Lazy image loading + CSS transform

[rwlbuis]

I noticed implementations behave differently on Intersection Observer combined with CSS transform:
https://jsfiddle.net/38v2dots/2/

In Firefox the callback is triggered as soon as 1 pixel of the image is visible in the viewport. In Chrome the callback is triggered once the complete CSS transform is finished.

I personally like Firefox behaviour more here. Is there anything in the spec(s) about this? I also wonder what the rules are for CSS animations instead of transforms?

[rwlbuis]

BTW this is basically w3c/IntersectionObserver#484, but since lazy image loading is often/always implemented using intersection observer, the lines are blurred...

[annevk]

The standard uses Intersection Observer as its underlying primitive. We could keep this open to track that issue from our side and ensure that once it is resolved image loading also takes the resolution into account I suppose.

[rwlbuis]

The standard uses Intersection Observer as its underlying primitive. We could keep this open to track that issue from our side and ensure that once it is resolved image loading also takes the resolution into account I suppose.

Yes, to be clear, I opened this mainly because it would have bigger audience than just the Intersection Observer spec.