layout/fragment_tree/
box_fragment.rs

1/* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
4
5use std::cell::LazyCell;
6use std::sync::Arc;
7use std::sync::atomic::{AtomicBool, Ordering};
8
9use app_units::{Au, MAX_AU, MIN_AU};
10use atomic_refcell::{AtomicRef, AtomicRefCell, AtomicRefMut};
11use euclid::Rect;
12use malloc_size_of_derive::MallocSizeOf;
13use once_cell::race::OnceBox;
14use servo_arc::Arc as ServoArc;
15use servo_base::id::{AtomicOptionScrollTreeNodeId, ScrollTreeNodeId};
16use servo_base::print_tree::PrintTree;
17use servo_geometry::f32_rect_to_au_rect;
18use style::Zero;
19use style::computed_values::border_collapse::T as BorderCollapse;
20use style::computed_values::overflow_x::T as ComputedOverflow;
21use style::computed_values::position::T as ComputedPosition;
22use style::logical_geometry::WritingMode;
23use style::properties::ComputedValues;
24
25use super::{BaseFragment, BaseFragmentInfo, CollapsedBlockMargins, Fragment, FragmentFlags};
26use crate::SharedStyle;
27use crate::display_list::{ClipId, ToWebRender};
28use crate::formatting_contexts::Baselines;
29use crate::fragment_tree::ContainingBlockCalculation;
30use crate::geom::{
31    AuOrAuto, LengthPercentageOrAuto, PhysicalPoint, PhysicalRect, PhysicalSides,
32    SyncPhysicalRectAu, ToLogical,
33};
34use crate::style_ext::ComputedValuesExt;
35use crate::table::SpecificTableGridInfo;
36use crate::taffy::SpecificTaffyGridInfo;
37
38/// Describes how a [`BoxFragment`] paints its background.
39#[derive(Clone, MallocSizeOf)]
40pub(crate) enum BackgroundMode {
41    /// Draw the normal [`BoxFragment`] background as well as the extra backgrounds
42    /// based on the style and positioning rectangles in this data structure.
43    Extra(Vec<ExtraBackground>),
44    /// Do not draw a background for this Fragment. This is used for elements like
45    /// table tracks and table track groups, which rely on cells to paint their
46    /// backgrounds.
47    None,
48    /// Draw the background normally, getting information from the Fragment style.
49    Normal,
50}
51
52#[derive(Clone, MallocSizeOf)]
53pub(crate) struct ExtraBackground {
54    pub style: SharedStyle,
55    pub rect: PhysicalRect<Au>,
56}
57
58#[derive(Clone, Debug, MallocSizeOf)]
59pub(crate) enum SpecificLayoutInfo {
60    Grid(Box<SpecificTaffyGridInfo>),
61    TableCellWithCollapsedBorders,
62    TableGridWithCollapsedBorders(Box<SpecificTableGridInfo>),
63    TableWrapper,
64}
65
66#[derive(Clone, MallocSizeOf)]
67pub(crate) struct BlockLevelLayoutInfo {
68    /// When the `clear` property is not set to `none`, it may introduce clearance.
69    /// Clearance is some extra spacing that is added above the top margin,
70    /// so that the element doesn't overlap earlier floats in the same BFC.
71    /// The presence of clearance prevents the top margin from collapsing with
72    /// earlier margins or with the bottom margin of the parent block.
73    /// <https://drafts.csswg.org/css2/#clearance>
74    pub clearance: Option<Au>,
75
76    pub block_margins_collapsed_with_children: CollapsedBlockMargins,
77}
78
79#[derive(Clone, Default, MallocSizeOf)]
80pub(crate) struct BoxFragmentRareData {
81    /// The resolved box insets if this box is `position: sticky`. These are calculated
82    /// during `StackingContextTree` construction because they rely on the size of the
83    /// scroll container.
84    pub(crate) resolved_sticky_insets: Option<Box<PhysicalSides<AuOrAuto>>>,
85
86    /// Information that is specific to a layout system (e.g., grid, table, etc.).
87    pub specific_layout_info: Option<SpecificLayoutInfo>,
88
89    /// If the associated [`BoxFragment`] establishes a clip via CSS this holds the
90    /// [`ClipId`] for the generated clip set during stacking context tree construction.
91    pub generated_clip_id: Option<ClipId>,
92
93    /// If the associated [`BoxFragment`] establishes a spatial node via CSS this holds the
94    /// [`ScrollTreeNodeId`] for the generated node set during stacking context tree construction.
95    pub generated_scroll_tree_node_id: Option<ScrollTreeNodeId>,
96}
97
98impl BoxFragmentRareData {
99    /// Create a new rare data based on information given to the fragment. Ideally, We should
100    /// avoid creating rare data as much as possible to reduce the memory cost.
101    fn new(specific_layout_info: Option<SpecificLayoutInfo>) -> OnceBox<AtomicRefCell<Self>> {
102        specific_layout_info
103            .map(|info| {
104                OnceBox::with_value(Box::new(AtomicRefCell::new(BoxFragmentRareData {
105                    resolved_sticky_insets: None,
106                    specific_layout_info: Some(info),
107                    generated_clip_id: None,
108                    generated_scroll_tree_node_id: None,
109                })))
110            })
111            .unwrap_or_default()
112    }
113}
114
115#[derive(MallocSizeOf)]
116pub(crate) struct BoxFragment {
117    pub base: BaseFragment,
118
119    pub children: Vec<Fragment>,
120
121    /// This [`BoxFragment`]'s containing block rectangle in coordinates relative to
122    /// the initial containing block, but not taking into account any transforms.
123    pub cumulative_containing_block_rect: SyncPhysicalRectAu,
124
125    pub padding: PhysicalSides<Au>,
126    pub border: PhysicalSides<Au>,
127    pub margin: PhysicalSides<Au>,
128
129    /// When this [`BoxFragment`] is for content that has a baseline, this tracks
130    /// the first and last baselines of that content. This is used to propagate baselines
131    /// to things such as tables and inline formatting contexts.
132    baselines: Baselines,
133
134    /// The scrollable overflow of this box fragment in the same coordiante system as
135    /// [`Self::content_rect`] ie a rectangle within the parent fragment's content
136    /// rectangle. This does not take into account any transforms this fragment applies.
137    /// This is handled when calling [`Self::scrollable_overflow_for_parent`].
138    scrollable_overflow: SyncPhysicalRectAu,
139    scrollable_overflow_is_up_to_date: AtomicBool,
140
141    pub background_mode: BackgroundMode,
142
143    /// Rare data that not all kinds of [`BoxFragment`] would have.
144    pub rare_data: OnceBox<AtomicRefCell<BoxFragmentRareData>>,
145
146    /// Additional information for block-level boxes.
147    pub block_level_layout_info: Option<Box<BlockLevelLayoutInfo>>,
148
149    /// The containing spatial tree node of this [`BoxFragment`]. This is assigned during
150    /// `StackingContextTree` construction, so isn't available before that time. This is
151    /// used to for determining final viewport size and position of this node and will
152    /// also be used in the future for hit testing.
153    pub spatial_tree_node: AtomicOptionScrollTreeNodeId,
154}
155
156impl BoxFragment {
157    #[expect(clippy::too_many_arguments)]
158    pub(crate) fn new(
159        base_fragment_info: BaseFragmentInfo,
160        style: ServoArc<ComputedValues>,
161        children: Vec<Fragment>,
162        content_rect: PhysicalRect<Au>,
163        padding: PhysicalSides<Au>,
164        border: PhysicalSides<Au>,
165        margin: PhysicalSides<Au>,
166        specific_layout_info: Option<SpecificLayoutInfo>,
167    ) -> Self {
168        let rare_data = BoxFragmentRareData::new(specific_layout_info);
169        Self {
170            base: BaseFragment::new(base_fragment_info, style.into(), content_rect),
171            children,
172            cumulative_containing_block_rect: Default::default(),
173            padding,
174            border,
175            margin,
176            baselines: Baselines::default(),
177            scrollable_overflow: Default::default(),
178            scrollable_overflow_is_up_to_date: AtomicBool::new(false),
179            background_mode: BackgroundMode::Normal,
180            rare_data,
181            block_level_layout_info: None,
182            spatial_tree_node: AtomicOptionScrollTreeNodeId::new(None),
183        }
184    }
185
186    pub(crate) fn with_baselines(mut self, baselines: Baselines) -> Self {
187        self.baselines = baselines;
188        self
189    }
190
191    pub(crate) fn style<'a>(&'a self) -> AtomicRef<'a, ServoArc<ComputedValues>> {
192        self.base.style()
193    }
194
195    pub(crate) fn with_style(self: &Arc<Self>) -> BoxFragmentWithStyle<'_> {
196        BoxFragmentWithStyle {
197            box_fragment: self,
198            style: self.style(),
199        }
200    }
201
202    /// Get the baselines for this [`BoxFragment`] if they are compatible with the given [`WritingMode`].
203    /// If they are not compatible, [`Baselines::default()`] is returned.
204    pub(crate) fn baselines(&self, writing_mode: WritingMode) -> Baselines {
205        let style = self.style();
206        let mut baselines = if writing_mode.is_horizontal() == style.writing_mode.is_horizontal() {
207            self.baselines
208        } else {
209            // If the writing mode of the container requesting baselines is not
210            // compatible, ensure that the baselines established by this fragment are
211            // not used.
212            Baselines::default()
213        };
214
215        // From the https://drafts.csswg.org/css-align-3/#baseline-export section on "block containers":
216        // > However, for legacy reasons if its baseline-source is auto (the initial
217        // > value) a block-level or inline-level block container that is a scroll container
218        // > always has a last baseline set, whose baselines all correspond to its block-end
219        // > margin edge.
220        //
221        // This applies even if there is no baseline set, so we unconditionally set the value here
222        // and ignore anything that is set via [`Self::with_baselines`].
223        if style.establishes_scroll_container(self.base.flags) {
224            let content_rect_size = self.content_rect().size.to_logical(writing_mode);
225            let padding = self.padding.to_logical(writing_mode);
226            let border = self.border.to_logical(writing_mode);
227            let margin = self.margin.to_logical(writing_mode);
228            baselines.last = Some(
229                content_rect_size.block + padding.block_end + border.block_end + margin.block_end,
230            )
231        }
232        baselines
233    }
234
235    pub(crate) fn add_extra_background(&mut self, extra_background: ExtraBackground) {
236        match self.background_mode {
237            BackgroundMode::Extra(ref mut backgrounds) => backgrounds.push(extra_background),
238            _ => self.background_mode = BackgroundMode::Extra(vec![extra_background]),
239        }
240    }
241
242    pub(crate) fn set_does_not_paint_background(&mut self) {
243        self.background_mode = BackgroundMode::None;
244    }
245
246    pub(crate) fn ensure_rare_data(&self) -> AtomicRefMut<'_, BoxFragmentRareData> {
247        self.rare_data.get_or_init(Default::default).borrow_mut()
248    }
249
250    pub(crate) fn specific_layout_info(&self) -> Option<AtomicRef<'_, SpecificLayoutInfo>> {
251        let rare_data = self.rare_data.get()?.borrow();
252
253        AtomicRef::filter_map(rare_data, |rare_data| {
254            rare_data.specific_layout_info.as_ref()
255        })
256    }
257
258    pub(crate) fn resolved_sticky_insets(
259        &self,
260    ) -> Option<AtomicRef<'_, Box<PhysicalSides<AuOrAuto>>>> {
261        let rare_data = self.rare_data.get()?.borrow();
262
263        AtomicRef::filter_map(rare_data, |rare_data| {
264            rare_data.resolved_sticky_insets.as_ref()
265        })
266    }
267
268    pub(crate) fn set_resolved_sticky_insets(&self, sticky_insets: PhysicalSides<AuOrAuto>) {
269        self.ensure_rare_data().resolved_sticky_insets = Some(sticky_insets.into());
270    }
271
272    pub(crate) fn generated_clip_id(&self) -> Option<ClipId> {
273        self.rare_data.get()?.borrow().generated_clip_id
274    }
275
276    pub(crate) fn set_generated_clip_id(&self, generated_clip_id: ClipId) {
277        self.ensure_rare_data().generated_clip_id = Some(generated_clip_id);
278    }
279
280    pub(crate) fn generated_scroll_tree_node_id(&self) -> Option<ScrollTreeNodeId> {
281        self.rare_data.get()?.borrow().generated_scroll_tree_node_id
282    }
283
284    pub(crate) fn set_generated_scroll_tree_node_id(
285        &self,
286        generated_scroll_tree_node_id: ScrollTreeNodeId,
287    ) {
288        self.ensure_rare_data().generated_scroll_tree_node_id = Some(generated_scroll_tree_node_id);
289    }
290
291    pub(crate) fn with_block_level_layout_info(
292        mut self,
293        block_margins_collapsed_with_children: CollapsedBlockMargins,
294        clearance: Option<Au>,
295    ) -> Self {
296        self.block_level_layout_info = Some(Box::new(BlockLevelLayoutInfo {
297            block_margins_collapsed_with_children,
298            clearance,
299        }));
300        self
301    }
302
303    /// Clear the scrollable overflow on this [`BoxFragment`]. This is called
304    /// during damage propagation when a fragment is preserved, itself or one of its
305    /// descendants has scrollable overflow damage.
306    pub(crate) fn clear_scrollable_overflow(&self) {
307        self.scrollable_overflow_is_up_to_date
308            .store(false, Ordering::Release);
309    }
310
311    #[inline]
312    pub(crate) fn set_containing_block(&self, containing_block: &PhysicalRect<Au>) {
313        self.cumulative_containing_block_rect.set(*containing_block);
314    }
315
316    pub(crate) fn offset_by_containing_block(
317        &self,
318        rect: &PhysicalRect<Au>,
319        containing_block_computation: ContainingBlockCalculation<'_>,
320    ) -> PhysicalRect<Au> {
321        containing_block_computation.ensure();
322        rect.translate(self.cumulative_containing_block_rect.origin().to_vector())
323    }
324
325    pub(crate) fn cumulative_content_box_rect(
326        &self,
327        containing_block_computation: ContainingBlockCalculation<'_>,
328    ) -> PhysicalRect<Au> {
329        self.offset_by_containing_block(&self.base.rect(), containing_block_computation)
330    }
331
332    pub(crate) fn cumulative_padding_box_rect(
333        &self,
334        containing_block_computation: ContainingBlockCalculation<'_>,
335    ) -> PhysicalRect<Au> {
336        self.offset_by_containing_block(&self.padding_rect(), containing_block_computation)
337    }
338
339    pub(crate) fn cumulative_border_box_rect(
340        &self,
341        containing_block_computation: ContainingBlockCalculation<'_>,
342    ) -> PhysicalRect<Au> {
343        self.offset_by_containing_block(&self.border_rect(), containing_block_computation)
344    }
345
346    pub(crate) fn content_rect(&self) -> PhysicalRect<Au> {
347        self.base.rect()
348    }
349
350    pub(crate) fn padding_rect(&self) -> PhysicalRect<Au> {
351        self.content_rect().outer_rect(self.padding)
352    }
353
354    pub(crate) fn border_rect(&self) -> PhysicalRect<Au> {
355        self.padding_rect().outer_rect(self.border)
356    }
357
358    pub(crate) fn margin_rect(&self) -> PhysicalRect<Au> {
359        self.border_rect().outer_rect(self.margin)
360    }
361
362    pub(crate) fn padding_border_margin(&self) -> PhysicalSides<Au> {
363        self.margin + self.border + self.padding
364    }
365
366    pub(crate) fn is_root_element(&self) -> bool {
367        self.base.flags.intersects(FragmentFlags::IS_ROOT_ELEMENT)
368    }
369
370    pub(crate) fn is_body_element_of_html_element_root(&self) -> bool {
371        self.base
372            .flags
373            .intersects(FragmentFlags::IS_BODY_ELEMENT_OF_HTML_ELEMENT_ROOT)
374    }
375
376    pub(crate) fn print(self: &Arc<Self>, tree: &mut PrintTree) {
377        let with_style = self.with_style();
378        tree.new_level(format!(
379            "Box\
380                \nbase={:?}\
381                \ncontent={:?}\
382                \npadding rect={:?}\
383                \nborder rect={:?}\
384                \nmargin={:?}\
385                \nscrollable_overflow={:?}\
386                \nbaselines={:?}\
387                \noverflow={:?}",
388            self.base,
389            self.content_rect(),
390            self.padding_rect(),
391            self.border_rect(),
392            self.margin,
393            with_style.scrollable_overflow(),
394            self.baselines,
395            with_style.style().effective_overflow(self.base.flags),
396        ));
397
398        for child in &self.children {
399            child.print(tree);
400        }
401        tree.end_level();
402    }
403
404    pub(crate) fn calculate_resolved_insets_if_positioned(
405        &self,
406        containing_block_computation: ContainingBlockCalculation<'_>,
407    ) -> PhysicalSides<AuOrAuto> {
408        let style = self.style();
409        let position = style.get_box().position;
410        debug_assert_ne!(
411            position,
412            ComputedPosition::Static,
413            "Should not call this method on statically positioned box."
414        );
415
416        if let Some(resolved_sticky_insets) = self.resolved_sticky_insets() {
417            return **resolved_sticky_insets;
418        }
419
420        let convert_to_au_or_auto = |sides: PhysicalSides<Au>| {
421            PhysicalSides::new(
422                AuOrAuto::LengthPercentage(sides.top),
423                AuOrAuto::LengthPercentage(sides.right),
424                AuOrAuto::LengthPercentage(sides.bottom),
425                AuOrAuto::LengthPercentage(sides.left),
426            )
427        };
428
429        let containing_block_size = LazyCell::new(|| {
430            containing_block_computation.ensure();
431            self.cumulative_containing_block_rect.size()
432        });
433
434        // "A resolved value special case property like top defined in another
435        // specification If the property applies to a positioned element and the
436        // resolved value of the display property is not none or contents, and
437        // the property is not over-constrained, then the resolved value is the
438        // used value. Otherwise the resolved value is the computed value."
439        // https://drafts.csswg.org/cssom/#resolved-values
440        let insets = style.physical_box_offsets();
441        if position == ComputedPosition::Relative {
442            let get_resolved_axis = |start: &LengthPercentageOrAuto,
443                                     end: &LengthPercentageOrAuto,
444                                     container_length: Au| {
445                let start = start.map(|value| value.to_used_value(container_length));
446                let end = end.map(|value| value.to_used_value(container_length));
447                match (start.non_auto(), end.non_auto()) {
448                    (None, None) => (Au::zero(), Au::zero()),
449                    (None, Some(end)) => (-end, end),
450                    (Some(start), None) => (start, -start),
451                    // This is the overconstrained case, for which the resolved insets will
452                    // simply be the computed insets.
453                    (Some(start), Some(end)) => (start, end),
454                }
455            };
456
457            let (left, right) =
458                get_resolved_axis(&insets.left, &insets.right, containing_block_size.width);
459            let (top, bottom) =
460                get_resolved_axis(&insets.top, &insets.bottom, containing_block_size.height);
461            return convert_to_au_or_auto(PhysicalSides::new(top, right, bottom, left));
462        }
463
464        debug_assert!(position.is_absolutely_positioned());
465
466        let margin_rect = self.margin_rect();
467        let (top, bottom) = match (&insets.top, &insets.bottom) {
468            (
469                LengthPercentageOrAuto::LengthPercentage(top),
470                LengthPercentageOrAuto::LengthPercentage(bottom),
471            ) => (
472                top.to_used_value(containing_block_size.height),
473                bottom.to_used_value(containing_block_size.height),
474            ),
475            _ => (
476                margin_rect.origin.y,
477                containing_block_size.height - margin_rect.max_y(),
478            ),
479        };
480        let (left, right) = match (&insets.left, &insets.right) {
481            (
482                LengthPercentageOrAuto::LengthPercentage(left),
483                LengthPercentageOrAuto::LengthPercentage(right),
484            ) => (
485                left.to_used_value(containing_block_size.width),
486                right.to_used_value(containing_block_size.width),
487            ),
488            _ => (
489                margin_rect.origin.x,
490                containing_block_size.width - margin_rect.max_x(),
491            ),
492        };
493
494        convert_to_au_or_auto(PhysicalSides::new(top, right, bottom, left))
495    }
496
497    /// Whether or this is a flex or grid item.
498    pub(crate) fn is_flex_or_grid_item(&self) -> bool {
499        self.base
500            .flags
501            .contains(FragmentFlags::IS_FLEX_OR_GRID_ITEM)
502    }
503
504    /// Whether or this box is for replaced content.
505    pub(crate) fn is_replaced(&self) -> bool {
506        self.base.flags.contains(FragmentFlags::IS_REPLACED)
507    }
508
509    /// Whether this is a table wrapper box.
510    /// <https://www.w3.org/TR/css-tables-3/#table-wrapper-box>
511    pub(crate) fn is_table_wrapper(&self) -> bool {
512        matches!(
513            self.specific_layout_info().as_deref(),
514            Some(SpecificLayoutInfo::TableWrapper)
515        )
516    }
517
518    /// Whether or not this is the [`BoxFragment`] for a table grid with collapsed borders.
519    pub(crate) fn is_table_grid_with_collapsed_borders(&self) -> bool {
520        matches!(
521            self.specific_layout_info().as_deref(),
522            Some(SpecificLayoutInfo::TableGridWithCollapsedBorders(_))
523        )
524    }
525
526    pub(crate) fn spatial_tree_node(&self) -> Option<ScrollTreeNodeId> {
527        self.spatial_tree_node.get()
528    }
529}
530
531/// Contains `&Arc<BoxFragment>` and dereferences to it so it can mostly
532/// be used in the same ways, except the `.style()` method is shadowed to use an existing
533/// `atomic_refcell::AtomicRef` that lives as long as `BoxFragmentWithStyle`.
534///
535/// Compared to calling `BoxFragment::style()` repeatedly, this reduce the number of atomic
536/// increments and decrements on `ArcRefCell`’s borrow counter.
537pub(crate) struct BoxFragmentWithStyle<'a> {
538    pub(crate) box_fragment: &'a Arc<BoxFragment>,
539    pub(crate) style: AtomicRef<'a, ServoArc<ComputedValues>>,
540}
541
542impl std::ops::Deref for BoxFragmentWithStyle<'_> {
543    type Target = Arc<BoxFragment>;
544
545    fn deref(&self) -> &Self::Target {
546        self.box_fragment
547    }
548}
549
550impl<'a> BoxFragmentWithStyle<'a> {
551    pub(crate) fn style(&self) -> &ServoArc<ComputedValues> {
552        &self.style
553    }
554
555    /// Return the clipped scrollable overflow based on its scroll origin, determined by
556    /// overflow direction. Return [`None`] if the scrollable overflow from child is wholly
557    /// unreachable. For an element, the clip rect is the padding rect and for viewport,
558    /// it is the initial containing block.
559    pub(crate) fn clip_wholly_unreachable_scrollable_overflow(
560        &self,
561        scrollable_overflow_from_child: PhysicalRect<Au>,
562        clipping_rect: PhysicalRect<Au>,
563    ) -> PhysicalRect<Au> {
564        // From <https://drafts.csswg.org/css-overflow/#unreachable-scrollable-overflow-region>:
565        // > Unless otherwise adjusted (e.g. by content alignment [css-align-3]), the area
566        // > beyond the scroll origin in either axis is considered the unreachable scrollable
567        // > overflow region: content rendered here is not accessible to the reader, see § 2.2
568        // > Scrollable Overflow. A scroll container is said to be scrolled to its scroll
569        // > origin when its scroll origin coincides with the corresponding corner of its
570        // > scrollport. This scroll position, the scroll origin position, usually, but not
571        // > always, coincides with the initial scroll position.
572        let scrolling_direction = self.style().overflow_direction();
573        let mut clipping_box = clipping_rect.to_box2d();
574        if scrolling_direction.rightward {
575            clipping_box.max.x = MAX_AU;
576        } else {
577            clipping_box.min.x = MIN_AU;
578        }
579
580        if scrolling_direction.downward {
581            clipping_box.max.y = MAX_AU;
582        } else {
583            clipping_box.min.y = MIN_AU;
584        }
585
586        let scrollable_overflow_box = scrollable_overflow_from_child
587            .to_box2d()
588            .intersection_unchecked(&clipping_box);
589
590        match scrollable_overflow_box.is_negative() {
591            false => scrollable_overflow_box.to_rect(),
592            true => Rect::zero(),
593        }
594    }
595
596    pub(crate) fn scrollable_overflow_for_parent(&self) -> PhysicalRect<Au> {
597        let style = self.style();
598        let mut overflow = self.border_rect();
599        if !style.establishes_scroll_container(self.base.flags) {
600            // https://www.w3.org/TR/css-overflow-3/#scrollable
601            // Only include the scrollable overflow of a child box if it has overflow: visible.
602            let scrollable_overflow = self.scrollable_overflow();
603            let bottom_right = PhysicalPoint::new(
604                overflow.max_x().max(scrollable_overflow.max_x()),
605                overflow.max_y().max(scrollable_overflow.max_y()),
606            );
607
608            let overflow_style = style.effective_overflow(self.base.flags);
609            if overflow_style.y == ComputedOverflow::Visible {
610                overflow.origin.y = overflow.origin.y.min(scrollable_overflow.origin.y);
611                overflow.size.height = bottom_right.y - overflow.origin.y;
612            }
613
614            if overflow_style.x == ComputedOverflow::Visible {
615                overflow.origin.x = overflow.origin.x.min(scrollable_overflow.origin.x);
616                overflow.size.width = bottom_right.x - overflow.origin.x;
617            }
618        }
619
620        if !style.has_effective_transform_or_perspective(self.base.flags) {
621            return overflow;
622        }
623
624        // <https://drafts.csswg.org/css-overflow-3/#scrollable-overflow-region>
625        // > ...accounting for transforms by projecting each box onto the plane of
626        // > the element that establishes its 3D rendering context. [CSS3-TRANSFORMS]
627        // Both boxes and its scrollable overflow (if it is included) should be transformed accordingly.
628        //
629        // TODO(stevennovaryo): We are supposed to handle perspective transform and 3d
630        // contexts, but it is yet to happen.
631        self.calculate_transform_matrix(&self.border_rect())
632            .and_then(|transform| {
633                transform.outer_transformed_rect(&overflow.to_webrender().to_rect())
634            })
635            .map(|transformed_rect| f32_rect_to_au_rect(transformed_rect).cast_unit())
636            .unwrap_or(overflow)
637    }
638
639    /// Get the scrollable overflow for this [`BoxFragment`] relative to its containing
640    /// block, recalculating scrollable overflow when necessary, for instance after a
641    /// style change.
642    pub(crate) fn scrollable_overflow(&self) -> PhysicalRect<Au> {
643        if self
644            .scrollable_overflow_is_up_to_date
645            .load(Ordering::Acquire)
646        {
647            self.scrollable_overflow.get()
648        } else {
649            let rect = self.calculate_scrollable_overflow();
650            self.scrollable_overflow.set(rect);
651            self.scrollable_overflow_is_up_to_date
652                .store(true, Ordering::Release);
653            rect
654        }
655    }
656    /// This is an implementation of:
657    /// - <https://drafts.csswg.org/css-overflow-3/#scrollable>.
658    /// - <https://drafts.csswg.org/cssom-view/#scrolling-area>
659    fn calculate_scrollable_overflow(&self) -> PhysicalRect<Au> {
660        // Fragments with `IS_COLLAPSED` (currently only table cells that are part of
661        // table tracks with `visibility: collapse`) should not contribute to scrollable
662        // overflow. This behavior matches Chrome, but not Firefox.
663        // See https://github.com/w3c/csswg-drafts/issues/12689
664        if self.base.flags.contains(FragmentFlags::IS_COLLAPSED) {
665            return Rect::zero();
666        }
667
668        let physical_padding_rect = self.padding_rect();
669        let content_origin = self.base.rect().origin.to_vector();
670
671        // > The scrollable overflow area is the union of:
672        // > * The scroll container’s own padding box.
673        // > * All line boxes directly contained by the scroll container.
674        // > * The border boxes of all boxes for which it is the containing block and
675        // >   whose border boxes are positioned not wholly in the unreachable
676        // >   scrollable overflow region, accounting for transforms by projecting
677        // >   each box onto the plane of the element that establishes its 3D
678        // >   rendering context.
679        // > * The margin areas of grid item and flex item boxes for which the box
680        // >   establishes a containing block.
681        // > * The scrollable overflow areas of all of the above boxes (including zero-area
682        // >   boxes and accounting for transforms as described above), provided they
683        // >   themselves have overflow: visible (i.e. do not themselves trap the overflow)
684        // >   and that scrollable overflow is not already clipped (e.g. by the clip property
685        // >   or the contain property).
686        // > * Additional padding added to the scrollable overflow rectangle as necessary
687        //     to enable scroll positions that satisfy the requirements of both place-content:
688        //     start and place-content: end alignment.
689        //
690        // TODO(mrobinson): Below we are handling the border box and the scrollable
691        // overflow together, but from the specification it seems that if the border
692        // box of an item is in the "wholly unreachable scrollable overflow region", but
693        // its scrollable overflow is not, it should also be excluded.
694        let mut scrollable_overflow =
695            self.children
696                .iter()
697                .fold(physical_padding_rect, |acc, child| {
698                    let scrollable_overflow_from_child = child
699                        .scrollable_overflow_for_parent()
700                        .translate(content_origin);
701
702                    // Note that this doesn't just exclude the wholly unreachable
703                    // scrollable overflow area from the rectangle, but also clips it.
704                    // This makes the resulting value more like the "scroll area" rather
705                    // than the "scrollable overflow."
706                    let scrollable_overflow_from_child = self
707                        .clip_wholly_unreachable_scrollable_overflow(
708                            scrollable_overflow_from_child,
709                            physical_padding_rect,
710                        );
711
712                    acc.union(&scrollable_overflow_from_child)
713                });
714
715        // From <https://drafts.csswg.org/css-overflow-3/#scrollable>:
716        // > Additional padding added to the scrollable overflow rectangle as necessary to
717        // > enable scroll positions that satisfy the requirements of both place-content:
718        // > start and place-content: end alignment.
719        //
720        // Whether we should include additional padding to the scrollable overflow to satisfy
721        // the requirements of `place-content: start` and `place-content: end` for boxes that
722        // establish scroll containers. Note: This padding is different from the CSS concept
723        // of padding. See <https://github.com/w3c/csswg-drafts/issues/129>.
724        //
725        // TODO: For input elements, we also disable the padding in the inline direction, as we
726        // do not have a way to scroll the textual input element in inline direction yet.
727        let should_include_additional_padding =
728            self.style().establishes_scroll_container(self.base.flags) &&
729                !self.base.flags.intersects(FragmentFlags::IS_INPUT_ELEMENT);
730
731        if should_include_additional_padding {
732            scrollable_overflow = self
733                .children
734                .iter()
735                .fold(scrollable_overflow, |acc, child| {
736                    let Some(padding_contribution) =
737                        child.scrollable_overflow_padding_contribution_for_parent()
738                    else {
739                        return acc;
740                    };
741
742                    let padding_contribution = padding_contribution
743                        .translate(content_origin)
744                        .outer_rect(self.padding);
745
746                    // Applying padding could also cause the rectangle to overflow to
747                    // the wholly unreachable scrollable overflow, clipping the overflow
748                    // here prevents this.
749                    let padding_contribution = self.clip_wholly_unreachable_scrollable_overflow(
750                        padding_contribution,
751                        physical_padding_rect,
752                    );
753
754                    acc.union(&padding_contribution)
755                });
756        }
757        scrollable_overflow
758    }
759
760    /// Whether this is a non-replaced inline-level box whose inner display type is `flow`.
761    /// <https://drafts.csswg.org/css-display-3/#inline-box>
762    pub(crate) fn is_inline_box(&self) -> bool {
763        self.style().is_inline_box(self.base.flags)
764    }
765
766    /// Whether this is an atomic inline-level box.
767    /// <https://drafts.csswg.org/css-display-3/#atomic-inline>
768    pub(crate) fn is_atomic_inline_level(&self) -> bool {
769        self.style().is_atomic_inline_level(self.base.flags)
770    }
771
772    pub(crate) fn has_collapsed_borders(&self) -> bool {
773        match self.specific_layout_info().as_deref() {
774            Some(SpecificLayoutInfo::TableCellWithCollapsedBorders) => true,
775            Some(SpecificLayoutInfo::TableGridWithCollapsedBorders(_)) => true,
776            Some(SpecificLayoutInfo::TableWrapper) => {
777                self.style().get_inherited_table().border_collapse == BorderCollapse::Collapse
778            },
779            _ => false,
780        }
781    }
782
783    /// Whether or not this [`BoxFragment`] has outlines.
784    pub(crate) fn has_outline(&self) -> bool {
785        let style = self.style();
786        let outline = style.get_outline();
787        !outline.outline_style.none_or_hidden() && !outline.outline_width.0.is_zero()
788    }
789}
layout/fragment_tree/box_fragment.rs

layout/fragment_tree/
box_fragment.rs
