[wp-trac] [WordPress Trac] #33322: Theme Installer: spinner animated GIF and high CPU usage

[WordPress Trac]

#33322: Theme Installer: spinner animated GIF and high CPU usage
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 Reporter:  afercia         |      Owner:
     Type:  defect (bug)    |     Status:  new
 Priority:  normal          |  Milestone:  Awaiting Review
Component:  Themes          |    Version:  4.2
 Severity:  normal          |   Keywords:
  Focuses:  ui, javascript  |
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 In the Theme Installer (Themes > Add New > Preview a Theme), the spinner
 loading indicator causes the same performance issues noticed for the
 Customizer spinner a while ago, see
 https://core.trac.wordpress.org/ticket/31196#comment:14

 On modern hardware, with a dedicated GPU and hardware acceleration
 support, you will barely notice this but on old hardware the CPU usage can
 easily be over 50% and in the worst case always stuck at 100% since the
 spinner is always "spinning" in the background even when overlaid by the
 iframe.

 Looks like modern browser still have issues with animated GIFs especially
 when some CSS properties (e.g. opacity, box-shadow) are set on the GIF
 container. I can reproduce high CPU usage using both Chrome and Firefox,
 they behave differently but the result is the same.

 Regardless, when the preview iframe loads, the background spinner image
 should be removed as already done for the Customizer.

 See also related #33311 for the Thickbox spinner.

 [[Image(https://cldup.com/NUKm7LaRGM.png)]]

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Ticket URL: <https://core.trac.wordpress.org/ticket/33322>
WordPress Trac <https://core.trac.wordpress.org/>
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