Master ticket: Variable label placement enhancements

[chloekraw]

Earlier this year, we released a feature called variable label placement which enables map designers to try multiple (up to 9) placement options for labels around their anchor. This was added in #7596.

To enable variable label placement, set text-variable-anchor, text-radial-offset and text-justify on a symbol layer. For an excellent write-up of this feature and its benefits, see @nickidlugash's ticket #5038.

Since the initial launch of this feature, we've collected valuable insight into how we can improve these properties and their interaction with other style specification properties. We're doing a push to get some of these improvements landed in the next release, queso.

I'm cutting a ticket to help us stay organized and to collect future tickets that are open about this feature.

Enhancement	Ticket	Owner	Timeline	Status
Anchor positions should be cleared by setStyle	#8397	@asheemmamoowala	release-picklejuice	✅ closed by #8473 and mapbox/mapbox-gl-native#15129
Account for icon size/bounding boxes	#8598; mapbox/mapbox-gl-native#15365	@pozdnyakov	release-ristretto	✅ closed by #8642 and mapbox/mapbox-gl-native#15542
Account for character descenders	#8560; mapbox/mapbox-gl-native#15366	@pozdnyakov / @alexshalamov	none	Depends on #191
Use with icon-text-fit	#8583; mapbox/mapbox-gl-native#15346	@alexshalamov / @ansis	release-queso	✅ closed by mapbox/mapbox-gl-native#15367; JS PR forthcoming
Use with icon-/text-allow-overlap	#8527; mapbox/mapbox-gl-native#15357	@pozdnyakov / @ansis	release-queso	✅ closed by #8620 and mapbox/mapbox-gl-native#15354
Deduplicate anchor positions	#8445		release-ristretto (lower priority)	needs assignment
Reduce jumpiness	#8219		none

Feel free to update this table directly as work moves or assignments change.

cc @mapbox/gl-js @mapbox/gl-native @mapbox/map-design-team @mapbox/maps-android @mapbox/maps-ios @philogb

[asheemmamoowala]

After talking this over with @ansis last week, I'm moving 'Deduplicate anchor positions' from release-queso to release-r. It is a minor performance enhancement and should be done in both JS and Native.

cc @chloekraw

[xabbu42]

I have a situation where variable label placement for lines would be useful. That is I have a data file with line features for bicycle ways in Switzerland organized by the route number. Many of them partially overlap as often the same road is part of multiple national routes. If I do not preprocess the data at all and want to add symbols on the map using a symbol layer, sometime one line feature blocks out labels for the other completely. What I would want is for the symbols for the second line feature to be moved a bit along the line so they are drawn beside the symbols of the first line feature as the exact positions along the line are not important (but the symbol-spacing for each individual feature is).

Something like symbol-variable-spacing which allows the icons to be a bit closer or further away so they can still be drawn would be very useful in that case.

I have no idea how hard this is to implement and if this issue actually has anything todo with this. I can open a new feature request issue if anybody is interested. Unfortunately I'm in no position to implement it myself.