Largest element with a background-image that is not kept (such as linear-gradient) makes the OCI optimization have no LCP

[MathieuLamiot]

Context The issue is reported here: https://wp-media.slack.com/archives/C072P5EU5DF/p1718772180824549

Checking with WPR Inspector, I can see the beacon returns this to AJAX:

I added a JS file identical to the beacon in Chrome dev tools, added a log of firstElementWithInfo and found the LCP element was div.x-section.e9265-e1.m75d-0.m75d-1.hero-section. It is indeed the largest element with a background-image. But the background image is linear-gradient(164deg, rgb(0, 0, 0) 0%, rgb(0, 65, 85) 53%, rgb(35, 213, 171) 97%) which is not kept in the else branch of _getElementInfo (I think it does not passes the regex there). As a result, the method _getElementInfo returns an element with an elementInfo, but it is empty. This empty element takes the place of LCP.

Expected behavior TBC with Product team: I think we don't want to account for linear-gradient and instead, pick the next element as LCP. Is this correct?

Acceptance Criteria TBC with Product team.

Additional information If we want to skip elements with a background-image that is set but not as expected currently (for instance linaer-gradient), then I as able to get this behavior by just adding:

			if (element_info.bg_set.length <= 0) {
				return null;
			}

in _getElementInfo just before if (element_info.bg_set.length > 0) {

[DahmaniAdame]

LCP elements should only be considered if there is an actual image on it. It's safe to skip to the next candidate if only the gradient is declared.

The element will still be a valid LCP if a gradient + an image is being used. Example:

background: linear-gradient(164deg,rgba(0,0,0,1) 0%,rgba(0,65,85,1) 53%,rgba(35,213,171,1) 97%), url(https://dummyimage.com/600x400/000/fff);

We should still reference https://dummyimage.com/600x400/000/fff as the image to optimize in this case.

[tristan1970]

I really need this issue to be fixed. Any idea when this can be expected?

[piotrbak]

@MathieuLamiot Wouldn't it be related? https://github.com/wp-media/wp-rocket/issues/6599

[MathieuLamiot]

A little bit. 6599 can make the LCP field being empty. This issue is to fallback on another LCP candidate in that case.

[tristan1970]

Any updates? I am in dire need of having this fixed!

[juricazuanovic]

Another issue https://secure.helpscout.net/conversation/2670870897/506073/?folderId=3572910

[DahmaniAdame]

@piotrbak can we bump the priority on this one? I'm seeing more page builders/themes affected by this behavior. Sample for QA for testing: https://gist.github.com/DahmaniAdame/7ba7c1d11772fe33f2d6a1ad1488235b

[timbad2]

I signed up for WP Rocket only recently, only to discover that this is a crucial issue holding back my site's LCP problem. I use Thrive Theme Builder, from Thrive Themes, which has a background image just like this, and I'm currently wondering whether I wasted my money on this plugin WP Rocket.

Would you please share the projected ETA for this bugfix?

[WordPresseur]

https://secure.helpscout.net/conversation/2688201235/509015/

[timbad2]

https://secure.helpscout.net/conversation/2688201235/509015/

Hi, I cannot access that site. Does it say when this issue will be fixed?

If not, would someone please provide an ETA?

[viobru]

Related: https://secure.helpscout.net/conversation/2718462633/514407

[viobru]

Related: https://secure.helpscout.net/conversation/2685122326/508496/

[piotrbak]

We should make sure that https://github.com/wp-media/wp-rocket/issues/6995 is fixed while fixing this one.

[Miraeld]

Reproduce the problem

To reproduce the issue, refer to https://github.com/wp-media/wp-rocket/issues/6995 as it explains how to trigger the issue.

Identify the root cause

The issue is that the _getElementInfo method in BeaconLcp.js does not properly skip elements with background-images that do not contain actual image URLs, leading to incorrect LCP detection.

Scope a solution

To solve the issue, we must update the _getElementInfo method to skip elements with background-images that do not contain actual image URLs. Additionally, ensure elements with both gradients and image URLs are still considered valid LCP candidates. To do this, in here we can add the following:

            if (element_info.bg_set.length <= 0) {
                return null;
            }

This change ensures that elements with only gradients are evicted by checking if the bg_set array, which contains the URLs of background images, is empty. If bg_set is empty, it means there are no valid image URLs, and the element is skipped. Gradients do not have URLs, so this check effectively filters out elements with only gradients.

Also, we should change this line within _initWithFirstElementWithInfo to

const firstElementWithInfo = elements.find(item => {
            return item.elementInfo !== null && (item.elementInfo.src || item.elementInfo.srcset);
        });

in order to ensure that the firstElementWithInfo not only has a non-null elementInfo but also contains a valid src or srcset property

Development steps

• [ ] Modify _getElementInfo function
• [ ] Modify _initWithFirstElementWithInfo function
• [ ] Perform tests

Effort estimation

S

[Khadreal]

LGTM

[hanna-meda]

Related Test Plan HERE.