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layout: Rewrite clipping to be per-display-item instead of having

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a separate `ClipDisplayItem`.

We push down clipping areas during absolute position calculation. This
makes display items into a flat list, improving cache locality. It
dramatically simplifies the code all around.

Because we need to push down clip rects even for absolutely-positioned
children of non-absolutely-positioned flows, this patch alters the
parallel traversal to compute absolute positions for
absolutely-positioned children at the same time it computes absolute
positions for other children. This doesn't seem to break anything either
in theory (since the overall order remains correct) or in practice. It
simplifies the parallel traversal code quite a bit.

See the relevant Gecko bug:
https://bugzilla.mozilla.org/show_bug.cgi?id=615734
This commit is contained in:
Patrick Walton 2014-10-10 15:13:12 -07:00
parent f350879574
commit bffaad118e
12 changed files with 312 additions and 487 deletions
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38
components/layout/block.rs
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@ -37,7 +37,7 @@ use gfx::display_list::{RootOfStackingContextLevel};
use gfx::render_task::RenderLayer;
use serialize::{Encoder, Encodable};
use servo_msg::compositor_msg::{FixedPosition, LayerId, Scrollable};
use servo_util::geometry::{Au, MAX_AU};
use servo_util::geometry::{Au, MAX_AU, MAX_RECT};
use servo_util::logical_geometry::{LogicalPoint, LogicalRect, LogicalSize};
use std::cmp::{max, min};
use std::fmt;
@ -1078,18 +1078,19 @@ impl BlockFlow {
fn build_display_list_block_common(&mut self,
layout_context: &LayoutContext,
background_border_level: BackgroundAndBorderLevel) {
let rel_offset =
let relative_offset =
self.fragment.relative_position(&self.base
.absolute_position_info
.relative_containing_block_size);
.absolute_position_info
.relative_containing_block_size);
// Add the box that starts the block context.
let mut display_list = DisplayList::new();
let mut accumulator = self.fragment.build_display_list(
&mut display_list,
layout_context,
self.base.abs_position.add_size(&rel_offset.to_physical(self.base.writing_mode)),
background_border_level);
self.fragment.build_display_list(&mut display_list,
layout_context,
self.base.abs_position.add_size(
&relative_offset.to_physical(self.base.writing_mode)),
background_border_level,
&self.base.clip_rect);
let mut child_layers = DList::new();
for kid in self.base.child_iter() {
@ -1098,19 +1099,21 @@ impl BlockFlow {
continue
}
accumulator.push_child(&mut display_list, kid);
display_list.push_all_move(mem::replace(&mut flow::mut_base(kid).display_list,
DisplayList::new()));
child_layers.append(mem::replace(&mut flow::mut_base(kid).layers, DList::new()))
}
// Process absolute descendant links.
for abs_descendant_link in self.base.abs_descendants.iter() {
// TODO(pradeep): Send in our absolute position directly.
accumulator.push_child(&mut display_list, abs_descendant_link);
display_list.push_all_move(mem::replace(
&mut flow::mut_base(abs_descendant_link).display_list,
DisplayList::new()));
child_layers.append(mem::replace(&mut flow::mut_base(abs_descendant_link).layers,
DList::new()));
}
accumulator.finish(&mut display_list);
self.base.display_list = display_list;
self.base.layers = child_layers
}
@ -1696,6 +1699,10 @@ impl Flow for BlockFlow {
// FIXME(#2795): Get the real container size
let container_size = Size2D::zero();
if self.is_root() {
self.base.clip_rect = MAX_RECT;
}
if self.is_absolutely_positioned() {
let position_start = self.base.position.start.to_physical(
self.base.writing_mode, container_size);
@ -1737,8 +1744,11 @@ impl Flow for BlockFlow {
absolute_position_info.layers_needed_for_positioned_flows =
self.base.flags.layers_needed_for_descendants();
// Process children.
// Compute the clipping rectangle for children.
let this_position = self.base.abs_position;
let clip_rect = self.fragment.clip_rect_for_children(self.base.clip_rect, this_position);
// Process children.
let writing_mode = self.base.writing_mode;
for kid in self.base.child_iter() {
if !kid.is_absolutely_positioned() {
@ -1749,6 +1759,8 @@ impl Flow for BlockFlow {
container_size);
kid_base.absolute_position_info = absolute_position_info
}
flow::mut_base(kid).clip_rect = clip_rect
}
// Process absolute descendant links.