[wp-trac] [WordPress Trac] #35296: Image editor spinner and high CPU usage

[WordPress Trac]

#35296: Image editor spinner and high CPU usage
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 Reporter:  afercia       |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  4.5
Component:  Media         |    Version:  4.4
 Severity:  normal        |   Keywords:
  Focuses:  ui            |
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 Similar to other spinner performance-related issues, see #31196, #33311,
 #33322, and #34951.

 In the image editor (both in the Media Library and in the Media Modal),
 when performing an action a semi-transparent layer appears with a spinner
 set as background.

 While on powerful machines with a modern CPU and a dedicated GPU there's
 just a barely noticeable CPU usage increment, on older machines the
 spinner set on a so large area, especially when this area is semi-
 transparent, can make the CPU usage grow significantly and also get stuck
 at 100%.

 Tested on a very old desktop PC with Windows XP and Firefox 43, the time
 required for a single image "flip" decreases from '''minutes''' to about 2
 seconds when removing the spinner.

 As a best practice, spinners used as backgrounds should always be set on
 the smallest possible area. In this specific case there's no need to
 completely remove the spinner when the action completes because it's
 already in a `<div>` that gets hidden with `display: none`.

 See in the screenshot below: before the patch the whole image editor area
 gets continuously re-painted while after the patch it happens only on the
 20x20 pixels spinner area.

 [[Image(https://cldup.com/-FbBiJKev6.png)]]

 [[Image(https://cldup.com/8oh9_9F43G.png)]]

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Ticket URL: <https://core.trac.wordpress.org/ticket/35296>
WordPress Trac <https://core.trac.wordpress.org/>
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