Interaction calls getBoundingClientRect on mousemove events

[tmcw]

getBoundingClientRect triggers reflows because it requires style recalculation. It's best not to call this function on fast-firing event handlers.

[mourner]

Here's a way to approach this: Leaflet/Leaflet@5f85e12 — cache the value on map mouseenter (and assume the position of the map doesn't change while you're interacting with the map), then use the cached value.

Not sure why it didn't make much difference in my case though: Leaflet/Leaflet#2335 (comment) — needs reevaluation. Maybe I didn't see difference because I tested on barebones pages without a lot of elements.

[bhousel]

@mourner Can you review 4e19ca2 when you get a chance?

[bhousel]

Just putting a quick update here: I did try caching the offsets on mouseenter of the canvas container, but it caused some issues when there were multiple maps on the same page and they were both trying to reset the cache.

More info here: #1598 (comment)

@jfirebaugh and I chatted and we both agree that any minor performance bump this trick might get us is not worth the complexity of introducing a cache, and we can't think of a way to avoid calling getBoundingClientRect.

e.g. offset adjustment in the middle of a mousemove:

Closing this issue as "wontfix" for now..