Skip creating textures for empty atlases

[IvanSanchez]

Indirectly fixes most of the deprecation warnings from #2030.

By making the tile worker return undefined instead of empty 1x1 atlases, the main thread skips creating textures for those. Those empty textures were the source of most of the WebGL warnings, AFAICS.

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.
• Include before/after visuals or gifs if this PR includes visual changes.
• Write tests for all new functionality.
• Document any changes to public APIs.
• Post benchmark scores.
• Add an entry to CHANGELOG.md under the ## main section.

[HarelM]

Thanks for taking the time to open this PR!!
If this is still not complete, please use a draft PR.
Otherwise, please add changelog and tests.
Also would be nice to simply not initialize the image atlas and glyph atlas, if this is not possible I would feel better if empty would be a calculated property (getter only) according to the state of the class.

[IvanSanchez]

Initialization of the empty property of atlases should be fine now. I don't think it's possible to properly skip atlas initialization, as the worker code refers to the positions inside the (empty) atlases. Since this is my first foray into the MapLibre code, I'd rather make minimal changes.

Regarding tests, I'm unfamiliar with MapLibre's test scaffolding. I'm not sure if it's even possible to run an automated puppeteer/karma/whatever browser test on a headless Firefox instance and check for WebGL warnings in the console.

[IvanSanchez]

...and of course the unit tests assume that there are atlas images and textures for every tile, despite the if (data.imageAtlas) { line in tile.ts 😠

file:///home/runner/work/maplibre-gl-js/maplibre-gl-js/src/render/draw_fill_extrusion.ts:77
            tile.imageAtlasTexture.bind(gl.LINEAR, gl.CLAMP_TO_EDGE);
                                   ^
TypeError: Cannot read properties of undefined (reading 'bind')

[HarelM]

There are browser tests, but I agree FF is problematic here. Unit tests would be enough at this point.

[IvanSanchez]

The changes impact the behaviour of one specific render test: extrusion pattern with missing texture. The current expectation is a transparent image, but removing the texture (and running the shader with no bound texture) creates a black extrusion.

@HarelM Would this change in behaviour be OK? Otherwise it'd be possible to create an empty transparent texture just for this edge case.

[HarelM]

Can you fix the test so that I can see the change in the image?
I'm not sure I fully understand how it would look in this specific case.
Also maybe worth trying to find out when was this test added and the changes around it to maybe better understand the motivation behind this test and this behavior.

[HarelM]

The code you added is fairly simple and I don't see big issues with it.
There should be either failing unit tests that needs to be fixed as part of this PR or new unit tests that needs to be added - not just render tests.

[IvanSanchez]

I'm not sure I fully understand how it would look in this specific case.

So the problematic render test is tests/fill-extrusion-pattern/missing. AFAICS, it checks that a faulty stylesheet (one referring to a pattern image that doesn't exist in the spritesheet) doesn't crash the library. It does call console.warn to inform about this, so I'm not worrying much about changing the behaviour (since IMO using a non-existing image pattern is undefined behaviour).

For reference, most of tests/fill-extrusion-pattern/ looks like:

...except for tests/fill-extrusion-pattern/missing, which currently is a blank image.

After my changes, that specific render test looks like:

...this difference happens because, before this PR, tiles with no image atlas would allocate a transparent 1x1 texture - drawing an extrusion pattern with an invalid image would use that transparent 1x1 texture.

Since this PR skips the creation of those empty textures, the shader uses no texture - and the texture sampler somehow defaults to solid black.

Hope that helps?

[HarelM]

Yes, it does! Sorry for the delay in response.
I don't think this edge case is interesting, but this is a breaking change so we need to document it in the changelog.

[HarelM]

Please add unit test to cover the new functionality (besides fixing the render tests).

[HarelM]

Add that as part of the above item with a [Breaking] prefix, feel free to add the emoji to the other breaking items as well.

[HarelM]

Bummer, we didn't add it to version 3. :-(
Is there a way to keep this backward compatible somehow?
Also unit tests are still missing...

[HandyMenny]

This is the PR that added tests/fill-extrusion-pattern/missing: mapbox/mapbox-gl-js#4687

I would say that trasparent texture is intended behaviour