Account for margin when stretching
1use std::f32;
2
3use layout;
4use style;
5
6#[derive(Debug, Copy, Clone)]
7struct FlexSize {
8 width: f32,
9 height: f32,
10}
11
12impl FlexSize {
13 fn main(&self, direction: style::FlexDirection) -> f32 {
14 match direction {
15 style::FlexDirection::Row | style::FlexDirection::RowReverse => self.width,
16 style::FlexDirection::Column | style::FlexDirection::ColumnReverse => self.height,
17 }
18 }
19
20 fn cross(&self, direction: style::FlexDirection) -> f32 {
21 match direction {
22 style::FlexDirection::Row | style::FlexDirection::RowReverse => self.height,
23 style::FlexDirection::Column | style::FlexDirection::ColumnReverse => self.width,
24 }
25 }
26}
27
28struct FlexItem<'a> {
29 node: &'a style::Node,
30
31 // temporary values for main size determination
32 flex_basis: f32,
33 inner_flex_basis: f32,
34 hypothetical_inner_main_size: f32,
35 hypothetical_outer_main_size: f32,
36 target_main_size: f32,
37 outer_target_main_size: f32,
38 violation: f32,
39 frozen: bool,
40
41 // temporary values for cross size determination
42 hypothetical_inner_cross_size: f32,
43 hypothetical_outer_cross_size: f32,
44 target_cross_size: f32,
45 outer_target_cross_size: f32,
46
47 main_margin_start: f32,
48 main_margin_end: f32,
49 cross_margin_start: f32,
50 cross_margin_end: f32,
51
52 // temporary values for holding offset in the main / cross direction.
53 // offset is the relative position from the item's natural flow position based on
54 // relative position values, alignment, and justification. Does not unclude margin/padding/border.
55 offset_main: f32,
56 offset_cross: f32,
57}
58
59struct ComputeResult {
60 size: FlexSize,
61 children: Vec<layout::Node>,
62}
63
64struct FlexLine<'a> {
65 items: Vec<FlexItem<'a>>,
66 cross_size: f32,
67 offset_cross: f32,
68}
69
70pub fn compute(root: &style::Node) -> layout::Node {
71 let result = compute_internal(
72 root,
73 root.width
74 .resolve(f32::NAN, f32::NAN)
75 .max(root.min_width.resolve(f32::NAN, f32::NAN))
76 .min(root.max_width.resolve(f32::NAN, f32::NAN)),
77 root.height
78 .resolve(f32::NAN, f32::NAN)
79 .max(root.min_height.resolve(f32::NAN, f32::NAN))
80 .min(root.max_height.resolve(f32::NAN, f32::NAN)),
81 f32::NAN,
82 f32::NAN,
83 f32::NAN,
84 );
85
86 round_layout(
87 &layout::Node {
88 width: result.size.width,
89 height: result.size.height,
90 x: 0.0,
91 y: 0.0,
92 children: result.children,
93 },
94 0.0,
95 0.0,
96 )
97}
98
99fn round_layout(layout: &layout::Node, abs_x: f32, abs_y: f32) -> layout::Node {
100 let abs_x = abs_x + layout.x;
101 let abs_y = abs_y + layout.y;
102
103 let rounded_x = layout.x.round();
104 let rounded_y = layout.y.round();
105
106 let rounded_width = (abs_x + layout.width).round() - abs_x.round();
107 let rounded_height = (abs_y + layout.height).round() - abs_y.round();
108
109 let rounded_children = layout.children.iter().map(|child| round_layout(child, abs_x, abs_y)).collect();
110
111 layout::Node {
112 width: rounded_width,
113 height: rounded_height,
114 x: rounded_x,
115 y: rounded_y,
116 children: rounded_children,
117 }
118}
119
120fn compute_internal(
121 node: &style::Node,
122
123 // The width and the height of this node, if Some
124 // the node should be layed out at exactly this size.
125 // If None the node should at most be the size of
126 // available_width / available_height if present.
127 node_width: f32,
128 node_height: f32,
129
130 // This available width and height. This is the
131 // the inner node_width / node_height of the parent and should
132 // not be exceeded by this node unless node_width / node_height
133 // parameters say otherwise.
134 parent_inner_width: f32,
135 parent_inner_height: f32,
136
137 // This will always be the parent width except for the case when
138 // the child is in an absolute context. This value should only
139 // be used for calculated percentage values.
140 percent_calc_base: f32,
141) -> ComputeResult {
142 // Define some general constants we will need for the remainder
143 // of the algorithm.
144
145 let (node_main, node_cross) =
146 if node.flex_direction.is_row() { (node_width, node_height) } else { (node_height, node_width) };
147
148 let (parent_inner_main, parent_inner_cross) = if node.flex_direction.is_row() {
149 (parent_inner_width, parent_inner_height)
150 } else {
151 (parent_inner_height, parent_inner_width)
152 };
153
154 let (margin_main_start, margin_cross_start) = (
155 node.main_margin_start(node.flex_direction).resolve(percent_calc_base, 0.0),
156 node.cross_margin_start(node.flex_direction).resolve(percent_calc_base, 0.0),
157 );
158
159 let (margin_main_end, margin_cross_end) = (
160 node.main_margin_end(node.flex_direction).resolve(percent_calc_base, 0.0),
161 node.cross_margin_end(node.flex_direction).resolve(percent_calc_base, 0.0),
162 );
163
164 let (margin_main, margin_cross) = (margin_main_start + margin_main_end, margin_cross_start + margin_cross_end);
165
166 let (padding_main_start, padding_cross_start) = (
167 node.main_padding_start(node.flex_direction).resolve(percent_calc_base, 0.0),
168 node.cross_padding_start(node.flex_direction).resolve(percent_calc_base, 0.0),
169 );
170
171 let (padding_main_end, padding_cross_end) = (
172 node.main_padding_end(node.flex_direction).resolve(percent_calc_base, 0.0),
173 node.cross_padding_end(node.flex_direction).resolve(percent_calc_base, 0.0),
174 );
175
176 let (padding_main, padding_cross) =
177 (padding_main_start + padding_main_end, padding_cross_start + padding_cross_end);
178
179 let (border_main_start, border_cross_start) = (
180 node.main_border_start(node.flex_direction).resolve(percent_calc_base, 0.0),
181 node.cross_border_start(node.flex_direction).resolve(percent_calc_base, 0.0),
182 );
183
184 let (border_main_end, border_cross_end) = (
185 node.main_border_end(node.flex_direction).resolve(percent_calc_base, 0.0),
186 node.cross_border_end(node.flex_direction).resolve(percent_calc_base, 0.0),
187 );
188
189 let (border_main, border_cross) = (border_main_start + border_main_end, border_cross_start + border_cross_end);
190
191 let (node_inner_main, node_inner_cross) =
192 (node_main - border_main - padding_main, node_cross - border_cross - padding_cross);
193
194 let wrap_reverse = node.flex_wrap == style::FlexWrap::WrapReverse;
195
196 let percent_calc_base_child = node.width.resolve(percent_calc_base, f32::NAN);
197
198 // 9.2. Line Length Determination
199
200 // 1. Generate anonymous flex items as described in §4 Flex Items.
201
202 let mut flex_items: Vec<FlexItem> = node
203 .children
204 .iter()
205 .filter(|child| child.position != style::Position::Absolute)
206 .map(|child| FlexItem {
207 node: child,
208
209 flex_basis: 0.0,
210 inner_flex_basis: 0.0,
211 hypothetical_inner_main_size: 0.0,
212 hypothetical_outer_main_size: 0.0,
213 target_main_size: 0.0,
214 outer_target_main_size: 0.0,
215 violation: 0.0,
216 frozen: false,
217
218 hypothetical_inner_cross_size: 0.0,
219 hypothetical_outer_cross_size: 0.0,
220 target_cross_size: 0.0,
221 outer_target_cross_size: 0.0,
222
223 main_margin_start: 0.0,
224 main_margin_end: 0.0,
225 cross_margin_start: 0.0,
226 cross_margin_end: 0.0,
227
228 offset_main: 0.0,
229 offset_cross: 0.0,
230 }).collect();
231
232 // 2. Determine the available main and cross space for the flex items.
233 // For each dimension, if that dimension of the flex container’s content box
234 // is a definite size, use that; if that dimension of the flex container is
235 // being sized under a min or max-content constraint, the available space in
236 // that dimension is that constraint; otherwise, subtract the flex container’s
237 // margin, border, and padding from the space available to the flex container
238 // in that dimension and use that value. This might result in an infinite value.
239
240 let available_main = {
241 let base = if node_main.is_finite() { node_main } else { parent_inner_main - margin_main };
242 base - padding_main - border_main
243 };
244
245 let available_cross = {
246 let base = if node_cross.is_finite() { node_cross } else { parent_inner_cross - margin_cross };
247 base - padding_cross - border_cross
248 };
249
250 // 3. Determine the flex base size and hypothetical main size of each item:
251 for child in &mut flex_items {
252 // A. If the item has a definite used flex basis, that’s the flex base size.
253
254 let flex_basis = child.node.flex_basis.resolve(percent_calc_base_child, f32::NAN);
255 if flex_basis.is_finite() {
256 child.flex_basis = flex_basis;
257 continue;
258 }
259
260 // B. If the flex item has an intrinsic aspect ratio,
261 // a used flex basis of content, and a definite cross size,
262 // then the flex base size is calculated from its inner
263 // cross size and the flex item’s intrinsic aspect ratio.
264
265 if let Some(ratio) = child.node.aspect_ratio {
266 if node_cross.is_finite() && child.node.flex_basis == style::Dimension::Auto {
267 child.flex_basis = ratio * node_cross;
268 continue;
269 }
270 }
271
272 // C. If the used flex basis is content or depends on its available space,
273 // and the flex container is being sized under a min-content or max-content
274 // constraint (e.g. when performing automatic table layout [CSS21]),
275 // size the item under that constraint. The flex base size is the item’s
276 // resulting main size.
277
278 // if main_constraint.min.is_finite() || main_constraint.max.is_finite() {
279 // let size = compute_internal(
280 // child.node,
281 // if node.flex_direction.is_row() { main_constraint } else { SizeConstraint::undefined() },
282 // if node.flex_direction.is_column() { main_constraint } else { SizeConstraint::undefined() },
283 // percent_calc_base_child,
284 // ).size;
285 // child.flex_basis = size.main(node.flex_direction);
286 // continue;
287 // }
288
289 // D. Otherwise, if the used flex basis is content or depends on its
290 // available space, the available main size is infinite, and the flex item’s
291 // inline axis is parallel to the main axis, lay the item out using the rules
292 // for a box in an orthogonal flow [CSS3-WRITING-MODES]. The flex base size
293 // is the item’s max-content main size.
294
295 if available_main.is_nan() {
296 let size = compute_internal(
297 child.node,
298 child
299 .node
300 .width
301 .resolve(percent_calc_base_child, f32::NAN)
302 .max(child.node.min_width.resolve(percent_calc_base_child, f32::NAN))
303 .min(child.node.max_width.resolve(percent_calc_base_child, f32::NAN)),
304 child
305 .node
306 .height
307 .resolve(percent_calc_base_child, f32::NAN)
308 .max(child.node.min_height.resolve(percent_calc_base_child, f32::NAN))
309 .min(child.node.max_height.resolve(percent_calc_base_child, f32::NAN)),
310 if node.flex_direction.is_row() { available_main } else { available_cross },
311 if node.flex_direction.is_row() { available_cross } else { available_main },
312 percent_calc_base_child,
313 ).size;
314 child.flex_basis = size.main(node.flex_direction);
315 continue;
316 }
317
318 // E. Otherwise, size the item into the available space using its used flex basis
319 // in place of its main size, treating a value of content as max-content.
320 // If a cross size is needed to determine the main size (e.g. when the
321 // flex item’s main size is in its block axis) and the flex item’s cross size
322 // is auto and not definite, in this calculation use fit-content as the
323 // flex item’s cross size. The flex base size is the item’s resulting main size.
324
325 let size = compute_internal(
326 child.node,
327 child
328 .node
329 .width
330 .resolve(percent_calc_base_child, f32::NAN)
331 .max(child.node.min_width.resolve(percent_calc_base_child, f32::NAN))
332 .min(child.node.max_width.resolve(percent_calc_base_child, f32::NAN)),
333 child
334 .node
335 .height
336 .resolve(percent_calc_base_child, f32::NAN)
337 .max(child.node.min_height.resolve(percent_calc_base_child, f32::NAN))
338 .min(child.node.max_height.resolve(percent_calc_base_child, f32::NAN)),
339 if node.flex_direction.is_row() { available_main } else { available_cross },
340 if node.flex_direction.is_row() { available_cross } else { available_main },
341 percent_calc_base_child,
342 ).size;
343 child.flex_basis = size.main(node.flex_direction);
344 }
345
346 // The hypothetical main size is the item’s flex base size clamped according to its
347 // used min and max main sizes (and flooring the content box size at zero).
348
349 for child in &mut flex_items {
350 let padding_start = child.node.main_padding_start(node.flex_direction).resolve(percent_calc_base_child, 0.0);
351 let padding_end = child.node.main_padding_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
352 let border_start = child.node.main_border_start(node.flex_direction).resolve(percent_calc_base_child, 0.0);
353 let border_end = child.node.main_border_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
354 child.inner_flex_basis = child.flex_basis - (padding_start + padding_end + border_start + border_end);
355
356 child.hypothetical_inner_main_size = child
357 .flex_basis
358 .max(child.node.min_main_size(node.flex_direction).resolve(percent_calc_base_child, f32::MIN))
359 .min(child.node.max_main_size(node.flex_direction).resolve(percent_calc_base_child, f32::MAX))
360 .max(0.0);
361
362 child.hypothetical_outer_main_size = child.hypothetical_inner_main_size
363 + child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
364 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
365 }
366
367 // 9.3. Main Size Determination
368
369 // 5. Collect flex items into flex lines:
370 // - If the flex container is single-line, collect all the flex items into
371 // a single flex line.
372 // - Otherwise, starting from the first uncollected item, collect consecutive
373 // items one by one until the first time that the next collected item would
374 // not fit into the flex container’s inner main size (or until a forced break
375 // is encountered, see §10 Fragmenting Flex Layout). If the very first
376 // uncollected item wouldn’t fit, collect just it into the line.
377 //
378 // For this step, the size of a flex item is its outer hypothetical main size. (Note: This can be negative.)
379 // Repeat until all flex items have been collected into flex lines
380 //
381 // Note that the "collect as many" line will collect zero-sized flex items onto
382 // the end of the previous line even if the last non-zero item exactly "filled up" the line.
383
384 let mut flex_lines = {
385 let mut lines: Vec<FlexLine> = vec![];
386 let mut line_length = 0.0;
387
388 if node.flex_wrap == style::FlexWrap::NoWrap {
389 lines.push(FlexLine { items: flex_items, cross_size: 0.0, offset_cross: 0.0 });
390 } else {
391 let mut line = FlexLine { items: vec![], cross_size: 0.0, offset_cross: 0.0 };
392
393 for child in flex_items {
394 line_length += child.hypothetical_outer_main_size;
395
396 if line_length > available_main && line.items.len() > 0 {
397 line_length = child.hypothetical_outer_main_size;
398 lines.push(line);
399 line = FlexLine { items: vec![], cross_size: 0.0, offset_cross: 0.0 };
400 }
401
402 line.items.push(child);
403 }
404
405 lines.push(line);
406 }
407
408 lines
409 };
410
411 // 6. Resolve the flexible lengths of all the flex items to find their used main size.
412 // See §9.7 Resolving Flexible Lengths.
413 //
414 // 9.7. Resolving Flexible Lengths
415
416 for line in &mut flex_lines {
417 // 1. Determine the used flex factor. Sum the outer hypothetical main sizes of all
418 // items on the line. If the sum is less than the flex container’s inner main size,
419 // use the flex grow factor for the rest of this algorithm; otherwise, use the
420 // flex shrink factor.
421
422 let used_flex_factor: f32 = line.items.iter().map(|child| child.hypothetical_outer_main_size).sum();
423 let growing = used_flex_factor < node_inner_main;
424 let shrinking = !growing;
425
426 // 2. Size inflexible items. Freeze, setting its target main size to its hypothetical main size
427 // - Any item that has a flex factor of zero
428 // - If using the flex grow factor: any item that has a flex base size
429 // greater than its hypothetical main size
430 // - If using the flex shrink factor: any item that has a flex base size
431 // smaller than its hypothetical main size
432
433 for child in line.items.iter_mut() {
434 child.target_main_size = child.hypothetical_inner_main_size;
435 child.outer_target_main_size = child.target_main_size
436 + child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
437 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
438
439 if (child.node.flex_grow == 0.0 && child.node.flex_shrink == 0.0)
440 || (growing && child.flex_basis > child.hypothetical_inner_main_size)
441 || (shrinking && child.flex_basis < child.hypothetical_inner_main_size)
442 {
443 child.frozen = true;
444 }
445 }
446
447 // 3. Calculate initial free space. Sum the outer sizes of all items on the line,
448 // and subtract this from the flex container’s inner main size. For frozen items,
449 // use their outer target main size; for other items, use their outer flex base size.
450
451 let used_space: f32 = line
452 .items
453 .iter()
454 .map(|child| {
455 child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
456 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0)
457 + if child.frozen { child.target_main_size } else { child.flex_basis }
458 }).sum();
459
460 let initial_free_space = node_inner_main - used_space;
461
462 // 4. Loop
463
464 loop {
465 // a. Check for flexible items. If all the flex items on the line are frozen,
466 // free space has been distributed; exit this loop.
467
468 let mut frozen: Vec<&mut FlexItem> = vec![];
469 let mut unfrozen: Vec<&mut FlexItem> = vec![];
470
471 for child in line.items.iter_mut() {
472 if child.frozen {
473 frozen.push(child);
474 } else {
475 unfrozen.push(child);
476 }
477 }
478
479 if unfrozen.len() == 0 {
480 break;
481 }
482
483 // b. Calculate the remaining free space as for initial free space, above.
484 // If the sum of the unfrozen flex items’ flex factors is less than one,
485 // multiply the initial free space by this sum. If the magnitude of this
486 // value is less than the magnitude of the remaining free space, use this
487 // as the remaining free space.
488
489 let used_space: f32 = Iterator::chain(frozen.iter(), unfrozen.iter())
490 .map(|child| {
491 child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
492 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0)
493 + if child.frozen { child.target_main_size } else { child.flex_basis }
494 }).sum();
495
496 let sum_flex_grow: f32 = unfrozen.iter().map(|item| item.node.flex_grow).sum();
497 let sum_flex_shrink: f32 = unfrozen.iter().map(|item| item.node.flex_shrink).sum();
498
499 let free_space = if growing && sum_flex_grow < 1.0 {
500 (initial_free_space * sum_flex_grow).min(node_inner_main - used_space)
501 } else if shrinking && sum_flex_shrink < 1.0 {
502 (initial_free_space * sum_flex_shrink).max(node_inner_main - used_space)
503 } else {
504 node_inner_main - used_space
505 };
506
507 // c. Distribute free space proportional to the flex factors.
508 // - If the remaining free space is zero
509 // Do Nothing
510 // - If using the flex grow factor
511 // Find the ratio of the item’s flex grow factor to the sum of the
512 // flex grow factors of all unfrozen items on the line. Set the item’s
513 // target main size to its flex base size plus a fraction of the remaining
514 // free space proportional to the ratio.
515 // - If using the flex shrink factor
516 // For every unfrozen item on the line, multiply its flex shrink factor by
517 // its inner flex base size, and note this as its scaled flex shrink factor.
518 // Find the ratio of the item’s scaled flex shrink factor to the sum of the
519 // scaled flex shrink factors of all unfrozen items on the line. Set the item’s
520 // target main size to its flex base size minus a fraction of the absolute value
521 // of the remaining free space proportional to the ratio. Note this may result
522 // in a negative inner main size; it will be corrected in the next step.
523 // - Otherwise
524 // Do Nothing
525
526 if free_space > 0.0 && growing && sum_flex_grow > 0.0 {
527 for child in &mut unfrozen {
528 child.target_main_size = child.flex_basis + free_space * (child.node.flex_grow / sum_flex_grow);
529 }
530 } else if free_space < 0.0 && shrinking && sum_flex_shrink > 0.0 {
531 let sum_scaled_shrink_factor: f32 =
532 unfrozen.iter().map(|child| child.inner_flex_basis * child.node.flex_shrink).sum();
533
534 for child in &mut unfrozen {
535 let scaled_shrink_factor = child.inner_flex_basis * child.node.flex_shrink;
536 child.target_main_size =
537 child.flex_basis + free_space * (scaled_shrink_factor / sum_scaled_shrink_factor);
538 }
539 }
540
541 // d. Fix min/max violations. Clamp each non-frozen item’s target main size by its
542 // used min and max main sizes and floor its content-box size at zero. If the
543 // item’s target main size was made smaller by this, it’s a max violation.
544 // If the item’s target main size was made larger by this, it’s a min violation.
545
546 let mut total_violation = 0.0;
547 for child in &mut unfrozen {
548 let max = child.node.max_main_size(node.flex_direction).resolve(percent_calc_base_child, f32::MAX);
549 let min =
550 child.node.min_main_size(node.flex_direction).resolve(percent_calc_base_child, f32::MIN).max(0.0);
551
552 let clamped = if child.target_main_size > max {
553 max
554 } else if child.target_main_size < min {
555 min
556 } else {
557 child.target_main_size
558 };
559
560 child.violation = clamped - child.target_main_size;
561 total_violation += child.violation;
562 child.target_main_size = clamped;
563 child.outer_target_main_size = child.target_main_size
564 + child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
565 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
566 }
567
568 // e. Freeze over-flexed items. The total violation is the sum of the adjustments
569 // from the previous step ∑(clamped size - unclamped size). If the total violation is:
570 // - Zero
571 // Freeze all items.
572 // - Positive
573 // Freeze all the items with min violations.
574 // - Negative
575 // Freeze all the items with max violations.
576
577 if total_violation > 0.0 {
578 for child in &mut unfrozen {
579 child.frozen = child.violation > 0.0;
580 }
581 } else if total_violation < 0.0 {
582 for child in &mut unfrozen {
583 child.frozen = child.violation < 0.0;
584 }
585 } else {
586 for child in &mut unfrozen {
587 child.frozen = true;
588 }
589 }
590
591 // f. Return to the start of this loop.
592 }
593 }
594
595 // Not part of the spec from what i can see but seems correct
596 let container_main_size = if node_main.is_finite() {
597 node_main
598 } else {
599 let mut longest_line = f32::MIN;
600
601 for line in &flex_lines {
602 let length: f32 = line.items.iter().map(|item| item.outer_target_main_size).sum();
603 longest_line = if length > longest_line { length } else { longest_line };
604 }
605
606 let size = longest_line + padding_main + border_main;
607 if available_main.is_finite() && flex_lines.len() > 1 && size < available_main {
608 available_main
609 } else {
610 size
611 }
612 };
613
614 let inner_container_main_size = container_main_size - padding_main - border_main;
615
616 // 9.4. Cross Size Determination
617
618 // 7. Determine the hypothetical cross size of each item by performing layout with the
619 // used main size and the available space, treating auto as fit-content.
620
621 for line in &mut flex_lines {
622 for child in &mut line.items {
623 let child_cross = child
624 .node
625 .cross_size(node.flex_direction)
626 .resolve(percent_calc_base_child, f32::NAN)
627 .max(child.node.min_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::NAN))
628 .min(child.node.max_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::NAN));
629
630 let size = compute_internal(
631 child.node,
632 if node.flex_direction.is_row() { child.target_main_size } else { child_cross },
633 if node.flex_direction.is_row() { child_cross } else { child.target_main_size },
634 if node.flex_direction.is_row() { container_main_size } else { available_cross },
635 if node.flex_direction.is_row() { available_cross } else { container_main_size },
636 percent_calc_base_child,
637 ).size;
638
639 child.hypothetical_inner_cross_size = size
640 .cross(node.flex_direction)
641 .max(child.node.min_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::MIN))
642 .min(child.node.max_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::MAX))
643 .max(0.0);
644
645 child.hypothetical_outer_cross_size = child.hypothetical_inner_cross_size
646 + child.node.cross_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
647 + child.node.cross_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
648 }
649 }
650
651 // 8. Calculate the cross size of each flex line.
652 // If the flex container is single-line and has a definite cross size, the cross size
653 // of the flex line is the flex container’s inner cross size. Otherwise, for each flex line:
654 //
655 // 1. Collect all the flex items whose inline-axis is parallel to the main-axis, whose
656 // align-self is baseline, and whose cross-axis margins are both non-auto. Find the
657 // largest of the distances between each item’s baseline and its hypothetical outer
658 // cross-start edge, and the largest of the distances between each item’s baseline
659 // and its hypothetical outer cross-end edge, and sum these two values.
660 // 2. Among all the items not collected by the previous step, find the largest
661 // outer hypothetical cross size.
662 // 3. The used cross-size of the flex line is the largest of the numbers found in the
663 // previous two steps and zero.
664 //
665 // If the flex container is single-line, then clamp the line’s cross-size to be within
666 // the container’s computed min and max cross sizes. Note that if CSS 2.1’s definition
667 // of min/max-width/height applied more generally, this behavior would fall out automatically.
668
669 if flex_lines.len() == 1 && node_cross.is_finite() {
670 flex_lines[0].cross_size = node_cross - padding_cross - border_cross;
671 } else {
672 for line in &mut flex_lines {
673 // TODO handle baseline (1)
674
675 line.cross_size =
676 line.items.iter().map(|child| child.hypothetical_outer_cross_size).fold(0.0, |acc, x| acc.max(x));
677 }
678 }
679
680 // 9. Handle 'align-content: stretch'. If the flex container has a definite cross size,
681 // align-content is stretch, and the sum of the flex lines' cross sizes is less than
682 // the flex container’s inner cross size, increase the cross size of each flex line
683 // by equal amounts such that the sum of their cross sizes exactly equals the
684 // flex container’s inner cross size.
685
686 if node.align_content == style::AlignContent::Stretch && node_cross.is_finite() {
687 let total_cross: f32 = flex_lines.iter().map(|line| line.cross_size).sum();
688 let inner_cross = node_cross - padding_cross - border_cross;
689
690 if total_cross < inner_cross {
691 let remaining = inner_cross - total_cross;
692 let addition = remaining / flex_lines.len() as f32;
693
694 for line in &mut flex_lines {
695 line.cross_size += addition;
696 }
697 }
698 }
699
700 // 10. Collapse visibility:collapse items. If any flex items have visibility: collapse,
701 // note the cross size of the line they’re in as the item’s strut size, and restart
702 // layout from the beginning.
703 //
704 // In this second layout round, when collecting items into lines, treat the collapsed
705 // items as having zero main size. For the rest of the algorithm following that step,
706 // ignore the collapsed items entirely (as if they were display:none) except that after
707 // calculating the cross size of the lines, if any line’s cross size is less than the
708 // largest strut size among all the collapsed items in the line, set its cross size to
709 // that strut size.
710 //
711 // Skip this step in the second layout round.
712
713 // TODO implement once (if ever) we support visibility:collapse
714
715 // 11. Determine the used cross size of each flex item. If a flex item has align-self: stretch,
716 // its computed cross size property is auto, and neither of its cross-axis margins are auto,
717 // the used outer cross size is the used cross size of its flex line, clamped according to
718 // the item’s used min and max cross sizes. Otherwise, the used cross size is the item’s
719 // hypothetical cross size.
720 //
721 // If the flex item has align-self: stretch, redo layout for its contents, treating this
722 // used size as its definite cross size so that percentage-sized children can be resolved.
723 //
724 // Note that this step does not affect the main size of the flex item, even if it has an
725 // intrinsic aspect ratio.
726
727 for line in &mut flex_lines {
728 for child in &mut line.items {
729 let is_stretch = child.node.align_self(node) == style::AlignSelf::Stretch;
730
731 child.target_cross_size = if is_stretch
732 && child.node.cross_margin_start(node.flex_direction) != style::Dimension::Auto
733 && child.node.cross_margin_end(node.flex_direction) != style::Dimension::Auto
734 && child.node.cross_size(node.flex_direction) == style::Dimension::Auto
735 {
736 (line.cross_size
737 - child.node.cross_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
738 - child.node.cross_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0))
739 .max(child.node.min_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::MIN))
740 .min(child.node.max_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::MAX))
741 } else {
742 child.hypothetical_inner_cross_size
743 };
744
745 child.outer_target_cross_size = child.target_cross_size
746 + child.node.cross_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
747 + child.node.cross_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
748 }
749 }
750
751 // 9.5. Main-Axis Alignment
752
753 // 12. Distribute any remaining free space. For each flex line:
754 // 1. If the remaining free space is positive and at least one main-axis margin on this
755 // line is auto, distribute the free space equally among these margins. Otherwise,
756 // set all auto margins to zero.
757 // 2. Align the items along the main-axis per justify-content.
758
759 for line in &mut flex_lines {
760 let used_space: f32 = line.items.iter().map(|child| child.outer_target_main_size).sum();
761 let free_space = inner_container_main_size - used_space;
762
763 // TODO does not make a ton of sense to have this here but we want to have this somewhere.
764 for child in &mut line.items {
765 child.main_margin_start =
766 child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0);
767 child.main_margin_end =
768 child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
769 }
770
771 if free_space > 0.0 {
772 let mut num_auto_margins = 0;
773
774 for child in &mut line.items {
775 if child.node.main_margin_start(node.flex_direction) == style::Dimension::Auto {
776 num_auto_margins += 1;
777 }
778 if child.node.main_margin_end(node.flex_direction) == style::Dimension::Auto {
779 num_auto_margins += 1;
780 }
781 }
782
783 if num_auto_margins > 0 {
784 let margin = free_space / num_auto_margins as f32;
785
786 for child in &mut line.items {
787 if child.node.main_margin_start(node.flex_direction) == style::Dimension::Auto {
788 child.main_margin_start = margin;
789 }
790 if child.node.main_margin_end(node.flex_direction) == style::Dimension::Auto {
791 child.main_margin_end = margin;
792 }
793 }
794 } else {
795 let num_items = line.items.len();
796 let mut is_first = true;
797
798 for child in &mut line.items {
799 child.offset_main = match node.justify_content {
800 style::JustifyContent::FlexStart => 0.0,
801 style::JustifyContent::Center => if is_first {
802 free_space / 2.0
803 } else {
804 0.0
805 },
806 style::JustifyContent::FlexEnd => if is_first {
807 free_space
808 } else {
809 0.0
810 },
811 style::JustifyContent::SpaceBetween => if is_first {
812 0.0
813 } else {
814 free_space / (num_items - 1) as f32
815 },
816 style::JustifyContent::SpaceAround => if is_first {
817 (free_space / num_items as f32) / 2.0
818 } else {
819 free_space / num_items as f32
820 },
821 style::JustifyContent::SpaceEvenly => free_space / (num_items + 1) as f32,
822 };
823
824 is_first = false;
825 }
826 }
827 }
828 }
829
830 // 9.6. Cross-Axis Alignment
831
832 // 13. Resolve cross-axis auto margins. If a flex item has auto cross-axis margins:
833 // - If its outer cross size (treating those auto margins as zero) is less than the
834 // cross size of its flex line, distribute the difference in those sizes equally
835 // to the auto margins.
836 // - Otherwise, if the block-start or inline-start margin (whichever is in the cross axis)
837 // is auto, set it to zero. Set the opposite margin so that the outer cross size of the
838 // item equals the cross size of its flex line.
839
840 for line in &mut flex_lines {
841 for child in &mut line.items {
842 // TODO probably move this somewhere else, as with main margin resolution. Only auto margins should be resolved here.
843 child.cross_margin_start =
844 child.node.cross_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0);
845 child.cross_margin_end =
846 child.node.cross_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
847
848 if child.outer_target_cross_size < line.cross_size {
849 let free_space = line.cross_size - child.outer_target_cross_size;
850
851 if child.node.cross_margin_start(node.flex_direction) == style::Dimension::Auto
852 && child.node.cross_margin_end(node.flex_direction) == style::Dimension::Auto
853 {
854 child.cross_margin_start = free_space / 2.0;
855 child.cross_margin_end = free_space / 2.0;
856 } else if child.node.cross_margin_start(node.flex_direction) == style::Dimension::Auto {
857 child.cross_margin_start = free_space;
858 } else if child.node.cross_margin_end(node.flex_direction) == style::Dimension::Auto {
859 child.cross_margin_end = free_space;
860 } else {
861 // 14. Align all flex items along the cross-axis per align-self, if neither of the item’s
862 // cross-axis margins are auto.
863
864 child.offset_cross = match child.node.align_self(node) {
865 style::AlignSelf::Auto => 0.0, // Should never happen
866 style::AlignSelf::FlexStart => if wrap_reverse {
867 free_space
868 } else {
869 0.0
870 },
871 style::AlignSelf::FlexEnd => if wrap_reverse {
872 0.0
873 } else {
874 free_space
875 },
876 style::AlignSelf::Center => free_space / 2.0,
877 style::AlignSelf::Baseline => free_space / 2.0, // Treat as center for now until we have baseline support
878 style::AlignSelf::Stretch => if wrap_reverse {
879 free_space
880 } else {
881 0.0
882 },
883 };
884 }
885 }
886 }
887 }
888
889 // 15. Determine the flex container’s used cross size:
890 // - If the cross size property is a definite size, use that, clamped by the used
891 // min and max cross sizes of the flex container.
892 // - Otherwise, use the sum of the flex lines' cross sizes, clamped by the used
893 // min and max cross sizes of the flex container.
894
895 let total_cross_size: f32 = flex_lines.iter().map(|line| line.cross_size).sum();
896 let container_cross_size =
897 if node_cross.is_finite() { node_cross } else { (total_cross_size + padding_cross + border_cross) };
898 let inner_container_cross_size = container_cross_size - padding_cross - border_cross;
899
900 // 16. Align all flex lines per align-content.
901
902 let free_space = inner_container_cross_size - total_cross_size;
903 let num_lines = flex_lines.len();
904 let mut is_first = true;
905
906 let align_line = |line: &mut FlexLine| {
907 line.offset_cross = match node.align_content {
908 style::AlignContent::FlexStart => if is_first && wrap_reverse {
909 free_space
910 } else {
911 0.0
912 },
913 style::AlignContent::FlexEnd => if is_first && !wrap_reverse {
914 free_space
915 } else {
916 0.0
917 },
918 style::AlignContent::Center => if is_first {
919 free_space / 2.0
920 } else {
921 0.0
922 },
923 style::AlignContent::Stretch => 0.0,
924 style::AlignContent::SpaceBetween => if is_first {
925 0.0
926 } else {
927 free_space / (num_lines - 1) as f32
928 },
929 style::AlignContent::SpaceAround => if is_first {
930 (free_space / num_lines as f32) / 2.0
931 } else {
932 free_space / num_lines as f32
933 },
934 };
935 is_first = false;
936 };
937
938 if wrap_reverse {
939 flex_lines.iter_mut().rev().for_each(align_line);
940 } else {
941 flex_lines.iter_mut().for_each(align_line);
942 }
943
944 // Do a final layout pass and gather the resulting layouts
945
946 let mut children: Vec<layout::Node> = {
947 let mut lines: Vec<Vec<layout::Node>> = vec![];
948 let mut total_offset_cross = padding_cross_start + border_cross_start;
949
950 {
951 let layout_line = |line: &mut FlexLine| {
952 let mut children: Vec<layout::Node> = vec![];
953 let mut total_offset_main = padding_main_start + border_main_start;
954
955 for child in &mut line.items {
956 let result = compute_internal(
957 child.node,
958 if node.flex_direction.is_row() { child.target_main_size } else { child.target_cross_size },
959 if node.flex_direction.is_row() { child.target_cross_size } else { child.target_main_size },
960 if node.flex_direction.is_row() { container_main_size } else { container_cross_size },
961 if node.flex_direction.is_row() { container_cross_size } else { container_main_size },
962 percent_calc_base_child,
963 );
964
965 let offset_main = {
966 total_offset_main
967 + child.offset_main
968 + child.main_margin_start
969 + (child.node.main_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
970 - child.node.main_end(node.flex_direction).resolve(percent_calc_base_child, 0.0))
971 };
972
973 let offset_cross = {
974 total_offset_cross
975 + child.offset_cross
976 + line.offset_cross
977 + child.cross_margin_start
978 + (child.node.cross_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
979 - child.node.cross_end(node.flex_direction).resolve(percent_calc_base_child, 0.0))
980 };
981
982 children.push(layout::Node {
983 width: result.size.width,
984 height: result.size.height,
985 x: if node.flex_direction.is_row() { offset_main } else { offset_cross },
986 y: if node.flex_direction.is_column() { offset_main } else { offset_cross },
987 children: result.children,
988 });
989
990 total_offset_main = offset_main + result.size.main(node.flex_direction) + child.main_margin_end;
991 }
992
993 total_offset_cross += line.offset_cross + line.cross_size;
994 lines.push(children);
995 };
996
997 if wrap_reverse {
998 flex_lines.iter_mut().rev().for_each(layout_line);
999 } else {
1000 flex_lines.iter_mut().for_each(layout_line);
1001 }
1002 }
1003
1004 if wrap_reverse {
1005 lines.into_iter().rev().flat_map(|x| x).collect()
1006 } else {
1007 lines.into_iter().flat_map(|x| x).collect()
1008 }
1009 };
1010
1011 let container_width = if node.flex_direction.is_row() { container_main_size } else { container_cross_size };
1012 let container_height = if node.flex_direction.is_column() { container_main_size } else { container_cross_size };
1013
1014 // Before returning we perform absolute layout on all absolutely positioned children
1015
1016 let absolute_children: Vec<&style::Node> =
1017 node.children.iter().filter(|child| child.position == style::Position::Absolute).collect();
1018
1019 for child in absolute_children {
1020 let start =
1021 child.start.resolve(container_width, f32::NAN) + child.margin.start.resolve(container_width, f32::NAN);
1022
1023 let end = child.end.resolve(container_width, f32::NAN) + child.margin.end.resolve(container_width, f32::NAN);
1024
1025 let top = child.top.resolve(container_height, f32::NAN) + child.margin.top.resolve(container_height, f32::NAN);
1026
1027 let bottom =
1028 child.bottom.resolve(container_height, f32::NAN) + child.margin.bottom.resolve(container_height, f32::NAN);
1029
1030 let (start_main, end_main) = if node.flex_direction.is_row() { (start, end) } else { (top, bottom) };
1031
1032 let (start_cross, end_cross) = if node.flex_direction.is_row() { (top, bottom) } else { (start, end) };
1033
1034 let width = if start.is_finite() && end.is_finite() {
1035 container_width - start - end
1036 } else {
1037 child
1038 .width
1039 .resolve(container_width, f32::NAN)
1040 .max(child.min_width.resolve(container_width, f32::NAN))
1041 .min(child.max_width.resolve(container_width, f32::NAN))
1042 };
1043
1044 let height = if top.is_finite() && bottom.is_finite() {
1045 container_height - top - bottom
1046 } else {
1047 child
1048 .height
1049 .resolve(container_height, f32::NAN)
1050 .max(child.min_height.resolve(container_height, f32::NAN))
1051 .min(child.max_height.resolve(container_height, f32::NAN))
1052 };
1053
1054 let result = compute_internal(
1055 child,
1056 width,
1057 height,
1058 if node.flex_direction.is_row() { container_main_size } else { container_cross_size },
1059 if node.flex_direction.is_row() { container_cross_size } else { container_main_size },
1060 container_main_size,
1061 );
1062
1063 let free_cross_space = container_cross_size - result.size.cross(node.flex_direction);
1064 let free_main_space = container_main_size - result.size.main(node.flex_direction);
1065
1066 let offset_main = if start_main.is_finite() {
1067 start_main + border_main_start
1068 } else if end_main.is_finite() {
1069 free_main_space - end_main - border_main_end
1070 } else {
1071 match node.justify_content {
1072 style::JustifyContent::SpaceBetween | style::JustifyContent::FlexStart => {
1073 padding_main_start + border_main_start
1074 }
1075 style::JustifyContent::FlexEnd => free_main_space - end_main - padding_main_end - border_main_end,
1076 style::JustifyContent::SpaceEvenly
1077 | style::JustifyContent::SpaceAround
1078 | style::JustifyContent::Center => free_main_space / 2.0,
1079 }
1080 };
1081
1082 let offset_cross = if start_cross.is_finite() {
1083 start_cross + border_cross_start
1084 } else if end_cross.is_finite() {
1085 free_cross_space - end_cross - border_cross_end
1086 } else {
1087 match child.align_self(node) {
1088 style::AlignSelf::Auto => 0.0, // Should never happen
1089 style::AlignSelf::FlexStart => if wrap_reverse {
1090 free_cross_space - padding_cross_end - border_cross_end
1091 } else {
1092 padding_cross_start + border_cross_start
1093 },
1094 style::AlignSelf::FlexEnd => if wrap_reverse {
1095 padding_cross_start + border_cross_start
1096 } else {
1097 free_cross_space - padding_cross_end - border_cross_end
1098 },
1099 style::AlignSelf::Center => free_cross_space / 2.0,
1100 style::AlignSelf::Baseline => free_cross_space / 2.0, // Treat as center for now until we have baseline support
1101 style::AlignSelf::Stretch => if wrap_reverse {
1102 free_cross_space - padding_cross_end - border_cross_end
1103 } else {
1104 padding_cross_start + border_cross_start
1105 },
1106 }
1107 };
1108
1109 children.push(layout::Node {
1110 width: result.size.width,
1111 height: result.size.height,
1112 x: if node.flex_direction.is_row() { offset_main } else { offset_cross },
1113 y: if node.flex_direction.is_column() { offset_main } else { offset_cross },
1114 children: result.children,
1115 });
1116 }
1117
1118 ComputeResult { size: FlexSize { width: container_width, height: container_height }, children }
1119}