Fixed GIF Freezing After Returning to Unfocused Tab

[frigorific44]

Resolves #5434

Changes:
GIFs now only use _lastFrameTime to track when to show the next frame. A sum with deltaTime was used before to estimate what the current time was in a way which would keep frames across all GIFs synchronized, but had the side effect of freezing a GIF when returning from a different tab or window, as the estimate would use the large deltaTime between the previous frames to estimate a curTime which has not yet been reached. Everything is effectively the same, except GIF frames are no longer translated by the running-average of deltaTime.

PR Checklist

• npm run lint passes
• [Inline documentation] is included / updated
• [Unit tests] are included / updated

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[stalgiag]

Thank you for this contribution! Returning to this after a long time away and trying to wrap my head around the messy stuff done here in the name of 'real-time'. I sometimes return to #3380 as that was the original spec for the GIF implementation.

First things first, I am not sure but I believe that + deltaTime was put in place to account for the time between the current frame and the previous frame. This is a minor sync issue and is probably a worthy trade to keep the GIFs from breaking with unfocused tabs.

Second, this PR is affected by a different but similar problem. It seems that when a GIF is not looping and the tab is unfocused long enough to reach the end, p5 never paints the final frame. This wasn't introduced by you but is likely a side effect of fixing the main issue with unfocused tabs.

I would be willing to merge this if we open another issue that clearly explains the known imperfections of the current implementation.

[stalgiag]

Thank you!!