Sometimes positioned content needs to be layered on top of stacking
contexts. The layer synthesis code can do this, but the current design
prevents it because stacking contexts are stored in a separate struct
member. In order to preserve tree order, mix stacking contexts into the
positioned content list, by adding a new StackingContextClass
DisplayItem. Such items do not have a base DisplayItem.
In some ways this simplifies the code, because we no longer have to
have a separate code path in the StackingContextLayerCreator.
Fixes#7779.
Fixes#7983.
Fixes#8122.
Fixes#8310.
Previously, StackingContexts might have a PaintLayer. We switch the
ownership, for several reasons:
* We want PaintLayers to potentially contain something other
than a StackingContext soon.
* We want to delay the creation of PaintLayers until the last
minute, so that we can synthesize new layers for sandwiched
content.
This commit also implements the second goal. Instead of creating
PaintLayers during layout itself, wait until we are sorting and
layerizing a completed DisplayList.
This commit introduces the `serde` dependency, which we will use to
serialize messages going between processes in multiprocess Servo.
This also adds a new debugging flag, `-Z print-display-list-json`,
allowing the output of display list serialization to be visualized.
This will be useful for our experiments with alternate rasterizers.
Reasons behind existing unstable features:
alloc:
- weak pointers (may not belong)
- boxed::into_raw and from_raw (naming)
collections:
- `Vec.push_all()` (May be replaced)
- Replace with loop
core:
- `min_by` (#15311)
- `PI_2` (naming)
rustc_private:
- FnVHasher
- Can be replaced by rust-fnv
std_misc:
- Hash state stuff (no option here unless we want to stop using it)
str_char:
- CharRange usage
- Can be replaced by regular iterators (char_indices)
This used to conflict with the util crate from the standard library, which
has long since been removed.
The import in layout has not been changed because of a conflict with the
util mod there.
`invert` is not yet supported.
Objects that get layers will not yet display outlines properly. This is
because our overflow calculation doesn't take styles into account and
because layers are always anchored to the top left of the border box.
Since fixing this is work that is not related to outline *per se* I'm
leaving that to a followup and making a note in the code.
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.
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
