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The progress bar should accelerate as it nears completion
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There exists a body of empirical evidence that suggests users have a preference for progress bars that accelerate as they near completion. The same body of evidence suggests that any pauses in the progress process, but especially late pauses, have a profound negative impact on how users experience the process as a while.

The best paper on this subject is

So the progress bar should ideally accelerate and never stops.
Some things we could do to achieve this are:

  • Make the loading of VisualEditor correspond to the first 40% of the progress bar, giving us the remaining 60% as breathing room.
  • If everything loads super-fast, then the remaining 60% are filled in instantly.
  • If a part of the loading process starts taking long, we can start utilizing the 60%.
  • As a last resort, slow down progress exponentially in lieu of pausing.

The 40% / 60% numbers are guesses; some experimentation will disclose the best values.

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The only problem here is the second half corresponds to the converter which is slow because of heavy client-side computation so it may be unavoidable to have any animation stutter.

Tried and failed to add this to the #OriLivnehMindControlDept project.

Change 209869 had a related patch set uploaded (by Esanders):
Improve progress bar

Change 209869 merged by jenkins-bot:
Improve progress bar

Would it be helpful to add this functionality in ProgressBarWidget's setProgress method? An interpolator like the ones in the paper?