1613053 - Simplify WebRender's internal storage of clip chains

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, enhancement, P3)

Description

[Nicolas Silva [:nical]]

Following up on a Berlin allhands discussion about frame building performance, I'll try to reproduce Glenn's wording as best as I can: Clip chains are currently stored as an intrusive linked list within a vector (where links are indices). There is a bunch of complicated (and expensive?) code for generating the proper chains.

Glenn proposes storing chip chains as ranges of clips in a vector, at the expense of duplicating common parents, but making building and iterating clip chains more straightforward and cheap.

Comment 1

[Nicolas Silva [:nical]]

For reference, the percentage of total frame building time spent in clipping related functions when scrolling gmail's thread list (measured on a xps13 laptop):

• ClipStore::build_clip_chain_instance: 2%
• ClipStore::set_active_clips: 1.5%
• ClipChainStack::push_clip: 1.5%
• BrushSegment::update_clip_task: 0.5%
• ...a few others below 0.1%

The wins to be had look modest on this particular testcase (where frame building struggles). Other more clipping-heavy pages will probably look different, I'll update the numbers if I run into one.

Comment 2

[Glenn Watson [:gw]]

This is no longer relevant, due to the work in bug #1779952.