Block: don't set_unrounded_layout when measuring (#971)
1//! Computes the CSS block layout algorithm in the case that the block container being laid out contains only block-level boxes
2use crate::geometry::{Line, Point, Rect, Size};
3use crate::style::{AvailableSpace, CoreStyle, LengthPercentageAuto, Overflow, Position};
4use crate::style_helpers::TaffyMaxContent;
5use crate::tree::{CollapsibleMarginSet, Layout, LayoutInput, LayoutOutput, RunMode, SizingMode};
6use crate::tree::{LayoutPartialTree, LayoutPartialTreeExt, NodeId};
7use crate::util::debug::debug_log;
8use crate::util::sys::f32_max;
9use crate::util::sys::Vec;
10use crate::util::MaybeMath;
11use crate::util::{MaybeResolve, ResolveOrZero};
12use crate::{
13 BlockContainerStyle, BlockItemStyle, BoxGenerationMode, BoxSizing, Direction, LayoutBlockContainer, RequestedAxis,
14 TextAlign,
15};
16
17#[cfg(feature = "float_layout")]
18use super::float::{ContentSlot, FloatContext, FloatIntrinsicWidthCalculator};
19#[cfg(feature = "float_layout")]
20use crate::{Clear, Float, FloatDirection};
21
22/// Context for positioning Block and Float boxes within a Block Formatting Context
23pub struct BlockFormattingContext {
24 /// The float positioning context that handles positioning floats within this Block Formatting Context
25 #[cfg(feature = "float_layout")]
26 float_context: FloatContext,
27}
28
29impl Default for BlockFormattingContext {
30 fn default() -> Self {
31 Self {
32 #[cfg(feature = "float_layout")]
33 float_context: FloatContext::new(),
34 }
35 }
36}
37
38impl BlockFormattingContext {
39 /// Create a new `BlockFormattingContext` with the specified width constraint
40 pub fn new() -> Self {
41 Default::default()
42 }
43
44 /// Create an initial `BlockContext` for this `BlockFormattingContext`
45 pub fn root_block_context(&mut self) -> BlockContext<'_> {
46 BlockContext {
47 bfc: self,
48 y_offset: 0.0,
49 insets: [0.0, 0.0],
50 content_box_insets: [0.0, 0.0],
51 float_content_contribution: 0.0,
52 is_root: true,
53 }
54 }
55}
56
57/// Context for each individual Block within a Block Formatting Context
58///
59/// Contains a mutable reference to the BlockFormattingContext + block-specific data
60pub struct BlockContext<'bfc> {
61 /// A mutable reference to the root BlockFormatttingContext that this BlockContext belongs to
62 bfc: &'bfc mut BlockFormattingContext,
63 /// The y-offset of the border-top of the block node, relative to the to the border-top of the
64 /// root node of the Block Formatting Context it belongs to.
65 y_offset: f32,
66 /// The x-inset of the border-box in from each side of the block node, relative to the root node of the Block Formatting Context it belongs to.
67 insets: [f32; 2],
68 /// The x-insets of the content box
69 content_box_insets: [f32; 2],
70 /// The height that floats take up in the element
71 float_content_contribution: f32,
72 /// Whether the node is the root of the Block Formatting Context is belongs to.
73 is_root: bool,
74}
75
76impl BlockContext<'_> {
77 /// Create a sub-`BlockContext` for a child block node
78 pub fn sub_context(&mut self, additional_y_offset: f32, insets: [f32; 2]) -> BlockContext<'_> {
79 let insets = [self.insets[0] + insets[0], self.insets[1] + insets[1]];
80 BlockContext {
81 bfc: self.bfc,
82 y_offset: self.y_offset + additional_y_offset,
83 insets,
84 content_box_insets: insets,
85 float_content_contribution: 0.0,
86 is_root: false,
87 }
88 }
89
90 /// Returns whether this block is the root block of it's Block Formatting Context
91 pub fn is_bfc_root(&self) -> bool {
92 self.is_root
93 }
94}
95
96#[cfg(feature = "float_layout")]
97impl BlockContext<'_> {
98 /// Set the width of the overall Block Formatting Context. This is used to resolve positions
99 /// that are relative to the right of the context such as right-floated boxes.
100 ///
101 /// Sub-blocks within a Block Formatting Context should use the `Self::sub_context` method to create
102 /// a sub-`BlockContext` with `insets` instead.
103 pub fn set_width(&mut self, available_width: f32) {
104 self.bfc.float_context.set_width(available_width);
105 }
106
107 /// Set the x-axis content-box insets of the `BlockContext`. These are the difference between the border-box
108 /// and the content-box of the box (padding + border + scrollbar_gutter).
109 pub fn apply_content_box_inset(&mut self, content_box_x_insets: [f32; 2]) {
110 self.content_box_insets[0] = self.insets[0] + content_box_x_insets[0];
111 self.content_box_insets[1] = self.insets[1] + content_box_x_insets[1];
112 }
113
114 /// Whether the float context contains any floats
115 #[inline(always)]
116 pub fn has_floats(&self) -> bool {
117 self.bfc.float_context.has_floats()
118 }
119
120 /// Whether the float context contains any floats that extend to or below min_y
121 #[inline(always)]
122 pub fn has_active_floats(&self, min_y: f32) -> bool {
123 self.bfc.float_context.has_active_floats(min_y + self.y_offset)
124 }
125
126 /// Position a floated box with the context
127 pub fn place_floated_box(
128 &mut self,
129 floated_box: Size<f32>,
130 min_y: f32,
131 direction: FloatDirection,
132 clear: Clear,
133 ) -> Point<f32> {
134 let mut pos = self.bfc.float_context.place_floated_box(
135 floated_box,
136 min_y + self.y_offset,
137 self.content_box_insets,
138 direction,
139 clear,
140 );
141 pos.y -= self.y_offset;
142 pos.x -= self.insets[0];
143
144 self.float_content_contribution = self.float_content_contribution.max(pos.y + floated_box.height);
145
146 pos
147 }
148
149 /// Search a space suitable for laying out non-floated content into
150 pub fn find_content_slot(&self, min_y: f32, clear: Clear, after: Option<usize>) -> ContentSlot {
151 let mut slot =
152 self.bfc.float_context.find_content_slot(min_y + self.y_offset, self.content_box_insets, clear, after);
153 slot.y -= self.y_offset;
154 slot.x -= self.insets[0];
155 slot
156 }
157
158 /// Get the bottom of lowest relevant float for the specific clear property
159 pub fn cleared_threshold(&self, clear: Clear) -> Option<f32> {
160 self.bfc.float_context.cleared_threshold(clear).map(|threshold| threshold - self.y_offset)
161 }
162
163 /// Update the height that descendent floats with the height that floats consume
164 /// within a particular child
165 fn add_child_floated_content_height_contribution(&mut self, child_contribution: f32) {
166 self.float_content_contribution = self.float_content_contribution.max(child_contribution);
167 }
168
169 /// Returns the height that descendent floats consume
170 pub fn floated_content_height_contribution(&self) -> f32 {
171 self.float_content_contribution
172 }
173}
174
175#[cfg(not(feature = "float_layout"))]
176impl BlockContext<'_> {
177 #[inline(always)]
178 /// Returns the height that descendent floats consume (always 0.0 when the float feature is disabled)
179 fn float_content_contribution(&self) -> f32 {
180 0.0
181 }
182}
183
184use super::common::alignment::{apply_alignment_fallback, compute_alignment_offset};
185#[cfg(feature = "content_size")]
186use super::common::content_size::compute_content_size_contribution;
187
188/// Per-child data that is accumulated and modified over the course of the layout algorithm
189struct BlockItem {
190 /// The identifier for the associated node
191 node_id: NodeId,
192
193 /// The "source order" of the item. This is the index of the item within the children iterator,
194 /// and controls the order in which the nodes are placed
195 order: u32,
196
197 /// Items that are tables don't have stretch sizing applied to them
198 is_table: bool,
199
200 /// Whether the child is a non-independent block or inline node
201 is_in_same_bfc: bool,
202
203 #[cfg(feature = "float_layout")]
204 /// The `float` style of the node
205 float: Float,
206 #[cfg(feature = "float_layout")]
207 /// The `clear` style of the node
208 clear: Clear,
209
210 /// The base size of this item
211 size: Size<Option<f32>>,
212 /// The minimum allowable size of this item
213 min_size: Size<Option<f32>>,
214 /// The maximum allowable size of this item
215 max_size: Size<Option<f32>>,
216
217 /// The overflow style of the item
218 overflow: Point<Overflow>,
219 /// The width of the item's scrollbars (if it has scrollbars)
220 scrollbar_width: f32,
221
222 /// The position style of the item
223 position: Position,
224 /// The final offset of this item
225 inset: Rect<LengthPercentageAuto>,
226 /// The margin of this item
227 margin: Rect<LengthPercentageAuto>,
228 /// The margin of this item
229 padding: Rect<f32>,
230 /// The margin of this item
231 border: Rect<f32>,
232 /// The sum of padding and border for this item
233 padding_border_sum: Size<f32>,
234
235 /// The computed border box size of this item
236 computed_size: Size<f32>,
237 /// The computed "static position" of this item. The static position is the position
238 /// taking into account padding, border, margins, and scrollbar_gutters but not inset
239 static_position: Point<f32>,
240 /// Whether margins can be collapsed through this item
241 can_be_collapsed_through: bool,
242
243 /// Pending layout for in-flow non-floated items. Held back from `set_unrounded_layout` so the
244 /// post-loop `align-content` pass in `compute_inner` can shift `location.y` before commit.
245 final_layout: Option<Layout>,
246}
247
248/// Computes the layout of [`LayoutPartialTree`] according to the block layout algorithm
249pub fn compute_block_layout(
250 tree: &mut impl LayoutBlockContainer,
251 node_id: NodeId,
252 inputs: LayoutInput,
253 block_ctx: Option<&mut BlockContext<'_>>,
254) -> LayoutOutput {
255 let LayoutInput { known_dimensions, parent_size, run_mode, .. } = inputs;
256 let style = tree.get_block_container_style(node_id);
257
258 // Pull these out earlier to avoid borrowing issues
259 let overflow = style.overflow();
260 let is_scroll_container = overflow.x.is_scroll_container() || overflow.y.is_scroll_container();
261 let aspect_ratio = style.aspect_ratio();
262 let padding = style.padding().resolve_or_zero(parent_size.width, |val, basis| tree.calc(val, basis));
263 let border = style.border().resolve_or_zero(parent_size.width, |val, basis| tree.calc(val, basis));
264 let padding_border_size = (padding + border).sum_axes();
265 let box_sizing_adjustment =
266 if style.box_sizing() == BoxSizing::ContentBox { padding_border_size } else { Size::ZERO };
267
268 let min_size = style
269 .min_size()
270 .maybe_resolve(parent_size, |val, basis| tree.calc(val, basis))
271 .maybe_apply_aspect_ratio(aspect_ratio)
272 .maybe_add(box_sizing_adjustment);
273 let max_size = style
274 .max_size()
275 .maybe_resolve(parent_size, |val, basis| tree.calc(val, basis))
276 .maybe_apply_aspect_ratio(aspect_ratio)
277 .maybe_add(box_sizing_adjustment);
278 let clamped_style_size = if inputs.sizing_mode == SizingMode::InherentSize {
279 style
280 .size()
281 .maybe_resolve(parent_size, |val, basis| tree.calc(val, basis))
282 .maybe_apply_aspect_ratio(aspect_ratio)
283 .maybe_add(box_sizing_adjustment)
284 .maybe_clamp(min_size, max_size)
285 } else {
286 Size::NONE
287 };
288
289 drop(style);
290
291 // If both min and max in a given axis are set and max <= min then this determines the size in that axis
292 let min_max_definite_size = min_size.zip_map(max_size, |min, max| match (min, max) {
293 (Some(min), Some(max)) if max <= min => Some(min),
294 _ => None,
295 });
296
297 let styled_based_known_dimensions =
298 known_dimensions.or(min_max_definite_size).or(clamped_style_size).maybe_max(padding_border_size);
299
300 // Short-circuit layout if the container's size is fully determined by the container's size and the run mode
301 // is ComputeSize (and thus the container's size is all that we're interested in)
302 if run_mode == RunMode::ComputeSize {
303 if let Size { width: Some(width), height: Some(height) } = styled_based_known_dimensions {
304 return LayoutOutput::from_outer_size(Size { width, height });
305 }
306
307 // We can also short-circuit if the width is known and only the width has been requested.
308 if inputs.axis == RequestedAxis::Horizontal {
309 if let Some(width) = styled_based_known_dimensions.width {
310 return LayoutOutput::from_outer_size(Size { width, height: 0.0 });
311 }
312 }
313 }
314
315 // Unwrap the block formatting context if one was passed, or else create a new one
316 debug_log!("BLOCK");
317 match block_ctx {
318 Some(inherited_bfc) if !is_scroll_container => compute_inner(
319 tree,
320 node_id,
321 LayoutInput { known_dimensions: styled_based_known_dimensions, ..inputs },
322 inherited_bfc,
323 ),
324 _ => {
325 let mut root_bfc = BlockFormattingContext::new();
326 let mut root_ctx = root_bfc.root_block_context();
327 compute_inner(
328 tree,
329 node_id,
330 LayoutInput { known_dimensions: styled_based_known_dimensions, ..inputs },
331 &mut root_ctx,
332 )
333 }
334 }
335}
336
337/// Computes the layout of [`LayoutBlockContainer`] according to the block layout algorithm
338fn compute_inner(
339 tree: &mut impl LayoutBlockContainer,
340 node_id: NodeId,
341 inputs: LayoutInput,
342 #[allow(unused_mut)] mut block_ctx: &mut BlockContext<'_>,
343) -> LayoutOutput {
344 let LayoutInput {
345 known_dimensions, parent_size, available_space, run_mode, vertical_margins_are_collapsible, ..
346 } = inputs;
347
348 let style = tree.get_block_container_style(node_id);
349 let raw_padding = style.padding();
350 let raw_border = style.border();
351 let raw_margin = style.margin();
352 let aspect_ratio = style.aspect_ratio();
353 let padding = raw_padding.resolve_or_zero(parent_size.width, |val, basis| tree.calc(val, basis));
354 let border = raw_border.resolve_or_zero(parent_size.width, |val, basis| tree.calc(val, basis));
355 let direction = style.direction();
356
357 // Scrollbar gutters are reserved when the `overflow` property is set to `Overflow::Scroll`.
358 // However, the axis are switched (transposed) because a node that scrolls vertically needs
359 // *horizontal* space to be reserved for a scrollbar
360 let scrollbar_gutter = {
361 let offsets = style.overflow().transpose().map(|overflow| match overflow {
362 Overflow::Scroll => style.scrollbar_width(),
363 _ => 0.0,
364 });
365 match direction {
366 Direction::Ltr => Rect { top: 0.0, left: 0.0, right: offsets.x, bottom: offsets.y },
367 Direction::Rtl => Rect { top: 0.0, left: offsets.x, right: 0.0, bottom: offsets.y },
368 }
369 };
370 let padding_border = padding + border;
371 let padding_border_size = padding_border.sum_axes();
372 let content_box_inset = padding_border + scrollbar_gutter;
373
374 // Apply content box inset
375 #[cfg(feature = "float_layout")]
376 block_ctx.apply_content_box_inset([content_box_inset.left, content_box_inset.right]);
377
378 let box_sizing_adjustment =
379 if style.box_sizing() == BoxSizing::ContentBox { padding_border_size } else { Size::ZERO };
380 let size = style
381 .size()
382 .maybe_resolve(parent_size, |val, basis| tree.calc(val, basis))
383 .maybe_apply_aspect_ratio(aspect_ratio)
384 .maybe_add(box_sizing_adjustment);
385 let min_size = style
386 .min_size()
387 .maybe_resolve(parent_size, |val, basis| tree.calc(val, basis))
388 .maybe_apply_aspect_ratio(aspect_ratio)
389 .maybe_add(box_sizing_adjustment);
390 let max_size = style
391 .max_size()
392 .maybe_resolve(parent_size, |val, basis| tree.calc(val, basis))
393 .maybe_apply_aspect_ratio(aspect_ratio)
394 .maybe_add(box_sizing_adjustment);
395
396 // css-sizing-4: a definite size in one axis transfers through `aspect-ratio`
397 // to make the other definite. Deriving it from `known_dimensions` self-gates
398 // the transfer — a block parent fills an axis only when it's a real
399 // constraint (e.g. the stretched width at final layout) and leaves it None
400 // while probing intrinsic sizes, so measure passes stay content-based. Only a
401 // newly-filled axis is adopted (and clamped); an incoming known size is left
402 // as the parent resolved it (re-clamping would undo padding/border overrides).
403 let known_dimensions = {
404 let derived = known_dimensions.maybe_apply_aspect_ratio(aspect_ratio).maybe_clamp(min_size, max_size);
405 Size { width: known_dimensions.width.or(derived.width), height: known_dimensions.height.or(derived.height) }
406 };
407 let container_content_box_size = known_dimensions.maybe_sub(content_box_inset.sum_axes());
408
409 let overflow = style.overflow();
410 let is_scroll_container = overflow.x.is_scroll_container() || overflow.y.is_scroll_container();
411
412 // Determine margin collapsing behaviour
413 let own_margins_collapse_with_children = Line {
414 start: vertical_margins_are_collapsible.start
415 && !is_scroll_container
416 && style.position() == Position::Relative
417 && padding.top == 0.0
418 && border.top == 0.0,
419 end: vertical_margins_are_collapsible.end
420 && !is_scroll_container
421 && style.position() == Position::Relative
422 && padding.bottom == 0.0
423 && border.bottom == 0.0
424 && size.height.is_none(),
425 };
426 let has_styles_preventing_being_collapsed_through = !style.is_block()
427 || block_ctx.is_bfc_root()
428 || is_scroll_container
429 || style.position() == Position::Absolute
430 || padding.top > 0.0
431 || padding.bottom > 0.0
432 || border.top > 0.0
433 || border.bottom > 0.0
434 || matches!(size.height, Some(h) if h > 0.0)
435 || matches!(min_size.height, Some(h) if h > 0.0);
436
437 let text_align = style.text_align();
438 let align_content = style.align_content();
439 drop(style);
440
441 // 1. Generate items
442 let mut items = generate_item_list(tree, node_id, container_content_box_size);
443
444 // 2. Compute container width
445 let container_outer_width = known_dimensions.width.unwrap_or_else(|| {
446 let available_width = available_space.width.maybe_sub(content_box_inset.horizontal_axis_sum());
447 let intrinsic_width = determine_content_based_container_width(tree, &items, available_width)
448 + content_box_inset.horizontal_axis_sum();
449 intrinsic_width.maybe_clamp(min_size.width, max_size.width).maybe_max(Some(padding_border_size.width))
450 });
451
452 // Short-circuit if computing size and both dimensions known
453 if let (RunMode::ComputeSize, Some(container_outer_height)) = (run_mode, known_dimensions.height) {
454 return LayoutOutput::from_outer_size(Size { width: container_outer_width, height: container_outer_height });
455 }
456
457 // We can also short-circuit if the width is known and only the width has been requested.
458 if run_mode == RunMode::ComputeSize && inputs.axis == RequestedAxis::Horizontal {
459 return LayoutOutput::from_outer_size(Size { width: container_outer_width, height: 0.0 });
460 }
461
462 let container_percentage_resolution_height =
463 known_dimensions.height.or(size.height.maybe_max(min_size.height)).or(min_size.height);
464
465 // 3. Perform final item layout and return content height
466 let resolved_padding = raw_padding.resolve_or_zero(Some(container_outer_width), |val, basis| tree.calc(val, basis));
467 let resolved_border = raw_border.resolve_or_zero(Some(container_outer_width), |val, basis| tree.calc(val, basis));
468 let resolved_content_box_inset = resolved_padding + resolved_border + scrollbar_gutter;
469 #[cfg_attr(not(feature = "content_size"), allow(unused_mut))]
470 let (mut inflow_content_size, mut intrinsic_outer_height, first_child_top_margin_set, last_child_bottom_margin_set) =
471 perform_final_layout_on_in_flow_children(
472 tree,
473 &mut items,
474 container_outer_width,
475 container_percentage_resolution_height,
476 content_box_inset,
477 resolved_content_box_inset,
478 text_align,
479 direction,
480 own_margins_collapse_with_children,
481 block_ctx,
482 );
483
484 // Root BFCs contain floats
485 #[cfg(feature = "float_layout")]
486 if block_ctx.is_bfc_root() || is_scroll_container {
487 intrinsic_outer_height = intrinsic_outer_height.max(block_ctx.floated_content_height_contribution());
488 }
489
490 let container_outer_height = known_dimensions
491 .height
492 .unwrap_or(intrinsic_outer_height.maybe_clamp(min_size.height, max_size.height))
493 .maybe_max(Some(padding_border_size.height));
494 let final_outer_size = Size { width: container_outer_width, height: container_outer_height };
495
496 // Apply `align-content` to in-flow non-floated items if requested. The per-item layouts were
497 // held back in `item.final_layout` so that this step can shift `location.y` before tree commit.
498 //
499 // For block layout the entire stack of in-flow children is treated as a single alignment
500 // subject. That means distribution keywords (`space-between`, `space-around`,
501 // `space-evenly`, `stretch`) must invoke the single-subject fallback unconditionally —
502 // which is what passing `num_items = 1` to `apply_alignment_fallback` does. The whole
503 // group then shifts by one offset, with zero inter-item gap.
504 if let Some(align_content) = align_content {
505 let container_inner_height = container_outer_height - resolved_content_box_inset.vertical_axis_sum();
506 let inflow_content_height = intrinsic_outer_height - resolved_content_box_inset.vertical_axis_sum();
507 let free_space = container_inner_height - inflow_content_height;
508 let any_in_flow = items.iter().any(|item| item.final_layout.is_some());
509 if any_in_flow {
510 let keyword = apply_alignment_fallback(free_space, 1, align_content);
511 let group_offset = compute_alignment_offset(free_space, 1, 0.0, keyword, false, true);
512 for item in items.iter_mut() {
513 if let Some(layout) = item.final_layout.as_mut() {
514 layout.location.y += group_offset;
515 }
516 }
517
518 #[cfg(feature = "content_size")]
519 {
520 inflow_content_size = Size::ZERO;
521 for item in items.iter() {
522 if let Some(layout) = item.final_layout.as_ref() {
523 inflow_content_size = inflow_content_size.f32_max(compute_content_size_contribution(
524 layout.location
525 + Point { x: -resolved_content_box_inset.left, y: -resolved_content_box_inset.top },
526 layout.size,
527 layout.content_size,
528 item.overflow,
529 ));
530 }
531 }
532 }
533 }
534 }
535
536 // Short-circuit if computing size
537 if run_mode == RunMode::ComputeSize {
538 return LayoutOutput::from_outer_size(final_outer_size);
539 }
540
541 // Commit deferred in-flow layouts to the tree. Floated items already wrote their own layouts.
542 for item in items.iter() {
543 if let Some(layout) = item.final_layout.as_ref() {
544 tree.set_unrounded_layout(item.node_id, layout);
545 }
546 }
547
548 // 4. Layout absolutely positioned children
549 let absolute_position_inset = resolved_border + scrollbar_gutter;
550 let absolute_position_area = final_outer_size - absolute_position_inset.sum_axes();
551 let absolute_position_offset = Point { x: absolute_position_inset.left, y: absolute_position_inset.top };
552 let absolute_content_size = perform_absolute_layout_on_absolute_children(
553 tree,
554 &items,
555 absolute_position_area,
556 absolute_position_offset,
557 direction,
558 );
559
560 // 5. Perform hidden layout on hidden children
561 let len = tree.child_count(node_id);
562 for order in 0..len {
563 let child = tree.get_child_id(node_id, order);
564 let child_style = tree.get_block_child_style(child);
565 if child_style.box_generation_mode() == BoxGenerationMode::None {
566 drop(child_style);
567 tree.set_unrounded_layout(child, &Layout::with_order(order as u32));
568 tree.perform_child_layout(
569 child,
570 Size::NONE,
571 Size::NONE,
572 Size::MAX_CONTENT,
573 SizingMode::InherentSize,
574 Line::FALSE,
575 );
576 }
577 }
578
579 // 7. Determine whether this node can be collapsed through
580 let all_in_flow_children_can_be_collapsed_through =
581 items.iter().all(|item| item.position == Position::Absolute || item.can_be_collapsed_through);
582 let can_be_collapsed_through =
583 !has_styles_preventing_being_collapsed_through && all_in_flow_children_can_be_collapsed_through;
584
585 #[cfg_attr(not(feature = "content_size"), allow(unused_variables))]
586 let content_size = inflow_content_size.f32_max(absolute_content_size);
587
588 LayoutOutput {
589 size: final_outer_size,
590 #[cfg(feature = "content_size")]
591 content_size,
592 first_baselines: Point::NONE,
593 top_margin: if own_margins_collapse_with_children.start {
594 first_child_top_margin_set
595 } else {
596 let margin_top = raw_margin.top.resolve_or_zero(parent_size.width, |val, basis| tree.calc(val, basis));
597 CollapsibleMarginSet::from_margin(margin_top)
598 },
599 bottom_margin: if own_margins_collapse_with_children.end {
600 last_child_bottom_margin_set
601 } else {
602 let margin_bottom =
603 raw_margin.bottom.resolve_or_zero(parent_size.width, |val, basis| tree.calc(val, basis));
604 CollapsibleMarginSet::from_margin(margin_bottom)
605 },
606 margins_can_collapse_through: can_be_collapsed_through,
607 }
608}
609
610/// Create a `Vec` of `BlockItem` structs where each item in the `Vec` represents a child of the current node
611#[inline]
612fn generate_item_list(
613 tree: &impl LayoutBlockContainer,
614 node: NodeId,
615 node_inner_size: Size<Option<f32>>,
616) -> Vec<BlockItem> {
617 tree.child_ids(node)
618 .map(|child_node_id| (child_node_id, tree.get_block_child_style(child_node_id)))
619 .filter(|(_, style)| style.box_generation_mode() != BoxGenerationMode::None)
620 .enumerate()
621 .map(|(order, (child_node_id, child_style))| {
622 let aspect_ratio = child_style.aspect_ratio();
623 let padding = child_style.padding().resolve_or_zero(node_inner_size, |val, basis| tree.calc(val, basis));
624 let border = child_style.border().resolve_or_zero(node_inner_size, |val, basis| tree.calc(val, basis));
625 let pb_sum = (padding + border).sum_axes();
626 let box_sizing_adjustment =
627 if child_style.box_sizing() == BoxSizing::ContentBox { pb_sum } else { Size::ZERO };
628
629 let position = child_style.position();
630 let overflow = child_style.overflow();
631
632 #[cfg(feature = "float_layout")]
633 let float = child_style.float();
634 #[cfg(feature = "float_layout")]
635 let is_not_floated = float == Float::None;
636
637 #[cfg(not(feature = "float_layout"))]
638 let is_not_floated = true;
639
640 let is_block = child_style.is_block();
641 let is_table = child_style.is_table();
642 let is_scroll_container = overflow.x.is_scroll_container() || overflow.y.is_scroll_container();
643
644 let is_in_same_bfc: bool =
645 is_block && !is_table && position != Position::Absolute && is_not_floated && !is_scroll_container;
646
647 BlockItem {
648 node_id: child_node_id,
649 order: order as u32,
650 is_table,
651 is_in_same_bfc,
652 #[cfg(feature = "float_layout")]
653 float,
654 #[cfg(feature = "float_layout")]
655 clear: child_style.clear(),
656 size: child_style
657 .size()
658 .maybe_resolve(node_inner_size, |val, basis| tree.calc(val, basis))
659 .maybe_apply_aspect_ratio(aspect_ratio)
660 .maybe_add(box_sizing_adjustment),
661 min_size: child_style
662 .min_size()
663 .maybe_resolve(node_inner_size, |val, basis| tree.calc(val, basis))
664 .maybe_apply_aspect_ratio(aspect_ratio)
665 .maybe_add(box_sizing_adjustment),
666 max_size: child_style
667 .max_size()
668 .maybe_resolve(node_inner_size, |val, basis| tree.calc(val, basis))
669 .maybe_apply_aspect_ratio(aspect_ratio)
670 .maybe_add(box_sizing_adjustment),
671 overflow,
672 scrollbar_width: child_style.scrollbar_width(),
673 position,
674 inset: child_style.inset(),
675 margin: child_style.margin(),
676 padding,
677 border,
678 padding_border_sum: pb_sum,
679
680 // Fields to be computed later (for now we initialise with dummy values)
681 computed_size: Size::zero(),
682 static_position: Point::zero(),
683 can_be_collapsed_through: false,
684 final_layout: None,
685 }
686 })
687 .collect()
688}
689
690/// Compute the content-based width in the case that the width of the container is not known
691#[inline]
692fn determine_content_based_container_width(
693 tree: &mut impl LayoutPartialTree,
694 items: &[BlockItem],
695 available_width: AvailableSpace,
696) -> f32 {
697 let available_space = Size { width: available_width, height: AvailableSpace::MinContent };
698
699 let mut max_child_width = 0.0;
700 #[cfg(feature = "float_layout")]
701 let mut float_contribution = FloatIntrinsicWidthCalculator::new(available_width);
702 for item in items.iter().filter(|item| item.position != Position::Absolute) {
703 let known_dimensions = item.size.maybe_clamp(item.min_size, item.max_size);
704
705 let item_x_margin_sum = item
706 .margin
707 .resolve_or_zero(available_space.width.into_option(), |val, basis| tree.calc(val, basis))
708 .horizontal_axis_sum();
709 let width = known_dimensions.width.unwrap_or_else(|| {
710 tree.measure_child_size(
711 item.node_id,
712 known_dimensions,
713 Size::NONE,
714 available_space.map_width(|w| w.maybe_sub(item_x_margin_sum)),
715 SizingMode::InherentSize,
716 crate::AbsoluteAxis::Horizontal,
717 Line::TRUE,
718 )
719 });
720
721 let width = f32_max(width, item.padding_border_sum.width) + item_x_margin_sum;
722
723 #[cfg(feature = "float_layout")]
724 if let Some(direction) = item.float.float_direction() {
725 float_contribution.add_float(width, direction, item.clear);
726 continue;
727 }
728
729 max_child_width = f32_max(max_child_width, width);
730 }
731
732 #[cfg(feature = "float_layout")]
733 {
734 max_child_width = max_child_width.max(float_contribution.result());
735 }
736
737 max_child_width
738}
739
740/// Compute each child's final size and position
741#[inline]
742#[allow(clippy::too_many_arguments)]
743fn perform_final_layout_on_in_flow_children(
744 tree: &mut impl LayoutBlockContainer,
745 items: &mut [BlockItem],
746 container_outer_width: f32,
747 container_percentage_resolution_height: Option<f32>,
748 content_box_inset: Rect<f32>,
749 resolved_content_box_inset: Rect<f32>,
750 text_align: TextAlign,
751 direction: Direction,
752 own_margins_collapse_with_children: Line<bool>,
753 block_ctx: &mut BlockContext<'_>,
754) -> (Size<f32>, f32, CollapsibleMarginSet, CollapsibleMarginSet) {
755 // Resolve container_inner_width for sizing child nodes using initial content_box_inset
756 let container_inner_width = container_outer_width - resolved_content_box_inset.horizontal_axis_sum();
757 let container_percentage_resolution_height =
758 container_percentage_resolution_height.maybe_sub(resolved_content_box_inset.vertical_axis_sum());
759 let parent_size = Size { width: Some(container_inner_width), height: container_percentage_resolution_height };
760 // Vertical available space in block flow is indefinite, NOT a min-content
761 // constraint: MaxContent is taffy's representation of "indefinite".
762 // Passing MinContent here made every descendant grid believe it was being
763 // sized under a min-content constraint, in which the maximize-tracks step
764 // has zero free space — so auto rows containing only scroll-container
765 // items (overflow != visible, automatic minimum size = 0) collapsed to
766 // zero height. Browsers size such rows to the item's content.
767 let available_space =
768 Size { width: AvailableSpace::Definite(container_inner_width), height: AvailableSpace::MaxContent };
769
770 // TODO: handle nested blocks with different widths
771 #[cfg(feature = "float_layout")]
772 if block_ctx.is_bfc_root() {
773 block_ctx.set_width(container_outer_width);
774 block_ctx.apply_content_box_inset([resolved_content_box_inset.left, resolved_content_box_inset.right]);
775 }
776
777 #[cfg_attr(not(feature = "content_size"), allow(unused_mut))]
778 let mut inflow_content_size = Size::ZERO;
779 let mut committed_y_offset = resolved_content_box_inset.top;
780 let mut y_offset_for_absolute = resolved_content_box_inset.top;
781 let mut first_child_top_margin_set = CollapsibleMarginSet::ZERO;
782 let mut active_collapsible_margin_set = CollapsibleMarginSet::ZERO;
783 let mut is_collapsing_with_first_margin_set = true;
784
785 #[cfg(feature = "float_layout")]
786 let mut has_active_floats = block_ctx.has_active_floats(committed_y_offset);
787 #[cfg(not(feature = "float_layout"))]
788 let has_active_floats = false;
789 #[cfg(feature = "float_layout")]
790 let mut y_offset_for_float = resolved_content_box_inset.top;
791
792 for item in items.iter_mut() {
793 if item.position == Position::Absolute {
794 let x = match direction {
795 Direction::Ltr => resolved_content_box_inset.left,
796 Direction::Rtl => container_outer_width - resolved_content_box_inset.right,
797 };
798 item.static_position = Point { x, y: y_offset_for_absolute }
799 } else {
800 let item_margin = item
801 .margin
802 .map(|margin| margin.resolve_to_option(container_outer_width, |val, basis| tree.calc(val, basis)));
803 let item_non_auto_margin = item_margin.map(|m| m.unwrap_or(0.0));
804 let item_non_auto_x_margin_sum = item_non_auto_margin.horizontal_axis_sum();
805
806 let scrollbar_size = Size {
807 width: if item.overflow.y == Overflow::Scroll { item.scrollbar_width } else { 0.0 },
808 height: if item.overflow.x == Overflow::Scroll { item.scrollbar_width } else { 0.0 },
809 };
810
811 // Handle floated boxes
812 #[cfg(feature = "float_layout")]
813 if let Some(float_direction) = item.float.float_direction() {
814 has_active_floats = true;
815
816 let item_layout = tree.perform_child_layout(
817 item.node_id,
818 Size::NONE,
819 parent_size,
820 // available_space,
821 Size::MAX_CONTENT,
822 SizingMode::InherentSize,
823 Line::TRUE,
824 );
825 let margin_box = item_layout.size + item_non_auto_margin.sum_axes();
826
827 let mut location =
828 block_ctx.place_floated_box(margin_box, y_offset_for_float, float_direction, item.clear);
829
830 // Ensure that content that appears after a float does not get positioned before/above the float
831 //
832 // FIXME: this isn't quite right, because a second float at the same location
833 // shouldn't cause content to push down to it's level
834 // committed_y_offset = committed_y_offset.max(location.y);
835 // y_offset_for_absolute = y_offset_for_absolute.max(location.y);
836 // y_offset_for_float = y_offset_for_float.max(location.y);
837
838 // Convert the margin-box location returned by float placement into a border-box location
839 // for the output Layout
840 location.y += item_non_auto_margin.top;
841 location.x += item_non_auto_margin.left;
842
843 // println!("BLOCK FLOATED BOX ({:?}) {:?}", item.node_id, float_direction);
844 // println!("w:{} h:{} x:{}, y:{}", margin_box.width, margin_box.height, location.x, location.y);
845
846 tree.set_unrounded_layout(
847 item.node_id,
848 &Layout {
849 order: item.order,
850 size: item_layout.size,
851 #[cfg(feature = "content_size")]
852 content_size: item_layout.content_size,
853 scrollbar_size,
854 location,
855 padding: item.padding,
856 border: item.border,
857 margin: item_non_auto_margin,
858 },
859 );
860
861 #[cfg(feature = "content_size")]
862 {
863 // TODO: Should content size of floated boxes count as "inflow_content_size"
864 // or should it be counted separately?
865 inflow_content_size = inflow_content_size.f32_max(compute_content_size_contribution(
866 location,
867 item_layout.size,
868 item_layout.content_size,
869 item.overflow,
870 ));
871 }
872
873 continue;
874 }
875
876 // Handle non-floated boxes
877
878 let mut y_margin_offset: f32 = 0.0;
879
880 let (stretch_width, float_avoiding_position, float_avoiding_width) = if item.is_in_same_bfc {
881 let stretch_width = container_inner_width - item_non_auto_x_margin_sum;
882 let position = Point { x: 0.0, y: 0.0 };
883 let width = 0.0;
884
885 (stretch_width, position, width)
886 } else {
887 'block: {
888 // Set y_margin_offset (different bfc child)
889 if !is_collapsing_with_first_margin_set || !own_margins_collapse_with_children.start {
890 y_margin_offset =
891 active_collapsible_margin_set.collapse_with_margin(item_non_auto_margin.top).resolve();
892 };
893 let min_y = committed_y_offset + y_margin_offset;
894
895 #[cfg(feature = "float_layout")]
896 if has_active_floats {
897 let slot = block_ctx.find_content_slot(min_y, item.clear, None);
898 has_active_floats = slot.segment_id.is_some();
899 let stretch_width = slot.width - item_non_auto_x_margin_sum;
900 break 'block (stretch_width, Point { x: slot.x, y: slot.y }, slot.width);
901 }
902
903 if !has_active_floats {
904 let stretch_width = container_inner_width - item_non_auto_x_margin_sum;
905 break 'block (
906 stretch_width,
907 Point { x: resolved_content_box_inset.left, y: min_y },
908 container_inner_width,
909 );
910 }
911
912 unreachable!("One of the above cases will always be hit");
913 }
914 };
915
916 let known_dimensions = if item.is_table {
917 Size::NONE
918 } else {
919 item.size
920 .map_width(|width| {
921 // TODO: Allow stretch-sizing to be conditional, as there are exceptions.
922 // e.g. Table children of blocks do not stretch fit
923 Some(width.unwrap_or(stretch_width).maybe_clamp(item.min_size.width, item.max_size.width))
924 })
925 .maybe_clamp(item.min_size, item.max_size)
926 };
927
928 //
929
930 let inputs = LayoutInput {
931 run_mode: RunMode::PerformLayout,
932 sizing_mode: SizingMode::InherentSize,
933 axis: RequestedAxis::Both,
934 known_dimensions,
935 parent_size,
936 available_space: available_space.map_width(|_| AvailableSpace::Definite(stretch_width)),
937 vertical_margins_are_collapsible: if item.is_in_same_bfc { Line::TRUE } else { Line::FALSE },
938 };
939
940 #[cfg(feature = "float_layout")]
941 let clear_pos = block_ctx.cleared_threshold(item.clear).unwrap_or(0.0);
942 #[cfg(not(feature = "float_layout"))]
943 let clear_pos = 0.0;
944
945 let item_layout = if item.is_in_same_bfc {
946 let width = known_dimensions
947 .width
948 .expect("Same-bfc child will always have defined width due to stretch sizing");
949
950 // TODO: account for auto margins
951 let inset_left = item_non_auto_margin.left + content_box_inset.left;
952 let inset_right = container_outer_width - width - inset_left;
953 let insets = [inset_left, inset_right];
954
955 // Compute child layout
956 let mut child_block_ctx =
957 block_ctx.sub_context((y_offset_for_absolute + item_non_auto_margin.top).max(clear_pos), insets);
958 let output = tree.compute_block_child_layout(item.node_id, inputs, Some(&mut child_block_ctx));
959
960 // Extract float contribution from child block context
961 #[cfg(feature = "float_layout")]
962 {
963 let child_contribution = child_block_ctx.floated_content_height_contribution();
964 block_ctx.add_child_floated_content_height_contribution(y_offset_for_absolute + child_contribution);
965 }
966
967 output
968 } else {
969 tree.compute_child_layout(item.node_id, inputs)
970 };
971 let final_size = item_layout.size;
972
973 let top_margin_set = item_layout.top_margin.collapse_with_margin(item_margin.top.unwrap_or(0.0));
974 let bottom_margin_set = item_layout.bottom_margin.collapse_with_margin(item_margin.bottom.unwrap_or(0.0));
975
976 // Expand auto margins to fill available space
977 // Note: Vertical auto-margins for relatively positioned block items simply resolve to 0.
978 // See: https://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width
979 let free_x_space = f32_max(0.0, stretch_width - final_size.width);
980 let x_axis_auto_margin_size = {
981 let auto_margin_count = item_margin.left.is_none() as u8 + item_margin.right.is_none() as u8;
982 if auto_margin_count > 0 {
983 free_x_space / auto_margin_count as f32
984 } else {
985 0.0
986 }
987 };
988 let resolved_margin = Rect {
989 left: item_margin.left.unwrap_or(x_axis_auto_margin_size),
990 right: item_margin.right.unwrap_or(x_axis_auto_margin_size),
991 top: top_margin_set.resolve(),
992 bottom: bottom_margin_set.resolve(),
993 };
994
995 // Resolve item inset
996 let inset = item.inset.zip_size(Size { width: container_inner_width, height: 0.0 }, |p, s| {
997 p.maybe_resolve(s, |val, basis| tree.calc(val, basis))
998 });
999 let inset_offset = Point {
1000 x: if direction.is_rtl() {
1001 inset.right.map(|x| -x).or(inset.left).unwrap_or(0.0)
1002 } else {
1003 inset.left.or(inset.right.map(|x| -x)).unwrap_or(0.0)
1004 },
1005 y: inset.top.or(inset.bottom.map(|x| -x)).unwrap_or(0.0),
1006 };
1007
1008 // Set y_margin_offset (same bfc child)
1009 if item.is_in_same_bfc
1010 && (!is_collapsing_with_first_margin_set || !own_margins_collapse_with_children.start)
1011 {
1012 y_margin_offset = active_collapsible_margin_set.collapse_with_margin(resolved_margin.top).resolve()
1013 };
1014
1015 #[cfg(feature = "float_layout")]
1016 let float_or_not_clear = item.float.is_floated() || item.clear == Clear::None;
1017 #[cfg(not(feature = "float_layout"))]
1018 let float_or_not_clear = true;
1019
1020 item.computed_size = item_layout.size;
1021 item.can_be_collapsed_through = item_layout.margins_can_collapse_through && float_or_not_clear;
1022 item.static_position = if item.is_in_same_bfc {
1023 let uncleared_y = committed_y_offset + active_collapsible_margin_set.resolve();
1024 Point {
1025 x: match direction {
1026 Direction::Ltr => resolved_content_box_inset.left,
1027 Direction::Rtl => container_outer_width - resolved_content_box_inset.right - final_size.width,
1028 },
1029 y: uncleared_y.max(clear_pos),
1030 }
1031 } else {
1032 // TODO: handle inset and margins
1033 Point {
1034 x: match direction {
1035 Direction::Ltr => float_avoiding_position.x,
1036 Direction::Rtl => float_avoiding_position.x + float_avoiding_width - final_size.width,
1037 },
1038 y: float_avoiding_position.y,
1039 }
1040 };
1041 let mut location = if item.is_in_same_bfc {
1042 Point {
1043 x: match direction {
1044 Direction::Ltr => resolved_content_box_inset.left + inset_offset.x + resolved_margin.left,
1045 Direction::Rtl => {
1046 container_outer_width
1047 - resolved_content_box_inset.right
1048 - final_size.width
1049 - resolved_margin.right
1050 + inset_offset.x
1051 }
1052 },
1053 y: committed_y_offset.max(clear_pos) + y_margin_offset + inset_offset.y,
1054 }
1055 } else {
1056 // TODO: handle inset and margins
1057 Point {
1058 x: match direction {
1059 Direction::Ltr => float_avoiding_position.x + resolved_margin.left + inset_offset.x,
1060 Direction::Rtl => {
1061 float_avoiding_position.x + float_avoiding_width - final_size.width - resolved_margin.right
1062 + inset_offset.x
1063 }
1064 },
1065 y: float_avoiding_position.y + inset_offset.y,
1066 }
1067 };
1068
1069 // Apply alignment
1070 let item_outer_width = item_layout.size.width + resolved_margin.horizontal_axis_sum();
1071 if item_outer_width < container_inner_width {
1072 let free_x_space = container_inner_width - item_outer_width;
1073 match (text_align, direction) {
1074 (TextAlign::Auto, _) => {
1075 // Do nothing
1076 }
1077 (TextAlign::LegacyLeft, Direction::Ltr) => {
1078 // Do nothing. Left aligned by default.
1079 }
1080 (TextAlign::LegacyLeft, Direction::Rtl) => location.x -= free_x_space,
1081 (TextAlign::LegacyRight, Direction::Ltr) => location.x += free_x_space,
1082 (TextAlign::LegacyRight, Direction::Rtl) => {
1083 // Do nothing. Right aligned by default.
1084 }
1085 (TextAlign::LegacyCenter, Direction::Ltr) => location.x += free_x_space / 2.0,
1086 (TextAlign::LegacyCenter, Direction::Rtl) => location.x -= free_x_space / 2.0,
1087 }
1088 }
1089
1090 // Defer `set_unrounded_layout` to the post-loop pass in `compute_inner` so that
1091 // `align-content` can shift `location.y` before the layout is committed to the tree.
1092 item.final_layout = Some(Layout {
1093 order: item.order,
1094 size: item_layout.size,
1095 #[cfg(feature = "content_size")]
1096 content_size: item_layout.content_size,
1097 scrollbar_size,
1098 location,
1099 padding: item.padding,
1100 border: item.border,
1101 margin: resolved_margin,
1102 });
1103
1104 #[cfg(feature = "content_size")]
1105 {
1106 inflow_content_size = inflow_content_size.f32_max(compute_content_size_contribution(
1107 location + Point { x: -resolved_content_box_inset.left, y: -resolved_content_box_inset.top },
1108 final_size,
1109 item_layout.content_size,
1110 item.overflow,
1111 ));
1112 }
1113
1114 // Update first_child_top_margin_set
1115 if is_collapsing_with_first_margin_set {
1116 if item.can_be_collapsed_through {
1117 first_child_top_margin_set = first_child_top_margin_set
1118 .collapse_with_set(top_margin_set)
1119 .collapse_with_set(bottom_margin_set);
1120 } else {
1121 first_child_top_margin_set = first_child_top_margin_set.collapse_with_set(top_margin_set);
1122 is_collapsing_with_first_margin_set = false;
1123 }
1124 }
1125
1126 // Update active_collapsible_margin_set
1127 if item.can_be_collapsed_through {
1128 active_collapsible_margin_set = active_collapsible_margin_set
1129 .collapse_with_set(top_margin_set)
1130 .collapse_with_set(bottom_margin_set);
1131 y_offset_for_absolute = committed_y_offset + item_layout.size.height + y_margin_offset;
1132 #[cfg(feature = "float_layout")]
1133 {
1134 y_offset_for_float = committed_y_offset + item_layout.size.height + y_margin_offset;
1135 }
1136 } else {
1137 committed_y_offset = location.y - inset_offset.y + item_layout.size.height;
1138 active_collapsible_margin_set = bottom_margin_set;
1139 y_offset_for_absolute = committed_y_offset + active_collapsible_margin_set.resolve();
1140 #[cfg(feature = "float_layout")]
1141 {
1142 y_offset_for_float = committed_y_offset;
1143 }
1144 }
1145 }
1146 }
1147
1148 let last_child_bottom_margin_set = active_collapsible_margin_set;
1149 let bottom_y_margin_offset =
1150 if own_margins_collapse_with_children.end { 0.0 } else { last_child_bottom_margin_set.resolve() };
1151
1152 committed_y_offset += resolved_content_box_inset.bottom + bottom_y_margin_offset;
1153 let content_height = f32_max(0.0, committed_y_offset);
1154 (inflow_content_size, content_height, first_child_top_margin_set, last_child_bottom_margin_set)
1155}
1156
1157/// Perform absolute layout on all absolutely positioned children.
1158#[inline]
1159fn perform_absolute_layout_on_absolute_children(
1160 tree: &mut impl LayoutBlockContainer,
1161 items: &[BlockItem],
1162 area_size: Size<f32>,
1163 area_offset: Point<f32>,
1164 direction: Direction,
1165) -> Size<f32> {
1166 let area_width = area_size.width;
1167 let area_height = area_size.height;
1168
1169 #[cfg_attr(not(feature = "content_size"), allow(unused_mut))]
1170 let mut absolute_content_size = Size::ZERO;
1171
1172 for item in items.iter().filter(|item| item.position == Position::Absolute) {
1173 let child_style = tree.get_block_child_style(item.node_id);
1174
1175 // Skip items that are display:none or are not position:absolute
1176 if child_style.box_generation_mode() == BoxGenerationMode::None || child_style.position() != Position::Absolute
1177 {
1178 continue;
1179 }
1180
1181 let aspect_ratio = child_style.aspect_ratio();
1182 let margin =
1183 child_style.margin().map(|margin| margin.resolve_to_option(area_width, |val, basis| tree.calc(val, basis)));
1184 let padding = child_style.padding().resolve_or_zero(Some(area_width), |val, basis| tree.calc(val, basis));
1185 let border = child_style.border().resolve_or_zero(Some(area_width), |val, basis| tree.calc(val, basis));
1186 let padding_border_sum = (padding + border).sum_axes();
1187 let box_sizing_adjustment =
1188 if child_style.box_sizing() == BoxSizing::ContentBox { padding_border_sum } else { Size::ZERO };
1189
1190 // Resolve inset
1191 let left = child_style.inset().left.maybe_resolve(area_width, |val, basis| tree.calc(val, basis));
1192 let right = child_style.inset().right.maybe_resolve(area_width, |val, basis| tree.calc(val, basis));
1193 let top = child_style.inset().top.maybe_resolve(area_height, |val, basis| tree.calc(val, basis));
1194 let bottom = child_style.inset().bottom.maybe_resolve(area_height, |val, basis| tree.calc(val, basis));
1195
1196 // Compute known dimensions from min/max/inherent size styles
1197 let style_size = child_style
1198 .size()
1199 .maybe_resolve(area_size, |val, basis| tree.calc(val, basis))
1200 .maybe_apply_aspect_ratio(aspect_ratio)
1201 .maybe_add(box_sizing_adjustment);
1202 let min_size = child_style
1203 .min_size()
1204 .maybe_resolve(area_size, |val, basis| tree.calc(val, basis))
1205 .maybe_apply_aspect_ratio(aspect_ratio)
1206 .maybe_add(box_sizing_adjustment)
1207 .or(padding_border_sum.map(Some))
1208 .maybe_max(padding_border_sum);
1209 let max_size = child_style
1210 .max_size()
1211 .maybe_resolve(area_size, |val, basis| tree.calc(val, basis))
1212 .maybe_apply_aspect_ratio(aspect_ratio)
1213 .maybe_add(box_sizing_adjustment);
1214 let mut known_dimensions = style_size.maybe_clamp(min_size, max_size);
1215
1216 drop(child_style);
1217
1218 // Fill in width from left/right and reapply aspect ratio if:
1219 // - Width is not already known
1220 // - Item has both left and right inset properties set
1221 if let (None, Some(left), Some(right)) = (known_dimensions.width, left, right) {
1222 let new_width_raw = area_width.maybe_sub(margin.left).maybe_sub(margin.right) - left - right;
1223 known_dimensions.width = Some(f32_max(new_width_raw, 0.0));
1224 known_dimensions = known_dimensions.maybe_apply_aspect_ratio(aspect_ratio).maybe_clamp(min_size, max_size);
1225 }
1226
1227 // Fill in height from top/bottom and reapply aspect ratio if:
1228 // - Height is not already known
1229 // - Item has both top and bottom inset properties set
1230 if let (None, Some(top), Some(bottom)) = (known_dimensions.height, top, bottom) {
1231 let new_height_raw = area_height.maybe_sub(margin.top).maybe_sub(margin.bottom) - top - bottom;
1232 known_dimensions.height = Some(f32_max(new_height_raw, 0.0));
1233 known_dimensions = known_dimensions.maybe_apply_aspect_ratio(aspect_ratio).maybe_clamp(min_size, max_size);
1234 }
1235
1236 let measured_size = tree.measure_child_size_both(
1237 item.node_id,
1238 known_dimensions,
1239 area_size.map(Some),
1240 Size {
1241 width: AvailableSpace::Definite(area_width.maybe_clamp(min_size.width, max_size.width)),
1242 height: AvailableSpace::Definite(area_height.maybe_clamp(min_size.height, max_size.height)),
1243 },
1244 SizingMode::ContentSize,
1245 Line::FALSE,
1246 );
1247
1248 let final_size = known_dimensions.unwrap_or(measured_size).maybe_clamp(min_size, max_size);
1249
1250 let layout_output = tree.perform_child_layout(
1251 item.node_id,
1252 final_size.map(Some),
1253 area_size.map(Some),
1254 Size {
1255 width: AvailableSpace::Definite(area_width.maybe_clamp(min_size.width, max_size.width)),
1256 height: AvailableSpace::Definite(area_height.maybe_clamp(min_size.height, max_size.height)),
1257 },
1258 SizingMode::ContentSize,
1259 Line::FALSE,
1260 );
1261
1262 let non_auto_margin = Rect {
1263 left: if left.is_some() { margin.left.unwrap_or(0.0) } else { 0.0 },
1264 right: if right.is_some() { margin.right.unwrap_or(0.0) } else { 0.0 },
1265 top: if top.is_some() { margin.top.unwrap_or(0.0) } else { 0.0 },
1266 bottom: if bottom.is_some() { margin.bottom.unwrap_or(0.0) } else { 0.0 },
1267 };
1268
1269 // Expand auto margins to fill available space
1270 // https://www.w3.org/TR/CSS21/visudet.html#abs-non-replaced-width
1271 let auto_margin = {
1272 // Auto margins for absolutely positioned elements in block containers only resolve
1273 // if inset is set. Otherwise they resolve to 0.
1274 let absolute_auto_margin_space = Point {
1275 x: right.map(|right| area_size.width - right - left.unwrap_or(0.0)).unwrap_or(final_size.width),
1276 y: bottom.map(|bottom| area_size.height - bottom - top.unwrap_or(0.0)).unwrap_or(final_size.height),
1277 };
1278 let free_space = Size {
1279 width: absolute_auto_margin_space.x - final_size.width - non_auto_margin.horizontal_axis_sum(),
1280 height: absolute_auto_margin_space.y - final_size.height - non_auto_margin.vertical_axis_sum(),
1281 };
1282
1283 let auto_margin_size = Size {
1284 // If all three of 'left', 'width', and 'right' are 'auto': First set any 'auto' values for 'margin-left' and 'margin-right' to 0.
1285 // Then, if the 'direction' property of the element establishing the static-position containing block is 'ltr' set 'left' to the
1286 // static position and apply rule number three below; otherwise, set 'right' to the static position and apply rule number one below.
1287 //
1288 // If none of the three is 'auto': If both 'margin-left' and 'margin-right' are 'auto', solve the equation under the extra constraint
1289 // that the two margins get equal values, unless this would make them negative, in which case when direction of the containing block is
1290 // 'ltr' ('rtl'), set 'margin-left' ('margin-right') to zero and solve for 'margin-right' ('margin-left'). If one of 'margin-left' or
1291 // 'margin-right' is 'auto', solve the equation for that value. If the values are over-constrained, ignore the value for 'left' (in case
1292 // the 'direction' property of the containing block is 'rtl') or 'right' (in case 'direction' is 'ltr') and solve for that value.
1293 width: {
1294 let auto_margin_count = margin.left.is_none() as u8 + margin.right.is_none() as u8;
1295 if auto_margin_count == 2
1296 && (style_size.width.is_none() || style_size.width.unwrap() >= free_space.width)
1297 {
1298 0.0
1299 } else if auto_margin_count > 0 {
1300 free_space.width / auto_margin_count as f32
1301 } else {
1302 0.0
1303 }
1304 },
1305 height: {
1306 let auto_margin_count = margin.top.is_none() as u8 + margin.bottom.is_none() as u8;
1307 if auto_margin_count == 2
1308 && (style_size.height.is_none() || style_size.height.unwrap() >= free_space.height)
1309 {
1310 0.0
1311 } else if auto_margin_count > 0 {
1312 free_space.height / auto_margin_count as f32
1313 } else {
1314 0.0
1315 }
1316 },
1317 };
1318
1319 Rect {
1320 left: margin.left.map(|_| 0.0).unwrap_or(auto_margin_size.width),
1321 right: margin.right.map(|_| 0.0).unwrap_or(auto_margin_size.width),
1322 top: margin.top.map(|_| 0.0).unwrap_or(auto_margin_size.height),
1323 bottom: margin.bottom.map(|_| 0.0).unwrap_or(auto_margin_size.height),
1324 }
1325 };
1326
1327 let resolved_margin = Rect {
1328 left: margin.left.unwrap_or(auto_margin.left),
1329 right: margin.right.unwrap_or(auto_margin.right),
1330 top: margin.top.unwrap_or(auto_margin.top),
1331 bottom: margin.bottom.unwrap_or(auto_margin.bottom),
1332 };
1333
1334 let x_offset = match (left, right) {
1335 (Some(left), Some(right)) => {
1336 if direction.is_rtl() {
1337 area_size.width - final_size.width - right - resolved_margin.right
1338 } else {
1339 left + resolved_margin.left
1340 }
1341 }
1342 (Some(left), None) => left + resolved_margin.left,
1343 (None, Some(right)) => area_size.width - final_size.width - right - resolved_margin.right,
1344 (None, None) => {
1345 if direction.is_rtl() {
1346 item.static_position.x - final_size.width - resolved_margin.right - area_offset.x
1347 } else {
1348 item.static_position.x + resolved_margin.left - area_offset.x
1349 }
1350 }
1351 };
1352 let location = Point {
1353 x: x_offset + area_offset.x,
1354 y: top
1355 .map(|top| top + resolved_margin.top)
1356 .or(bottom.map(|bottom| area_size.height - final_size.height - bottom - resolved_margin.bottom))
1357 .maybe_add(area_offset.y)
1358 .unwrap_or(item.static_position.y + resolved_margin.top),
1359 };
1360 // Note: axis intentionally switched here as scrollbars take up space in the opposite axis
1361 // to the axis in which scrolling is enabled.
1362 let scrollbar_size = Size {
1363 width: if item.overflow.y == Overflow::Scroll { item.scrollbar_width } else { 0.0 },
1364 height: if item.overflow.x == Overflow::Scroll { item.scrollbar_width } else { 0.0 },
1365 };
1366
1367 tree.set_unrounded_layout(
1368 item.node_id,
1369 &Layout {
1370 order: item.order,
1371 size: final_size,
1372 #[cfg(feature = "content_size")]
1373 content_size: layout_output.content_size,
1374 scrollbar_size,
1375 location,
1376 padding,
1377 border,
1378 margin: resolved_margin,
1379 },
1380 );
1381
1382 #[cfg(feature = "content_size")]
1383 {
1384 let relative_location = Point { x: location.x - area_offset.x, y: location.y - area_offset.y };
1385 absolute_content_size = absolute_content_size.f32_max(compute_content_size_contribution(
1386 relative_location,
1387 final_size,
1388 layout_output.content_size,
1389 item.overflow,
1390 ));
1391 }
1392 }
1393
1394 absolute_content_size
1395}