xterm.js: Render performance degradation from 3.0.2 to 3.7.0

Update: This issue should be introduced between 3.3.0 and 3.4.0.

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Originally reported at: https://github.com/tsl0922/ttyd/issues/126

Details

• Browser and browser version: Chrome69.0.3497.81
• OS version: macOS High Sierra 10.13.6
• xterm.js version: 3.7.0

Steps to reproduce

1. Start the 3.7.0 demo.
2. Open the demo with chrome, and turn on the FPS meter.
3. Resize it to a larger size (155 cols / 40 rows).
4. Run: vtop (npm install -g vtop).
5. Press and hold the down arrow button.
6. Result: 4-14 PFS on 3.7.0 (not stable) and 30-35 FPS on 3.3.0 (stable).

It’s much smoother on 3.0.2 (ttyd 1.4.0) than 3.7.0 (ttyd 1.4.1).