A live price on a monotone spline that never invents a low: it streams while you watch it, bends between three ranges, and answers your finger.
The prompt32,575 characters
Add the "Chart" component from notboring to my project.
It is licensed for use in my projects — notboring.dev/license. Please:
1. Create the component at a sensible path for this
project, named Chart, from the source below.
2. It needs nothing beyond React.
3. Add the CSS to the project's stylesheet.
4. THE PART THAT NEEDS YOUR JUDGMENT. The CSS reads
these custom properties and does not define them:
--font-ui
--ink
--ink-3
--ink-4
--ink-5
--on-ink
They are notboring's design tokens. Map each one to
whatever this project already uses for the same
job — its own ink, ground, surface and UI font —
rather than defining them as new globals. If the
project has no equivalent, define it locally on
the component's own root so nothing leaks out.
Anything ending -rgb wants three bare numbers,
because the CSS builds rgba() from it.
5. IF YOU CHANGE IT, GO ALL THE WAY. This block is
built for every state its object can really be
in — empty, one, full, refused, undone, pressed
twice, interrupted halfway — and not only the one
the demo opens on. Adapt it and the same standard
holds: work out that list before you write, and
build the whole of it. Never settle for the
minimum that makes the screenshot right. A
component somebody has to come back and finish is
the thing this was written to replace.
Keep the comments. They say why the numbers are what
they are, and they are most of what makes this worth
copying rather than rewriting.
--- Chart.tsx ---
import { useEffect, useRef, useState } from "react";
/* ══ Chart ════════════════════════════════════════════════
A price, live, and the line it is drawing.
AFTER BENJI TAYLOR'S LIVELINE, and the block says so on its
face. What is taken is the technique, which is the part that
is hard: the clock as the x axis, the tip drawn at the
present instant, the frame-rate-proof chase, the monotone
spline with its constraint, and the burst on a swing.
IT IS DRAWN EVERY FRAME, NOT EVERY POINT. The first build
of this put a new point on an SVG path and slid the whole
group over with a tween, which is a line that redraws twice
a second and coasts in between — and you can see it, because
a tween restarted on each point can never be seamless across
the seam. Here the canvas is repainted on every animation
frame and the x of every point is computed from the clock:
`x = width - (now - t) / window * width`. The line is not
moved, it is drawn where it is, and where it is depends on
what time it is. There is no seam to stutter at.
THE TIP IS AT `now`, NOT AT THE LAST READING. The newest
reading landed some fraction of a second ago, so a line
The rest — the source and its comments — is what the plan opens.