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gfx: Rewrite display list construction to make stacking-contexts more
first-class.
This implements the scheme described here:
https://groups.google.com/forum/#!topic/mozilla.dev.servo/sZVPSfPVfkg
This commit changes Servo to generate one display list per stacking
context instead of one display list per layer. This is purely a
refactoring; there are no functional changes. Performance is essentially
the same as before. However, there should be numerous future benefits
that this is intended to allow for:
* It makes the code simpler to understand because the "new layer needed"
vs. "no new layer needed" code paths are more consolidated.
* It makes it easy to support CSS properties that did not fit into our
previous flat display list model (without unconditionally layerizing
them):
o `opacity` should be easy to support because the stacking context
provides the higher-level grouping of display items to which opacity
is to be applied.
o `transform` can be easily supported because the stacking context
provides a place to stash the transformation matrix. This has the side
benefit of nicely separating the transformation matrix from the
clipping regions.
* The `flatten` logic is now O(1) instead of O(n) and now only needs to
be invoked for pseudo-stacking contexts (right now: just floats),
instead of for every stacking context.
* Layers are now a proper tree instead of a flat list as far as layout
is concerned, bringing us closer to a production-quality
compositing/layers framework.
* This commit opens the door to incremental display list construction at
the level of stacking contexts.
Future performance improvements could come from optimizing allocation of
display list items, and, of course, incremental display list
construction.
This commit is contained in:
Patrick Walton
parent
0ab70dd539
commit
a4a9a46a87
13 changed files with 812 additions and 550 deletions
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@ -30,9 +30,9 @@
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use construct::FlowConstructor;
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use context::LayoutContext;
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use css::node_style::StyledNode;
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use display_list_builder::{BlockFlowDisplayListBuilding, FragmentDisplayListBuilding};
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use display_list_builder::{BlockFlowDisplayListBuilding, BlockLevel, FragmentDisplayListBuilding};
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use floats::{ClearBoth, ClearLeft, ClearRight, FloatKind, FloatLeft, Floats, PlacementInfo};
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use flow::{BaseFlow, BlockFlowClass, FlowClass, Flow, ImmutableFlowUtils};
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use flow::{AbsolutePositionInfo, BaseFlow, BlockFlowClass, FlowClass, Flow, ImmutableFlowUtils};
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use flow::{MutableFlowUtils, PreorderFlowTraversal, PostorderFlowTraversal, mut_base};
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use flow;
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use fragment::{Fragment, ImageFragment, InlineBlockFragment, FragmentBoundsIterator};
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@ -45,10 +45,9 @@ use table::ColumnInlineSize;
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use wrapper::ThreadSafeLayoutNode;
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use geom::Size2D;
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use gfx::display_list::BlockLevel;
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use serialize::{Encoder, Encodable};
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use servo_msg::compositor_msg::LayerId;
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use servo_util::geometry::{Au, MAX_AU};
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use servo_util::geometry::{Au, MAX_AU, MAX_RECT, ZERO_POINT};
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use servo_util::logical_geometry::{LogicalPoint, LogicalRect, LogicalSize};
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use servo_util::opts;
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use std::cmp::{max, min};
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@ -1665,24 +1664,26 @@ impl Flow for BlockFlow {
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// FIXME(#2795): Get the real container size
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let container_size = Size2D::zero();
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if self.is_root() {
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self.base.clip_rect = MAX_RECT
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}
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if self.base.flags.is_absolutely_positioned() {
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let position_start = self.base.position.start.to_physical(self.base.writing_mode,
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container_size);
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self.base.absolute_position_info.absolute_containing_block_position =
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if self.is_fixed() {
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// The viewport is initially at (0, 0).
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position_start
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} else {
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// Absolute position of the containing block + position of absolute
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// flow w.r.t. the containing block.
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self.base.absolute_position_info.absolute_containing_block_position
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+ position_start
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};
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// Set the absolute position, which will be passed down later as part
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// of containing block details for absolute descendants.
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self.base.abs_position =
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self.base.absolute_position_info.absolute_containing_block_position;
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// Compute our position relative to the nearest ancestor stacking context. This will be
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// passed down later as part of containing block details for absolute descendants.
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self.base.stacking_relative_position = if self.is_fixed() {
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// The viewport is initially at (0, 0).
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position_start
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} else {
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// Absolute position of the containing block + position of absolute
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// flow w.r.t. the containing block.
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self.base
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.absolute_position_info
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.stacking_relative_position_of_absolute_containing_block + position_start
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}
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}
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// For relatively-positioned descendants, the containing block formed by a block is just
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@ -1693,32 +1694,52 @@ impl Flow for BlockFlow {
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.absolute_position_info
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.relative_containing_block_size);
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if self.is_positioned() {
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self.base.absolute_position_info.absolute_containing_block_position =
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self.base.abs_position
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+ (self.generated_containing_block_rect().start
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+ relative_offset).to_physical(self.base.writing_mode, container_size)
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self.base
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.absolute_position_info
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.stacking_relative_position_of_absolute_containing_block =
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self.base.stacking_relative_position +
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(self.generated_containing_block_rect().start +
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relative_offset).to_physical(self.base.writing_mode, container_size)
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}
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// Compute absolute position info for children.
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let mut absolute_position_info = self.base.absolute_position_info;
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absolute_position_info.relative_containing_block_size = self.fragment.content_box().size;
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absolute_position_info.layers_needed_for_positioned_flows =
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self.base.flags.layers_needed_for_descendants();
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let absolute_position_info_for_children = AbsolutePositionInfo {
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stacking_relative_position_of_absolute_containing_block:
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if self.fragment.establishes_stacking_context() {
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let logical_border_width = self.fragment.style().logical_border_width();
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LogicalPoint::new(self.base.writing_mode,
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logical_border_width.inline_start,
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logical_border_width.block_start).to_physical(
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self.base.writing_mode,
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container_size)
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} else {
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self.base
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.absolute_position_info
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.stacking_relative_position_of_absolute_containing_block
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},
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relative_containing_block_size: self.fragment.content_box().size,
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layers_needed_for_positioned_flows: self.base.flags.layers_needed_for_descendants(),
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};
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// Compute the clipping rectangle for children.
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let this_position = self.base.abs_position;
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let clip_rect = self.fragment.clip_rect_for_children(self.base.clip_rect, this_position);
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// Compute the origin and clipping rectangle for children.
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let origin_for_children = if self.fragment.establishes_stacking_context() {
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ZERO_POINT
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} else {
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self.base.stacking_relative_position
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};
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let clip_rect = self.fragment.clip_rect_for_children(self.base.clip_rect,
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origin_for_children);
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// Process children.
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let writing_mode = self.base.writing_mode;
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for kid in self.base.child_iter() {
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if !flow::base(kid).flags.is_absolutely_positioned() {
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let kid_base = flow::mut_base(kid);
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kid_base.abs_position =
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this_position +
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kid_base.stacking_relative_position =
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origin_for_children +
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(kid_base.position.start + relative_offset).to_physical(writing_mode,
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container_size);
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kid_base.absolute_position_info = absolute_position_info
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kid_base.absolute_position_info = absolute_position_info_for_children
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}
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flow::mut_base(kid).clip_rect = clip_rect
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@ -1726,7 +1747,8 @@ impl Flow for BlockFlow {
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// Process absolute descendant links.
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for absolute_descendant in self.base.abs_descendants.iter() {
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flow::mut_base(absolute_descendant).absolute_position_info = absolute_position_info
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flow::mut_base(absolute_descendant).absolute_position_info =
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absolute_position_info_for_children
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}
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}
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@ -1816,9 +1838,10 @@ impl Flow for BlockFlow {
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fn iterate_through_fragment_bounds(&self, iterator: &mut FragmentBoundsIterator) {
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if iterator.should_process(&self.fragment) {
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let fragment_origin = self.base.child_fragment_absolute_position(&self.fragment);
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let fragment_origin =
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self.base.stacking_relative_position_of_child_fragment(&self.fragment);
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iterator.process(&self.fragment,
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self.fragment.abs_bounds_from_origin(&fragment_origin));
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self.fragment.stacking_relative_bounds(&fragment_origin));
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}
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}
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}
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