[geo-layers] Prioritize tile requests near viewport center

[charlieforward9]

i want to explore a more responsive LoD refinementStrategy and globe cache approach for improving GlobeView initialization and flyToTransition UX - Google Earth feel. Latest experiment in this direction

Summary

Adds a Tileset2D request priority callback so visible tile requests can be ordered by distance from the viewport center.

This keeps center tiles ahead of edge tiles during throttled loading without changing TileLayer's public API.

Validation

• npx vitest run --project headless test/modules/geo-layers/tileset-2d/tile-2d-header.spec.ts

Stacked on #10250 / cr/feat/terrain-layer-globe-grid.

[coveralls]

Coverage is 83.428% — NEW-HEAT:codex/tile-center-priority into visgl:cr/feat/terrain-layer-globe-grid. No base build found for visgl:cr/feat/terrain-layer-globe-grid.

[felixpalmer]

Would be nice to see a video of this in action, shouldn't be too hard if you use a small tile size and potentially throttle your network.

Otherwise, like the idea - integrates nicely

[felixpalmer]

Isn't this backwards? the further we are from center, the higher this value and thus the higher the priority?

[charlieforward9]

Addressed in 426b06e. This is intentionally ordered this way: loaders.gl RequestScheduler sorts queued requests ascending and loads lower priority values first, so smaller squared distance means higher effective priority. I added a code comment at the call site to make that explicit.

[felixpalmer]

So why the -1? Doesn't this mean tiles which are not selected and not visible get loaded first?

[felixpalmer]

Suggested change

	private _getTileDistanceToViewportCenter(tile: Tile2DHeader): number {
	private _getTileDistanceSquared(tile: Tile2DHeader): number {

[charlieforward9]

Addressed in 426b06e. Renamed the helper to _getTileDistanceSquared so the method name matches the value returned.

[charlieforward9]

Review follow-up pushed in 426b06e.

What changed:

• Added an explicit comment that RequestScheduler loads lower numeric priority values first, which is why smaller viewport-center distance is returned directly.
• Renamed _getTileDistanceToViewportCenter to _getTileDistanceSquared.

Verification:

• yarn test node test/modules/geo-layers/tileset-2d/tile-2d-header.spec.ts test/modules/geo-layers/tileset-2d/tileset-2d.spec.ts
• Built a local TileLayer/GlobeView satellite demo against the PR branch, with maxRequests: 4, request-order overlay, and z20 zoom verification. The demo shows lower-priority-number requests loading first near the viewport center.