Fix event.isSourceLoaded to reflect the state of source loading for sourcedata event

[ambientlight]

Fixes #2539

• use sourceCache.loaded() for event.isSourceLoaded
• sourceCache.loaded() is true, if used or usedForTerrain in set to false (after source loaded)
• do not consider source cache as loaded before update is called (because we don't know if we need to fetch tiles yet).
• added new idle sourcedatatype used in event emissions to propagate the source_cache.loaded() change to true for cases when aren't any tile loads pending: on sourceCache.update() called when viewport is outside of source bounds, on image/video/canvas source.prepare()

Context

The goal of this change is to make sure we have a single sourcedata invocation with event.isSourceLoaded true for each source at the end after initial load and subsequent interactions that result in tile fetches. Current behavior has used style.loaded() for the value of event.isSourceLoaded and this would result in whatever source tile load that comes last to have this set. Flipping the

maplibre-gl-js/src/style/style.ts

Line 744 in e43e6ef

isSourceLoaded: this.loaded(),

to sourceCache.loaded() is not enough because we will have event.isSourceLoaded set to true after the source is ready (tilejson fetched), but prior to any tiles actually being fetched.

We may only know whether the source will have tiles to fetch once the source receives transform (on update on render), and thus source_cache.loaded() would now require update to be called at least once on the source to be considered loaded.

Additionally, because the sourcedata event emissions are not tied to source_cache.loaded(), we are not guaranteed we will actually receive the emission with isSourceLoaded set to true. This applies to cases, when:

• we don't have any tiles to fetch when our source has bounds outside of the viewport (and all sourcedata invocations may happen prior to the first source_cache.update())
• we use image_source, canvas_source, video_source that will not set the tile state to loaded on its load, and will only set the tile state later on prepare() on map.painter.render().

To compensate for this, additional sourcedata event invocations with sourcedatatype idle have been added.

Launch Checklist

• Confirm your changes do not include backports from Mapbox projects (unless with compliant license) - if you are not sure about this, please ask!
• Briefly describe the changes in this PR.
• Link to related issues.
• Handle the source with bounds outside of the viewport, where on initial load there may be no events with isSourceLoaded true until the camera is moved to tileBounds.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Add an entry to CHANGELOG.md under the ## main section.

[HarelM]

Note that we will release 3.0 soon. If you would like to have this in please finish the changes and request for review.
Thanks!!

[ambientlight]

@HarelM: yes, I would like to have this in, sure, need to add the tests now, probably need a few hours, thanks.

[birkskyum]

just fyi - the breaking render test ( /debug/collision , pitched-rotated-debug, and ~3 other ) are known to be a bit flaky since the migration from node mocks to puppeteer, because of what I think is a race-condition, so don't mind it.

[birkskyum]

@ambientlight , is this ready for review?

[ambientlight]

@birkskyum: yes, it is ready for review.

[HarelM]

It's a bit more complicated than I expected, so I'll need a bit more time to review this, hopefully tonight.

[HarelM]

Can you also check the code coverage for the new code in the report here in the CI to make sure the new code is covered?

[ambientlight]

@HarelM, @birkskyum: I've addressed comments and added remaining tests for coverage of idle emissions in canvas / image / video sources. Let me know if there are more questions here, thanks.

[birkskyum]

Thanks @ambientlight !