feat(GlobeController): terrain-aware default

[charlieforward9]

Goal

Make the default GlobeView controller terrain-aware — following picked 3D terrain during navigation — without applications swapping controller classes, and without the globe inheriting Web-Mercator (MapController) semantics.

Approach (updated)

An earlier revision had GlobeController extend TerrainController extends MapController, which required a normalize:false / maxBounds band-aid to stop Mercator constraints from leaking onto the globe (they inflated globe zoom and halved the pan rate). This reworks it as a mixin so the globe stays free of Mercator semantics:

• New withTerrain(Base) mixin — holds the terrain-follow logic (per-frame altitude polling via pickPosition, altitude smoothing, viewport rebasing), retyped to a generic controller state.
• TerrainController = withTerrain(MapController) — behavior, props, and instanceof MapController unchanged.
• GlobeController = withTerrain(Controller) — terrain-aware without inheriting MapController; the Mercator band-aid is removed (constrained globe pan/zoom is now structurally correct rather than patched).
• rotationPivot + _getAltitude moved to the base Controller — so the globe inherits rotate-around-the-picked-3D-point. MapController keeps only its Mercator position/maxBounds handling in setProps.
• GlobeViewport#panByPosition3D — globe-native 3D anchor used by terrain rebasing and the rotation pivot.

Public API is unchanged: MapView → MapController, GlobeView → GlobeController, identical exports.

Tests (25/25 headless)

• controllers.spec — terrain-aware default now asserts instanceof GlobeController + rotationPivot: '3d' (no longer instanceof TerrainController).
• view-states.spec — constrained globe pan/zoom correct without the band-aid.
• globe-viewport.spec — panByPosition3D.

[coveralls]

coverage: 83.589% (+0.2%) from 83.424% — codex/globe-controller-terrain into master

[chrisgervang]

Any limitations or drawbacks to changing the base class?

Is the old behavior available with a prop change, or is this backwards compatible OOB? (Note on upgrade guide if there's a change to default behavior)

[charlieforward9]

@chrisgervang

I was noticing some issues with interactivity when extending the MapController within the GlobeController.

I experiemented with a terrain mixin for controllers that can be applied ontop of MapController and GlobeController independently, and believe this is a much more robust approach to getting terrain handling to work for any controller without duplicating a bunch of logic

Lets see what @felixpalmer thinks?

[chrisgervang]

Yeah I think it'd be ideal to keep the inheritance tree shallow and instead composite this enhancement in with something like a mixin or just two independent implementations.