LargestContentfulPaint has both `renderTime` and `paintTime` via the mixin. Are they different?

[smfr]

https://w3c.github.io/largest-contentful-paint/#sec-largest-contentful-paint-interface has:

readonly attribute [DOMHighResTimeStamp](https://w3c.github.io/hr-time#dom-domhighrestimestamp) renderTime;

but also includes PaintTimingMixin which supplies paintTime, so there are two paint-time-related members.

https://w3c.github.io/paint-timing/#sec-PaintTimingMixin says:

To get the default paint timestamp for a paint timing info paintTimingInfo, return paintTimingInfo’s implementation-defined presentation time if it is non-null, otherwise paintTimingInfo’s rendering update end time.

LCP says:

The renderTime attribute must return the default paint timestamp given this’s paint timing info.

which is the same thing.

Why does renderTime exist?

[smfr]

Chrome doesn't seem to include the PaintTimingMixin so it doesn't expose paintTime or presentationTime

[noamr]

renderTime would return presentationTime if it is supported and paintTime otherwise. However, it is equivalent to startTime which makes it redundant. Perhaps it should be deprecated but I think it can't be removed due to legacy use.

Chrome doesn't seem to include the PaintTimingMixin so it doesn't expose paintTime or presentationTime

It's still behind a flag until event timing support is completed, but it is en route.

[smfr]

But isn't paintTime also defined to return presentationTime?

I think we need a table somewhere with all these timestamps and what they mean.

[noamr]

But isn't paintTime also defined to return presentationTime?

I think we need a table somewhere with all these timestamps and what they mean.

You mean this?
https://github.com/w3c/paint-timing/blob/main/presentation-timestamps.md :)

[smfr]

Something like this. Free free to edit.

Name	On	Denotes	Notes
rendering update end time		Where is this defined?
default paint timestamp		presentation time or rendering update end time
startTime	PerformanceEntry	"when the paint occured(sic)"
paintTime	PaintTimingMixin	rendering update end time
presentationTime	PaintTimingMixin	implementation-defined presentation time	Optional
loadTime	LargestContentfulPaint	When an image load completes
renderTime	LargestContentfulPaint	default paint timestamp

[smfr]

I don't like these circular links. At https://w3c.github.io/paint-timing/#sec-PaintTimingMixin, the last "rendering update end time" links back to the line a few lines above (which doesn't match the paintTime structure member name), rather than linking to some fundamental definition of "rendering update end time" which I'd expect to come from the HTML spec.

[noamr]

The "rendering update end time" is defined as a struct member. What it means is normatively defined by when it is populated (though we can always add informative text), and you can backstep from it using references via "mark paint timing" all the way to the HTML spec.

This is a very common practice all over the place in specs, especially when interfacing with the HTML standard.

By "circular links" you mean back references?

[noamr]

Anyway, I will add an intro to PaintTimingMixin that helps with this.

[smfr]

you can backstep from it using references via "mark paint timing" all the way to the HTML spec.

I was not able to find the chain of links for this.