[PERFORMANCE] Per-frame flowBorder computations waste CPU on non-active themes

[Kirtan-pc]

Description

Every animation frame in renderer.js, the code unconditionally computes getFlowSpeedProfile(), getFlowDirectionValue(), and flowTravelDistance regardless of which theme is active. These computations create merged settings objects and parse theme config — all wasted work for 11 out of 12 themes. On multi-monitor setups with multiple overlay windows, this waste is multiplied.

Steps to Reproduce

1. Launch Paraline with any theme other than flowBorder active.
2. Open the DevTools Performance tab on the overlay window.
3. Record a profile and look for getFlowSpeedProfile, getFlowDirectionValue in the call tree.
4. Observe that these functions execute every frame despite being irrelevant to the active theme.

Expected Behaviour

Flow border calculations should be guarded behind if (visualizerState.selectedTheme === "flowBorder").

Actual Behaviour

The computations run unconditionally on every animation frame (~16ms interval at 60fps).

[github-actions]

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[Kirtan-pc]

Hi @SamXop123,

I would like to work on this issue under GSSoC 2026.

Could you please assign this issue to me?

Thank you!