webgl: fix ROI/sulci/label overlay toggles racing the texture bake

[jackgallant]

Problem

On the WebGL make_static viewers (e.g. viewer-stories-group, viewer-chen-2026), the ROI-boundary / sulci / label switches often fail to take effect — the rendered overlay disagrees with the checkbox state. It's intermittent and feels like a buffering issue.

Root cause

The overlay layers are SVG display_layers. Each switch calls Overlay.show()/hide(), which flips the layer's display style and dispatches "update", driving SVGOverlay.prototype.update(). That re-bakes the whole overlay into a GPU texture asynchronously:

svg.toDataURL("image/png", …) → new Image() → img.onload → new THREE.Texture → dispatch("update", {texture})

and the viewer commits whatever arrives:

this.uniforms.overlay.value = evt.texture;   // last to RESOLVE wins

There was no sequencing guard. Toggling layers in quick succession starts several bakes concurrently; they can resolve out of order, so the last bake to finish — not the last one requested — is left on the GPU. The overlay then drifts out of sync with the switches.

Fix

Tag each bake with a per-SVGOverlay generation id and discard any bake whose generation is stale, so only the most recent toggle's texture is ever committed. Also removes a stray console.log("Updating overlay!") that fired on every update.

7 insertions, 1 deletion; no behavior change other than correctness. node --check passes.

Verification

Repro: open a viewer, rapidly toggle ROIs / sulci / labels — before, the picture frequently lands on a state that doesn't match the boxes; after, it always settles on the current switch state. Re-baking each affected viewer via the pycortex-roidraw reengine.py tooling propagates the fix into the deployed exports.

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request introduces a generation tracking mechanism (_updateGen) to the SVG overlay update process in svgoverlay.js. This ensures that asynchronous texture bakes finishing out of order do not overwrite newer updates, preventing stale textures from being displayed. There are no review comments, and we have no feedback to provide.