5-Year Plan: A Retrospective

by Simon Fraser

5 years ago, in a meeting room not so far away…

• DOM Event Loop
  • Started working on it.
  • Now called the Event Loop
  • Benefits and problems are still accurate
• Render Tree Refcounting
  • Not done this
  • Haven’t found a real need to do this yet
• Painting: Display Lists
  • Have done experiments
  • Testing with MotionMark is a performance regression
  • Lost parallelism
  • Didn’t turn it on, may come back and revisit it
• Image Decoding
  • Knew we had problems with this on main thread
  • Decoding sync on main thread
  • Can’t do it by default because of flashy painting
  • Added decoding=async on img element to turn it on
  • Or call API to ask for decoding on image and get a Promise
  • Async decoding on first load
  • This is done and we’re pretty happy with it
• Layout State Machine
  • Making it harder to make mistakes interacting with RenderTree
  • Be on a call stack iterating on layer list for hit testing
  • Detect when mistakes happen and trigger assertions
  • Fixed a bunch of issues of mutating trees in the middle of…
  • Big benefit of event loop is: move all code that fires events to updateRendering steps and other well defined places
  • Made good progress
• Compositing
  • Downstream was making compositing decisions by looking at whole list of drawing commands
    • Haven’t done it
    • Earlier this year I did compositing updates are incremental with dirty bits
• Hackability
  • RenderRegions were removed which was good
  • Working on inline layout
    • Goals to simplify inline layout code
  • ScrollableArea and FrameVIew
    • Nothing really changed
    • State of FrameLoader et. al… still not great
  • Relationships between Document Frame, Dom Window and page are still pretty confusing
  • Selection still has specialized versions
• Threading
  • Can we do more in threads?

4 years ago, in the same meeting room not so far away…

• Optimizing layout
• IndexedDB optimizations
• Cleaning up loading code
• Page cache clean up
  • We’re doing it!
• CSS properties status JSON and on webkit.org
• Event Loop
  • Same stuff, making progress
• Fetch API
  • Done
• Service Worker
  • Done
• Intersection Observer
  • Done
• Scroll-linked Effects
  • Some work, but no really progress
• Houdini proposal
  • Prototype of custom paint, but no where accessible
• Page & Friends
  • Too many scrolling architectures
  • iOS WK1 is different, iOS WK2 uses UI side compositing
• Code Organization
  • PAL library
    • Some of its there
• Layout & Rendering
  • Fundamentally hasn’t changed
  • LFC work is still underway, beyond experimental
    • Rewrite of the layout code
    • Making good progress
    • Block layout 80-90% done
    • Now doing table layout
  • Inine layout work too
• Remove widgets
  • Still have them
  • Need to get rid of it
• Continuations
  • Nothing happened
• Compositing
  • Still do compositing updates on every forced layout
  • Ideally only once every rendering step
    • Hoping to do it this year
• Debuggability
  • Log Channels: new log channels
  • Use TextStream to make things log-able
  • I want to log a RenderStyle and only the properties different from the default
    • And show diff
  • Still have progress to be made
• Next Year
  • Figure out where logging goes