Multi-select: high cpu and unresponsive ui

[blackboxlogic]

In the dev branch of ID 2.17.3 (currently here) where multi-select has been implemented, when I select many (25) nodes, my cpu sits at 60% and click events in iD start to "miss", meaning that the user actions occasionally don't illicit any response from the UI.

I suspect that the pulsing red boarder on selected elements is expensive. Consider:

• Limit the quantity of elements which can be selected simultaneously
• Reduce the cost of the pulsing selection-highlighter
• Add a setting for the selection-highlighter to be static (non-animated)
• Make the selection-highlighter static when multiple elements are selected

[quincylvania]

The good news is: this used to be a lot worse! See #3571. On my setup I can select a few hundred nodes and suffer only a minor performance hit. But I'm concerned that you're seeing something worse. What browser/system are you testing with?

#2911 #3919 was also about improving the selection animation performance but was closed as stale.

[blackboxlogic]

Windows 10 home
Intel Core i7-7500 @ 2.8 GHz
16 gigs ram
Firefox 77.0.1 (64-bit)

No errors in the developer console in Firefox. The selection-highlighter also gets jittery and starts skipping transparency frames, jumping from opaque to not.

I just tested on chrome and CPU stays much lower but click events get dropped about the same.