| // Tiny FPS tracker fed by ink's onFrame callback. Each entry is an Ink | |
| // frame (React commit + drain-only frames) — the right notion for | |
| // user-perceived motion. | |
| // | |
| // Zero-cost when HERMES_TUI_FPS is unset: trackFrame is undefined so the | |
| // onFrame callback short-circuits at the optional chain. | |
| import { atom } from 'nanostores' | |
| import { SHOW_FPS } from '../config/env.js' | |
| const WINDOW_SIZE = 30 | |
| export type FpsState = { | |
| fps: number | |
| /** Wraps at JS-safe int — diff pairs in a debug overlay safely. */ | |
| totalFrames: number | |
| /** Ink render-phase total for the last frame. */ | |
| lastDurationMs: number | |
| } | |
| export const $fpsState = atom<FpsState>({ fps: 0, lastDurationMs: 0, totalFrames: 0 }) | |
| const timestamps: number[] = [] | |
| let totalFrames = 0 | |
| export const trackFrame = SHOW_FPS | |
| ? (durationMs: number) => { | |
| timestamps.push(performance.now()) | |
| if (timestamps.length > WINDOW_SIZE) { | |
| timestamps.shift() | |
| } | |
| totalFrames++ | |
| if (timestamps.length < 2) { | |
| return | |
| } | |
| const elapsed = (timestamps[timestamps.length - 1]! - timestamps[0]!) / 1000 | |
| if (elapsed > 0) { | |
| $fpsState.set({ | |
| fps: Math.round(((timestamps.length - 1) / elapsed) * 10) / 10, | |
| lastDurationMs: Math.round(durationMs * 100) / 100, | |
| totalFrames | |
| }) | |
| } | |
| } | |
| : undefined | |