07ドラッグした速度のまま飛ぶ投げボール

<main class="stage">
<div class="bp is-demo" id="bpRoot" tabindex="0">
  <canvas class="bp__canvas" id="bpCanvas" width="480" height="300"></canvas>
  <p class="bp__caption">ボールをつかんで動かした直近数フレームの移動量から速度を計算し、放した瞬間にその速度のまま投げ出され、壁に当たると反射する。</p>
</div>
</main>

@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-orange);

.bp {
  position: relative;
  width: min(92vw, calc(160vh - 12.8vw));
  aspect-ratio: 480 / 300;
  margin: 0 auto;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $stage-orange;
  touch-action: none;
}

.bp__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.bp__caption {
  position: absolute;
  left: $sp-3;
  bottom: $sp-3;
  max-width: 80%;
  margin: 0;
  padding: $sp-1 $sp-3;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .85);
  color: $subject-ink;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .bp__caption { font-size: 10px; padding: $sp-1 $sp-2; }
}

@media (prefers-reduced-motion: reduce) {
  .bp { cursor: default; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.bp {
  position: relative;
  width: min(92vw, 160vh - 12.8vw);
  aspect-ratio: 480/300;
  margin: 0 auto;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #ff4d1f;
  touch-action: none;
}

.bp__canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.bp__caption {
  position: absolute;
  left: 12px;
  bottom: 12px;
  max-width: 80%;
  margin: 0;
  padding: 4px 12px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.85);
  color: #17141a;
  font-weight: 500;
  font-size: 12px;
  line-height: 1.4;
  pointer-events: none;
}

@media (max-width: 340px) {
  .bp__caption {
    font-size: 10px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .bp {
    cursor: default;
  }
}

(function () {
  // 기법: 드래그 중 포인터 위치·시각을 최근 몇 개만 버퍼에 담아 두고, 놓는 순간 버퍼의
  // 처음-마지막 샘플로 속도(이동거리/경과시간)를 계산해 그 속도로 공을 던진다(스냅샷
  // 한 프레임 차분이 아니라 최근 구간 평균이라 손떨림에 덜 흔들린다). 던져진 공은
  // 공기 저항으로 서서히 느려지며 벽에 부딪힐 때마다 WALL_BOUNCE 만큼 반사·감쇠한다.
  var root = document.getElementById('bpRoot');
  var canvas = document.getElementById('bpCanvas');
  var ctx = canvas.getContext('2d');
  var wrap = canvas.parentElement;

  var CALC_W = 320, CALC_H = 200;
  var WALL_BOUNCE = 0.72;
  var AIR_DRAG = 0.55;
  var SAMPLE_WINDOW_MS = 140;
  var KEY_IMPULSE = 130;
  var THROW_IMPULSE = 260;

  function seedRand(seed) {
    var s = seed >>> 0;
    return function () { s = (s * 1664525 + 1013904223) >>> 0; return s / 4294967296; };
  }
  var rand = seedRand(427071);

  var ball = { x: CALC_W * 0.5, y: CALC_H * 0.5, vx: 90, vy: -60, r: 18, color: '#ffcf7a', squash: 0, heading: -0.9 };
  var dragging = false;
  var samples = [];

  function recordSample(x, y, t) {
    samples.push({ x: x, y: y, t: t });
    while (samples.length && t - samples[0].t > SAMPLE_WINDOW_MS) samples.shift();
  }

  function releaseVelocity(nowT) {
    if (samples.length < 2) return { vx: 0, vy: 0 };
    var a = samples[0], b = samples[samples.length - 1];
    var dt = Math.max(16, b.t - a.t) / 1000;
    return { vx: (b.x - a.x) / dt, vy: (b.y - a.y) / dt };
  }

  function throwBall(vx, vy) {
    ball.vx = vx; ball.vy = vy;
    if (Math.hypot(vx, vy) > 1) ball.heading = Math.atan2(vy, vx);
  }

  function stepSim(dtMs) {
    var dtS = dtMs / 1000;
    if (dragging) return;
    ball.vx -= ball.vx * AIR_DRAG * dtS;
    ball.vy -= ball.vy * AIR_DRAG * dtS;
    ball.x += ball.vx * dtS;
    ball.y += ball.vy * dtS;
    var hit = false;
    if (ball.x - ball.r < 0) { ball.x = ball.r; ball.vx = -ball.vx * WALL_BOUNCE; hit = true; }
    if (ball.x + ball.r > CALC_W) { ball.x = CALC_W - ball.r; ball.vx = -ball.vx * WALL_BOUNCE; hit = true; }
    if (ball.y - ball.r < 0) { ball.y = ball.r; ball.vy = -ball.vy * WALL_BOUNCE; hit = true; }
    if (ball.y + ball.r > CALC_H) { ball.y = CALC_H - ball.r; ball.vy = -ball.vy * WALL_BOUNCE; hit = true; }
    if (hit) ball.squash = Math.min(1, Math.hypot(ball.vx, ball.vy) / 260 + 0.2);
    ball.squash = Math.max(0, ball.squash - dtS * 3.4);
  }

  function draw() {
    var sx = cw / CALC_W, sy = ch / CALC_H;
    ctx.fillStyle = 'rgba(255,110,46,0.24)';
    ctx.fillRect(0, 0, cw, ch);
    ctx.strokeStyle = 'rgba(255,255,255,0.3)';
    ctx.lineWidth = 2;
    ctx.strokeRect(2, 2, cw - 4, ch - 4);
    var px = ball.x * sx, py = ball.y * sy, pr = ball.r * ((sx + sy) / 2);
    var speed = Math.hypot(ball.vx, ball.vy);
    var stretch = dragging ? 1.08 : 1 + Math.min(0.4, speed / 600);
    ctx.save();
    ctx.translate(px, py);
    ctx.rotate(ball.heading);
    ctx.scale(stretch, (1 - ball.squash * 0.3) / stretch);
    ctx.beginPath();
    ctx.arc(0, 0, pr, 0, Math.PI * 2);
    ctx.fillStyle = ball.color;
    ctx.fill();
    ctx.restore();
    if (dragging) {
      ctx.beginPath();
      ctx.arc(px, py, pr + 6, 0, Math.PI * 2);
      ctx.strokeStyle = 'rgba(255,255,255,0.6)';
      ctx.lineWidth = 2;
      ctx.stroke();
    }
  }

  var cw = 480, ch = 300;
  function fit() {
    var r = wrap.getBoundingClientRect();
    cw = Math.max(1, Math.round(r.width));
    ch = Math.max(1, Math.round(r.height));
    canvas.width = cw; canvas.height = ch;
    draw();
  }

  var reduce = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
  var elapsed = 0;
  if (reduce) root.classList.remove('is-demo');

  function toCalc(clientX, clientY) {
    var rect = canvas.getBoundingClientRect();
    var nx = (clientX - rect.left) / rect.width;
    var ny = (clientY - rect.top) / rect.height;
    return { x: nx * CALC_W, y: ny * CALC_H };
  }

  function startDrag(cx, cy) {
    root.classList.remove('is-demo');
    var p = toCalc(cx, cy);
    if (Math.hypot(p.x - ball.x, p.y - ball.y) > ball.r * 2.2) return;
    dragging = true;
    samples = [];
    recordSample(p.x, p.y, performance.now());
  }
  function moveDrag(cx, cy) {
    if (!dragging) return;
    var p = toCalc(cx, cy);
    ball.x = Math.max(ball.r, Math.min(CALC_W - ball.r, p.x));
    ball.y = Math.max(ball.r, Math.min(CALC_H - ball.r, p.y));
    recordSample(ball.x, ball.y, performance.now());
    if (reduce) draw();
  }
  function endDrag() {
    if (!dragging) return;
    dragging = false;
    var v = releaseVelocity(performance.now());
    var mag = Math.hypot(v.vx, v.vy);
    var maxSpeed = 420;
    if (mag > maxSpeed) { v.vx = v.vx / mag * maxSpeed; v.vy = v.vy / mag * maxSpeed; }
    throwBall(v.vx, v.vy);
    if (reduce) { stepSim(16); draw(); }
  }

  canvas.addEventListener('mousedown', function (e) { startDrag(e.clientX, e.clientY); });
  window.addEventListener('mousemove', function (e) { moveDrag(e.clientX, e.clientY); });
  window.addEventListener('mouseup', endDrag);
  canvas.addEventListener('touchstart', function (e) {
    if (e.touches && e.touches[0]) startDrag(e.touches[0].clientX, e.touches[0].clientY);
  }, { passive: true });
  canvas.addEventListener('touchmove', function (e) {
    if (e.touches && e.touches[0]) moveDrag(e.touches[0].clientX, e.touches[0].clientY);
  }, { passive: true });
  canvas.addEventListener('touchend', endDrag);

  root.addEventListener('keydown', function (e) {
    var handled = true;
    if (e.key === 'ArrowLeft') throwBall(ball.vx - KEY_IMPULSE, ball.vy);
    else if (e.key === 'ArrowRight') throwBall(ball.vx + KEY_IMPULSE, ball.vy);
    else if (e.key === 'ArrowUp') throwBall(ball.vx, ball.vy - KEY_IMPULSE);
    else if (e.key === 'ArrowDown') throwBall(ball.vx, ball.vy + KEY_IMPULSE);
    else if (e.key === ' ' || e.code === 'Space') {
      var ang = ball.heading;
      throwBall(Math.cos(ang) * THROW_IMPULSE, Math.sin(ang) * THROW_IMPULSE);
    } else handled = false;
    if (handled) {
      e.preventDefault();
      root.classList.remove('is-demo');
      if (reduce) { stepSim(16); draw(); }
    }
  });

  // 자동재생: 가상 드래그 경로를 샘플로 기록한 뒤 같은 releaseVelocity/throwBall 을
  // 호출한다 — 실제 입력과 동일한 함수 경로다.
  var demoState = 'idle';
  var demoT0 = 0;
  function demoDrive(nowMs) {
    var cyc = nowMs % 1600;
    if (cyc < 480) {
      if (demoState !== 'drag') { demoState = 'drag'; dragging = true; samples = []; demoT0 = nowMs; }
      var f = cyc / 480;
      var sx0 = CALC_W * 0.28, sy0 = CALC_H * 0.7;
      var ex0 = CALC_W * 0.62, ey0 = CALC_H * 0.32;
      ball.x = sx0 + (ex0 - sx0) * f;
      ball.y = sy0 + (ey0 - sy0) * f;
      recordSample(ball.x, ball.y, nowMs);
    } else if (demoState !== 'thrown') {
      demoState = 'thrown';
      dragging = false;
      var v = releaseVelocity(nowMs);
      var mag = Math.hypot(v.vx, v.vy) || 1;
      var target = 300;
      throwBall(v.vx / mag * target, v.vy / mag * target);
    }
  }

  var lastTs = null;
  var acc = 0;
  var FIXED_DT = 16;
  function tick(ts) {
    if (lastTs === null) lastTs = ts;
    var frameDt = Math.min(ts - lastTs, 48);
    lastTs = ts;
    if (!reduce) {
      acc += frameDt;
      while (acc >= FIXED_DT) {
        elapsed += FIXED_DT;
        if (root.classList.contains('is-demo')) demoDrive(elapsed);
        stepSim(FIXED_DT);
        acc -= FIXED_DT;
      }
      draw();
    }
    requestAnimationFrame(tick);
  }
  fit();
  window.addEventListener('resize', fit);
  draw();
  requestAnimationFrame(tick);
})();

import { useEffect, useRef } from "react";
import styles from "./BallPhysicsDragThrowMomentum.module.scss";

type Sample = { x: number; y: number; t: number };

export default function BallPhysicsDragThrowMomentum() {
  const rootRef = useRef<HTMLDivElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);

  useEffect(() => {
    const root = rootRef.current;
    const canvas = canvasRef.current;
    if (!root || !canvas) return;
    const ctx = canvas.getContext("2d");
    if (!ctx) return;
    const wrap = canvas.parentElement as HTMLElement;

    const CALC_W = 320, CALC_H = 200;
    const WALL_BOUNCE = 0.72;
    const AIR_DRAG = 0.55;
    const SAMPLE_WINDOW_MS = 140;
    const KEY_IMPULSE = 130;
    const THROW_IMPULSE = 260;

    const ball = { x: CALC_W * 0.5, y: CALC_H * 0.5, vx: 90, vy: -60, r: 18, color: "#ffcf7a", squash: 0, heading: -0.9 };
    let dragging = false;
    let samples: Sample[] = [];

    function recordSample(x: number, y: number, t: number) {
      samples.push({ x, y, t });
      while (samples.length && t - samples[0].t > SAMPLE_WINDOW_MS) samples.shift();
    }

    function releaseVelocity() {
      if (samples.length < 2) return { vx: 0, vy: 0 };
      const a = samples[0], b = samples[samples.length - 1];
      const dt = Math.max(16, b.t - a.t) / 1000;
      return { vx: (b.x - a.x) / dt, vy: (b.y - a.y) / dt };
    }

    function throwBall(vx: number, vy: number) {
      ball.vx = vx; ball.vy = vy;
      if (Math.hypot(vx, vy) > 1) ball.heading = Math.atan2(vy, vx);
    }

    function stepSim(dtMs: number) {
      const dtS = dtMs / 1000;
      if (dragging) return;
      ball.vx -= ball.vx * AIR_DRAG * dtS;
      ball.vy -= ball.vy * AIR_DRAG * dtS;
      ball.x += ball.vx * dtS;
      ball.y += ball.vy * dtS;
      let hit = false;
      if (ball.x - ball.r < 0) { ball.x = ball.r; ball.vx = -ball.vx * WALL_BOUNCE; hit = true; }
      if (ball.x + ball.r > CALC_W) { ball.x = CALC_W - ball.r; ball.vx = -ball.vx * WALL_BOUNCE; hit = true; }
      if (ball.y - ball.r < 0) { ball.y = ball.r; ball.vy = -ball.vy * WALL_BOUNCE; hit = true; }
      if (ball.y + ball.r > CALC_H) { ball.y = CALC_H - ball.r; ball.vy = -ball.vy * WALL_BOUNCE; hit = true; }
      if (hit) ball.squash = Math.min(1, Math.hypot(ball.vx, ball.vy) / 260 + 0.2);
      ball.squash = Math.max(0, ball.squash - dtS * 3.4);
    }

    let cw = 480, ch = 300;
    function draw() {
      const sx = cw / CALC_W, sy = ch / CALC_H;
      ctx!.fillStyle = "rgba(255,110,46,0.24)";
      ctx!.fillRect(0, 0, cw, ch);
      ctx!.strokeStyle = "rgba(255,255,255,0.3)";
      ctx!.lineWidth = 2;
      ctx!.strokeRect(2, 2, cw - 4, ch - 4);
      const px = ball.x * sx, py = ball.y * sy, pr = ball.r * ((sx + sy) / 2);
      const speed = Math.hypot(ball.vx, ball.vy);
      const stretch = dragging ? 1.08 : 1 + Math.min(0.4, speed / 600);
      ctx!.save();
      ctx!.translate(px, py);
      ctx!.rotate(ball.heading);
      ctx!.scale(stretch, (1 - ball.squash * 0.3) / stretch);
      ctx!.beginPath();
      ctx!.arc(0, 0, pr, 0, Math.PI * 2);
      ctx!.fillStyle = ball.color;
      ctx!.fill();
      ctx!.restore();
      if (dragging) {
        ctx!.beginPath();
        ctx!.arc(px, py, pr + 6, 0, Math.PI * 2);
        ctx!.strokeStyle = "rgba(255,255,255,0.6)";
        ctx!.lineWidth = 2;
        ctx!.stroke();
      }
    }

    function fit() {
      const r = wrap.getBoundingClientRect();
      cw = Math.max(1, Math.round(r.width));
      ch = Math.max(1, Math.round(r.height));
      canvas!.width = cw; canvas!.height = ch;
      draw();
    }

    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
    let elapsed = 0;
    if (reduce) root.classList.remove("is-demo");

    function toCalc(clientX: number, clientY: number) {
      const rect = canvas!.getBoundingClientRect();
      const nx = (clientX - rect.left) / rect.width;
      const ny = (clientY - rect.top) / rect.height;
      return { x: nx * CALC_W, y: ny * CALC_H };
    }

    function startDrag(cx: number, cy: number) {
      root!.classList.remove("is-demo");
      const p = toCalc(cx, cy);
      if (Math.hypot(p.x - ball.x, p.y - ball.y) > ball.r * 2.2) return;
      dragging = true;
      samples = [];
      recordSample(p.x, p.y, performance.now());
    }
    function moveDrag(cx: number, cy: number) {
      if (!dragging) return;
      const p = toCalc(cx, cy);
      ball.x = Math.max(ball.r, Math.min(CALC_W - ball.r, p.x));
      ball.y = Math.max(ball.r, Math.min(CALC_H - ball.r, p.y));
      recordSample(ball.x, ball.y, performance.now());
      if (reduce) draw();
    }
    function endDrag() {
      if (!dragging) return;
      dragging = false;
      const v = releaseVelocity();
      const mag = Math.hypot(v.vx, v.vy);
      const maxSpeed = 420;
      if (mag > maxSpeed) { v.vx = (v.vx / mag) * maxSpeed; v.vy = (v.vy / mag) * maxSpeed; }
      throwBall(v.vx, v.vy);
      if (reduce) { stepSim(16); draw(); }
    }

    function onMouseDown(e: MouseEvent) { startDrag(e.clientX, e.clientY); }
    function onMouseMove(e: MouseEvent) { moveDrag(e.clientX, e.clientY); }
    function onMouseUp() { endDrag(); }
    function onTouchStart(e: TouchEvent) { if (e.touches[0]) startDrag(e.touches[0].clientX, e.touches[0].clientY); }
    function onTouchMove(e: TouchEvent) { if (e.touches[0]) moveDrag(e.touches[0].clientX, e.touches[0].clientY); }
    function onTouchEnd() { endDrag(); }
    canvas.addEventListener("mousedown", onMouseDown);
    window.addEventListener("mousemove", onMouseMove);
    window.addEventListener("mouseup", onMouseUp);
    canvas.addEventListener("touchstart", onTouchStart, { passive: true });
    canvas.addEventListener("touchmove", onTouchMove, { passive: true });
    canvas.addEventListener("touchend", onTouchEnd);

    function onKeyDown(e: KeyboardEvent) {
      let handled = true;
      if (e.key === "ArrowLeft") throwBall(ball.vx - KEY_IMPULSE, ball.vy);
      else if (e.key === "ArrowRight") throwBall(ball.vx + KEY_IMPULSE, ball.vy);
      else if (e.key === "ArrowUp") throwBall(ball.vx, ball.vy - KEY_IMPULSE);
      else if (e.key === "ArrowDown") throwBall(ball.vx, ball.vy + KEY_IMPULSE);
      else if (e.key === " " || e.code === "Space") {
        const ang = ball.heading;
        throwBall(Math.cos(ang) * THROW_IMPULSE, Math.sin(ang) * THROW_IMPULSE);
      } else handled = false;
      if (handled) {
        e.preventDefault();
        root!.classList.remove("is-demo");
        if (reduce) { stepSim(16); draw(); }
      }
    }
    root.addEventListener("keydown", onKeyDown);

    let demoState = "idle";
    function demoDrive(nowMs: number) {
      const cyc = nowMs % 1600;
      if (cyc < 480) {
        if (demoState !== "drag") { demoState = "drag"; dragging = true; samples = []; }
        const f = cyc / 480;
        const sx0 = CALC_W * 0.28, sy0 = CALC_H * 0.7;
        const ex0 = CALC_W * 0.62, ey0 = CALC_H * 0.32;
        ball.x = sx0 + (ex0 - sx0) * f;
        ball.y = sy0 + (ey0 - sy0) * f;
        recordSample(ball.x, ball.y, nowMs);
      } else if (demoState !== "thrown") {
        demoState = "thrown";
        dragging = false;
        const v = releaseVelocity();
        const mag = Math.hypot(v.vx, v.vy) || 1;
        const target = 300;
        throwBall((v.vx / mag) * target, (v.vy / mag) * target);
      }
    }

    let lastTs: number | null = null;
    let acc = 0;
    const FIXED_DT = 16;
    let raf = 0;
    function tick(ts: number) {
      if (lastTs === null) lastTs = ts;
      const frameDt = Math.min(ts - lastTs, 48);
      lastTs = ts;
      if (!reduce) {
        acc += frameDt;
        while (acc >= FIXED_DT) {
          elapsed += FIXED_DT;
          if (root!.classList.contains("is-demo")) demoDrive(elapsed);
          stepSim(FIXED_DT);
          acc -= FIXED_DT;
        }
        draw();
      }
      raf = requestAnimationFrame(tick);
    }
    fit();
    window.addEventListener("resize", fit);
    draw();
    raf = requestAnimationFrame(tick);

    return () => {
      cancelAnimationFrame(raf);
      window.removeEventListener("resize", fit);
      canvas!.removeEventListener("mousedown", onMouseDown);
      window.removeEventListener("mousemove", onMouseMove);
      window.removeEventListener("mouseup", onMouseUp);
      canvas!.removeEventListener("touchstart", onTouchStart);
      canvas!.removeEventListener("touchmove", onTouchMove);
      canvas!.removeEventListener("touchend", onTouchEnd);
      root!.removeEventListener("keydown", onKeyDown);
    };
  }, []);

  return (
    <main className={styles.stage}>
      <div className={`${styles.bp} is-demo`} ref={rootRef} tabIndex={0}>
        <canvas className={styles.bp__canvas} ref={canvasRef} width={480} height={300} />
        <p className={styles.bp__caption}>공을 쥐고 움직인 최근 몇 프레임의 이동량으로 속도를 계산해, 놓는 순간 그 속도 그대로 던져지고 벽에 부딪히면 반사된다</p>
      </div>
    </main>
  );
}