03A Drag Snap That Predicts the Landing Point From Release Speed and Springs Into the Nearest Slot
Release speed times a time constant gives the expected landing spot, and the slot nearest to it becomes the target, followed with a spring and damping.
Best forMobile card carousels and onboarding screens
TAUSNAP_KSNAP_CPITCH
<main class="stage">
<div class="hs is-demo" id="hs">
<canvas class="hs__canvas" data-role="canvas" width="480" height="300" tabindex="0" aria-label="Drag a card and let go: the release speed picks the landing slot in advance and a spring pulls it in"></canvas>
<p class="hs__status" data-role="status" aria-live="off">Snapped to a slot</p>
<div class="hs__tools">
<button class="hs__btn" data-role="prev" type="button">Previous</button>
<button class="hs__btn" data-role="next" type="button">Next</button>
</div>
</div>
</main>@use "../../../../site/static/demo-tokens" as *;
@include stage($stage-ink);
.hs {
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: $subject-ink;
}
.hs__canvas {
display: block;
width: 100%;
height: 100%;
cursor: grab;
}
.hs__canvas:active {
cursor: grabbing;
}
.hs__canvas:focus-visible {
outline: 2px solid rgba(255, 255, 255, .85);
outline-offset: -6px;
}
.hs__status {
position: absolute;
left: $sp-3;
bottom: $sp-3;
max-width: 46%;
margin: 0;
padding: $sp-1 $sp-3;
border-radius: $r-control;
background: rgba(255, 255, 255, .85);
color: $subject-ink;
font-weight: 500;
font-size: 11px;
line-height: 1.4;
pointer-events: none;
}
.hs__tools {
position: absolute;
right: $sp-3;
bottom: $sp-3;
display: flex;
gap: $sp-2;
}
.hs__btn {
margin: 0;
padding: $sp-1 $sp-3;
border: 0;
border-radius: $r-pill;
background: rgba(255, 255, 255, .85);
color: $subject-ink;
font: inherit;
font-weight: 500;
font-size: 12px;
line-height: 1.4;
cursor: pointer;
transition: background-color $dur-quick ease-out;
}
.hs__btn:hover {
background: $subject-cream;
}
.hs__btn[aria-pressed="true"] {
background: $subject-mint;
}
.hs__btn:focus-visible {
outline: 2px solid rgba(255, 255, 255, .95);
outline-offset: 2px;
}
// 손가락 가로 끌기는 이 캔버스가 받고, 세로 쓸기는 브라우저에 남겨 페이지 스크롤이 막히지 않게 한다
.hs__canvas { touch-action: pan-y; }
@media (max-width: 340px) {
.hs__btn { font-size: 10px; padding: $sp-1 $sp-2; }
.hs__status { font-size: 10px; padding: $sp-1 $sp-2; }
}
@media (prefers-reduced-motion: reduce) {
.hs__btn { transition: none; }
}html, body {
margin: 0;
overflow: hidden;
}
.stage {
box-sizing: border-box;
min-height: 100vh;
display: grid;
place-items: center;
margin: 0;
background: #17141a;
font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
padding: clamp(8px, 4vw, 24px);
}
.hs {
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: #17141a;
}
.hs__canvas {
display: block;
width: 100%;
height: 100%;
cursor: grab;
}
.hs__canvas:active {
cursor: grabbing;
}
.hs__canvas:focus-visible {
outline: 2px solid rgba(255, 255, 255, 0.85);
outline-offset: -6px;
}
.hs__status {
position: absolute;
left: 12px;
bottom: 12px;
max-width: 46%;
margin: 0;
padding: 4px 12px;
border-radius: 12px;
background: rgba(255, 255, 255, 0.85);
color: #17141a;
font-weight: 500;
font-size: 11px;
line-height: 1.4;
pointer-events: none;
}
.hs__tools {
position: absolute;
right: 12px;
bottom: 12px;
display: flex;
gap: 8px;
}
.hs__btn {
margin: 0;
padding: 4px 12px;
border: 0;
border-radius: 999px;
background: rgba(255, 255, 255, 0.85);
color: #17141a;
font: inherit;
font-weight: 500;
font-size: 12px;
line-height: 1.4;
cursor: pointer;
transition: background-color 220ms ease-out;
}
.hs__btn:hover {
background: #fff7e6;
}
.hs__btn[aria-pressed=true] {
background: #4cd4a6;
}
.hs__btn:focus-visible {
outline: 2px solid rgba(255, 255, 255, 0.95);
outline-offset: 2px;
}
.hs__canvas {
touch-action: pan-y;
}
@media (max-width: 340px) {
.hs__btn {
font-size: 10px;
padding: 4px 8px;
}
.hs__status {
font-size: 10px;
padding: 4px 8px;
}
}
@media (prefers-reduced-motion: reduce) {
.hs__btn {
transition: none;
}
}(function () {
const root = document.getElementById("hs");
if (!root) return;
const W = 480;
const H = 300;
const FIXED_DT = 16;
// 파스텔 팔레트 — 어두운 무대 위에 밝은 카드를 얹어 명도 차로 읽힌다
const BG = [29, 26, 44];
const PAPER = [255, 248, 234];
const INK = [58, 48, 76];
const MINT = [126, 226, 192];
const SKY = [124, 196, 255];
const LILAC = [190, 164, 255];
const PINK = [255, 160, 190];
const PEACH = [255, 208, 168];
const TINTS = [SKY, PINK, MINT, LILAC, PEACH];
function clamp(v, lo, hi) { return v < lo ? lo : (v > hi ? hi : v); }
function lerp(a, b, k) { return a + (b - a) * k; }
function smooth(x) { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
function rgba(c, a) {
return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + clamp(a, 0, 1).toFixed(3) + ')';
}
function mix(a, b, k) { return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]; }
const canvasEl = root.querySelector('[data-role="canvas"]');
const statusEl = root.querySelector('[data-role="status"]');
const ctxRaw = canvasEl ? canvasEl.getContext('2d') : null;
if (!canvasEl || !ctxRaw || !statusEl) {
return;
}
const cv = canvasEl;
const ctx = ctxRaw;
const status = statusEl;
const reduceQuery = window.matchMedia('(prefers-reduced-motion: reduce)');
const still = reduceQuery.matches;
// 자동 시연 중인가 — 사람이 처음 만지는 순간 시연을 멈추고 상태 줄을 읽어 주기 시작한다
let demo = root.classList.contains('is-demo');
function wake() {
if (!demo) {
return;
}
demo = false;
root.classList.remove('is-demo');
status.setAttribute('aria-live', 'polite');
}
function say(text) {
if (status.textContent !== text) {
status.textContent = text;
}
}
// 휠 한 번의 이동량을 px 로 — 줄 단위(deltaMode 1)·쪽 단위(deltaMode 2) 장치도 같은 눈금으로 맞춘다.
// 가로·세로 중 큰 쪽을 쓴다: 트랙패드의 가로 쓸기와 마우스 휠의 세로 굴림이 같은 방향으로 들어온다
function wheelPx(ev) {
const unit = ev.deltaMode === 1 ? 16 : (ev.deltaMode === 2 ? W : 1);
const d = Math.abs(ev.deltaX) > Math.abs(ev.deltaY) ? ev.deltaX : ev.deltaY;
return d * unit;
}
// 시연 시계가 loop 주기 안의 at 시각을 이번 스텝에 막 지났는가
function crossed(t, at, loop) {
const p = t % loop;
return p >= at && p - FIXED_DT < at;
}
function fitCanvas() {
const dpr = window.devicePixelRatio || 1;
cv.width = Math.round(W * dpr);
cv.height = Math.round(H * dpr);
ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
}
function onResize() {
fitCanvas();
draw();
}
fitCanvas();
window.addEventListener('resize', onResize);
// 화면 좌표(CSS px) → 장면 좌표(480x300). 리사이즈 뒤에도 늘 현재 크기로 다시 잰다
function toScene(ev) {
const r = cv.getBoundingClientRect();
return [((ev.clientX - r.left) / r.width) * W, ((ev.clientY - r.top) / r.height) * H];
}
function roundRectPath(c, x, y, w, h, r) {
const rr = Math.min(r, w / 2, h / 2);
c.beginPath();
c.moveTo(x + rr, y);
c.lineTo(x + w - rr, y);
c.quadraticCurveTo(x + w, y, x + w, y + rr);
c.lineTo(x + w, y + h - rr);
c.quadraticCurveTo(x + w, y + h, x + w - rr, y + h);
c.lineTo(x + rr, y + h);
c.quadraticCurveTo(x, y + h, x, y + h - rr);
c.lineTo(x, y + rr);
c.quadraticCurveTo(x, y, x + rr, y);
c.closePath();
}
// 카드 한 장 — 사진 대신 계산한 그림 칸(그라디언트 하늘·해·언덕) + 글줄 막대 두 개 + 번호
function drawCard(c, x, y, w, h, i, light) {
const t1 = TINTS[i % TINTS.length];
const t2 = TINTS[(i + 2) % TINTS.length];
const k = clamp(light, 0, 1);
roundRectPath(c, x, y, w, h, 10);
c.fillStyle = rgba(mix(BG, PAPER, k), 1);
c.fill();
const ih = h * 0.58;
const g = c.createLinearGradient(x, y, x + w, y + ih);
g.addColorStop(0, rgba(mix(BG, t1, k), 1));
g.addColorStop(1, rgba(mix(BG, t2, k * 0.92), 1));
c.save();
roundRectPath(c, x + 6, y + 6, w - 12, ih - 6, 7);
c.fillStyle = g;
c.fill();
c.clip();
c.fillStyle = rgba(mix(BG, PAPER, k * 0.9), 0.9);
c.beginPath();
c.arc(x + w * 0.7, y + ih * 0.36, Math.min(w, ih) * 0.13, 0, Math.PI * 2);
c.fill();
c.fillStyle = rgba(mix(BG, INK, k), 0.55);
c.beginPath();
c.moveTo(x, y + ih);
c.lineTo(x + w * 0.32, y + ih * 0.55);
c.lineTo(x + w * 0.55, y + ih * 0.8);
c.lineTo(x + w * 0.78, y + ih * 0.62);
c.lineTo(x + w, y + ih);
c.closePath();
c.fill();
c.restore();
c.fillStyle = rgba(mix(BG, INK, k), 0.75);
c.fillRect(x + 10, y + ih + 12, w * 0.62, 6);
c.fillStyle = rgba(mix(BG, INK, k), 0.4);
c.fillRect(x + 10, y + ih + 24, w * 0.44, 5);
c.fillStyle = rgba(mix(BG, INK, k), 0.9);
c.font = '700 13px sans-serif';
c.textAlign = 'right';
c.textBaseline = 'alphabetic';
c.fillText(String(i + 1).padStart(2, '0'), x + w - 9, y + h - 10);
}
const CARD_N = 8;
const CARD_W = 210;
const CARD_H = 172;
const PITCH = 232;
const CARD_TOP = 50;
const MAX_X = (CARD_N - 1) * PITCH;
const TAU = 0.2;
const SNAP_K = 120;
const SNAP_C = 14;
const RUBBER_PX = 120;
const WHEEL_IDLE = 140;
const DEMO_LOOP = 3600;
const TXT_DRAG = 'Dragging';
const TXT_FLING = 'Snapping to the predicted slot';
const TXT_SNAP = 'Snapped to a slot';
const prevBtn = root.querySelector('[data-role="prev"]');
const nextBtn = root.querySelector('[data-role="next"]');
let raw = 0;
let x = 0;
let v = 0;
let target = 0;
let snapping = false;
let ghostX = 0;
let ghostSlot = 0;
let ghostA = 0;
let dragId = -1;
let dragX = 0;
let dragT = 0;
let wheeling = false;
let lastWheel = 0;
let demoDragging = false;
// 끝 밖으로 끈 거리는 줄여서 보여 준다 — 고무줄
function rubberClamp(p) {
if (p < 0) {
return p / (1 - p / RUBBER_PX);
}
if (p > MAX_X) {
const o = p - MAX_X;
return MAX_X + o / (1 + o / RUBBER_PX);
}
return p;
}
// 놓는 순간의 속도로 τ 초 뒤 위치를 미리 내다보고 가장 가까운 칸을 고른다
function predictSlot(x0, v0) {
return clamp(Math.round((x0 + v0 * TAU) / PITCH), 0, CARD_N - 1);
}
function release() {
ghostX = x + v * TAU;
ghostA = 1;
ghostSlot = predictSlot(x, v);
target = ghostSlot * PITCH;
snapping = true;
say(TXT_FLING);
if (still) {
x = target;
raw = x;
v = 0;
snapping = false;
say(TXT_SNAP);
draw();
}
}
// 스프링·댐퍼 한 스텝 — 가속 = K·(목표−위치) − C·속도 (반암시 오일러)
function springStep(dt) {
const a = SNAP_K * (target - x) - SNAP_C * v;
v += a * dt;
x += v * dt;
}
function canMove(d) { return d > 0 ? x < MAX_X - 0.5 : x > 0.5; }
function step() {
const dt = FIXED_DT / 1000;
ghostA = Math.max(0, ghostA - dt * 0.9);
if (wheeling && clock - lastWheel > WHEEL_IDLE) {
wheeling = false;
release();
}
if (snapping) {
springStep(dt);
raw = x;
if (Math.abs(target - x) < 0.3 && Math.abs(v) < 3) {
x = target;
raw = x;
v = 0;
snapping = false;
say(TXT_SNAP);
}
}
}
function settle() {
x = 0;
raw = 0;
v = 0;
say(TXT_SNAP);
}
function demoMove(dxPerSec) {
const dt = FIXED_DT / 1000;
raw += dxPerSec * dt;
x = rubberClamp(raw);
v = dxPerSec;
}
function demoTick(t) {
const p = t % DEMO_LOOP;
if (p >= 220 && p < 520) {
demoDragging = true;
snapping = false;
demoMove(900);
say(TXT_DRAG);
}
else if (p >= 1300 && p < 1500) {
demoDragging = true;
snapping = false;
demoMove(-1100);
say(TXT_DRAG);
}
else if (demoDragging) {
demoDragging = false;
release();
}
}
function draw() {
ctx.fillStyle = rgba(BG, 1);
ctx.fillRect(0, 0, W, H);
const originX = W / 2 - CARD_W / 2;
for (let i = 0; i < CARD_N; i += 1) {
const cx = originX + i * PITCH - x;
if (cx > W || cx + CARD_W < 0) {
continue;
}
// 가운데에서 멀수록 살짝 작고 어둡다 — 지금 칸이 어디인지 읽힌다
const d = clamp(Math.abs(cx - originX) / PITCH, 0, 1);
const s = 1 - 0.1 * d;
const w = CARD_W * s;
const h = CARD_H * s;
drawCard(ctx, cx + (CARD_W - w) / 2, CARD_TOP + (CARD_H - h) / 2, w, h, i, 1 - 0.35 * d);
}
// 착지 예측 표시 — 놓는 순간 x + v·τ 로 고른 칸의 카드에 점선 테두리를 두르고, 위 점 줄에 예측 위치를 찍는다
if (ghostA > 0.01) {
const gx = originX + ghostSlot * PITCH - x;
ctx.save();
ctx.setLineDash([6, 6]);
ctx.lineWidth = 2;
ctx.strokeStyle = rgba(PEACH, ghostA);
roundRectPath(ctx, gx, CARD_TOP - 6, CARD_W, CARD_H + 12, 14);
ctx.stroke();
ctx.restore();
ctx.fillStyle = rgba(PEACH, ghostA);
ctx.beginPath();
ctx.arc(W / 2 - 70 + clamp(ghostX / PITCH, -0.5, CARD_N - 0.5) * 20, 40, 4, 0, Math.PI * 2);
ctx.fill();
}
// 칸 점
for (let i = 0; i < CARD_N; i += 1) {
const near = clamp(1 - Math.abs(x / PITCH - i), 0, 1);
ctx.fillStyle = rgba(mix(mix(BG, PAPER, 0.25), MINT, near), 1);
ctx.beginPath();
ctx.arc(W / 2 - 70 + i * 20, 26, 3.5 + near * 2.5, 0, Math.PI * 2);
ctx.fill();
}
}
cv.addEventListener('pointerdown', function (ev) {
wake();
dragId = ev.pointerId;
cv.setPointerCapture(ev.pointerId);
dragX = toScene(ev)[0];
dragT = ev.timeStamp;
raw = x;
v = 0;
snapping = false;
say(TXT_DRAG);
});
cv.addEventListener('pointermove', function (ev) {
if (ev.pointerId !== dragId) {
return;
}
const sx = toScene(ev)[0];
const dt = Math.max(1, ev.timeStamp - dragT) / 1000;
raw -= sx - dragX;
x = rubberClamp(raw);
v = lerp(v, -(sx - dragX) / dt, 0.4);
dragX = sx;
dragT = ev.timeStamp;
if (still) {
draw();
}
});
function endDrag(ev) {
if (ev.pointerId !== dragId) {
return;
}
dragId = -1;
release();
}
cv.addEventListener('pointerup', endDrag);
cv.addEventListener('pointercancel', endDrag);
function onWheel(ev) {
const d = wheelPx(ev);
if (d === 0 || !canMove(d)) {
return;
}
ev.preventDefault();
wake();
snapping = false;
raw = clamp(x + d, 0, MAX_X);
x = raw;
// 휠은 속도를 남기지 않는다 — 멈춘 뒤 WHEEL_IDLE 이 지나면 지금 자리에서 가장 가까운 칸으로 붙는다
v = 0;
if (still) {
release();
return;
}
wheeling = true;
lastWheel = clock;
}
cv.addEventListener('wheel', onWheel, { passive: false });
function goSlot(k) {
const kk = clamp(k, 0, CARD_N - 1);
if (kk * PITCH === target && !snapping && x === target) {
return false;
}
target = kk * PITCH;
v = 0;
ghostX = target;
ghostSlot = kk;
ghostA = 1;
snapping = true;
say(TXT_FLING);
if (still) {
x = target;
raw = x;
snapping = false;
say(TXT_SNAP);
draw();
}
return true;
}
cv.addEventListener('keydown', function (ev) {
const cur = Math.round(target / PITCH);
let moved = false;
if (ev.key === 'ArrowRight' && cur < CARD_N - 1) {
moved = goSlot(cur + 1);
}
else if (ev.key === 'ArrowLeft' && cur > 0) {
moved = goSlot(cur - 1);
}
else if (ev.key === 'Home' && cur > 0) {
moved = goSlot(0);
}
else if (ev.key === 'End' && cur < CARD_N - 1) {
moved = goSlot(CARD_N - 1);
}
if (!moved) {
return;
}
ev.preventDefault();
wake();
});
if (prevBtn) {
prevBtn.addEventListener('click', function () { wake(); goSlot(Math.round(target / PITCH) - 1); });
}
if (nextBtn) {
nextBtn.addEventListener('click', function () { wake(); goSlot(Math.round(target / PITCH) + 1); });
}
say(TXT_SNAP);
let rafId = 0;
let lastTs = -1;
let acc = 0;
let clock = 0;
function frame(ts) {
if (lastTs < 0) {
lastTs = ts;
}
// 탭이 숨었다 돌아와도 한 번에 100ms 까지만 따라잡는다 — 순간이동 대신 이어서 움직인다
acc += Math.min(ts - lastTs, 100);
lastTs = ts;
let n = 0;
while (acc >= FIXED_DT && n < 6) {
clock += FIXED_DT;
if (demo) {
demoTick(clock);
}
step();
acc -= FIXED_DT;
n += 1;
}
draw();
rafId = window.requestAnimationFrame(frame);
}
if (still) {
settle();
draw();
}
else {
rafId = window.requestAnimationFrame(frame);
}
return function () {
window.cancelAnimationFrame(rafId);
window.removeEventListener('resize', onResize);
};
})();// HscDragFlingProjectedSnapSpring - vanilla 판(03-hsc-drag-fling-projected-snap-spring) 의 React 포트. 같은 계산을 useEffect 안에서 돌린다.
import { useEffect, useRef } from "react";
import styles from "./HscDragFlingProjectedSnapSpring.module.scss";
const cx = (s: string): string => s.split(" ").map((n) => styles[n] ?? n).join(" ");
export default function HscDragFlingProjectedSnapSpring() {
const rootRef = useRef<HTMLDivElement | null>(null);
useEffect(() => {
const rootEl = rootRef.current;
if (!rootEl) return;
const root: HTMLElement = rootEl;
type RGB = [number, number, number];
const W = 480;
const H = 300;
const FIXED_DT = 16;
// 파스텔 팔레트 — 어두운 무대 위에 밝은 카드를 얹어 명도 차로 읽힌다
const BG: RGB = [29, 26, 44];
const PAPER: RGB = [255, 248, 234];
const INK: RGB = [58, 48, 76];
const MINT: RGB = [126, 226, 192];
const SKY: RGB = [124, 196, 255];
const LILAC: RGB = [190, 164, 255];
const PINK: RGB = [255, 160, 190];
const PEACH: RGB = [255, 208, 168];
const TINTS: RGB[] = [SKY, PINK, MINT, LILAC, PEACH];
function clamp(v: number, lo: number, hi: number): number { return v < lo ? lo : (v > hi ? hi : v); }
function lerp(a: number, b: number, k: number): number { return a + (b - a) * k; }
function smooth(x: number): number { const c = clamp(x, 0, 1); return c * c * (3 - 2 * c); }
function rgba(c: RGB, a: number): string {
return 'rgba(' + Math.round(c[0]) + ',' + Math.round(c[1]) + ',' + Math.round(c[2]) + ',' + clamp(a, 0, 1).toFixed(3) + ')';
}
function mix(a: RGB, b: RGB, k: number): RGB { return [lerp(a[0], b[0], k), lerp(a[1], b[1], k), lerp(a[2], b[2], k)]; }
const canvasEl = root.querySelector('[data-role="canvas"]') as HTMLCanvasElement | null;
const statusEl = root.querySelector('[data-role="status"]') as HTMLElement | null;
const ctxRaw = canvasEl ? canvasEl.getContext('2d') : null;
if (!canvasEl || !ctxRaw || !statusEl) { return; }
const cv: HTMLCanvasElement = canvasEl;
const ctx: CanvasRenderingContext2D = ctxRaw;
const status: HTMLElement = statusEl;
const reduceQuery = window.matchMedia('(prefers-reduced-motion: reduce)');
const still = reduceQuery.matches;
// 자동 시연 중인가 — 사람이 처음 만지는 순간 시연을 멈추고 상태 줄을 읽어 주기 시작한다
let demo = root.classList.contains('is-demo');
function wake(): void {
if (!demo) { return; }
demo = false;
root.classList.remove('is-demo');
status.setAttribute('aria-live', 'polite');
}
function say(text: string): void {
if (status.textContent !== text) { status.textContent = text; }
}
// 휠 한 번의 이동량을 px 로 — 줄 단위(deltaMode 1)·쪽 단위(deltaMode 2) 장치도 같은 눈금으로 맞춘다.
// 가로·세로 중 큰 쪽을 쓴다: 트랙패드의 가로 쓸기와 마우스 휠의 세로 굴림이 같은 방향으로 들어온다
function wheelPx(ev: WheelEvent): number {
const unit = ev.deltaMode === 1 ? 16 : (ev.deltaMode === 2 ? W : 1);
const d = Math.abs(ev.deltaX) > Math.abs(ev.deltaY) ? ev.deltaX : ev.deltaY;
return d * unit;
}
// 시연 시계가 loop 주기 안의 at 시각을 이번 스텝에 막 지났는가
function crossed(t: number, at: number, loop: number): boolean {
const p = t % loop;
return p >= at && p - FIXED_DT < at;
}
function fitCanvas(): void {
const dpr = window.devicePixelRatio || 1;
cv.width = Math.round(W * dpr);
cv.height = Math.round(H * dpr);
ctx.setTransform(dpr, 0, 0, dpr, 0, 0);
}
function onResize(): void {
fitCanvas();
draw();
}
fitCanvas();
window.addEventListener('resize', onResize);
// 화면 좌표(CSS px) → 장면 좌표(480x300). 리사이즈 뒤에도 늘 현재 크기로 다시 잰다
function toScene(ev: PointerEvent): [number, number] {
const r = cv.getBoundingClientRect();
return [((ev.clientX - r.left) / r.width) * W, ((ev.clientY - r.top) / r.height) * H];
}
function roundRectPath(c: CanvasRenderingContext2D, x: number, y: number, w: number, h: number, r: number): void {
const rr = Math.min(r, w / 2, h / 2);
c.beginPath();
c.moveTo(x + rr, y);
c.lineTo(x + w - rr, y);
c.quadraticCurveTo(x + w, y, x + w, y + rr);
c.lineTo(x + w, y + h - rr);
c.quadraticCurveTo(x + w, y + h, x + w - rr, y + h);
c.lineTo(x + rr, y + h);
c.quadraticCurveTo(x, y + h, x, y + h - rr);
c.lineTo(x, y + rr);
c.quadraticCurveTo(x, y, x + rr, y);
c.closePath();
}
// 카드 한 장 — 사진 대신 계산한 그림 칸(그라디언트 하늘·해·언덕) + 글줄 막대 두 개 + 번호
function drawCard(c: CanvasRenderingContext2D, x: number, y: number, w: number, h: number, i: number, light: number): void {
const t1 = TINTS[i % TINTS.length];
const t2 = TINTS[(i + 2) % TINTS.length];
const k = clamp(light, 0, 1);
roundRectPath(c, x, y, w, h, 10);
c.fillStyle = rgba(mix(BG, PAPER, k), 1);
c.fill();
const ih = h * 0.58;
const g = c.createLinearGradient(x, y, x + w, y + ih);
g.addColorStop(0, rgba(mix(BG, t1, k), 1));
g.addColorStop(1, rgba(mix(BG, t2, k * 0.92), 1));
c.save();
roundRectPath(c, x + 6, y + 6, w - 12, ih - 6, 7);
c.fillStyle = g;
c.fill();
c.clip();
c.fillStyle = rgba(mix(BG, PAPER, k * 0.9), 0.9);
c.beginPath();
c.arc(x + w * 0.7, y + ih * 0.36, Math.min(w, ih) * 0.13, 0, Math.PI * 2);
c.fill();
c.fillStyle = rgba(mix(BG, INK, k), 0.55);
c.beginPath();
c.moveTo(x, y + ih);
c.lineTo(x + w * 0.32, y + ih * 0.55);
c.lineTo(x + w * 0.55, y + ih * 0.8);
c.lineTo(x + w * 0.78, y + ih * 0.62);
c.lineTo(x + w, y + ih);
c.closePath();
c.fill();
c.restore();
c.fillStyle = rgba(mix(BG, INK, k), 0.75);
c.fillRect(x + 10, y + ih + 12, w * 0.62, 6);
c.fillStyle = rgba(mix(BG, INK, k), 0.4);
c.fillRect(x + 10, y + ih + 24, w * 0.44, 5);
c.fillStyle = rgba(mix(BG, INK, k), 0.9);
c.font = '700 13px sans-serif';
c.textAlign = 'right';
c.textBaseline = 'alphabetic';
c.fillText(String(i + 1).padStart(2, '0'), x + w - 9, y + h - 10);
}
const CARD_N = 8;
const CARD_W = 210;
const CARD_H = 172;
const PITCH = 232;
const CARD_TOP = 50;
const MAX_X = (CARD_N - 1) * PITCH;
const TAU = 0.2;
const SNAP_K = 120;
const SNAP_C = 14;
const RUBBER_PX = 120;
const WHEEL_IDLE = 140;
const DEMO_LOOP = 3600;
const TXT_DRAG = '끄는 중';
const TXT_FLING = '착지 칸을 미리 계산해 붙는 중';
const TXT_SNAP = '칸에 붙음';
const prevBtn = root.querySelector('[data-role="prev"]') as HTMLButtonElement | null;
const nextBtn = root.querySelector('[data-role="next"]') as HTMLButtonElement | null;
let raw = 0;
let x = 0;
let v = 0;
let target = 0;
let snapping = false;
let ghostX = 0;
let ghostSlot = 0;
let ghostA = 0;
let dragId = -1;
let dragX = 0;
let dragT = 0;
let wheeling = false;
let lastWheel = 0;
let demoDragging = false;
// 끝 밖으로 끈 거리는 줄여서 보여 준다 — 고무줄
function rubberClamp(p: number): number {
if (p < 0) { return p / (1 - p / RUBBER_PX); }
if (p > MAX_X) { const o = p - MAX_X; return MAX_X + o / (1 + o / RUBBER_PX); }
return p;
}
// 놓는 순간의 속도로 τ 초 뒤 위치를 미리 내다보고 가장 가까운 칸을 고른다
function predictSlot(x0: number, v0: number): number {
return clamp(Math.round((x0 + v0 * TAU) / PITCH), 0, CARD_N - 1);
}
function release(): void {
ghostX = x + v * TAU;
ghostA = 1;
ghostSlot = predictSlot(x, v);
target = ghostSlot * PITCH;
snapping = true;
say(TXT_FLING);
if (still) { x = target; raw = x; v = 0; snapping = false; say(TXT_SNAP); draw(); }
}
// 스프링·댐퍼 한 스텝 — 가속 = K·(목표−위치) − C·속도 (반암시 오일러)
function springStep(dt: number): void {
const a = SNAP_K * (target - x) - SNAP_C * v;
v += a * dt;
x += v * dt;
}
function canMove(d: number): boolean { return d > 0 ? x < MAX_X - 0.5 : x > 0.5; }
function step(): void {
const dt = FIXED_DT / 1000;
ghostA = Math.max(0, ghostA - dt * 0.9);
if (wheeling && clock - lastWheel > WHEEL_IDLE) {
wheeling = false;
release();
}
if (snapping) {
springStep(dt);
raw = x;
if (Math.abs(target - x) < 0.3 && Math.abs(v) < 3) {
x = target;
raw = x;
v = 0;
snapping = false;
say(TXT_SNAP);
}
}
}
function settle(): void {
x = 0;
raw = 0;
v = 0;
say(TXT_SNAP);
}
function demoMove(dxPerSec: number): void {
const dt = FIXED_DT / 1000;
raw += dxPerSec * dt;
x = rubberClamp(raw);
v = dxPerSec;
}
function demoTick(t: number): void {
const p = t % DEMO_LOOP;
if (p >= 220 && p < 520) { demoDragging = true; snapping = false; demoMove(900); say(TXT_DRAG); }
else if (p >= 1300 && p < 1500) { demoDragging = true; snapping = false; demoMove(-1100); say(TXT_DRAG); }
else if (demoDragging) { demoDragging = false; release(); }
}
function draw(): void {
ctx.fillStyle = rgba(BG, 1);
ctx.fillRect(0, 0, W, H);
const originX = W / 2 - CARD_W / 2;
for (let i = 0; i < CARD_N; i += 1) {
const cx = originX + i * PITCH - x;
if (cx > W || cx + CARD_W < 0) { continue; }
// 가운데에서 멀수록 살짝 작고 어둡다 — 지금 칸이 어디인지 읽힌다
const d = clamp(Math.abs(cx - originX) / PITCH, 0, 1);
const s = 1 - 0.1 * d;
const w = CARD_W * s;
const h = CARD_H * s;
drawCard(ctx, cx + (CARD_W - w) / 2, CARD_TOP + (CARD_H - h) / 2, w, h, i, 1 - 0.35 * d);
}
// 착지 예측 표시 — 놓는 순간 x + v·τ 로 고른 칸의 카드에 점선 테두리를 두르고, 위 점 줄에 예측 위치를 찍는다
if (ghostA > 0.01) {
const gx = originX + ghostSlot * PITCH - x;
ctx.save();
ctx.setLineDash([6, 6]);
ctx.lineWidth = 2;
ctx.strokeStyle = rgba(PEACH, ghostA);
roundRectPath(ctx, gx, CARD_TOP - 6, CARD_W, CARD_H + 12, 14);
ctx.stroke();
ctx.restore();
ctx.fillStyle = rgba(PEACH, ghostA);
ctx.beginPath();
ctx.arc(W / 2 - 70 + clamp(ghostX / PITCH, -0.5, CARD_N - 0.5) * 20, 40, 4, 0, Math.PI * 2);
ctx.fill();
}
// 칸 점
for (let i = 0; i < CARD_N; i += 1) {
const near = clamp(1 - Math.abs(x / PITCH - i), 0, 1);
ctx.fillStyle = rgba(mix(mix(BG, PAPER, 0.25), MINT, near), 1);
ctx.beginPath();
ctx.arc(W / 2 - 70 + i * 20, 26, 3.5 + near * 2.5, 0, Math.PI * 2);
ctx.fill();
}
}
cv.addEventListener('pointerdown', function (ev: PointerEvent): void {
wake();
dragId = ev.pointerId;
cv.setPointerCapture(ev.pointerId);
dragX = toScene(ev)[0];
dragT = ev.timeStamp;
raw = x;
v = 0;
snapping = false;
say(TXT_DRAG);
});
cv.addEventListener('pointermove', function (ev: PointerEvent): void {
if (ev.pointerId !== dragId) { return; }
const sx = toScene(ev)[0];
const dt = Math.max(1, ev.timeStamp - dragT) / 1000;
raw -= sx - dragX;
x = rubberClamp(raw);
v = lerp(v, -(sx - dragX) / dt, 0.4);
dragX = sx;
dragT = ev.timeStamp;
if (still) { draw(); }
});
function endDrag(ev: PointerEvent): void {
if (ev.pointerId !== dragId) { return; }
dragId = -1;
release();
}
cv.addEventListener('pointerup', endDrag);
cv.addEventListener('pointercancel', endDrag);
function onWheel(ev: WheelEvent): void {
const d = wheelPx(ev);
if (d === 0 || !canMove(d)) { return; }
ev.preventDefault();
wake();
snapping = false;
raw = clamp(x + d, 0, MAX_X);
x = raw;
// 휠은 속도를 남기지 않는다 — 멈춘 뒤 WHEEL_IDLE 이 지나면 지금 자리에서 가장 가까운 칸으로 붙는다
v = 0;
if (still) { release(); return; }
wheeling = true;
lastWheel = clock;
}
cv.addEventListener('wheel', onWheel, { passive: false });
function goSlot(k: number): boolean {
const kk = clamp(k, 0, CARD_N - 1);
if (kk * PITCH === target && !snapping && x === target) { return false; }
target = kk * PITCH;
v = 0;
ghostX = target;
ghostSlot = kk;
ghostA = 1;
snapping = true;
say(TXT_FLING);
if (still) { x = target; raw = x; snapping = false; say(TXT_SNAP); draw(); }
return true;
}
cv.addEventListener('keydown', function (ev: KeyboardEvent): void {
const cur = Math.round(target / PITCH);
let moved = false;
if (ev.key === 'ArrowRight' && cur < CARD_N - 1) { moved = goSlot(cur + 1); }
else if (ev.key === 'ArrowLeft' && cur > 0) { moved = goSlot(cur - 1); }
else if (ev.key === 'Home' && cur > 0) { moved = goSlot(0); }
else if (ev.key === 'End' && cur < CARD_N - 1) { moved = goSlot(CARD_N - 1); }
if (!moved) { return; }
ev.preventDefault();
wake();
});
if (prevBtn) { prevBtn.addEventListener('click', function (): void { wake(); goSlot(Math.round(target / PITCH) - 1); }); }
if (nextBtn) { nextBtn.addEventListener('click', function (): void { wake(); goSlot(Math.round(target / PITCH) + 1); }); }
say(TXT_SNAP);
let rafId = 0;
let lastTs = -1;
let acc = 0;
let clock = 0;
function frame(ts: number): void {
if (lastTs < 0) { lastTs = ts; }
// 탭이 숨었다 돌아와도 한 번에 100ms 까지만 따라잡는다 — 순간이동 대신 이어서 움직인다
acc += Math.min(ts - lastTs, 100);
lastTs = ts;
let n = 0;
while (acc >= FIXED_DT && n < 6) {
clock += FIXED_DT;
if (demo) { demoTick(clock); }
step();
acc -= FIXED_DT;
n += 1;
}
draw();
rafId = window.requestAnimationFrame(frame);
}
if (still) {
settle();
draw();
} else {
rafId = window.requestAnimationFrame(frame);
}
return function (): void {
window.cancelAnimationFrame(rafId);
window.removeEventListener('resize', onResize);
};
}, []);
return (
<div className={cx("hs") + " is-demo"} ref={rootRef}>
<canvas className={cx("hs__canvas")} data-role="canvas" width={480} height={300} tabIndex={0} aria-label="카드를 끌었다 놓으면 놓는 순간의 속도로 착지 칸을 미리 고르고 스프링으로 붙는 장면"></canvas>
<p className={cx("hs__status")} data-role="status" aria-live="off">칸에 붙음</p>
<div className={cx("hs__tools")}>
<button className={cx("hs__btn")} data-role="prev" type="button">이전</button>
<button className={cx("hs__btn")} data-role="next" type="button">다음</button>
</div>
</div>
);
}03 A Drag Snap That Predicts the Landing Point From Release Speed and Springs Into the Nearest Slot — Measured area 46.493% · moving frames 21/23Original by GODRICH · SCSS and React ship in the zip · Horizontal Scroll Animation CSS: 9 Inertia Scenes
The post this demo lives in
Horizontal Scroll Animation CSS: 9 Inertia ScenesHorizontal scroll animation css is more than turning wheel input sideways — scene 01 glides it on inertia, 06 projects c See all demos in this post
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