[scroll-animations-1] Where is the range of threshold values checked?

[birtles]

For element-based offsets, the threshold member has the following description:

A double in the range of [0.0, 1.0] that represent the precentage[sic] of the target that is expected to be visible in source's scrollport at the intersection offset.

But we don't seem to validate anywhere that that is the case. Should be check it in the constructor for ScrollTimeline?

[birtles]

That said, I'm not sure if we want to enforce that range or not. Maybe -0.1 is a useful measure? If so, we should probably say that.

[bramus]

Having the ability to — for example — set end 1.2 as the from-offset sure comes in handy, as it allows you to add some “breathing room” to all of your animations.

A from-offset of selector(#element) end 1.2 basically translates to “the element is 1/5th over the bottom edge”. In that case the animation will not start when #element is stuck against the bottom, but only after it's "120%" into the scrollport.

Also see #6068, where taking scroll-padding into account is suggested.

Both these use-cases could be allowed I guess:

• Over/undershooting the threshold is calculated in relation to block-size of the #element
• scroll-padding (if expressed as a percentage) is calculated in relation to the block-size of the scrollport

[MattWilcox]

I'd prefer it to not clamp to a "valid range" when that "valid range" is entirely arbitrary and restricts design possibilities.

[flackr]

I suspect this may still be applicable for View Timelines, i.e. a desire to be able to extend the effective element size for the purpose of its fit to the view timeline. In scroll snap terms this would be scroll-margin. Note that scroll-margin does not seem to accept a percentage currently so view-timeline-inset seems at least as flexible as what you can do with scroll snap as you can simply add / subtract what the offset relative to the element should be from the inset.

[fantasai]

@flackr Isn't this exactly what view-timeline-inset is for? Or am I missing something?

[flackr]

Right, the gap between view-timeline-inset and end: 1.2 is if you specify view-timeline-inset: 20% my understanding is it will be 20% of the scroll range rather than 20% of the element. I don't think this will be significant and imagine we don't need to worry about this.

The percentages we have in the spec don't seem to have precise limits so I'd propose we close this one.

[fantasai]

@birtles @bramus Can you confirm if you're ok to close based on @flackr's comment above?

[birtles]

It looks like the threshold member no longer exists so it seems fine to close this.

[bramus]

The thresholds are now gone indeed. To mimic what used to be possible, one could set the timeline range percentages to a value lower than 0% or greater than 100%. This however, is not allowed. The keyframe block will be dropped in that case, and I’m perfectly fine with that.

Closing issue. Adjusting labels.