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Only create scrolling overflow regions when necessary

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Only create scroll roots for overflow regions when the overflow region
is actually larger than the container size. This prevents creating
scrolling roots for elements that do not have overflow scroll as a
side-effect of the way their height and width is defined. For example,
tables should never respect overflow:scroll since their height and
width should always be large enough to prevent overflow. This also
decreases the size and complexity of the display list in many other
circumstances.

As part of this change, transformed overflow calculation is moved from
display list construction to layout. This should mean that overflow is
handled more accurately earlier.

Fixes #14574.
This commit is contained in:
Martin Robinson 2017-01-10 09:49:06 +01:00
parent 14aa666a5a
commit 44b24de60f
10 changed files with 139 additions and 63 deletions
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49
components/layout/flow.rs
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@ -43,6 +43,7 @@ use model::{CollapsibleMargins, IntrinsicISizes, MarginCollapseInfo};
use multicol::MulticolFlow;
use parallel::FlowParallelInfo;
use serde::{Serialize, Serializer};
use servo_geometry::{au_rect_to_f32_rect, f32_rect_to_au_rect};
use std::{fmt, mem, raw};
use std::iter::Zip;
use std::slice::IterMut;
@ -248,6 +249,46 @@ pub trait Flow: fmt::Debug + Sync + Send + 'static {
might_have_floats_in_or_out
}
fn get_overflow_in_parent_coordinates(&self) -> Overflow {
// FIXME(#2795): Get the real container size.
let container_size = Size2D::zero();
let position = base(self).position.to_physical(base(self).writing_mode, container_size);
let mut overflow = base(self).overflow;
match self.class() {
FlowClass::Block | FlowClass::TableCaption | FlowClass::TableCell => {}
_ => {
overflow.translate(&position.origin);
return overflow;
}
}
if !self.as_block().fragment.establishes_stacking_context() ||
self.as_block().fragment.style.get_box().transform.0.is_none() {
overflow.translate(&position.origin);
return overflow;
}
// TODO: Take into account 3d transforms, even though it's a fairly
// uncommon case.
let transform_2d = self.as_block().fragment.transform_matrix(&position).to_2d();
let transformed_overflow = Overflow {
paint: f32_rect_to_au_rect(transform_2d.transform_rect(
&au_rect_to_f32_rect(overflow.paint))),
scroll: f32_rect_to_au_rect(transform_2d.transform_rect(
&au_rect_to_f32_rect(overflow.scroll))),
};
// TODO: We are taking the union of the overflow and transformed overflow here, which
// happened implicitly in the previous version of this code. This will probably be
// unnecessary once we are taking into account 3D transformations above.
overflow.union(&transformed_overflow);
overflow.translate(&position.origin);
overflow
}
///
/// CSS Section 11.1
/// This is the union of rectangles of the flows for which we define the
@ -266,17 +307,11 @@ pub trait Flow: fmt::Debug + Sync + Send + 'static {
FlowClass::Block |
FlowClass::TableCaption |
FlowClass::TableCell => {
// FIXME(#2795): Get the real container size.
let container_size = Size2D::zero();
let overflow_x = self.as_block().fragment.style.get_box().overflow_x;
let overflow_y = self.as_block().fragment.style.get_box().overflow_y;
for kid in mut_base(self).children.iter_mut() {
let mut kid_overflow = base(kid).overflow;
let kid_position = base(kid).position.to_physical(base(kid).writing_mode,
container_size);
kid_overflow.translate(&kid_position.origin);
let mut kid_overflow = kid.get_overflow_in_parent_coordinates();
// If the overflow for this flow is hidden on a given axis, just
// put the existing overflow in the kid rect, so that the union