Point hover animation flicker since 2.9.0

[emmcb]

Expected Behavior

When moving the mouse on a line chart, we should have a smooth animation on point hover.

Current Behavior

The animation flickers a lot when moving the mouse while triggering new animations at the same time. By looking at the behavior it seems that the first animation restarts at the beginning each time a new animation starts, explaining the flicker.

Steps to Reproduce (for bugs)

Can be reproduced on https://www.chartjs.org/samples/latest/scales/time/financial.html
Put the mouse cursor on a line point, then move the mouse left along the line. You will notice that the first hovered point flickers instead of disappearing smoothly.

Context

Started right after I upgraded to 2.9.0. I saw that #6129 was introduced in 2.9.0, so this bug was probably here before, but masked because there was no animation.

Environment

• Chart.js version: 2.9.0
• Browser name and version: Chromium 78, Linux

[benmccann]

Animations are actually disabled on that sample:

animation: {
  duration: 0
},

[emmcb]

Does the point hover animation uses the same animation system that other animations in chart ? Because when I enter and leave the mouse cursor on a line point I did see the point appearing and disappearing with animation.

Are you able to reproduce what I discribed on this sample ?

[benmccann]

Yes, it does use the same animation system.

No, I don't notice anything particularly jarring in the financial sample you linked to

[emmcb]

Ok maybe it is a bit hard to see this when you do not know exactly what to look for, so I made a small screen record of the issue: (compressed as a zip because github upload does not seem to support uploading video files directly)

simplescreenrecorder-2019-10-27_17.43.02.zip

[benmccann]

I actually discovered that there are multiple animation options. See the docs here: #6643. You may try options.hover.animationDuration

[kurkle]

I've noticed this issue also. By making the hoverAnimationDuration long, it becomes really noticeable:
(it works right, if you wait the complete 5 seconds before hovering next item)

https://codepen.io/kurkle/pen/dyyVVxm?editors=1010

[kurkle]

Fixed by #6845