fix(core): terrain cover passes no longer re-update draped layers

[chrisgervang]

For #10850

Background

Terrain covers render into a WebMercatorViewport of their own making, one per terrain tile. LayersPass activated that viewport on every layer it drew, which immediately re-ran Layer.updateState, and the screen pass undid it. A draped PathLayer re-tessellated twice a frame and kept needsRedraw set, so every cover re-rendered forever. Projection uniforms already come from the pass viewport, so layers never needed to adopt it.

terrain-extension-drape-fill-globe with stroked: true, webgl/SwiftShader:

	frames to capture	needsRedraw	duration
before	26, still climbing	set from frame 3 on, never clears	43.0 s
after	12	false every frame	12.0 s

A GlobeView + TerrainExtension app containing any PathLayer now reaches idle instead of re-tessellating and re-draping its whole dataset every frame.

Change List

• LayersPassRenderOptions: add isAuxiliaryPass
• LayersPass: auxiliary passes skip layer.activateViewport
• TerrainPass/TerrainPickingPass: mark cover and height-map passes auxiliary
• Drop a stale comment in the globe drape render case
• Unit tests

TODO

• Per-feature culling in TerrainCover (second bug in [Bug] TerrainExtension drape: draped layers never settle, and every cover draws every feature #10850) is untouched.
• MaskPass builds its own viewport the same way and may want the same flag.

---

Note

Medium Risk
Changes when layers see viewport changes during multi-pass rendering; limited to auxiliary passes and terrain paths, but could affect layer update timing if mis-flagged.

Overview
Adds an isAuxiliaryPass render option so offscreen passes (terrain height maps and per-tile covers, including picking) no longer call layer.activateViewport for their transient viewports. Layers keep update/tessellation state tied to the primary screen viewport while projection uniforms still come from the pass viewport, which stops draped layers (e.g. PathLayer on GlobeView) from re-tessellating every frame and leaving needsRedraw stuck on.

Terrain TerrainPass / TerrainPickingPass set the flag on those auxiliary renders. A new LayersPass#isAuxiliaryPass unit test locks in the behavior; the globe terrain drape render test comment is updated to reflect performance-only stroke omission.

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[coveralls]

coverage: 83.521% (-0.02%) from 83.541% — chr/terrain-cover-auxiliary-pass into master

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Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

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[cursor]

Picking covers still activate viewports

Medium Severity

Setting isAuxiliaryPass in renderTerrainCover has no effect because PickLayersPass._drawPickingBuffer rebuilds the options object and omits the flag. Cover picking still calls activateViewport, so a draped PathLayer on GlobeView re-tessellates on hover and can leave needsRedraw set.

 

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[greptile-apps]

Confidence Score: 4/5

[Medium impact] Adjusts layer update behavior for auxiliary rendering passes.

The PR appears safe to merge, with a non-blocking cleanup issue in the new test.

Findings

1.  Test leaves GPU resources allocated ▶

Summary

Adds isAuxiliaryPass so terrain covers and height maps draw without changing each layer's saved viewport.

• Terrain passes stop resetting layers to their temporary viewports.

Acknowledged scope:

• chrisgervang explicitly keeps globe strokes disabled for render-test speed.
• chrisgervang explicitly leaves per-feature TerrainCover culling untouched and defers applying the flag to MaskPass.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Prepare layers for primary viewport] --> B[Render terrain cover or height map]
  B --> C[isAuxiliaryPass is true]
  C --> D[Skip layer.activateViewport]
  D --> E[Keep primary layer geometry]
  E --> F[Draw using pass projection uniforms]
  F --> G[Render primary view]

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[greptile-apps]

Test leaves GPU resources allocated

The new test initializes a PathLayer but never calls layerManager.finalize(). Its model and attribute buffers stay allocated on the shared test device. Wrap the test body in try/finally and finalize the manager so resources are released even when an assertion fails.