[anthonykim1]

Part of: #6038
Follow-up to: #6042
Follow-up to: #6043

• Add a Chromium Playwright test that simulates TUI-style alternate-buffer redraws and generates enough unique glyphs to exercise multiple atlas pages.
• Verify the atlas stays within the renderer's texture capacity, no rendering errors occur, and primary-buffer text and pixels remain unchanged afterward.
• Refine the existing manual atlas stress demo by separating its controls and renaming the scrolling option to Scroll output.
• Keep deterministic merge and eviction coverage in the existing focused regression tests.

Manual verification

npm run build
npm run esbuild
npm run esbuild-demo-client
npm run esbuild-demo-server
npm start

Open http://localhost:3000, select the WebGL demo, and click atlas stress start. Enable Scroll output to append lines instead of redrawing the same viewport.

Watch for missing glyphs, blank regions, visual corruption, or rendering stalls.

Focused automated verification

DEBUG=1 npm run test-integration-debug -- \
  --suite=addon-webgl WebglAtlasStress.test.ts --project=Chromium

This opens Chromium so the synthetic alternate-buffer workload can be observed. The result appears in the terminal, with screenshots written to:

• out-esbuild-test/playwright/atlas-stress-reference.png
• out-esbuild-test/playwright/atlas-stress-after.png

Also verified the full addon WebGL suites in Chromium, Firefox, and WebKit. The new stress test runs only in Chromium.

---

Inspirations from:

• Rendered-pixel comparisons follow WebglSharedAtlasGarble.test.ts.
• Texture-capacity assertions follow WebglAtlasOverflow.test.ts.
• Manual testing builds on the existing webglWindow.ts atlas stress workflow.

[Copilot]

Pull request overview

This PR extends xterm.js’s WebGL renderer validation by adding a Chromium-only Playwright stress test that mimics TUI-like alternate-buffer redraw patterns and forces significant glyph churn, while also refining the demo’s manual “atlas stress” controls to better match the workflow being tested.

Changes:

• Added a new Chromium-only Playwright integration test that alternates buffers, redraws synthetic TUI frames, floods unique glyphs to force multi-page atlas usage, and verifies both atlas capacity invariants and post-stress primary-buffer pixel/text stability.
• Updated the WebGL demo’s manual atlas stress UI by separating action buttons from options and renaming the scrolling toggle to Scroll output.

Show a summary per file

File	Description
demo/client/components/window/webglWindow.ts	Refactors the manual atlas stress demo UI controls and renames the scrolling option to “Scroll output”.
addons/addon-webgl/test/WebglAtlasStress.test.ts	Adds a Chromium-only Playwright stress test covering alternate-buffer redraws, atlas page churn, capacity checks, and pixel/text stability assertions.

Review details

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• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Low

[anthonykim1]

atlasStressStart.mov