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;
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 // TODO - this does not follow spec. See commented out code below
251 // 3. Determine the flex base size and hypothetical main size of each item:
252 for child in &mut flex_items {
253 // A. If the item has a definite used flex basis, that’s the flex base size.
254
255 let flex_basis = child.node.flex_basis.resolve(percent_calc_base_child, f32::NAN);
256 if flex_basis.is_finite() {
257 child.flex_basis = flex_basis;
258 continue;
259 };
260
261 // B. If the flex item has an intrinsic aspect ratio,
262 // a used flex basis of content, and a definite cross size,
263 // then the flex base size is calculated from its inner
264 // cross size and the flex item’s intrinsic aspect ratio.
265
266 if let Some(ratio) = child.node.aspect_ratio {
267 if node_cross.is_finite() && child.node.flex_basis == style::Dimension::Auto {
268 child.flex_basis = ratio * node_cross;
269 continue;
270 }
271 }
272
273 // C. If the used flex basis is content or depends on its available space,
274 // and the flex container is being sized under a min-content or max-content
275 // constraint (e.g. when performing automatic table layout [CSS21]),
276 // size the item under that constraint. The flex base size is the item’s
277 // resulting main size.
278
279 // if main_constraint.min.is_finite() || main_constraint.max.is_finite() {
280 // let size = compute_internal(
281 // child.node,
282 // if node.flex_direction.is_row() { main_constraint } else { SizeConstraint::undefined() },
283 // if node.flex_direction.is_column() { main_constraint } else { SizeConstraint::undefined() },
284 // percent_calc_base_child,
285 // ).size;
286 // child.flex_basis = size.main(node.flex_direction);
287 // continue;
288 // }
289
290 // D. Otherwise, if the used flex basis is content or depends on its
291 // available space, the available main size is infinite, and the flex item’s
292 // inline axis is parallel to the main axis, lay the item out using the rules
293 // for a box in an orthogonal flow [CSS3-WRITING-MODES]. The flex base size
294 // is the item’s max-content main size.
295
296 // if available_main.is_nan() {
297 // let size = compute_internal(
298 // child.node,
299 // child
300 // .node
301 // .width
302 // .resolve(percent_calc_base_child, f32::NAN)
303 // .max(child.node.min_width.resolve(percent_calc_base_child, f32::NAN))
304 // .min(child.node.max_width.resolve(percent_calc_base_child, f32::NAN)),
305 // child
306 // .node
307 // .height
308 // .resolve(percent_calc_base_child, f32::NAN)
309 // .max(child.node.min_height.resolve(percent_calc_base_child, f32::NAN))
310 // .min(child.node.max_height.resolve(percent_calc_base_child, f32::NAN)),
311 // if node.flex_direction.is_row() { available_main } else { available_cross },
312 // if node.flex_direction.is_row() { available_cross } else { available_main },
313 // percent_calc_base_child,
314 // ).size;
315 // child.flex_basis = size.main(node.flex_direction);
316 // continue;
317 // }
318
319 // E. Otherwise, size the item into the available space using its used flex basis
320 // in place of its main size, treating a value of content as max-content.
321 // If a cross size is needed to determine the main size (e.g. when the
322 // flex item’s main size is in its block axis) and the flex item’s cross size
323 // is auto and not definite, in this calculation use fit-content as the
324 // flex item’s cross size. The flex base size is the item’s resulting main size.
325
326 let size = compute_internal(
327 child.node,
328 child
329 .node
330 .width
331 .resolve(percent_calc_base_child, f32::NAN)
332 .max(child.node.min_width.resolve(percent_calc_base_child, f32::NAN))
333 .min(child.node.max_width.resolve(percent_calc_base_child, f32::NAN)),
334 child
335 .node
336 .height
337 .resolve(percent_calc_base_child, f32::NAN)
338 .max(child.node.min_height.resolve(percent_calc_base_child, f32::NAN))
339 .min(child.node.max_height.resolve(percent_calc_base_child, f32::NAN)),
340 if node.flex_direction.is_row() { available_main } else { available_cross },
341 if node.flex_direction.is_row() { available_cross } else { available_main },
342 percent_calc_base_child,
343 ).size;
344 child.flex_basis = size.main(node.flex_direction);
345 }
346
347 // The hypothetical main size is the item’s flex base size clamped according to its
348 // used min and max main sizes (and flooring the content box size at zero).
349
350 for child in &mut flex_items {
351 let padding_start = child.node.main_padding_start(node.flex_direction).resolve(percent_calc_base_child, 0.0);
352 let padding_end = child.node.main_padding_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
353 let border_start = child.node.main_border_start(node.flex_direction).resolve(percent_calc_base_child, 0.0);
354 let border_end = child.node.main_border_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
355 child.inner_flex_basis = child.flex_basis - (padding_start + padding_end + border_start + border_end);
356
357 // TODO - not really spec abiding but needs to be done somewhere. probably somewhere else though.
358 // The following logic was developed not from the spec but by trail and error looking into how
359 // webkit handled various scenarios. Can probably be solved better by passing in
360 // min-content max-content constraints fromt the top
361 let min_main = if node.flex_direction.is_row() {
362 compute_internal(
363 child.node,
364 f32::NAN,
365 f32::NAN,
366 if node.flex_direction.is_row() { available_main } else { available_cross },
367 if node.flex_direction.is_row() { available_cross } else { available_main },
368 percent_calc_base_child,
369 ).size
370 .width
371 .min(child.node.width.resolve(percent_calc_base_child, f32::MAX))
372 } else {
373 child.node.min_main_size(node.flex_direction).resolve(percent_calc_base_child, f32::MIN)
374 };
375
376 child.hypothetical_inner_main_size = child
377 .flex_basis
378 .max(min_main)
379 .min(child.node.max_main_size(node.flex_direction).resolve(percent_calc_base_child, f32::MAX))
380 .max(0.0);
381
382 child.hypothetical_outer_main_size = child.hypothetical_inner_main_size
383 + child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
384 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
385 }
386
387 // 9.3. Main Size Determination
388
389 // 5. Collect flex items into flex lines:
390 // - If the flex container is single-line, collect all the flex items into
391 // a single flex line.
392 // - Otherwise, starting from the first uncollected item, collect consecutive
393 // items one by one until the first time that the next collected item would
394 // not fit into the flex container’s inner main size (or until a forced break
395 // is encountered, see §10 Fragmenting Flex Layout). If the very first
396 // uncollected item wouldn’t fit, collect just it into the line.
397 //
398 // For this step, the size of a flex item is its outer hypothetical main size. (Note: This can be negative.)
399 // Repeat until all flex items have been collected into flex lines
400 //
401 // Note that the "collect as many" line will collect zero-sized flex items onto
402 // the end of the previous line even if the last non-zero item exactly "filled up" the line.
403
404 let mut flex_lines = {
405 let mut lines: Vec<FlexLine> = vec![];
406 let mut line_length = 0.0;
407
408 if node.flex_wrap == style::FlexWrap::NoWrap {
409 lines.push(FlexLine { items: flex_items, cross_size: 0.0, offset_cross: 0.0 });
410 } else {
411 let mut line = FlexLine { items: vec![], cross_size: 0.0, offset_cross: 0.0 };
412
413 for child in flex_items {
414 line_length += child.hypothetical_outer_main_size;
415
416 if line_length > available_main && line.items.len() > 0 {
417 line_length = child.hypothetical_outer_main_size;
418 lines.push(line);
419 line = FlexLine { items: vec![], cross_size: 0.0, offset_cross: 0.0 };
420 }
421
422 line.items.push(child);
423 }
424
425 lines.push(line);
426 }
427
428 lines
429 };
430
431 // 6. Resolve the flexible lengths of all the flex items to find their used main size.
432 // See §9.7 Resolving Flexible Lengths.
433 //
434 // 9.7. Resolving Flexible Lengths
435
436 for line in &mut flex_lines {
437 // 1. Determine the used flex factor. Sum the outer hypothetical main sizes of all
438 // items on the line. If the sum is less than the flex container’s inner main size,
439 // use the flex grow factor for the rest of this algorithm; otherwise, use the
440 // flex shrink factor.
441
442 let used_flex_factor: f32 = line.items.iter().map(|child| child.hypothetical_outer_main_size).sum();
443 let growing = used_flex_factor < node_inner_main;
444 let shrinking = !growing;
445
446 // 2. Size inflexible items. Freeze, setting its target main size to its hypothetical main size
447 // - Any item that has a flex factor of zero
448 // - If using the flex grow factor: any item that has a flex base size
449 // greater than its hypothetical main size
450 // - If using the flex shrink factor: any item that has a flex base size
451 // smaller than its hypothetical main size
452
453 for child in line.items.iter_mut() {
454 // TODO - This is not found by reading the spec. Maybe this can be done in some other place
455 // instead. This was found by trail and error fixing tests to align with webkit output.
456 if node_inner_main.is_nan() && node.flex_direction.is_row() {
457 child.target_main_size = compute_internal(
458 child.node,
459 child
460 .node
461 .width
462 .resolve(percent_calc_base_child, f32::NAN)
463 .max(child.node.min_width.resolve(percent_calc_base_child, f32::NAN))
464 .min(child.node.max_width.resolve(percent_calc_base_child, f32::NAN)),
465 child
466 .node
467 .height
468 .resolve(percent_calc_base_child, f32::NAN)
469 .max(child.node.min_height.resolve(percent_calc_base_child, f32::NAN))
470 .min(child.node.max_height.resolve(percent_calc_base_child, f32::NAN)),
471 if node.flex_direction.is_row() { available_main } else { available_cross },
472 if node.flex_direction.is_row() { available_cross } else { available_main },
473 percent_calc_base_child,
474 ).size
475 .main(node.flex_direction);
476 } else {
477 child.target_main_size = child.hypothetical_inner_main_size;
478 }
479
480 // TODO this should really only be set inside the if-statement below but
481 // that casues the target_main_size to never be set for some items
482
483 child.outer_target_main_size = child.target_main_size
484 + child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
485 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
486
487 if (child.node.flex_grow == 0.0 && child.node.flex_shrink == 0.0)
488 || (growing && child.flex_basis > child.hypothetical_inner_main_size)
489 || (shrinking && child.flex_basis < child.hypothetical_inner_main_size)
490 {
491 child.frozen = true;
492 }
493 }
494
495 // 3. Calculate initial free space. Sum the outer sizes of all items on the line,
496 // and subtract this from the flex container’s inner main size. For frozen items,
497 // use their outer target main size; for other items, use their outer flex base size.
498
499 let used_space: f32 = line
500 .items
501 .iter()
502 .map(|child| {
503 child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
504 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0)
505 + if child.frozen { child.target_main_size } else { child.flex_basis }
506 }).sum();
507
508 let initial_free_space = node_inner_main - used_space;
509
510 // 4. Loop
511
512 loop {
513 // a. Check for flexible items. If all the flex items on the line are frozen,
514 // free space has been distributed; exit this loop.
515
516 let mut frozen: Vec<&mut FlexItem> = vec![];
517 let mut unfrozen: Vec<&mut FlexItem> = vec![];
518
519 for child in line.items.iter_mut() {
520 if child.frozen {
521 frozen.push(child);
522 } else {
523 unfrozen.push(child);
524 }
525 }
526
527 if unfrozen.len() == 0 {
528 break;
529 }
530
531 // b. Calculate the remaining free space as for initial free space, above.
532 // If the sum of the unfrozen flex items’ flex factors is less than one,
533 // multiply the initial free space by this sum. If the magnitude of this
534 // value is less than the magnitude of the remaining free space, use this
535 // as the remaining free space.
536
537 let used_space: f32 = Iterator::chain(frozen.iter(), unfrozen.iter())
538 .map(|child| {
539 child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
540 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0)
541 + if child.frozen { child.target_main_size } else { child.flex_basis }
542 }).sum();
543
544 let sum_flex_grow: f32 = unfrozen.iter().map(|item| item.node.flex_grow).sum();
545 let sum_flex_shrink: f32 = unfrozen.iter().map(|item| item.node.flex_shrink).sum();
546
547 let free_space = if growing && sum_flex_grow < 1.0 {
548 (initial_free_space * sum_flex_grow).min(node_inner_main - used_space)
549 } else if shrinking && sum_flex_shrink < 1.0 {
550 (initial_free_space * sum_flex_shrink).max(node_inner_main - used_space)
551 } else {
552 node_inner_main - used_space
553 };
554
555 // c. Distribute free space proportional to the flex factors.
556 // - If the remaining free space is zero
557 // Do Nothing
558 // - If using the flex grow factor
559 // Find the ratio of the item’s flex grow factor to the sum of the
560 // flex grow factors of all unfrozen items on the line. Set the item’s
561 // target main size to its flex base size plus a fraction of the remaining
562 // free space proportional to the ratio.
563 // - If using the flex shrink factor
564 // For every unfrozen item on the line, multiply its flex shrink factor by
565 // its inner flex base size, and note this as its scaled flex shrink factor.
566 // Find the ratio of the item’s scaled flex shrink factor to the sum of the
567 // scaled flex shrink factors of all unfrozen items on the line. Set the item’s
568 // target main size to its flex base size minus a fraction of the absolute value
569 // of the remaining free space proportional to the ratio. Note this may result
570 // in a negative inner main size; it will be corrected in the next step.
571 // - Otherwise
572 // Do Nothing
573
574 if free_space.is_normal() {
575 if growing && sum_flex_grow > 0.0 {
576 for child in &mut unfrozen {
577 child.target_main_size = child.flex_basis + free_space * (child.node.flex_grow / sum_flex_grow);
578 }
579 } else if shrinking && sum_flex_shrink > 0.0 {
580 let sum_scaled_shrink_factor: f32 =
581 unfrozen.iter().map(|child| child.inner_flex_basis * child.node.flex_shrink).sum();
582
583 for child in &mut unfrozen {
584 let scaled_shrink_factor = child.inner_flex_basis * child.node.flex_shrink;
585 child.target_main_size =
586 child.flex_basis + free_space * (scaled_shrink_factor / sum_scaled_shrink_factor);
587 }
588 }
589 }
590
591 // d. Fix min/max violations. Clamp each non-frozen item’s target main size by its
592 // used min and max main sizes and floor its content-box size at zero. If the
593 // item’s target main size was made smaller by this, it’s a max violation.
594 // If the item’s target main size was made larger by this, it’s a min violation.
595
596 let mut total_violation = 0.0;
597 for child in &mut unfrozen {
598 // TODO - not really spec abiding but needs to be done somewhere. probably somewhere else though.
599 // The following logic was developed not from the spec but by trail and error looking into how
600 // webkit handled various scenarios. Can probably be solved better by passing in
601 // min-content max-content constraints fromt the top
602 let min_main = if node.flex_direction.is_row() {
603 compute_internal(
604 child.node,
605 f32::NAN,
606 f32::NAN,
607 if node.flex_direction.is_row() { available_main } else { available_cross },
608 if node.flex_direction.is_row() { available_cross } else { available_main },
609 percent_calc_base_child,
610 ).size
611 .width
612 .min(child.node.width.resolve(percent_calc_base_child, f32::NAN))
613 .max(child.node.min_width.resolve(percent_calc_base_child, f32::MIN))
614 } else {
615 child.node.min_main_size(node.flex_direction).resolve(percent_calc_base_child, f32::MIN)
616 };
617
618 let max_main = child.node.max_main_size(node.flex_direction).resolve(percent_calc_base_child, f32::MAX);
619
620 let clamped = child.target_main_size.min(max_main).max(min_main);
621 child.violation = clamped - child.target_main_size;
622 total_violation += child.violation;
623 child.target_main_size = clamped;
624 child.outer_target_main_size = child.target_main_size
625 + child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
626 + child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
627 }
628
629 // e. Freeze over-flexed items. The total violation is the sum of the adjustments
630 // from the previous step ∑(clamped size - unclamped size). If the total violation is:
631 // - Zero
632 // Freeze all items.
633 // - Positive
634 // Freeze all the items with min violations.
635 // - Negative
636 // Freeze all the items with max violations.
637
638 if !total_violation.is_normal() {
639 for child in &mut unfrozen {
640 child.frozen = true;
641 }
642 } else if total_violation > 0.0 {
643 for child in &mut unfrozen {
644 child.frozen = child.violation > 0.0;
645 }
646 } else if total_violation < 0.0 {
647 for child in &mut unfrozen {
648 child.frozen = child.violation < 0.0;
649 }
650 }
651
652 // f. Return to the start of this loop.
653 }
654 }
655
656 // Not part of the spec from what i can see but seems correct
657 let container_main_size = if node_main.is_finite() {
658 node_main
659 } else {
660 let mut longest_line = f32::MIN;
661
662 for line in &flex_lines {
663 let length: f32 = line.items.iter().map(|item| item.outer_target_main_size).sum();
664 longest_line = if length > longest_line { length } else { longest_line };
665 }
666
667 let size = longest_line + padding_main + border_main;
668 if available_main.is_finite() && flex_lines.len() > 1 && size < available_main {
669 available_main
670 } else {
671 size
672 }
673 };
674
675 let inner_container_main_size = container_main_size - padding_main - border_main;
676
677 // 9.4. Cross Size Determination
678
679 // 7. Determine the hypothetical cross size of each item by performing layout with the
680 // used main size and the available space, treating auto as fit-content.
681
682 for line in &mut flex_lines {
683 for child in &mut line.items {
684 let child_cross = child
685 .node
686 .cross_size(node.flex_direction)
687 .resolve(percent_calc_base_child, f32::NAN)
688 .max(child.node.min_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::NAN))
689 .min(child.node.max_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::NAN));
690
691 let size = compute_internal(
692 child.node,
693 if node.flex_direction.is_row() { child.target_main_size } else { child_cross },
694 if node.flex_direction.is_row() { child_cross } else { child.target_main_size },
695 if node.flex_direction.is_row() { container_main_size } else { available_cross },
696 if node.flex_direction.is_row() { available_cross } else { container_main_size },
697 percent_calc_base_child,
698 ).size;
699
700 child.hypothetical_inner_cross_size = size
701 .cross(node.flex_direction)
702 .max(child.node.min_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::MIN))
703 .min(child.node.max_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::MAX))
704 .max(0.0);
705
706 child.hypothetical_outer_cross_size = child.hypothetical_inner_cross_size
707 + child.node.cross_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
708 + child.node.cross_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
709 }
710 }
711
712 // 8. Calculate the cross size of each flex line.
713 // If the flex container is single-line and has a definite cross size, the cross size
714 // of the flex line is the flex container’s inner cross size. Otherwise, for each flex line:
715 //
716 // 1. Collect all the flex items whose inline-axis is parallel to the main-axis, whose
717 // align-self is baseline, and whose cross-axis margins are both non-auto. Find the
718 // largest of the distances between each item’s baseline and its hypothetical outer
719 // cross-start edge, and the largest of the distances between each item’s baseline
720 // and its hypothetical outer cross-end edge, and sum these two values.
721 // 2. Among all the items not collected by the previous step, find the largest
722 // outer hypothetical cross size.
723 // 3. The used cross-size of the flex line is the largest of the numbers found in the
724 // previous two steps and zero.
725 //
726 // If the flex container is single-line, then clamp the line’s cross-size to be within
727 // the container’s computed min and max cross sizes. Note that if CSS 2.1’s definition
728 // of min/max-width/height applied more generally, this behavior would fall out automatically.
729
730 if flex_lines.len() == 1 && node_cross.is_finite() {
731 flex_lines[0].cross_size = node_cross - padding_cross - border_cross;
732 } else {
733 for line in &mut flex_lines {
734 // TODO handle baseline (1)
735
736 line.cross_size =
737 line.items.iter().map(|child| child.hypothetical_outer_cross_size).fold(0.0, |acc, x| acc.max(x));
738 }
739 }
740
741 // 9. Handle 'align-content: stretch'. If the flex container has a definite cross size,
742 // align-content is stretch, and the sum of the flex lines' cross sizes is less than
743 // the flex container’s inner cross size, increase the cross size of each flex line
744 // by equal amounts such that the sum of their cross sizes exactly equals the
745 // flex container’s inner cross size.
746
747 if node.align_content == style::AlignContent::Stretch && node_cross.is_finite() {
748 let total_cross: f32 = flex_lines.iter().map(|line| line.cross_size).sum();
749 let inner_cross = node_cross - padding_cross - border_cross;
750
751 if total_cross < inner_cross {
752 let remaining = inner_cross - total_cross;
753 let addition = remaining / flex_lines.len() as f32;
754
755 for line in &mut flex_lines {
756 line.cross_size += addition;
757 }
758 }
759 }
760
761 // 10. Collapse visibility:collapse items. If any flex items have visibility: collapse,
762 // note the cross size of the line they’re in as the item’s strut size, and restart
763 // layout from the beginning.
764 //
765 // In this second layout round, when collecting items into lines, treat the collapsed
766 // items as having zero main size. For the rest of the algorithm following that step,
767 // ignore the collapsed items entirely (as if they were display:none) except that after
768 // calculating the cross size of the lines, if any line’s cross size is less than the
769 // largest strut size among all the collapsed items in the line, set its cross size to
770 // that strut size.
771 //
772 // Skip this step in the second layout round.
773
774 // TODO implement once (if ever) we support visibility:collapse
775
776 // 11. Determine the used cross size of each flex item. If a flex item has align-self: stretch,
777 // its computed cross size property is auto, and neither of its cross-axis margins are auto,
778 // the used outer cross size is the used cross size of its flex line, clamped according to
779 // the item’s used min and max cross sizes. Otherwise, the used cross size is the item’s
780 // hypothetical cross size.
781 //
782 // If the flex item has align-self: stretch, redo layout for its contents, treating this
783 // used size as its definite cross size so that percentage-sized children can be resolved.
784 //
785 // Note that this step does not affect the main size of the flex item, even if it has an
786 // intrinsic aspect ratio.
787
788 for line in &mut flex_lines {
789 for child in &mut line.items {
790 let is_stretch = child.node.align_self(node) == style::AlignSelf::Stretch;
791
792 child.target_cross_size = if is_stretch
793 && child.node.cross_margin_start(node.flex_direction) != style::Dimension::Auto
794 && child.node.cross_margin_end(node.flex_direction) != style::Dimension::Auto
795 && child.node.cross_size(node.flex_direction) == style::Dimension::Auto
796 {
797 (line.cross_size
798 - child.node.cross_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
799 - child.node.cross_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0))
800 .max(child.node.min_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::MIN))
801 .min(child.node.max_cross_size(node.flex_direction).resolve(percent_calc_base_child, f32::MAX))
802 } else {
803 child.hypothetical_inner_cross_size
804 };
805
806 child.outer_target_cross_size = child.target_cross_size
807 + child.node.cross_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
808 + child.node.cross_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
809 }
810 }
811
812 // 9.5. Main-Axis Alignment
813
814 // 12. Distribute any remaining free space. For each flex line:
815 // 1. If the remaining free space is positive and at least one main-axis margin on this
816 // line is auto, distribute the free space equally among these margins. Otherwise,
817 // set all auto margins to zero.
818 // 2. Align the items along the main-axis per justify-content.
819
820 for line in &mut flex_lines {
821 let used_space: f32 = line.items.iter().map(|child| child.outer_target_main_size).sum();
822 let free_space = inner_container_main_size - used_space;
823
824 // TODO does not make a ton of sense to have this here but we want to have this somewhere.
825 for child in &mut line.items {
826 child.main_margin_start =
827 child.node.main_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0);
828 child.main_margin_end =
829 child.node.main_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
830 }
831
832 let mut num_auto_margins = 0;
833
834 for child in &mut line.items {
835 if child.node.main_margin_start(node.flex_direction) == style::Dimension::Auto {
836 num_auto_margins += 1;
837 }
838 if child.node.main_margin_end(node.flex_direction) == style::Dimension::Auto {
839 num_auto_margins += 1;
840 }
841 }
842
843 if free_space > 0.0 && num_auto_margins > 0 {
844 let margin = free_space / num_auto_margins as f32;
845
846 for child in &mut line.items {
847 if child.node.main_margin_start(node.flex_direction) == style::Dimension::Auto {
848 child.main_margin_start = margin;
849 }
850 if child.node.main_margin_end(node.flex_direction) == style::Dimension::Auto {
851 child.main_margin_end = margin;
852 }
853 }
854 } else {
855 let num_items = line.items.len();
856 let mut is_first = true;
857
858 for child in &mut line.items {
859 child.offset_main = match node.justify_content {
860 style::JustifyContent::FlexStart => 0.0,
861 style::JustifyContent::Center => if is_first {
862 free_space / 2.0
863 } else {
864 0.0
865 },
866 style::JustifyContent::FlexEnd => if is_first {
867 free_space
868 } else {
869 0.0
870 },
871 style::JustifyContent::SpaceBetween => if is_first {
872 0.0
873 } else {
874 free_space / (num_items - 1) as f32
875 },
876 style::JustifyContent::SpaceAround => if is_first {
877 (free_space / num_items as f32) / 2.0
878 } else {
879 free_space / num_items as f32
880 },
881 style::JustifyContent::SpaceEvenly => free_space / (num_items + 1) as f32,
882 };
883
884 is_first = false;
885 }
886 }
887 }
888
889 // 9.6. Cross-Axis Alignment
890
891 // 13. Resolve cross-axis auto margins. If a flex item has auto cross-axis margins:
892 // - If its outer cross size (treating those auto margins as zero) is less than the
893 // cross size of its flex line, distribute the difference in those sizes equally
894 // to the auto margins.
895 // - Otherwise, if the block-start or inline-start margin (whichever is in the cross axis)
896 // is auto, set it to zero. Set the opposite margin so that the outer cross size of the
897 // item equals the cross size of its flex line.
898
899 for line in &mut flex_lines {
900 // TODO this is super basic and has to be fixed to support a lot more such as custom baselines
901 // as well as nested children.
902 let baseline: f32 =
903 line.items.iter().map(|child| child.hypothetical_outer_cross_size).fold(0.0, |acc, x| acc.max(x));
904
905 for child in &mut line.items {
906 // TODO probably move this somewhere else, as with main margin resolution. Only auto margins should be resolved here.
907 child.cross_margin_start =
908 child.node.cross_margin_start(node.flex_direction).resolve(percent_calc_base_child, 0.0);
909 child.cross_margin_end =
910 child.node.cross_margin_end(node.flex_direction).resolve(percent_calc_base_child, 0.0);
911
912 let free_space = line.cross_size - child.outer_target_cross_size;
913
914 if child.node.cross_margin_start(node.flex_direction) == style::Dimension::Auto
915 && child.node.cross_margin_end(node.flex_direction) == style::Dimension::Auto
916 {
917 child.cross_margin_start = free_space / 2.0;
918 child.cross_margin_end = free_space / 2.0;
919 } else if child.node.cross_margin_start(node.flex_direction) == style::Dimension::Auto {
920 child.cross_margin_start = free_space;
921 } else if child.node.cross_margin_end(node.flex_direction) == style::Dimension::Auto {
922 child.cross_margin_end = free_space;
923 } else {
924 // 14. Align all flex items along the cross-axis per align-self, if neither of the item’s
925 // cross-axis margins are auto.
926
927 child.offset_cross = match child.node.align_self(node) {
928 style::AlignSelf::Auto => 0.0, // Should never happen
929 style::AlignSelf::FlexStart => if wrap_reverse {
930 free_space
931 } else {
932 0.0
933 },
934 style::AlignSelf::FlexEnd => if wrap_reverse {
935 0.0
936 } else {
937 free_space
938 },
939 style::AlignSelf::Center => free_space / 2.0,
940 style::AlignSelf::Baseline => {
941 if node.flex_direction.is_row() {
942 // TODO need more sophisticated baseline support,
943 // especially for basline aligning text.
944 baseline - child.target_cross_size
945 } else {
946 // basline alignment only makes sense if the direction is row
947 // we treat it as flex-start alignment in columns.
948 if wrap_reverse {
949 free_space
950 } else {
951 0.0
952 }
953 }
954 }
955 style::AlignSelf::Stretch => if wrap_reverse {
956 free_space
957 } else {
958 0.0
959 },
960 };
961 }
962 }
963 }
964
965 // 15. Determine the flex container’s used cross size:
966 // - If the cross size property is a definite size, use that, clamped by the used
967 // min and max cross sizes of the flex container.
968 // - Otherwise, use the sum of the flex lines' cross sizes, clamped by the used
969 // min and max cross sizes of the flex container.
970
971 let total_cross_size: f32 = flex_lines.iter().map(|line| line.cross_size).sum();
972 let container_cross_size =
973 if node_cross.is_finite() { node_cross } else { (total_cross_size + padding_cross + border_cross) };
974 let inner_container_cross_size = container_cross_size - padding_cross - border_cross;
975
976 // 16. Align all flex lines per align-content.
977
978 let free_space = inner_container_cross_size - total_cross_size;
979 let num_lines = flex_lines.len();
980 let mut is_first = true;
981
982 let align_line = |line: &mut FlexLine| {
983 line.offset_cross = match node.align_content {
984 style::AlignContent::FlexStart => if is_first && wrap_reverse {
985 free_space
986 } else {
987 0.0
988 },
989 style::AlignContent::FlexEnd => if is_first && !wrap_reverse {
990 free_space
991 } else {
992 0.0
993 },
994 style::AlignContent::Center => if is_first {
995 free_space / 2.0
996 } else {
997 0.0
998 },
999 style::AlignContent::Stretch => 0.0,
1000 style::AlignContent::SpaceBetween => if is_first {
1001 0.0
1002 } else {
1003 free_space / (num_lines - 1) as f32
1004 },
1005 style::AlignContent::SpaceAround => if is_first {
1006 (free_space / num_lines as f32) / 2.0
1007 } else {
1008 free_space / num_lines as f32
1009 },
1010 };
1011 is_first = false;
1012 };
1013
1014 if wrap_reverse {
1015 flex_lines.iter_mut().rev().for_each(align_line);
1016 } else {
1017 flex_lines.iter_mut().for_each(align_line);
1018 }
1019
1020 // Do a final layout pass and gather the resulting layouts
1021 let percent_calc_base_child = if node.flex_direction.is_row() { container_main_size } else { container_cross_size };
1022
1023 let mut children: Vec<layout::Node> = {
1024 let mut lines: Vec<Vec<layout::Node>> = vec![];
1025 let mut total_offset_cross = padding_cross_start + border_cross_start;
1026
1027 {
1028 let layout_line = |line: &mut FlexLine| {
1029 let mut children: Vec<layout::Node> = vec![];
1030 let mut total_offset_main = padding_main_start + border_main_start;
1031
1032 for child in &mut line.items {
1033 let result = compute_internal(
1034 child.node,
1035 if node.flex_direction.is_row() { child.target_main_size } else { child.target_cross_size },
1036 if node.flex_direction.is_row() { child.target_cross_size } else { child.target_main_size },
1037 if node.flex_direction.is_row() { container_main_size } else { container_cross_size },
1038 if node.flex_direction.is_row() { container_cross_size } else { container_main_size },
1039 percent_calc_base_child,
1040 );
1041
1042 let offset_main = {
1043 total_offset_main
1044 + child.offset_main
1045 + child.main_margin_start
1046 + (child.node.main_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
1047 - child.node.main_end(node.flex_direction).resolve(percent_calc_base_child, 0.0))
1048 };
1049
1050 let offset_cross = {
1051 total_offset_cross
1052 + child.offset_cross
1053 + line.offset_cross
1054 + child.cross_margin_start
1055 + (child.node.cross_start(node.flex_direction).resolve(percent_calc_base_child, 0.0)
1056 - child.node.cross_end(node.flex_direction).resolve(percent_calc_base_child, 0.0))
1057 };
1058
1059 children.push(layout::Node {
1060 width: result.size.width,
1061 height: result.size.height,
1062 x: if node.flex_direction.is_row() { offset_main } else { offset_cross },
1063 y: if node.flex_direction.is_column() { offset_main } else { offset_cross },
1064 children: result.children,
1065 });
1066
1067 total_offset_main = offset_main + result.size.main(node.flex_direction) + child.main_margin_end;
1068 }
1069
1070 total_offset_cross += line.offset_cross + line.cross_size;
1071 lines.push(children);
1072 };
1073
1074 if wrap_reverse {
1075 flex_lines.iter_mut().rev().for_each(layout_line);
1076 } else {
1077 flex_lines.iter_mut().for_each(layout_line);
1078 }
1079 }
1080
1081 if wrap_reverse {
1082 lines.into_iter().rev().flat_map(|x| x).collect()
1083 } else {
1084 lines.into_iter().flat_map(|x| x).collect()
1085 }
1086 };
1087
1088 let container_width = if node.flex_direction.is_row() { container_main_size } else { container_cross_size };
1089 let container_height = if node.flex_direction.is_column() { container_main_size } else { container_cross_size };
1090
1091 // Before returning we perform absolute layout on all absolutely positioned children
1092
1093 let absolute_children: Vec<&style::Node> =
1094 node.children.iter().filter(|child| child.position == style::Position::Absolute).collect();
1095
1096 for child in absolute_children {
1097 let start =
1098 child.start.resolve(container_width, f32::NAN) + child.margin.start.resolve(container_width, f32::NAN);
1099 let end = child.end.resolve(container_width, f32::NAN) + child.margin.end.resolve(container_width, f32::NAN);
1100 let top = child.top.resolve(container_height, f32::NAN) + child.margin.top.resolve(container_height, f32::NAN);
1101 let bottom =
1102 child.bottom.resolve(container_height, f32::NAN) + child.margin.bottom.resolve(container_height, f32::NAN);
1103
1104 let (start_main, end_main) = if node.flex_direction.is_row() { (start, end) } else { (top, bottom) };
1105 let (start_cross, end_cross) = if node.flex_direction.is_row() { (top, bottom) } else { (start, end) };
1106
1107 let child_width = child
1108 .width
1109 .resolve(container_width, f32::NAN)
1110 .max(child.min_width.resolve(container_width, f32::NAN))
1111 .min(child.max_width.resolve(container_width, f32::NAN));
1112
1113 let child_height = child
1114 .height
1115 .resolve(container_height, f32::NAN)
1116 .max(child.min_height.resolve(container_height, f32::NAN))
1117 .min(child.max_height.resolve(container_height, f32::NAN));
1118
1119 let width = if child_width.is_finite() { child_width } else { container_width - start - end };
1120
1121 let height = if child_height.is_finite() { child_height } else { container_height - top - bottom };
1122
1123 let result = compute_internal(
1124 child,
1125 width,
1126 height,
1127 if node.flex_direction.is_row() { container_main_size } else { container_cross_size },
1128 if node.flex_direction.is_row() { container_cross_size } else { container_main_size },
1129 container_main_size,
1130 );
1131
1132 let free_cross_space = container_cross_size - result.size.cross(node.flex_direction);
1133 let free_main_space = container_main_size - result.size.main(node.flex_direction);
1134
1135 let offset_main = if start_main.is_finite() {
1136 start_main + border_main_start
1137 } else if end_main.is_finite() {
1138 free_main_space - end_main - border_main_end
1139 } else {
1140 match node.justify_content {
1141 style::JustifyContent::SpaceBetween | style::JustifyContent::FlexStart => {
1142 padding_main_start + border_main_start
1143 }
1144 style::JustifyContent::FlexEnd => free_main_space - padding_main_end - border_main_end,
1145 style::JustifyContent::SpaceEvenly
1146 | style::JustifyContent::SpaceAround
1147 | style::JustifyContent::Center => free_main_space / 2.0,
1148 }
1149 };
1150
1151 let offset_cross = if start_cross.is_finite() {
1152 start_cross + border_cross_start
1153 } else if end_cross.is_finite() {
1154 free_cross_space - end_cross - border_cross_end
1155 } else {
1156 match child.align_self(node) {
1157 style::AlignSelf::Auto => 0.0, // Should never happen
1158 style::AlignSelf::FlexStart => if wrap_reverse {
1159 free_cross_space - padding_cross_end - border_cross_end
1160 } else {
1161 padding_cross_start + border_cross_start
1162 },
1163 style::AlignSelf::FlexEnd => if wrap_reverse {
1164 padding_cross_start + border_cross_start
1165 } else {
1166 free_cross_space - padding_cross_end - border_cross_end
1167 },
1168 style::AlignSelf::Center => free_cross_space / 2.0,
1169 style::AlignSelf::Baseline => free_cross_space / 2.0, // Treat as center for now until we have baseline support
1170 style::AlignSelf::Stretch => if wrap_reverse {
1171 free_cross_space - padding_cross_end - border_cross_end
1172 } else {
1173 padding_cross_start + border_cross_start
1174 },
1175 }
1176 };
1177
1178 children.push(layout::Node {
1179 width: result.size.width,
1180 height: result.size.height,
1181 x: if node.flex_direction.is_row() { offset_main } else { offset_cross },
1182 y: if node.flex_direction.is_column() { offset_main } else { offset_cross },
1183 children: result.children,
1184 });
1185 }
1186
1187 ComputeResult { size: FlexSize { width: container_width, height: container_height }, children }
1188}