Play Button

1"use client";
2 
3import * as React from "react";
4import {
5  animate,
6  motion,
7  useMotionValue,
8  useReducedMotion,
9  type Transition,
10} from "motion/react";
11 
12import { cn } from "@/lib/utils";
13 
14// YouTube's play button is one `<path>` whose `d` is rewritten frame by frame,
15// and the shape of that data is the whole trick: the play triangle is split
16// down x=17 into two sub-paths, each written as a four-corner rounded quad.
17// The pause icon is the same two quads with different corners, so the morph is
18// a straight lerp of eight points instead of a path diff — the triangle's left
19// half straightens into the first bar while its tip unfolds into the second.
20//
21// The play numbers below are recovered from the player's own path data: the
22// corner vertices sit at (7.5, 3) / (7.5, 33) with a 3.93 tangent length, and
23// the tip is a degenerate corner pair at (33, 18).
24 
25const ICON_VIEW_BOX = 36;
26const EPSILON = 1e-4;
27 
28type Point = readonly [number, number];
29type Corner = { readonly point: Point; readonly radius: number };
30/** Corners run top-left → bottom-left → bottom-right → top-right. */
31type Shape = readonly Corner[];
32 
33const PLAY_SHAPES: readonly [Shape, Shape] = [
34  [
35    { point: [7.5, 3], radius: 3.93 },
36    { point: [7.5, 33], radius: 3.93 },
37    { point: [17, 27.4], radius: 0 },
38    { point: [17, 8.6], radius: 0 },
39  ],
40  [
41    { point: [17, 8.6], radius: 0 },
42    { point: [17, 27.4], radius: 0 },
43    { point: [33, 18], radius: 0 },
44    { point: [33, 18], radius: 0 },
45  ],
46];
47 
48const PAUSE_SHAPES: readonly [Shape, Shape] = [
49  [
50    { point: [8.5, 4.5], radius: 2.5 },
51    { point: [8.5, 31.5], radius: 2.5 },
52    { point: [15.5, 31.5], radius: 2.5 },
53    { point: [15.5, 4.5], radius: 2.5 },
54  ],
55  [
56    { point: [20.5, 4.5], radius: 2.5 },
57    { point: [20.5, 31.5], radius: 2.5 },
58    { point: [27.5, 31.5], radius: 2.5 },
59    { point: [27.5, 4.5], radius: 2.5 },
60  ],
61];
62 
63// A morph is only a lerp while both icons keep the same corner count.
64if (
65  process.env.NODE_ENV !== "production" &&
66  PLAY_SHAPES.some((shape, index) => shape.length !== PAUSE_SHAPES[index].length)
67) {
68  throw new Error("play-button: play and pause shapes must share a corner count.");
69}
70 
71function lerp(from: number, to: number, progress: number) {
72  return from + (to - from) * progress;
73}
74 
75function round(value: number) {
76  return Math.round(value * 100) / 100;
77}
78 
79function coords([x, y]: Point) {
80  return `${round(x)} ${round(y)}`;
81}
82 
83/**
84// … truncated