layout: Make absolutely-positioned elements with z-index: auto not

stacking contexts.

Improves many sites.

Closes #7069.
This commit is contained in:
Patrick Walton 2015-08-10 12:26:03 -07:00
parent 84c4a26e4d
commit d3d59ced36
26 changed files with 58 additions and 80 deletions

View file

@ -1631,15 +1631,28 @@ impl BlockFlowDisplayListBuilding for BlockFlow {
Some(outer_display_list_for_overflow_scroll)
}
_ => {
self.build_display_list_for_block_base(
&mut *display_list,
layout_context,
border_painting_mode,
BackgroundAndBorderLevel::RootOfStackingContext);
let establishes_stacking_context = self.fragment.establishes_stacking_context();
let background_and_border_level = if establishes_stacking_context {
BackgroundAndBorderLevel::RootOfStackingContext
} else {
BackgroundAndBorderLevel::Block
};
self.build_display_list_for_block_base(&mut *display_list,
layout_context,
border_painting_mode,
background_and_border_level);
None
}
};
if !self.fragment.establishes_stacking_context() {
display_list.form_pseudo_stacking_context_for_positioned_content();
self.base.display_list_building_result =
DisplayListBuildingResult::Normal(display_list);
return
}
if !self.will_get_layer() {
// We didn't need a layer.
self.base.display_list_building_result =

View file

@ -35,9 +35,9 @@ use std::fmt;
use std::sync::{Arc, Mutex};
use string_cache::Atom;
use style::computed_values::content::ContentItem;
use style::computed_values::{border_collapse, clear, mix_blend_mode, overflow_wrap, position};
use style::computed_values::{text_align, text_decoration, white_space, word_break};
use style::computed_values::transform_style;
use style::computed_values::{border_collapse, clear, mix_blend_mode, overflow_wrap, overflow_x};
use style::computed_values::{position, text_align, text_decoration, transform_style, white_space};
use style::computed_values::{word_break, z_index};
use style::properties::{self, ComputedValues, cascade_anonymous};
use style::values::computed::{LengthOrPercentage, LengthOrPercentageOrAuto};
use style::values::computed::{LengthOrPercentageOrNone};
@ -2027,13 +2027,24 @@ impl Fragment {
return true
}
match self.style().get_box().position {
position::T::absolute | position::T::fixed => {
// FIXME(pcwalton): This should only establish a new stacking context when
// `z-index` is not `auto`. But this matches what we did before.
true
}
position::T::relative | position::T::static_ => {
// FIXME(pcwalton): Don't unconditionally form stacking contexts for `overflow_x: scroll`
// and `overflow_y: scroll`. This needs multiple layers per stacking context.
match (self.style().get_box().position,
self.style().get_box().z_index,
self.style().get_box().overflow_x,
self.style().get_box().overflow_y.0) {
(position::T::absolute,
z_index::T::Auto,
overflow_x::T::visible,
overflow_x::T::visible) |
(position::T::fixed,
z_index::T::Auto,
overflow_x::T::visible,
overflow_x::T::visible) => false,
(position::T::absolute, _, _, _) |
(position::T::fixed, _, _, _) => true,
(position::T::relative, _, _, _) |
(position::T::static_, _, _, _) => {
// FIXME(pcwalton): `position: relative` establishes a new stacking context if
// `z-index` is not `auto`. But this matches what we did before.
false