseline alignment
1299 if child.align_self != AlignSelf::Baseline {
1300 continue;
1301 }
1302
1303 let measured_size_and_baselines = GenericAlgorithm::perform_layout(
1304 tree,
1305 child.node,
1306 Size {
1307 width: if constants.is_row {
1308 child.target_size.width.into()
1309 } else {
1310 child.hypothetical_inner_size.width.into()
1311 },
1312 height: if constants.is_row {
1313 child.hypothetical_inner_size.height.into()
1314 } else {
1315 child.target_size.height.into()
1316 },
1317 },
1318 constants.node_inner_size,
1319 Size {
1320 width: if constants.is_row {
1321 constants.container_size.width.into()
1322 } else {
1323 available_space.width.maybe_set(node_size.width)
1324 },
1325 height: if constants.is_row {
1326 available_space.height.maybe_set(node_size.height)
1327 } else {
1328 constants.container_size.height.into()
1329 },
1330 },
1331 SizingMode::ContentSize,
1332 );
1333
1334 let baseline = measured_size_and_baselines.first_baselines.y;
1335 let height = measured_size_and_baselines.size.height;
1336
1337 child.baseline = baseline.unwrap_or(height) + child.margin.top;
1338 }
1339 }
1340}
1341
1342/// Calculate the cross size of each flex line.
1343///
1344/// # [9.4. Cross Size Determination](https://www.w3.org/TR/css-flexbox-1/#cross-sizing)
1345///
1346/// - [**Calculate the cross size of each flex line**](https://www.w3.org/TR/css-flexbox-1/#algo-cross-line).
1347///
1348/// If the flex container is single-line and has a definite cross size, the cross size of the flex line is the flex container’s inner cross size.
1349///
1350/// Otherwise, for each flex line:
1351///
1352/// 1. Collect all the flex items whose inline-axis is parallel to the main-axis, whose align-self is baseline, and whose cross-axis margins are both non-auto.
1353/// Find the largest of the distances between each item’s baseline and its hypothetical outer cross-start edge,
1354/// and the largest of the distances between each item’s baseline and its hypothetical outer cross-end edge, and sum these two values.
1355///
1356/// 2. Among all the items not collected by the previous step, find the largest outer hypothetical cross size.
1357///
1358/// 3. The used cross-size of the flex line is the largest of the numbers found in the previous two steps and zero.
1359///
1360/// If the flex container is single-line, then clamp the line’s cross-size to be within the container’s computed min and max cross sizes.
1361/// **Note that if CSS 2.1’s definition of min/max-width/height applied more generally, this behavior would fall out automatically**.
1362#[inline]
1363fn calculate_cross_size(flex_lines: &mut [FlexLine], node_size: Size<Option<f32>>, constants: &AlgoConstants) {
1364 // Note: AlignContent::SpaceEvenly and AlignContent::SpaceAround behave like AlignContent::Stretch when there is only
1365 // a single flex line in the container. See: https://www.w3.org/TR/css-flexbox-1/#align-content-property
1366 // Also: align_content is ignored entirely (and thus behaves like Stretch) when `flex_wrap` is set to `nowrap`.
1367 if flex_lines.len() == 1
1368 && node_size.cross(constants.dir).is_some()
1369 && (!constants.is_wrap
1370 || matches!(
1371 constants.align_content,
1372 AlignContent::Stretch | AlignContent::SpaceEvenly | AlignContent::SpaceAround
1373 ))
1374 {
1375 let cross_axis_padding_border = constants.padding_border.cross_axis_sum(constants.dir);
1376 let cross_min_size = constants.min_size.cross(constants.dir);
1377 let cross_max_size = constants.max_size.cross(constants.dir);
1378 flex_lines[0].cross_size = node_size
1379 .cross(constants.dir)
1380 .maybe_clamp(cross_min_size, cross_max_size)
1381 .maybe_sub(cross_axis_padding_border)
1382 .maybe_max(0.0)
1383 .unwrap_or(0.0);
1384 } else {
1385 for line in flex_lines.iter_mut() {
1386 // 1. Collect all the flex items whose inline-axis is parallel to the main-axis, whose
1387 // align-self is baseline, and whose cross-axis margins are both non-auto. Find the
1388 // largest of the distances between each item’s baseline and its hypothetical outer
1389 // cross-start edge, and the largest of the distances between each item’s baseline
1390 // and its hypothetical outer cross-end edge, and sum these two values.
1391
1392 // 2. Among all the items not collected by the previous step, find the largest
1393 // outer hypothetical cross size.
1394
1395 // 3. The used cross-size of the flex line is the largest of the numbers found in the
1396 // previous two steps and zero.
1397
1398 let max_baseline: f32 = line.items.iter().map(|child| child.baseline).fold(0.0, |acc, x| acc.max(x));
1399 line.cross_size = line
1400 .items
1401 .iter()
1402 .map(|child| {
1403 if child.align_self == AlignSelf::Baseline
1404 && !child.margin_is_auto.cross_start(constants.dir)
1405 && !child.margin_is_auto.cross_end(constants.dir)
1406 {
1407 max_baseline - child.baseline + child.hypothetical_outer_size.cross(constants.dir)
1408 } else {
1409 child.hypothetical_outer_size.cross(constants.dir)
1410 }
1411 })
1412 .fold(0.0, |acc, x| acc.max(x));
1413 }
1414 }
1415}
1416
1417/// Handle 'align-content: stretch'.
1418///
1419/// # [9.4. Cross Size Determination](https://www.w3.org/TR/css-flexbox-1/#cross-sizing)
1420///
1421/// - [**Handle 'align-content: stretch'**](https://www.w3.org/TR/css-flexbox-1/#algo-line-stretch). If the flex container has a definite cross size, align-content is stretch,
1422/// and the sum of the flex lines' cross sizes is less than the flex container’s inner cross size,
1423/// increase the cross size of each flex line by equal amounts such that the sum of their cross sizes exactly equals the flex container’s inner cross size.
1424#[inline]
1425fn handle_align_content_stretch(flex_lines: &mut [FlexLine], node_size: Size<Option<f32>>, constants: &AlgoConstants) {
1426 if constants.align_content == AlignContent::Stretch {
1427 let cross_axis_padding_border = constants.padding_border.cross_axis_sum(constants.dir);
1428 let cross_min_size = constants.min_size.cross(constants.dir);
1429 let cross_max_size = constants.max_size.cross(constants.dir);
1430 let container_min_inner_cross = node_size
1431 .cross(constants.dir)
1432 .or(cross_min_size)
1433 .maybe_clamp(cross_min_size, cross_max_size)
1434 .maybe_sub(cross_axis_padding_border)
1435 .maybe_max(0.0)
1436 .unwrap_or(0.0);
1437
1438 let total_cross_axis_gap = sum_axis_gaps(constants.gap.cross(constants.dir), flex_lines.len());
1439 let lines_total_cross: f32 = flex_lines.iter().map(|line| line.cross_size).sum::<f32>() + total_cross_axis_gap;
1440
1441 if lines_total_cross < container_min_inner_cross {
1442 let remaining = container_min_inner_cross - lines_total_cross;
1443 let addition = remaining / flex_lines.len() as f32;
1444 flex_lines.iter_mut().for_each(|line| line.cross_size += addition);
1445 }
1446 }
1447}
1448
1449/// Determine the used cross size of each flex item.
1450///
1451/// # [9.4. Cross Size Determination](https://www.w3.org/TR/css-flexbox-1/#cross-sizing)
1452///
1453/// - [**Determine the used cross size of each flex item**](https://www.w3.org/TR/css-flexbox-1/#algo-stretch). If a flex item has align-self: stretch, its computed cross size property is auto,
1454/// and neither of its cross-axis margins are auto, the used outer cross size is the used cross size of its flex line, clamped according to the item’s used min and max cross sizes.
1455/// Otherwise, the used cross size is the item’s hypothetical cross size.
1456///
1457/// If the flex item has align-self: stretch, redo layout for its contents, treating this used size as its definite cross size so that percentage-sized children can be resolved.
1458///
1459/// **Note that this step does not affect the main size of the flex item, even if it has an intrinsic aspect ratio**.
1460#[inline]
1461fn determine_used_cross_size(tree: &impl LayoutTree, flex_lines: &mut [FlexLine], constants: &AlgoConstants) {
1462 for line in flex_lines {
1463 let line_cross_size = line.cross_size;
1464
1465 for child in line.items.iter_mut() {
1466 let child_style = tree.style(child.node);
1467 child.target_size.set_cross(
1468 constants.dir,
1469 if child.align_self == AlignSelf::Stretch
1470 && !child.margin_is_auto.cross_start(constants.dir)
1471 && !child.margin_is_auto.cross_end(constants.dir)
1472 && child_style.size.cross(constants.dir) == Dimension::Auto
1473 {
1474 // For some reason this particular usage of max_width is an exception to the rule that max_width's transfer
1475 // using the aspect_ratio (if set). Both Chrome and Firefox agree on this. And reading the spec, it seems like
1476 // a reasonable interpretation. Although it seems to me that the spec *should* apply aspect_ratio here.
1477 let max_size_ignoring_aspect_ratio = child_style.max_size.maybe_resolve(constants.node_inner_size);
1478
1479 (line_cross_size - child.margin.cross_axis_sum(constants.dir)).maybe_clamp(
1480 child.min_size.cross(constants.dir),
1481 max_size_ignoring_aspect_ratio.cross(constants.dir),
1482 )
1483 } else {
1484 child.hypothetical_inner_size.cross(constants.dir)
1485 },
1486 );
1487
1488 child.outer_target_size.set_cross(
1489 constants.dir,
1490 child.target_size.cross(constants.dir) + child.margin.cross_axis_sum(constants.dir),
1491 );
1492 }
1493 }
1494}
1495
1496/// Distribute any remaining free space.
1497///
1498/// # [9.5. Main-Axis Alignment](https://www.w3.org/TR/css-flexbox-1/#main-alignment)
1499///
1500/// - [**Distribute any remaining free space**](https://www.w3.org/TR/css-flexbox-1/#algo-main-align). For each flex line:
1501///
1502/// 1. If the remaining free space is positive and at least one main-axis margin on this line is `auto`, distribute the free space equally among these margins.
1503/// Otherwise, set all `auto` margins to zero.
1504///
1505/// 2. Align the items along the main-axis per `justify-content`.
1506#[inline]
1507fn distribute_remaining_free_space(flex_lines: &mut [FlexLine], constants: &AlgoConstants) {
1508 for line in flex_lines {
1509 let total_main_axis_gap = sum_axis_gaps(constants.gap.main(constants.dir), line.items.len());
1510 let used_space: f32 = total_main_axis_gap
1511 + line.items.iter().map(|child| child.outer_target_size.main(constants.dir)).sum::<f32>();
1512 let free_space = constants.inner_container_size.main(constants.dir) - used_space;
1513 let mut num_auto_margins = 0;
1514
1515 for child in line.items.iter_mut() {
1516 if child.margin_is_auto.main_start(constants.dir) {
1517 num_auto_margins += 1;
1518 }
1519 if child.margin_is_auto.main_end(constants.dir) {
1520 num_auto_margins += 1;
1521 }
1522 }
1523
1524 if free_space > 0.0 && num_auto_margins > 0 {
1525 let margin = free_space / num_auto_margins as f32;
1526
1527 for child in line.items.iter_mut() {
1528 if child.margin_is_auto.main_start(constants.dir) {
1529 if constants.is_row {
1530 child.margin.left = margin;
1531 } else {
1532 child.margin.top = margin;
1533 }
1534 }
1535 if child.margin_is_auto.main_end(constants.dir) {
1536 if constants.is_row {
1537 child.margin.right = margin;
1538 } else {
1539 child.margin.bottom = margin;
1540 }
1541 }
1542 }
1543 } else {
1544 let num_items = line.items.len();
1545 let layout_reverse = constants.dir.is_reverse();
1546 let gap = constants.gap.main(constants.dir);
1547 let justify_content_mode = constants.justify_content.unwrap_or(JustifyContent::FlexStart);
1548
1549 let justify_item = |(i, child): (usize, &mut FlexItem)| {
1550 child.offset_main =
1551 compute_alignment_offset(free_space, num_items, gap, justify_content_mode, layout_reverse, i == 0);
1552 };
1553
1554 if layout_reverse {
1555 line.items.iter_mut().rev().enumerate().for_each(justify_item);
1556 } else {
1557 line.items.iter_mut().enumerate().for_each(justify_item);
1558 }
1559 }
1560 }
1561}
1562
1563/// Resolve cross-axis `auto` margins.
1564///
1565/// # [9.6. Cross-Axis Alignment](https://www.w3.org/TR/css-flexbox-1/#cross-alignment)
1566///
1567/// - [**Resolve cross-axis `auto` margins**](https://www.w3.org/TR/css-flexbox-1/#algo-cross-margins).
1568/// If a flex item has auto cross-axis margins:
1569///
1570/// - If its outer cross size (treating those auto margins as zero) is less than the cross size of its flex line,
1571/// distribute the difference in those sizes equally to the auto margins.
1572///
1573/// - Otherwise, if the block-start or inline-start margin (whichever is in the cross axis) is auto, set it to zero.
1574/// Set the opposite margin so that the outer cross size of the item equals the cross size of its flex line.
1575#[inline]
1576fn resolve_cross_axis_auto_margins(flex_lines: &mut [FlexLine], constants: &AlgoConstants) {
1577 for line in flex_lines {
1578 let line_cross_size = line.cross_size;
1579 let max_baseline: f32 = line.items.iter_mut().map(|child| child.baseline).fold(0.0, |acc, x| acc.max(x));
1580
1581 for child in line.items.iter_mut() {
1582 let free_space = line_cross_size - child.outer_target_size.cross(constants.dir);
1583
1584 if child.margin_is_auto.cross_start(constants.dir) && child.margin_is_auto.cross_end(constants.dir) {
1585 if constants.is_row {
1586 child.margin.top = free_space / 2.0;
1587 child.margin.bottom = free_space / 2.0;
1588 } else {
1589 child.margin.left = free_space / 2.0;
1590 child.margin.right = free_space / 2.0;
1591 }
1592 } else if child.margin_is_auto.cross_start(constants.dir) {
1593 if constants.is_row {
1594 child.margin.top = free_space;
1595 } else {
1596 child.margin.left = free_space;
1597 }
1598 } else if child.margin_is_auto.cross_end(constants.dir) {
1599 if constants.is_row {
1600 child.margin.bottom = free_space;
1601 } else {
1602 child.margin.right = free_space;
1603 }
1604 } else {
1605 // 14. Align all flex items along the cross-axis.
1606 child.offset_cross = align_flex_items_along_cross_axis(child, free_space, max_baseline, constants);
1607 }
1608 }
1609 }
1610}
1611
1612/// Align all flex items along the cross-axis.
1613///
1614/// # [9.6. Cross-Axis Alignment](https://www.w3.org/TR/css-flexbox-1/#cross-alignment)
1615///
1616/// - [**Align all flex items along the cross-axis**](https://www.w3.org/TR/css-flexbox-1/#algo-cross-align) per `align-self`,
1617/// if neither of the item's cross-axis margins are `auto`.
1618#[inline]
1619fn align_flex_items_along_cross_axis(
1620 child: &FlexItem,
1621 free_space: f32,
1622 max_baseline: f32,
1623 constants: &AlgoConstants,
1624) -> f32 {
1625 match child.align_self {
1626 AlignSelf::Start => 0.0,
1627 AlignSelf::FlexStart => {
1628 if constants.is_wrap_reverse {
1629 free_space
1630 } else {
1631 0.0
1632 }
1633 }
1634 AlignSelf::End => free_space,
1635 AlignSelf::FlexEnd => {
1636 if constants.is_wrap_reverse {
1637 0.0
1638 } else {
1639 free_space
1640 }
1641 }
1642 AlignSelf::Center => free_space / 2.0,
1643 AlignSelf::Baseline => {
1644 if constants.is_row {
1645 max_baseline - child.baseline
1646 } else {
1647 // Until we support vertical writing modes, baseline alignment only makes sense if
1648 // the constants.direction is row, so we treat it as flex-start alignment in columns.
1649 if constants.is_wrap_reverse {
1650 free_space
1651 } else {
1652 0.0
1653 }
1654 }
1655 }
1656 AlignSelf::Stretch => {
1657 if constants.is_wrap_reverse {
1658 free_space
1659 } else {
1660 0.0
1661 }
1662 }
1663 }
1664}
1665
1666/// Determine the flex container’s used cross size.
1667///
1668/// # [9.6. Cross-Axis Alignment](https://www.w3.org/TR/css-flexbox-1/#cross-alignment)
1669///
1670/// - [**Determine the flex container’s used cross size**](https://www.w3.org/TR/css-flexbox-1/#algo-cross-container):
1671///
1672/// - If the cross size property is a definite size, use that, clamped by the used min and max cross sizes of the flex container.
1673///
1674/// - Otherwise, use the sum of the flex lines' cross sizes, clamped by the used min and max cross sizes of the flex container.
1675#[inline]
1676#[must_use]
1677fn determine_container_cross_size(
1678 flex_lines: &[FlexLine],
1679 node_size: Size<Option<f32>>,
1680 constants: &mut AlgoConstants,
1681) -> f32 {
1682 let total_cross_axis_gap = sum_axis_gaps(constants.gap.cross(constants.dir), flex_lines.len());
1683 let total_line_cross_size: f32 = flex_lines.iter().map(|line| line.cross_size).sum::<f32>();
1684
1685 let padding_border_sum = constants.padding_border.cross_axis_sum(constants.dir);
1686 let min_cross_size = constants.min_size.cross(constants.dir);
1687 let max_cross_size = constants.max_size.cross(constants.dir);
1688 let outer_container_size = node_size
1689 .cross(constants.dir)
1690 .unwrap_or(total_line_cross_size + total_cross_axis_gap + padding_border_sum)
1691 .maybe_clamp(min_cross_size, max_cross_size)
1692 .max(padding_border_sum);
1693 let inner_container_size = outer_container_size - padding_border_sum;
1694
1695 constants.container_size.set_cross(constants.dir, outer_container_size);
1696 constants.inner_container_size.set_cross(constants.dir, inner_container_size);
1697
1698 total_line_cross_size
1699}
1700
1701/// Align all flex lines per `align-content`.
1702///
1703/// # [9.6. Cross-Axis Alignment](https://www.w3.org/TR/css-flexbox-1/#cross-alignment)
1704///
1705/// - [**Align all flex lines**](https://www.w3.org/TR/css-flexbox-1/#algo-line-align) per `align-content`.
1706#[inline]
1707fn align_flex_lines_per_align_content(flex_lines: &mut [FlexLine], constants: &AlgoConstants, total_cross_size: f32) {
1708 let num_lines = flex_lines.len();
1709 let gap = constants.gap.cross(constants.dir);
1710 let align_content_mode = constants.align_content;
1711 let total_cross_axis_gap = sum_axis_gaps(gap, num_lines);
1712 let free_space = constants.inner_container_size.cross(constants.dir) - total_cross_size - total_cross_axis_gap;
1713
1714 let align_line = |(i, line): (usize, &mut FlexLine)| {
1715 line.offset_cross =
1716 compute_alignment_offset(free_space, num_lines, gap, align_content_mode, constants.is_wrap_reverse, i == 0);
1717 };
1718
1719 if constants.is_wrap_reverse {
1720 flex_lines.iter_mut().rev().enumerate().for_each(align_line);
1721 } else {
1722 flex_lines.iter_mut().enumerate().for_each(align_line);
1723 }
1724}
1725
1726/// Calculates the layout for a flex-item
1727#[allow(clippy::too_many_arguments)]
1728fn calculate_flex_item(
1729 tree: &mut impl LayoutTree,
1730 node: Node,
1731 item: &mut FlexItem,
1732 total_offset_main: &mut f32,
1733 total_offset_cross: f32,
1734 line_offset_cross: f32,
1735 container_size: Size<f32>,
1736 node_inner_size: Size<Option<f32>>,
1737 direction: FlexDirection,
1738) {
1739 let preliminary_size_and_baselines = GenericAlgorithm::perform_layout(
1740 tree,
1741 item.node,
1742 item.target_size.map(|s| s.into()),
1743 node_inner_size,
1744 container_size.map(|s| s.into()),
1745 SizingMode::ContentSize,
1746 );
1747 let preliminary_size = preliminary_size_and_baselines.size;
1748
1749 let offset_main = *total_offset_main
1750 + item.offset_main
1751 + item.margin.main_start(direction)
1752 + (item.inset.main_start(direction).or(item.inset.main_end(direction).map(|pos| -pos)).unwrap_or(0.0));
1753
1754 let offset_cross = total_offset_cross
1755 + item.offset_cross
1756 + line_offset_cross
1757 + item.margin.cross_start(direction)
1758 + (item.inset.cross_start(direction).or(item.inset.cross_end(direction).map(|pos| -pos)).unwrap_or(0.0));
1759
1760 if direction.is_row() {
1761 let baseline_offset_cross = total_offset_cross + item.offset_cross + item.margin.cross_start(direction);
1762 let inner_baseline = preliminary_size_and_baselines.first_baselines.y.unwrap_or(preliminary_size.height);
1763 item.baseline = baseline_offset_cross + inner_baseline;
1764 } else {
1765 let baseline_offset_main = *total_offset_main + item.offset_main + item.margin.main_start(direction);
1766 let inner_baseline = preliminary_size_and_baselines.first_baselines.y.unwrap_or(preliminary_size.height);
1767 item.baseline = baseline_offset_main + inner_baseline;
1768 }
1769
1770 let order = tree.children(node).position(|n| *n == item.node).unwrap() as u32;
1771
1772 *tree.layout_mut(item.node) = Layout {
1773 order,
1774 size: preliminary_size_and_baselines.size,
1775 location: Point {
1776 x: if direction.is_row() { offset_main } else { offset_cross },
1777 y: if direction.is_column() { offset_main } else { offset_cross },
1778 },
1779 };
1780
1781 *total_offset_main += item.offset_main + item.margin.main_axis_sum(direction) + preliminary_size.main(direction);
1782}
1783
1784/// Calculates the layout line
1785#[allow(clippy::too_many_arguments)]
1786fn calculate_layout_line(
1787 tree: &mut impl LayoutTree,
1788 node: Node,
1789 line: &mut FlexLine,
1790 total_offset_cross: &mut f32,
1791 container_size: Size<f32>,
1792 node_inner_size: Size<Option<f32>>,
1793 padding_border: Rect<f32>,
1794 direction: FlexDirection,
1795) {
1796 let mut total_offset_main = padding_border.main_start(direction);
1797 let line_offset_cross = line.offset_cross;
1798
1799 if direction.is_reverse() {
1800 for item in line.items.iter_mut().rev() {
1801 calculate_flex_item(
1802 tree,
1803 node,
1804 item,
1805 &mut total_offset_main,
1806 *total_offset_cross,
1807 line_offset_cross,
1808 container_size,
1809 node_inner_size,
1810 direction,
1811 );
1812 }
1813 } else {
1814 for item in line.items.iter_mut() {
1815 calculate_flex_item(
1816 tree,
1817 node,
1818 item,
1819 &mut total_offset_main,
1820 *total_offset_cross,
1821 line_offset_cross,
1822 container_size,
1823 node_inner_size,
1824 direction,
1825 );
1826 }
1827 }
1828
1829 *total_offset_cross += line_offset_cross + line.cross_size;
1830}
1831
1832/// Do a final layout pass and collect the resulting layouts.
1833#[inline]
1834fn final_layout_pass(tree: &mut impl LayoutTree, node: Node, flex_lines: &mut [FlexLine], constants: &AlgoConstants) {
1835 let mut total_offset_cross = constants.padding_border.cross_start(constants.dir);
1836
1837 if constants.is_wrap_reverse {
1838 for line in flex_lines.iter_mut().rev() {
1839 calculate_layout_line(
1840 tree,
1841 node,
1842 line,
1843 &mut total_offset_cross,
1844 constants.container_size,
1845 constants.node_inner_size,
1846 constants.padding_border,
1847 constants.dir,
1848 );
1849 }
1850 } else {
1851 for line in flex_lines.iter_mut() {
1852 calculate_layout_line(
1853 tree,
1854 node,
1855 line,
1856 &mut total_offset_cross,
1857 constants.container_size,
1858 constants.node_inner_size,
1859 constants.padding_border,
1860 constants.dir,
1861 );
1862 }
1863 }
1864}
1865
1866/// Perform absolute layout on all absolutely positioned children.
1867#[inline]
1868fn perform_absolute_layout_on_absolute_children(tree: &mut impl LayoutTree, node: Node, constants: &AlgoConstants) {
1869 let container_width = constants.container_size.width;
1870 let container_height = constants.container_size.height;
1871
1872 for order in 0..tree.child_count(node) {
1873 let child = tree.child(node, order);
1874 let child_style = tree.style(child);
1875
1876 // Skip items that are display:none or are not position:absolute
1877 if child_style.display == Display::None || child_style.position != Position::Absolute {
1878 continue;
1879 }
1880
1881 let aspect_ratio = child_style.aspect_ratio;
1882 let align_self = child_style.align_self.unwrap_or(constants.align_items);
1883 let margin = child_style.margin.map(|margin| margin.resolve_to_option(container_width));
1884 let padding = child_style.padding.resolve_or_zero(Some(container_width));
1885 let border = child_style.border.resolve_or_zero(Some(container_width));
1886 let padding_border_sum = (padding + border).sum_axes();
1887
1888 // Resolve inset
1889 let left = child_style.inset.left.maybe_resolve(container_width);
1890 let right = child_style.inset.right.maybe_resolve(container_width);
1891 let top = child_style.inset.top.maybe_resolve(container_height);
1892 let bottom = child_style.inset.bottom.maybe_resolve(container_height);
1893
1894 // Compute known dimensions from min/max/inherent size styles
1895 let style_size =
1896 child_style.size.maybe_resolve(constants.container_size).maybe_apply_aspect_ratio(aspect_ratio);
1897 let min_size = child_style
1898 .min_size
1899 .maybe_resolve(constants.container_size)
1900 .maybe_apply_aspect_ratio(aspect_ratio)
1901 .or(padding_border_sum.map(Some))
1902 .maybe_max(padding_border_sum);
1903 let max_size =
1904 child_style.max_size.maybe_resolve(constants.container_size).maybe_apply_aspect_ratio(aspect_ratio);
1905 let mut known_dimensions = style_size.maybe_clamp(min_size, max_size);
1906
1907 // Fill in width from left/right and reapply aspect ratio if:
1908 // - Width is not already known
1909 // - Item has both left and right inset properties set
1910 if let (None, Some(left), Some(right)) = (known_dimensions.width, left, right) {
1911 let new_width_raw = container_width.maybe_sub(margin.left).maybe_sub(margin.right) - left - right;
1912 known_dimensions.width = Some(f32_max(new_width_raw, 0.0));
1913 known_dimensions = known_dimensions.maybe_apply_aspect_ratio(aspect_ratio).maybe_clamp(min_size, max_size);
1914 }
1915
1916 // Fill in height from top/bottom and reapply aspect ratio if:
1917 // - Height is not already known
1918 // - Item has both top and bottom inset properties set
1919 if let (None, Some(top), Some(bottom)) = (known_dimensions.height, top, bottom) {
1920 let new_height_raw = container_height.maybe_sub(margin.top).maybe_sub(margin.bottom) - top - bottom;
1921 known_dimensions.height = Some(f32_max(new_height_raw, 0.0));
1922 known_dimensions = known_dimensions.maybe_apply_aspect_ratio(aspect_ratio).maybe_clamp(min_size, max_size);
1923 }
1924
1925 let measured_size_and_baselines = GenericAlgorithm::perform_layout(
1926 tree,
1927 child,
1928 known_dimensions,
1929 constants.node_inner_size,
1930 Size {
1931 width: AvailableSpace::Definite(container_width.maybe_clamp(min_size.width, max_size.width)),
1932 height: AvailableSpace::Definite(container_height.maybe_clamp(min_size.height, max_size.height)),
1933 },
1934 SizingMode::ContentSize,
1935 );
1936 let measured_size = measured_size_and_baselines.size;
1937 let final_size = known_dimensions.unwrap_or(measured_size).maybe_clamp(min_size, max_size);
1938
1939 let non_auto_margin = margin.map(|m| m.unwrap_or(0.0));
1940
1941 let free_space = Size {
1942 width: constants.container_size.width - final_size.width - non_auto_margin.horizontal_axis_sum(),
1943 height: constants.container_size.height - final_size.height - non_auto_margin.vertical_axis_sum(),
1944 }
1945 .f32_max(Size::ZERO);
1946
1947 // Expand auto margins to fill available space
1948 let resolved_margin = {
1949 let auto_margin_size = Size {
1950 width: {
1951 let auto_margin_count = margin.left.is_none() as u8 + margin.right.is_none() as u8;
1952 if auto_margin_count > 0 {
1953 free_space.width / auto_margin_count as f32
1954 } else {
1955 0.0
1956 }
1957 },
1958 height: {
1959 let auto_margin_count = margin.top.is_none() as u8 + margin.bottom.is_none() as u8;
1960 if auto_margin_count > 0 {
1961 free_space.height / auto_margin_count as f32
1962 } else {
1963 0.0
1964 }
1965 },
1966 };
1967
1968 Rect {
1969 left: margin.left.unwrap_or(auto_margin_size.width),
1970 right: margin.right.unwrap_or(auto_margin_size.width),
1971 top: margin.top.unwrap_or(auto_margin_size.height),
1972 bottom: margin.bottom.unwrap_or(auto_margin_size.height),
1973 }
1974 };
1975
1976 // Determine flex-relative insets
1977 let (start_main, end_main) = if constants.is_row { (left, right) } else { (top, bottom) };
1978 let (start_cross, end_cross) = if constants.is_row { (top, bottom) } else { (left, right) };
1979
1980 // Apply main-axis alignment
1981 // let free_main_space = free_space.main(constants.dir) - resolved_margin.main_axis_sum(constants.dir);
1982 let offset_main = if let Some(start) = start_main {
1983 start + constants.border.main_start(constants.dir) + resolved_margin.main_start(constants.dir)
1984 } else if let Some(end) = end_main {
1985 constants.container_size.main(constants.dir)
1986 - constants.border.main_end(constants.dir)
1987 - final_size.main(constants.dir)
1988 - end
1989 - resolved_margin.main_end(constants.dir)
1990 } else {
1991 // Stretch is an invalid value for justify_content in the flexbox algorithm, so we
1992 // treat it as if it wasn't set (and thus we default to FlexStart behaviour)
1993 match (constants.justify_content.unwrap_or(JustifyContent::Start), constants.is_wrap_reverse) {
1994 (JustifyContent::SpaceBetween, _)
1995 | (JustifyContent::Start, _)
1996 | (JustifyContent::Stretch, false)
1997 | (JustifyContent::FlexStart, false)
1998 | (JustifyContent::FlexEnd, true) => {
1999 constants.padding_border.main_start(constants.dir) + resolved_margin.main_start(constants.dir)
2000 }
2001 (JustifyContent::End, _)
2002 | (JustifyContent::FlexEnd, false)
2003 | (JustifyContent::FlexStart, true)
2004 | (JustifyContent::Stretch, true) => {
2005 constants.container_size.main(constants.dir)
2006 - constants.padding_border.main_end(constants.dir)
2007 - final_size.main(constants.dir)
2008 - resolved_margin.main_end(constants.dir)
2009 }
2010 (JustifyContent::SpaceEvenly, _) | (JustifyContent::SpaceAround, _) | (JustifyContent::Center, _) => {
2011 (constants.container_size.main(constants.dir) + constants.padding_border.main_start(constants.dir)
2012 - constants.padding_border.main_end(constants.dir)
2013 - final_size.main(constants.dir)
2014 + resolved_margin.main_start(constants.dir)
2015 - resolved_margin.main_end(constants.dir))
2016 / 2.0
2017 }
2018 }
2019 };
2020
2021 // Apply cross-axis alignment
2022 // let free_cross_space = free_space.cross(constants.dir) - resolved_margin.cross_axis_sum(constants.dir);
2023 let offset_cross = if let Some(start) = start_cross {
2024 start + constants.border.cross_start(constants.dir) + resolved_margin.cross_start(constants.dir)
2025 } else if let Some(end) = end_cross {
2026 constants.container_size.cross(constants.dir)
2027 - constants.border.cross_end(constants.dir)
2028 - final_size.cross(constants.dir)
2029 - end
2030 - resolved_margin.cross_end(constants.dir)
2031 } else {
2032 match (align_self, constants.is_wrap_reverse) {
2033 // Stretch alignment does not apply to absolutely positioned items
2034 // See "Example 3" at https://www.w3.org/TR/css-flexbox-1/#abspos-items
2035 // Note: Stretch should be FlexStart not Start when we support both
2036 (AlignSelf::Start, _)
2037 | (AlignSelf::Baseline | AlignSelf::Stretch | AlignSelf::FlexStart, false)
2038 | (AlignSelf::FlexEnd, true) => {
2039 constants.padding_border.cross_start(constants.dir) + resolved_margin.cross_start(constants.dir)
2040 }
2041 (AlignSelf::End, _)
2042 | (AlignSelf::Baseline | AlignSelf::Stretch | AlignSelf::FlexStart, true)
2043 | (AlignSelf::FlexEnd, false) => {
2044 constants.container_size.cross(constants.dir)
2045 - constants.padding_border.cross_end(constants.dir)
2046 - final_size.cross(constants.dir)
2047 - resolved_margin.cross_end(constants.dir)
2048 }
2049 (AlignSelf::Center, _) => {
2050 (constants.container_size.cross(constants.dir)
2051 + constants.padding_border.cross_start(constants.dir)
2052 - constants.padding_border.cross_end(constants.dir)
2053 - final_size.cross(constants.dir)
2054 + resolved_margin.cross_start(constants.dir)
2055 - resolved_margin.cross_end(constants.dir))
2056 / 2.0
2057 }
2058 }
2059 };
2060
2061 *tree.layout_mut(child) = Layout {
2062 order: order as u32,
2063 size: final_size,
2064 location: Point {
2065 x: if constants.is_row { offset_main } else { offset_cross },
2066 y: if constants.is_column { offset_main } else { offset_cross },
2067 },
2068 };
2069 }
2070}
2071
2072/// Computes the total space taken up by gaps in an axis given:
2073/// - The size of each gap
2074/// - The number of items (children or flex-lines) between which there are gaps
2075#[inline(always)]
2076fn sum_axis_gaps(gap: f32, num_items: usize) -> f32 {
2077 // Gaps only exist between items, so...
2078 if num_items <= 1 {
2079 // ...if there are less than 2 items then there are no gaps
2080 0.0
2081 } else {
2082 // ...otherwise there are (num_items - 1) gaps
2083 gap * (num_items - 1) as f32
2084 }
2085}
2086
2087#[cfg(test)]
2088mod tests {
2089 #![allow(clippy::redundant_clone)]
2090
2091 use crate::{
2092 geometry::Size,
2093 math::MaybeMath,
2094 resolve::ResolveOrZero,
2095 style::{FlexWrap, Style},
2096 Taffy,
2097 };
2098
2099 // Make sure we get correct constants
2100 #[test]
2101 fn correct_constants() {
2102 let mut tree = Taffy::with_capacity(16);
2103
2104 let style = Style::default();
2105 let node_id = tree.new_leaf(style.clone()).unwrap();
2106
2107 let node_size = Size::NONE;
2108 let parent_size = Size::NONE;
2109
2110 let constants = super::compute_constants(tree.style(node_id).unwrap(), node_size, parent_size);
2111
2112 assert!(constants.dir == style.flex_direction);
2113 assert!(constants.is_row == style.flex_direction.is_row());
2114 assert!(constants.is_column == style.flex_direction.is_column());
2115 assert!(constants.is_wrap_reverse == (style.flex_wrap == FlexWrap::WrapReverse));
2116
2117 let margin = style.margin.resolve_or_zero(parent_size);
2118 assert_eq!(constants.margin, margin);
2119
2120 let border = style.border.resolve_or_zero(parent_size);
2121 let padding = style.padding.resolve_or_zero(parent_size);
2122 let padding_border = padding + border;
2123 assert_eq!(constants.border, border);
2124 assert_eq!(constants.padding_border, padding_border);
2125
2126 let inner_size = Size {
2127 width: node_size.width.maybe_sub(padding_border.horizontal_axis_sum()),
2128 height: node_size.height.maybe_sub(padding_border.vertical_axis_sum()),
2129 };
2130 assert_eq!(constants.node_inner_size, inner_size);
2131
2132 assert_eq!(constants.container_size, Size::zero());
2133 assert_eq!(constants.inner_container_size, Size::zero());
2134 }
2135}