This is the bulk of the changes.
- DisplayItemScrollClip is removed. Instead, we will have 1) ActiveScrolledRoot
and 2) DisplayItemClipChain.
- ActiveScrolledRoot points to a scroll frame and allows traversing up the
scroll frame chain.
- DisplayItemClipChain is a linked list of clips, each clip being associated
with the ActiveScrolledRoot that moves this clip.
- Each display item has an ActiveScrolledRoot and a clip chain.
- nsDisplayItem::GetClip returns the item of the clip chain that scrolls with
the item's ASR. The separation between "regular clip" and "scroll clips"
mostly goes away.
- Tracking clips in the display list builder's clip state happens very
similarly to how regular clips used to be tracked - there's a clip chain for
content descendants and a clip chain for containing block descendants. These
clip chains are intersected to create the combined clip chain.
- There are strict rules for the ASR of a container item: A container item's
ASR should be the innermost ASR which the item has finite clipped bounds with
respect to.
- At some point in the future, ASRs and AGRs should be reunified, but I haven't
done that yet, because I needed to limit the scope of the change.
MozReview-Commit-ID: KYEpWY7qgf2
--HG--
extra : rebase_source : c727f6300a35463750639e165bfa37374c06b851
Markus Stange
Ehsan Akhgari