Layers: Layer based scoring API

[jridgewell]

#11830 (comment)

Internally we can do math as we need. My question is what API we export outside and what API is actually needed. Local position, i.e. {layer, topInLayer, leftInLayer} totally always makes sense. But absolute position might not really exist in a general case, or it could be some weird that it'd be only usable in few cases, such as document ad position. But for runtime's scheduling what do we need?

• In-layer local top/left: clear.
• Intersection with any layer/viewport: intersection ratio is a great API and very clear and unambiguous.
• Scheduling scores: might be easier to pass a hierarchy-walker style callback to calculate double values?

Also, I have a performance question about the same: in theory calculating intersection ratio and distance scores does not require us to constantly recalculate structs of the form {top, left, right, bottom}. This likely would be impactful if these structs depend on scroll position and would help reduce object creates.

[ampprojectbot]

This is a high priority issue but it hasn't been updated in awhile. @jridgewell Do you have any updates?

[jridgewell]

@ampprojectbot is sooo needy. PR is #12958.