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Improve containing block creation for position:absolute flows

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Instead of only promoting flows with positioned fragments to containing
blocks, also do this for flows which have the transform, perspective or
filter properties set. This is what the spec requires and also fixes
some failing tests. It will allow us to stop creating stacking contexts
for overflow:hidden and overflow:scroll flows.

Fixes #18091.
This commit is contained in:
Martin Robinson 2017-08-17 11:44:19 +02:00
parent 0a24c2f03c
commit 57704b0481
15 changed files with 107 additions and 43 deletions
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29
components/layout/block.rs
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@ -448,20 +448,16 @@ pub struct AbsoluteAssignBSizesTraversal<'a>(pub &'a SharedStyleContext<'a>);
impl<'a> PreorderFlowTraversal for AbsoluteAssignBSizesTraversal<'a> {
#[inline]
fn process(&self, flow: &mut Flow) {
{
// The root of the absolute flow tree is definitely not absolutely
// positioned. Nothing to process here.
let flow: &Flow = flow;
if flow.contains_roots_of_absolute_flow_tree() {
return;
}
if !flow.is_block_like() {
return
}
if !flow.is_block_like() {
return
}
// This flow might not be an absolutely positioned flow if it is the root of the tree.
let block = flow.as_mut_block();
debug_assert!(block.base.flags.contains(IS_ABSOLUTELY_POSITIONED));
if !block.base.flags.contains(IS_ABSOLUTELY_POSITIONED) {
return;
}
if !block.base.restyle_damage.intersects(REFLOW_OUT_OF_FLOW | REFLOW) {
return
}
@ -2106,6 +2102,17 @@ impl Flow for BlockFlow {
(self.fragment.border_box - self.fragment.style().logical_border_width()).size
}
/// Returns true if this flow contains fragments that are roots of an absolute flow tree.
fn contains_roots_of_absolute_flow_tree(&self) -> bool {
self.contains_relatively_positioned_fragments() || self.is_root() ||
self.fragment.has_filter_transform_or_perspective()
}
/// Returns true if this is an absolute containing block.
fn is_absolute_containing_block(&self) -> bool {
self.contains_positioned_fragments() || self.fragment.has_filter_transform_or_perspective()
}
fn update_late_computed_inline_position_if_necessary(&mut self, inline_position: Au) {
if self.base.flags.contains(IS_ABSOLUTELY_POSITIONED) &&
self.fragment.style().logical_position().inline_start ==