A thick paper-faced card stands on an oak table in late afternoon sun, and a clear glass tube is bent around its front edge like a frame. Inside the tube a small, hot bead of light travels the whole way round. The scene is ray-marched in raw WebGL 2 with a real camera: the card throws a soft shadow across the planks, the tube throws a darker outline with a bright line of focused sun inside it, the varnish mirrors the card, and the far wall falls out of focus. Point at the card or tab to its link and the bead speeds up, overshoots a little and settles into a quick lap, and the places it has just passed keep a warm glow on the table and the paper that fades over a few seconds. The heading, paragraph and link are ordinary HTML laid onto the card face with a CSS projective matrix, so they stay selectable and readable by screen readers. On phones the card turns upright and the camera moves back, and browsers without WebGL 2 get a flat version with the same words.
import { useEffect, useRef, useState } from "react";
import { useReducedMotion } from "framer-motion";
/** The words on the card. Everything here is real page text laid onto the card face. */
const card = {
kicker: "Version history",
title: "Every draft kept. None of them in the way.",
body: "Roll any page back to how it looked on a given morning, compare two versions side by side, and restore one section without touching the rest.",
link: "See how versions work",
maker: "Quillmark Studio",
};
const SERIF = '"New York", ui-serif, "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, serif';
const GROTESK = '"Inter Tight", "Inter", ui-sans-serif, system-ui, sans-serif';
const INK = "#2b1c12";
const IDLE_SPEED = 0.075; // laps per second while nobody is near
const HOVER_SPEED = 0.46; // laps per second under the pointer
const SPEED_SPRING = 26; // how hard the bead is pulled to its new speed
const SPEED_DAMP = 6.5; // lower lets it overshoot more
const WARM_DECAY = 2.6; // seconds for the warmth on the table to fade to about a third
const DEMO_EVERY = 9000; // ms between automatic fast laps when nobody is interacting
const BINS = 24; // places around the edge that hold warmth
const GAP = 0.02; // air between the card's edge and the glass
const clamp = (v: number, lo: number, hi: number) => Math.min(hi, Math.max(lo, v));
type Layout = { hx: number; hy: number; rc: number; th: number; yaw: number; tr: number; pad: number; narrow: boolean };
const WIDE: Layout = { hx: 0.82, hy: 0.5, rc: 0.09, th: 0.028, yaw: -0.2, tr: 0.03, pad: 0.13, narrow: false };
const TALL: Layout = { hx: 0.5, hy: 0.7, rc: 0.08, th: 0.028, yaw: -0.16, tr: 0.026, pad: 0.095, narrow: true };
/** The centre line of the tube, a rounded rectangle on the card face. */
const tubePath = (l: Layout) => {
const ax = l.hx + GAP + l.tr, ay = l.hy + GAP + l.tr, pr = l.rc + GAP + l.tr;
const sx = ax - pr, sy = ay - pr, A = (pr * Math.PI) / 2;
const per = 4 * sx + 4 * sy + 4 * A;
/** A point on the line, s from 0 to 1, starting bottom centre and running anticlockwise as you face the card. */
const at = (s: number): [number, number] => {
let d = (((s % 1) + 1) % 1) * per;
const arc = (cx: number, cy: number, a0: number, len: number): [number, number] => {
const a = a0 + len / pr;
return [cx + pr * Math.cos(a), cy + pr * Math.sin(a)];
};
if (d < sx) return [d, -ay];
d -= sx;
if (d < A) return arc(sx, -sy, -Math.PI / 2, d);
d -= A;
if (d < 2 * sy) return [ax, -sy + d];
d -= 2 * sy;
if (d < A) return arc(sx, sy, 0, d);
d -= A;
if (d < 2 * sx) return [sx - d, ay];
d -= 2 * sx;
if (d < A) return arc(-sx, sy, Math.PI / 2, d);
d -= A;
if (d < 2 * sy) return [-ax, sy - d];
d -= 2 * sy;
if (d < A) return arc(-sx, -sy, Math.PI, d);
d -= A;
return [-sx + d, -ay];
};
return { ax, ay, pr, per, at, zt: 0, lift: 2 * l.tr + GAP };
};
const VS = `#version 300 es
void main() { vec2 p = vec2(float((gl_VertexID << 1) & 2), float(gl_VertexID & 2)); gl_Position = vec4(p * 2.0 - 1.0, 0.0, 1.0); }`;
const FS = `#version 300 es
precision highp float;
uniform vec2 uRes;
uniform vec3 uCam, uFw, uRt, uUp;
uniform float uTan;
uniform vec2 uHalf; uniform float uRc, uTh, uYaw, uLift;
uniform vec2 uPA; uniform float uPR, uTr, uZt, uPer;
uniform vec3 uBead, uTail; uniform float uBeadS, uBeadPow;
uniform vec3 uWarmPos[${BINS}]; uniform float uWarm[${BINS}];
uniform vec3 uL, uLu, uLv, uSun;
uniform float uTime, uFocus, uAperture;
out vec4 o;
const float WALLZ = -2.3;
const vec3 WARM = vec3(1.0, 0.5, 0.17);
const vec3 AMB = vec3(0.2, 0.21, 0.25);
float hash(vec2 p) { return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453); }
float vnoise(vec2 p) { vec2 i = floor(p), f = fract(p); f = f * f * (3.0 - 2.0 * f);
return mix(mix(hash(i), hash(i + vec2(1, 0)), f.x), mix(hash(i + vec2(0, 1)), hash(i + vec2(1, 1)), f.x), f.y); }
float fbm(vec2 p) { return 0.5 * vnoise(p) + 0.25 * vnoise(p * 2.03 + 7.3) + 0.125 * vnoise(p * 4.1 + 1.7) + 0.0625 * vnoise(p * 8.3 + 3.1); }
float sbox(vec2 p, vec2 h, float s) { vec2 d = smoothstep(h + s, h - s, abs(p)); return d.x * d.y; }
float sdRR(vec2 p, vec2 b, float r) { vec2 q = abs(p) - b + r; return length(max(q, 0.0)) + min(max(q.x, q.y), 0.0) - r; }
vec3 toL(vec3 p) { float c = cos(uYaw), s = sin(uYaw); vec3 d = p - vec3(0.0, uHalf.y + uLift, 0.0); return vec3(c * d.x - s * d.z, d.y, s * d.x + c * d.z); }
vec3 dirW(vec3 n) { float c = cos(uYaw), s = sin(uYaw); return vec3(c * n.x + s * n.z, n.y, -s * n.x + c * n.z); }
float sdCard(vec3 q) { float e = 0.007; vec2 w = vec2(sdRR(q.xy, uHalf - e, uRc - e), abs(q.z) - uTh + e); return min(max(w.x, w.y), 0.0) + length(max(w, 0.0)) - e; }
float sdTube(vec3 q) { return length(vec2(sdRR(q.xy, uPA, uPR), q.z - uZt)) - uTr; }
float sdBox(vec3 p, vec3 b) { vec3 q = abs(p) - b; return length(max(q, 0.0)) + min(max(q.x, max(q.y, q.z)), 0.0) - 0.002; }
// brass clips: a sleeve round the glass and a tab that holds the card's edge
float sdClip(vec3 q) {
vec3 a = vec3(abs(q.x), abs(q.y), q.z);
float cx = uHalf.x * 0.62;
float s1 = max(length(vec2(a.y - uPA.y, a.z)) - (uTr + 0.0045), abs(a.x - cx) - 0.012);
float t1 = sdBox(vec3(a.x - cx, a.y - (uHalf.y + uPA.y) * 0.5, a.z), vec3(0.009, (uPA.y - uHalf.y) * 0.5, uTh * 1.15));
float s2 = max(length(vec2(a.x - uPA.x, a.z)) - (uTr + 0.0045), abs(a.y) - 0.012);
float t2 = sdBox(vec3(a.x - (uHalf.x + uPA.x) * 0.5, a.y, a.z), vec3((uPA.x - uHalf.x) * 0.5, 0.009, uTh * 1.15));
return min(min(s1, t1), min(s2, t2));
}
vec2 mapL(vec3 q) { float a = sdCard(q), b = sdTube(q), c = sdClip(q); vec2 r = a < b ? vec2(a, 1.0) : vec2(b, 2.0); return c < r.x ? vec2(c, 3.0) : r; }
vec3 normL(vec3 q, float id) {
vec2 e = vec2(0.0007, -0.0007);
if (id < 1.5) return normalize(e.xyy * sdCard(q + e.xyy) + e.yyx * sdCard(q + e.yyx) + e.yxy * sdCard(q + e.yxy) + e.xxx * sdCard(q + e.xxx));
if (id > 2.5) return normalize(e.xyy * sdClip(q + e.xyy) + e.yyx * sdClip(q + e.yyx) + e.yxy * sdClip(q + e.yxy) + e.xxx * sdClip(q + e.xxx));
return normalize(e.xyy * sdTube(q + e.xyy) + e.yyx * sdTube(q + e.yyx) + e.yxy * sdTube(q + e.yxy) + e.xxx * sdTube(q + e.xxx));
}
// where along the tube (0 to 1) a point on the card face sits
float pathParam(vec2 p) {
float sx = uPA.x - uPR, sy = uPA.y - uPR, A = uPR * 1.5707963;
float c2 = sx + A, c3 = c2 + 2.0 * sy, c4 = c3 + A, c5 = c4 + 2.0 * sx, c6 = c5 + A, c7 = c6 + 2.0 * sy, c8 = c7 + A;
float d;
if (abs(p.x) <= sx) d = p.y < 0.0 ? (p.x >= 0.0 ? p.x : c8 + p.x + sx) : c4 + sx - p.x;
else if (abs(p.y) <= sy) d = p.x > 0.0 ? c2 + p.y + sy : c6 + sy - p.y;
else {
vec2 cc = vec2(sign(p.x) * sx, sign(p.y) * sy);
float a = atan(p.y - cc.y, p.x - cc.x);
if (p.x > 0.0 && p.y < 0.0) d = sx + uPR * (a + 1.5707963);
else if (p.x > 0.0) d = c3 + uPR * a;
else if (p.y > 0.0) d = c5 + uPR * (a - 1.5707963);
else d = c7 + uPR * ((a < 0.0 ? a + 6.2831853 : a) - 3.1415926);
}
return d / uPer;
}
// warmth stored around the edge, read at one place on the tube
float warmAt(float s) {
float f = s * ${BINS}.0 - 0.5;
int i0 = int(floor(f)); float t = fract(f);
int a = (i0 + ${BINS}) % ${BINS}, b = (i0 + 1 + ${BINS}) % ${BINS};
return mix(uWarm[a], uWarm[b], t);
}
float gobo(vec3 P, bool fine) {
vec2 g = vec2(dot(P, uLu), dot(P, uLv));
float w = sbox(g - vec2(0.15, 0.25), vec2(2.6, 1.9), 0.25);
float bars = 1.0 - 0.94 * smoothstep(0.05, 0.02, abs(g.x + 1.42)) - 0.94 * smoothstep(0.05, 0.02, abs(g.y - 1.62));
float leaf = 1.0;
if (fine) {
vec2 q = g * 2.4 + vec2(0.04 * sin(uTime * 0.6 + g.y * 3.0), 0.03 * cos(uTime * 0.45 + g.x * 2.0));
float n = fbm(q * 1.6 + 2.0);
leaf = 1.0 - 0.85 * smoothstep(0.52, 0.66, n) * smoothstep(-0.2, -1.6, g.x + 0.4 * g.y);
}
return w * clamp(bars, 0.0, 1.0) * leaf;
}
// light that the sun gets past the card and through the glass tube (which throws a bright line in its shadow)
float sunVis(vec3 P) {
vec3 o = toL(P);
vec3 d = toL(P + uL) - o;
float rc = 1.0, tm = 1.0, t = 0.006;
for (int i = 0; i < 96; i++) {
vec3 q = o + d * t;
float dc = sdCard(q), dt = sdTube(q);
rc = min(rc, 6.0 * dc / t);
tm = min(tm, dt);
if (rc < 0.002 || t > 3.5) break;
t += clamp(min(dc, dt), 0.005, 0.12);
}
rc = clamp(rc, 0.0, 1.0); rc = rc * rc * (3.0 - 2.0 * rc);
float c = clamp(-tm / uTr, 0.0, 1.0);
float glass = tm > 0.0 ? 1.0 - 0.25 * exp(-tm / 0.008) : mix(0.5, 0.75, smoothstep(0.0, 0.4, c)) + 1.1 * smoothstep(0.55, 0.95, c);
return rc * glass;
}
vec3 env(vec3 rd) {
vec3 c = mix(vec3(0.33, 0.22, 0.15), vec3(0.92, 0.85, 0.76), smoothstep(-0.15, 0.7, rd.y));
float f = dot(rd, uL);
if (f > 0.0) {
vec2 a = vec2(dot(rd, uLu), dot(rd, uLv)) / f;
float win = sbox(a - vec2(0.05, 0.1), vec2(0.42, 0.55), 0.03);
win *= 1.0 - 0.9 * smoothstep(0.02, 0.008, abs(a.x + 0.12));
win *= 1.0 - 0.9 * smoothstep(0.02, 0.008, abs(a.y - 0.25));
c += uSun * 5.5 * win;
}
if (rd.y < 0.0) c = mix(c, vec3(0.2, 0.11, 0.05), smoothstep(0.0, -0.2, rd.y));
return c;
}
// the bead and the warmth it has left behind, as light falling on a surface
vec3 beadLight(vec3 P, vec3 n) {
vec3 Lb = uBead - P; float d2 = dot(Lb, Lb);
float k = max(dot(n, Lb * inversesqrt(d2)), 0.0) * 0.6 + 0.4 * max(dot(n, Lb * inversesqrt(d2)), -0.2);
vec3 acc = WARM * uBeadPow * 0.08 * max(k, 0.0) / (d2 + 0.006);
float w = 0.0;
for (int i = 0; i < ${BINS}; i++) {
vec3 L = uWarmPos[i] - P; float e2 = dot(L, L);
w += uWarm[i] * max(dot(n, L * inversesqrt(e2)) * 0.7 + 0.3, 0.0) / (e2 + 0.03);
}
return acc + WARM * w * 0.11;
}
vec3 wood(vec3 P, out float rough, out vec3 n) {
float z = P.z * 4.4;
float id = floor(z);
float fr = fract(z);
float tone = hash(vec2(id, 3.1));
float off = hash(vec2(id, 9.7)) * 40.0;
float warp = 0.6 * fbm(vec2(P.x * 1.2 + off, z * 3.0));
float grain = mix(0.5, fbm(vec2(P.x * 1.4 + off, (fr + warp) * 26.0)), clamp(1.4 - fwidth(z * 26.0) * 0.7, 0.0, 1.0));
float fine = mix(0.5, vnoise(vec2(P.x * 90.0, z * 60.0 + off)), clamp(1.0 - max(fwidth(P.x * 90.0), fwidth(z * 60.0)) * 0.9, 0.0, 1.0));
vec3 alb = mix(vec3(0.26, 0.12, 0.05), vec3(0.55, 0.3, 0.13), 0.3 + 0.5 * tone) * (0.55 + 0.75 * grain) * (0.9 + 0.12 * fine);
float px = fwidth(z);
float seam = smoothstep(0.012 + px, 0.003, min(fr, 1.0 - fr)) / (1.0 + px * 40.0);
alb *= 1.0 - 0.75 * seam;
float x = P.x * 0.9 + off;
float pj = fwidth(x * 0.3);
float fj = fract(x * 0.3);
float joint = smoothstep(0.0012 + pj, 0.0, min(fj, 1.0 - fj)) / (1.0 + pj * 200.0);
alb *= 1.0 - 0.6 * joint;
rough = mix(0.05 + 0.08 * fine, 0.5, seam);
n = normalize(vec3(0.015 * (grain - 0.5), 1.0, 0.0));
return alb;
}
vec3 plaster(vec3 P) {
vec3 alb = vec3(0.72, 0.52, 0.36) * (0.88 + 0.22 * fbm(P.xy * 2.2));
float sun = max(uL.z, 0.0) * gobo(P, false) * sunVis(P);
return alb * (uSun * sun + AMB * 0.9);
}
vec3 paper(vec3 q) {
float f = vnoise(q.xy * 900.0) * 0.5 + vnoise(q.xy * vec2(260.0, 1700.0)) * 0.5;
return vec3(0.84, 0.79, 0.7) * (0.97 + 0.05 * f) * (0.98 + 0.04 * fbm(q.xy * 6.0));
}
vec3 shadeCard(vec3 P, vec3 q, vec3 nl, vec3 V, bool fine) {
vec3 n = dirW(nl);
vec3 alb = paper(q);
if (abs(nl.z) < 0.7) alb *= vec3(0.9, 0.86, 0.8);
float near = sdTube(q);
float ao = mix(0.55, 1.0, smoothstep(0.0, 0.03, near)) * mix(0.6, 1.0, smoothstep(0.0, 0.12, P.y));
float vis = fine ? sunVis(P + n * 0.002) : 1.0;
vec3 col = alb * (uSun * max(dot(n, uL), 0.0) * gobo(P, fine) * vis + AMB * ao + beadLight(P, n) + vec3(0.12, 0.06, 0.03) * exp(-P.y / 0.18));
float F = 0.03 + 0.97 * pow(1.0 - max(dot(n, V), 0.0), 5.0);
col += env(reflect(-V, n)) * F * 0.18;
return col;
}
vec3 shadeBrass(vec3 P, vec3 nl, vec3 V) {
vec3 n = dirW(nl);
vec3 alb = vec3(0.86, 0.6, 0.28);
vec3 R = reflect(-V, n);
float F = pow(1.0 - max(dot(n, V), 0.0), 5.0);
vec3 spec = env(R) * 0.7 + uSun * 8.0 * pow(max(dot(R, uL), 0.0), 120.0);
return (alb + (1.0 - alb) * F) * spec * 0.75 + alb * (uSun * max(dot(n, uL), 0.0) * 0.12 + beadLight(P, n) * 0.6);
}
vec3 shadeTable(vec3 P, vec3 V, vec3 rd, bool fine, out float far) {
float rough; vec3 n;
vec3 alb = wood(P, rough, n);
vec3 q = toL(P);
float dc = sdCard(q);
float ao = mix(0.32, 1.0, smoothstep(0.0, 0.16, dc)) * mix(0.75, 1.0, smoothstep(0.0, 0.05, sdTube(q)));
ao *= mix(0.7, 1.0, smoothstep(0.0, 0.5, P.z - WALLZ));
vec3 dif = uSun * max(dot(n, uL), 0.0) * gobo(P, fine) * (fine ? sunVis(P) : 1.0) + AMB * ao + beadLight(P, n);
vec3 col = alb * dif;
far = 0.0;
if (!fine) return col;
// varnish: one glossy bounce, jittered by the roughness of the grain
float j = hash(gl_FragCoord.xy + fract(uTime) * 13.0);
vec3 nr = normalize(n + rough * 0.1 * vec3(cos(j * 6.283), 0.0, sin(j * 6.283)) * sqrt(fract(j * 7.13)));
vec3 R = reflect(rd, nr);
vec3 ro = P + R * 0.003;
vec3 refl = vec3(0.0);
float t = 0.0; bool hit = false; float id = 0.0;
for (int i = 0; i < 48; i++) {
vec2 h = mapL(toL(ro + R * t));
if (h.x < 0.001) { hit = true; id = h.y; break; }
t += h.x;
if (t > 3.0) break;
}
if (hit) {
vec3 H = ro + R * t, hq = toL(H);
vec3 hn = normL(hq, id);
if (id < 1.5) refl = shadeCard(H, hq, hn, -R, false);
else if (id > 2.5) refl = shadeBrass(H, hn, -R);
else refl = env(reflect(R, dirW(hn))) * 0.22 + WARM * uBeadPow * 0.6 * exp(-pow((pathParam(hq.xy) - uBeadS) * uPer, 2.0) / 0.004) + WARM * warmAt(pathParam(hq.xy)) * 0.5;
far = t;
} else if (R.z < 0.0) {
float tw = (WALLZ - ro.z) / R.z;
refl = plaster(ro + R * tw);
far = tw;
} else { refl = env(R); far = 5.0; }
float F = 0.04 + 0.96 * pow(1.0 - max(dot(nr, V), 0.0), 5.0);
F *= 0.85;
return col * (1.0 - F) + refl * F * ao;
}
vec3 shadeGlass(vec3 P, vec3 q, vec3 nl, vec3 rd) {
vec3 n = dirW(nl);
float cosT = max(dot(n, -rd), 0.0);
float F = 0.04 + 0.96 * pow(1.0 - cosT, 5.0);
vec3 R = reflect(rd, n);
vec3 refl = env(R) + uSun * 22.0 * pow(max(dot(R, uL), 0.0), 260.0) * sunVis(P + n * 0.01);
// seen through the glass: the tube bends what is behind it a little
vec3 td = normalize(mix(rd, refract(rd, n, 0.67), 0.9));
vec3 ro = P + td * (uTr * 2.0 * cosT + 0.004);
vec3 seen;
float t = 0.0; bool hit = false;
for (int i = 0; i < 28; i++) {
float d = sdCard(toL(ro + td * t));
if (d < 0.0008) { hit = true; break; }
t += d;
if (t > 1.0) break;
}
if (hit) { vec3 H = ro + td * t, hq = toL(H); seen = shadeCard(H, hq, normL(hq, 1.0), -td, false); }
else { float tp = td.y < 0.0 ? -ro.y / td.y : 1e9; if (tp < 1e8) { float f; seen = shadeTable(ro + td * tp, -td, td, false, f); } else seen = env(td); }
vec3 tint = vec3(0.9, 0.93, 0.9) * exp(-(1.0 / max(cosT, 0.12) - 1.0) * vec3(0.3, 0.14, 0.22));
// the bead's light runs along inside the glass wall, brightest at the silhouette
float s = pathParam(q.xy);
float ds = fract(s - uBeadS + 0.5) - 0.5;
float dm = ds * uPer;
float pipe = 0.6 + 2.2 * pow(1.0 - cosT, 2.0);
float behind = dm < 0.0 ? exp(dm / 0.16) : exp(-dm / 0.025);
vec3 glow = WARM * (uBeadPow * (8.0 * exp(-dm * dm / 0.0025) + 1.5 * behind) + 0.55 * warmAt(s)) * pipe;
// a hollow tube: near its silhouette the eye looks along the wall and sees the dim room bent round
float rim = smoothstep(0.8, 0.12, cosT);
vec3 wall = mix(seen * tint, vec3(0.1, 0.085, 0.06) * (0.5 + 0.5 * env(R).r), rim * 0.9);
// an inner wall highlight, offset from the outer one
float inner = smoothstep(0.62, 0.7, cosT) * smoothstep(0.8, 0.7, cosT) * 0.35;
return wall * (1.0 - F) + refl * F + glow + vec3(1.0, 0.95, 0.88) * inner * max(dot(n, uL), 0.0);
}
vec3 tonemap(vec3 x) { x *= 0.66; return clamp((x * (2.51 * x + 0.03)) / (x * (2.43 * x + 0.59) + 0.14), 0.0, 1.0); }
void main() {
vec2 uv = (gl_FragCoord.xy / uRes) * 2.0 - 1.0;
float aspect = uRes.x / uRes.y;
vec3 rd = normalize(uFw + uRt * uv.x * uTan * aspect + uUp * uv.y * uTan);
vec3 ro = uCam;
float tp = rd.y < 0.0 ? -ro.y / rd.y : 1e9;
float tw = rd.z < 0.0 ? (WALLZ - ro.z) / rd.z : 1e9;
float tMax = min(min(tp, tw), 12.0);
// march the card and the tube from just before their bounds
float t = max(0.0, length(ro - vec3(0.0, uHalf.y + uLift, 0.0)) - max(uHalf.x, uHalf.y) - 0.4);
float id = 0.0;
for (int i = 0; i < 140; i++) {
vec2 h = mapL(toL(ro + rd * t));
if (h.x < 0.0001 * t) { id = h.y; break; }
t += h.x * 0.8;
if (t > tMax) break;
}
vec3 col; float depth; vec3 V = -rd;
if (id > 0.5 && t < tMax) {
vec3 P = ro + rd * t, q = toL(P);
vec3 nl = normL(q, id);
col = id < 1.5 ? shadeCard(P, q, nl, V, true) : id > 2.5 ? shadeBrass(P, nl, V) : shadeGlass(P, q, nl, rd);
depth = t;
} else if (tp < tw) {
float far;
vec3 P = ro + rd * tp;
col = shadeTable(P, V, rd, true, far);
depth = tp;
} else {
col = plaster(ro + rd * tw);
depth = tw;
}
// the bead itself: a short hot streak, drawn wherever it is not hidden behind the card
vec3 ba = uBead - uTail, w0 = ro - uTail;
float bb = dot(rd, ba), cc = max(dot(ba, ba), 1e-8), dd = dot(rd, w0), ee = dot(ba, w0);
float den = cc - bb * bb;
float sg = den > 1e-9 ? clamp((ee - bb * dd) / den, 0.0, 1.0) : 1.0;
vec3 Q = uTail + ba * sg;
float bt = dot(Q - ro, rd);
float best = length(ro + rd * bt - Q);
if (bt < depth + uTr * 2.5) {
float hot = 0.55 + 0.45 * sg; // brightest at the head
float core = exp(-best * best / (0.0075 * 0.0075)) * hot;
float halo = exp(-best / 0.05);
col += vec3(1.0, 0.88, 0.7) * core * 16.0 * uBeadPow + WARM * halo * 0.7 * uBeadPow;
}
float coc = clamp(uAperture * (1.0 - uFocus / max(depth, 0.05)), -1.0, 1.0);
o = vec4(pow(tonemap(col), vec3(1.0 / 2.2)), 0.5 + 0.5 * coc);
}`;
const FS_OUT = `#version 300 es
precision highp float;
uniform sampler2D uScene; uniform vec2 uPx; uniform float uMaxR, uTime;
out vec4 o;
float hash(vec2 p) { p = fract(p * vec2(123.34, 456.21)); p += dot(p, p + 45.32); return fract(p.x * p.y); }
void main() {
vec2 uv = gl_FragCoord.xy * uPx;
vec4 c0 = texture(uScene, uv);
float r0 = abs(c0.a * 2.0 - 1.0) * uMaxR;
vec3 acc = c0.rgb; float wsum = 1.0;
if (r0 > 0.6) {
float rot = hash(gl_FragCoord.xy) * 6.2832;
for (int i = 1; i < 28; i++) {
float f = float(i);
float a = f * 2.39996 + rot, r = sqrt(f / 27.0) * r0;
vec2 off = vec2(cos(a), sin(a)) * r * uPx;
vec4 s = texture(uScene, uv + off);
float rs = abs(s.a * 2.0 - 1.0) * uMaxR;
float w = smoothstep(r - 1.0, r + 1.0, rs + 0.5);
acc += s.rgb * w; wsum += w;
}
}
vec3 col = acc / wsum;
vec2 v = uv - 0.5;
col *= 1.0 - 0.32 * dot(v, v) * 1.6;
col += (hash(gl_FragCoord.xy + fract(uTime * 7.0) * 91.0) - 0.5) * 0.028;
o = vec4(col, 1.0);
}`;
function compile(gl: WebGL2RenderingContext, vs: string, fs: string) {
const p = gl.createProgram()!;
for (const [type, src] of [[gl.VERTEX_SHADER, vs], [gl.FRAGMENT_SHADER, fs]] as const) {
const sh = gl.createShader(type)!;
gl.shaderSource(sh, src);
gl.compileShader(sh);
if (!gl.getShaderParameter(sh, gl.COMPILE_STATUS)) throw new Error(gl.getShaderInfoLog(sh) || "shader");
gl.attachShader(p, sh);
}
gl.linkProgram(p);
if (!gl.getProgramParameter(p, gl.LINK_STATUS)) throw new Error(gl.getProgramInfoLog(p) || "link");
return p;
}
function CardText({ narrow }: { narrow: boolean }) {
return (
<div className="flex h-full flex-col" style={{ color: INK, fontFamily: GROTESK }}>
<p className="font-semibold uppercase" style={{ fontSize: narrow ? 11 : 12, letterSpacing: "0.24em" }}>
{card.kicker}
</p>
<h2 className="font-normal" style={{ textWrap: "balance", fontFamily: SERIF, fontSize: narrow ? 37 : 47, lineHeight: 1.02, letterSpacing: "-0.022em", marginTop: narrow ? 18 : 16, maxWidth: narrow ? 330 : 520 }}>
{card.title}
</h2>
<p style={{ fontSize: narrow ? 15 : 16, lineHeight: 1.5, marginTop: narrow ? 18 : 16, maxWidth: narrow ? 320 : 470, opacity: 0.86 }}>{card.body}</p>
<div className={`mt-auto flex gap-4 ${narrow ? "flex-col items-start" : "items-center justify-between"}`} style={{ paddingTop: 14 }}>
<a
href="#"
className="inline-flex min-h-[40px] items-center gap-2 rounded-full font-semibold underline decoration-1 underline-offset-[5px] outline-none focus-visible:ring-2 focus-visible:ring-[#2b1c12] focus-visible:ring-offset-4 focus-visible:ring-offset-transparent"
style={{ fontSize: narrow ? 15 : 16 }}
>
{card.link}
<svg aria-hidden="true" width="18" height="18" viewBox="0 0 20 20" fill="none" stroke="currentColor" strokeWidth="1.7" strokeLinecap="round" strokeLinejoin="round">
<path d="M4 10h11M11 5l5 5-5 5" />
</svg>
</a>
<span className="uppercase" style={{ fontSize: 10.5, letterSpacing: "0.2em", opacity: 0.7 }}>{card.maker}</span>
</div>
</div>
);
}
export default function GlassTubeBorderFeatureCard() {
const reduce = useReducedMotion();
const wrapRef = useRef<HTMLDivElement>(null);
const canvasRef = useRef<HTMLCanvasElement>(null);
const plateRef = useRef<HTMLDivElement>(null);
const [mode, setMode] = useState<"wait" | "gl" | "still">("wait");
const [narrow, setNarrow] = useState(false);
const sim = useRef({ hot: false, lastTouch: -1e9, px: 0, py: 0, cx: 0, cy: 0, narrow: false, dirty: true });
useEffect(() => {
const wrap = wrapRef.current;
if (!wrap) return;
const measure = () => {
const n = wrap.clientWidth < 640;
sim.current.narrow = n;
sim.current.dirty = true;
setNarrow(n);
};
measure();
const ro = new ResizeObserver(measure);
ro.observe(wrap);
return () => ro.disconnect();
}, []);
useEffect(() => {
const wrap = wrapRef.current, canvas = canvasRef.current, plate = plateRef.current;
if (!wrap || !canvas || !plate) return;
const gl = canvas.getContext("webgl2", { antialias: false, alpha: false, powerPreference: "high-performance" });
if (!gl) {
setMode("still");
return;
}
let prog: WebGLProgram, progOut: WebGLProgram;
try {
prog = compile(gl, VS, FS);
progOut = compile(gl, VS, FS_OUT);
} catch (err) {
console.warn(err);
setMode("still");
return;
}
setMode("gl");
const s = sim.current;
const vao = gl.createVertexArray();
const fbo = gl.createFramebuffer();
const tex = gl.createTexture();
let W = 0, H = 0, cw = 1, ch = 1;
let scale = Math.min(window.devicePixelRatio || 1, 1.5);
const resize = () => {
cw = wrap.clientWidth;
ch = wrap.clientHeight;
let k = scale;
if (cw * ch * k * k > 1.1e6) k = Math.sqrt(1.1e6 / (cw * ch));
const w = Math.max(2, Math.round(cw * k)), h = Math.max(2, Math.round(ch * k));
s.dirty = true;
if (w === W && h === H) return;
W = w;
H = h;
canvas.width = W;
canvas.height = H;
gl.activeTexture(gl.TEXTURE0);
gl.bindTexture(gl.TEXTURE_2D, tex);
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA8, W, H, 0, gl.RGBA, gl.UNSIGNED_BYTE, null);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);
gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, tex, 0);
};
resize();
const ro = new ResizeObserver(resize);
ro.observe(wrap);
const locs = new Map<string, WebGLUniformLocation | null>();
const U = (p: WebGLProgram, n: string) => {
const key = (p === prog ? "a" : "b") + n;
if (!locs.has(key)) locs.set(key, gl.getUniformLocation(p, n));
return locs.get(key)!;
};
// the sun: low, warm, from the front left
const Lraw = [-0.62, 0.5, 0.6];
const ll = Math.hypot(Lraw[0], Lraw[1], Lraw[2]);
const L = Lraw.map((v) => v / ll);
let Lu = [L[2], 0, -L[0]];
const lul = Math.hypot(Lu[0], Lu[2]);
Lu = Lu.map((v) => v / lul);
const Lv = [L[1] * Lu[2] - L[2] * Lu[1], L[2] * Lu[0] - L[0] * Lu[2], L[0] * Lu[1] - L[1] * Lu[0]];
// the bead's state
let bs = 0.36, v = IDLE_SPEED, vv = 0, heat = 0;
const warm = new Float32Array(BINS);
const warmPos = new Float32Array(BINS * 3);
const toWorld = (l: Layout, x: number, y: number, z: number) => {
const c = Math.cos(l.yaw), sn = Math.sin(l.yaw);
return [c * x + sn * z, y + l.hy + 2 * l.tr + GAP, -sn * x + c * z];
};
let lay = s.narrow ? TALL : WIDE;
let path = tubePath(lay);
const relayout = () => {
lay = s.narrow ? TALL : WIDE;
path = tubePath(lay);
for (let i = 0; i < BINS; i++) {
const [x, y] = path.at((i + 0.5) / BINS);
const p = toWorld(lay, x, y, path.zt);
warmPos.set(p, i * 3);
}
};
relayout();
let lastNarrow = s.narrow;
/** One step of the bead: a spring on its speed, and warmth laid down where it passes. */
const step = (dt: number, hot: boolean) => {
const target = hot ? HOVER_SPEED : IDLE_SPEED;
vv += (SPEED_SPRING * (target - v) - SPEED_DAMP * vv) * dt;
v += vv * dt;
heat += ((hot ? 1 : 0) - heat) * Math.min(1, dt * 2.2);
const prev = bs;
bs = (bs + Math.max(0.01, v) * dt) % 1;
const decay = Math.exp(-dt / WARM_DECAY);
for (let i = 0; i < BINS; i++) warm[i] *= decay;
// spread the deposit over the bins the bead crossed this step
const gain = (0.25 + 2.4 * heat) * Math.max(0, v) * dt * BINS * 0.9;
const a = prev * BINS - 0.5, b = a + Math.max(0.01, v) * dt * BINS;
for (let f = Math.floor(a); f <= Math.floor(b) + 1; f++) {
const i = ((f % BINS) + BINS) % BINS;
const cover = clamp(Math.min(b, f + 1.5) - Math.max(a, f - 0.5), 0, 1);
warm[i] = Math.min(1.5, warm[i] + gain * cover * 0.5);
}
};
// start already warm, as if the bead had just run a fast lap
// and finish that lap with the bead on the top run, where it shows best
const PARK = 0.47;
for (let i = 0; i < 240; i++) step(1 / 60, i < 170);
const travelled = bs - 0.36;
warm.fill(0);
bs = (((PARK - travelled) % 1) + 1) % 1;
v = IDLE_SPEED;
vv = 0;
heat = 0;
for (let i = 0; i < 240; i++) step(1 / 60, i < 170);
const draw = (t: number) => {
if (s.narrow !== lastNarrow) {
lastNarrow = s.narrow;
relayout();
}
const aspect = cw / ch;
const n = lay.narrow;
const look = n ? [0.02, 0.7, 0] : [0.04, 0.53, 0];
const dist = n ? 3.7 : 3.25;
const drift = reduce ? 0 : 1;
const cam = [
look[0] + (n ? 0.32 : 0.55) + s.cx * 0.22 + drift * 0.04 * Math.sin(t * 0.23),
look[1] + (n ? 0.62 : 0.5) - s.cy * 0.08 + drift * 0.012 * Math.sin(t * 0.31 + 1.3),
dist,
];
let fw = [look[0] - cam[0], look[1] - cam[1], look[2] - cam[2]];
const fl = Math.hypot(fw[0], fw[1], fw[2]);
fw = fw.map((x) => x / fl);
let rt = [-fw[2], 0, fw[0]];
const rl = Math.hypot(rt[0], rt[2]);
rt = rt.map((x) => x / rl);
const up = [rt[1] * fw[2] - rt[2] * fw[1], rt[2] * fw[0] - rt[0] * fw[2], rt[0] * fw[1] - rt[1] * fw[0]];
const needW = n ? 0.86 : 1.7, needH = n ? 1.2 : 1.02;
const TAN = Math.max(needW / aspect, needH) / fl;
const [bx, by] = path.at(bs);
const bead = toWorld(lay, bx, by, path.zt);
const [tx, ty] = path.at(bs - Math.min(0.06, Math.max(0.004, v * 0.045)));
const tail = toWorld(lay, tx, ty, path.zt);
const pow = 0.85 + 0.55 * heat;
gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);
gl.viewport(0, 0, W, H);
gl.useProgram(prog);
gl.uniform2f(U(prog, "uRes"), W, H);
gl.uniform3fv(U(prog, "uCam"), cam);
gl.uniform3fv(U(prog, "uFw"), fw);
gl.uniform3fv(U(prog, "uRt"), rt);
gl.uniform3fv(U(prog, "uUp"), up);
gl.uniform1f(U(prog, "uTan"), TAN);
gl.uniform2f(U(prog, "uHalf"), lay.hx, lay.hy);
gl.uniform1f(U(prog, "uRc"), lay.rc);
gl.uniform1f(U(prog, "uTh"), lay.th);
gl.uniform1f(U(prog, "uYaw"), lay.yaw);
gl.uniform1f(U(prog, "uLift"), path.lift);
gl.uniform2f(U(prog, "uPA"), path.ax, path.ay);
gl.uniform1f(U(prog, "uPR"), path.pr);
gl.uniform1f(U(prog, "uTr"), lay.tr);
gl.uniform1f(U(prog, "uZt"), path.zt);
gl.uniform1f(U(prog, "uPer"), path.per);
gl.uniform3fv(U(prog, "uBead"), bead);
gl.uniform3fv(U(prog, "uTail"), tail);
gl.uniform1f(U(prog, "uBeadS"), bs);
gl.uniform1f(U(prog, "uBeadPow"), pow);
gl.uniform3fv(U(prog, "uWarmPos[0]"), warmPos);
gl.uniform1fv(U(prog, "uWarm[0]"), warm);
gl.uniform3fv(U(prog, "uL"), L);
gl.uniform3fv(U(prog, "uLu"), Lu);
gl.uniform3fv(U(prog, "uLv"), Lv);
gl.uniform3f(U(prog, "uSun"), 2.5, 2.02, 1.5);
gl.uniform1f(U(prog, "uTime"), reduce ? 0 : t);
gl.uniform1f(U(prog, "uFocus"), fl);
gl.uniform1f(U(prog, "uAperture"), 1.1);
gl.bindVertexArray(vao);
gl.drawArrays(gl.TRIANGLES, 0, 3);
gl.bindFramebuffer(gl.FRAMEBUFFER, null);
gl.viewport(0, 0, W, H);
gl.useProgram(progOut);
gl.activeTexture(gl.TEXTURE0);
gl.bindTexture(gl.TEXTURE_2D, tex);
gl.uniform1i(U(progOut, "uScene"), 0);
gl.uniform2f(U(progOut, "uPx"), 1 / W, 1 / H);
gl.uniform1f(U(progOut, "uMaxR"), H * 0.009);
gl.uniform1f(U(progOut, "uTime"), reduce ? 0 : t);
gl.drawArrays(gl.TRIANGLES, 0, 3);
// lay the text on the card face with the same camera, as a CSS projective matrix
const proj = (p: number[]) => {
const d = [p[0] - cam[0], p[1] - cam[1], p[2] - cam[2]];
const xv = d[0] * rt[0] + d[1] * rt[1] + d[2] * rt[2];
const yv = d[0] * up[0] + d[1] * up[1] + d[2] * up[2];
const zv = d[0] * fw[0] + d[1] * fw[1] + d[2] * fw[2];
return [cw * 0.5 * (1 + xv / (zv * TAN * aspect)), ch * 0.5 * (1 - yv / (zv * TAN))];
};
const ix = lay.hx - lay.pad, iy = lay.hy - lay.pad;
const z = lay.th + 0.0005;
const [x0, y0] = proj(toWorld(lay, -ix, iy, z));
const [x1, y1] = proj(toWorld(lay, ix, iy, z));
const [x2, y2] = proj(toWorld(lay, ix, -iy, z));
const [x3, y3] = proj(toWorld(lay, -ix, -iy, z));
const dx1 = x1 - x2, dx2 = x3 - x2, dx3 = x0 - x1 + x2 - x3;
const dy1 = y1 - y2, dy2 = y3 - y2, dy3 = y0 - y1 + y2 - y3;
const den = dx1 * dy2 - dx2 * dy1;
const g = (dx3 * dy2 - dx2 * dy3) / den, h = (dx1 * dy3 - dx3 * dy1) / den;
const a = x1 - x0 + g * x1, b = x3 - x0 + h * x3, d = y1 - y0 + g * y1, e = y3 - y0 + h * y3;
const pw = n ? 340 : 620, ph = Math.round((pw * iy) / ix);
plate.style.width = `${pw}px`;
plate.style.height = `${ph}px`;
plate.style.transform = `matrix3d(${a / pw},${d / pw},0,${g / pw},${b / ph},${e / ph},0,${h / ph},0,0,1,0,${x0},${y0},0,1)`;
};
let raf = 0, visible = true, last = performance.now(), slow = 0, frames = 0, fpsT = last, fpsN = 0;
const t0 = last;
const tick = (now: number) => {
const real = now - last;
const dt = Math.min(0.05, real / 1000);
last = now;
if (reduce) {
if (s.dirty) {
draw(0);
s.dirty = false;
}
} else {
// a demo lap now and then, when nobody is touching it; the first one is under way at load
const idle = now - s.lastTouch > 4000;
const since = now - t0;
const demo = idle && (since < 3200 || (since - 3200) % DEMO_EVERY > DEMO_EVERY - 2600);
const sub = Math.max(1, Math.ceil(dt / 0.008));
for (let i = 0; i < sub; i++) step(dt / sub, s.hot || demo);
s.cx += (s.px - s.cx) * Math.min(1, dt * 2.5);
s.cy += (s.py - s.cy) * Math.min(1, dt * 2.5);
draw((now - t0) / 1000);
fpsN++;
if (now - fpsT > 1000) {
wrap.dataset.fps = String(Math.round((fpsN * 1000) / (now - fpsT)));
fpsN = 0;
fpsT = now;
}
// measure, do not guess: render fewer pixels if this machine cannot keep up
if (++frames > 30) {
slow = slow * 0.92 + (real > 22 ? 1 : 0) * 0.08;
if (slow > 0.6 && scale > 0.5) {
scale *= 0.85;
slow = 0;
frames = 0;
resize();
}
}
}
if (visible && !document.hidden) raf = requestAnimationFrame(tick);
else raf = 0;
};
const restart = () => {
if (!raf && visible && !document.hidden) {
last = performance.now();
raf = requestAnimationFrame(tick);
}
};
const io = new IntersectionObserver(([en]) => {
visible = en.isIntersecting;
restart();
});
io.observe(wrap);
document.addEventListener("visibilitychange", restart);
raf = requestAnimationFrame(tick);
const move = (ev: PointerEvent) => {
const r = wrap.getBoundingClientRect();
s.px = clamp(((ev.clientX - r.left) / r.width) * 2 - 1, -1, 1);
s.py = clamp(((ev.clientY - r.top) / r.height) * 2 - 1, -1, 1);
};
const leave = () => {
s.px = 0;
s.py = 0;
};
wrap.addEventListener("pointermove", move);
wrap.addEventListener("pointerleave", leave);
return () => {
cancelAnimationFrame(raf);
ro.disconnect();
io.disconnect();
document.removeEventListener("visibilitychange", restart);
wrap.removeEventListener("pointermove", move);
wrap.removeEventListener("pointerleave", leave);
gl.getExtension("WEBGL_lose_context")?.loseContext();
};
}, [reduce]);
const heat = (on: boolean) => () => {
sim.current.hot = on;
sim.current.lastTouch = performance.now();
};
return (
<section className="relative overflow-hidden bg-[#7a4a2a]">
<div
ref={wrapRef}
className="relative h-[640px] w-full select-none sm:h-[680px]"
onPointerDown={(e) => {
if (e.pointerType !== "mouse") {
sim.current.hot = !sim.current.hot;
sim.current.lastTouch = performance.now();
}
}}
>
<canvas ref={canvasRef} aria-hidden="true" className={`absolute inset-0 h-full w-full ${mode === "still" ? "hidden" : ""}`} />
{/* the card's words: real text, projected onto the card face and multiplied into the light */}
<div
ref={plateRef}
className={`absolute left-0 top-0 origin-top-left ${mode === "gl" ? "" : "hidden"}`}
style={{ mixBlendMode: "multiply", willChange: "transform" }}
onPointerEnter={heat(true)}
onPointerLeave={heat(false)}
onFocus={heat(true)}
onBlur={heat(false)}
>
<CardText narrow={narrow} />
</div>
{mode === "still" && <Still narrow={narrow} onHot={heat} />}
</div>
</section>
);
}
/** The same table and card for browsers without WebGL 2: a warm photograph-like composition in plain CSS. */
function Still({ narrow, onHot }: { narrow: boolean; onHot: (on: boolean) => () => void }) {
return (
<div className="absolute inset-0" style={{ background: "linear-gradient(180deg, #b9875f 0%, #a5734d 34%, #6b3b1d 34.2%, #8a5229 60%, #5a2f14 100%)" }}>
<div aria-hidden="true" className="absolute inset-x-0 bottom-0 top-[34%]" style={{ background: "repeating-linear-gradient(180deg, rgba(0,0,0,0) 0 26px, rgba(30,10,0,0.45) 26px 28px), radial-gradient(60% 50% at 30% 30%, rgba(255,214,160,0.35), transparent 70%)" }} />
<div className="absolute inset-0 grid place-items-center px-4">
<div
className="relative w-full"
style={{ maxWidth: narrow ? 360 : 700, aspectRatio: narrow ? "1 / 1.38" : "1.64 / 1", borderRadius: 22, background: "#e9e1d2", boxShadow: "30px 26px 40px -10px rgba(40,15,0,0.55), inset 0 0 0 1px rgba(0,0,0,0.06)" }}
onPointerEnter={onHot(true)}
onPointerLeave={onHot(false)}
>
<div aria-hidden="true" className="absolute inset-[6px] rounded-[18px]" style={{ boxShadow: "inset 0 0 0 7px rgba(255,255,255,0.35), inset 0 0 0 8px rgba(120,140,120,0.35), inset 0 0 14px 6px rgba(255,170,90,0.35)" }} />
<style>{`@keyframes glass-tube-border-card-bead { 0% { left: 6%; } 100% { left: 92%; } } .glass-tube-border-card-bead { animation: glass-tube-border-card-bead 5s cubic-bezier(0.45, 0, 0.3, 1) infinite alternate; } @media (prefers-reduced-motion: reduce) { .glass-tube-border-card-bead { animation: none; } }`}</style>
<div aria-hidden="true" className="glass-tube-border-card-bead absolute h-2 w-2 rounded-full" style={{ top: 8, left: "62%", background: "#fff3df", boxShadow: "0 0 8px 3px rgba(255,170,80,0.8), 0 0 30px 10px rgba(255,140,50,0.35)" }} />
<div className="absolute" style={{ inset: narrow ? "8% 10%" : "12% 9%" }}>
<CardText narrow={narrow} />
</div>
</div>
</div>
</div>
);
}
Install with one command: npx shadcn@latest add https://we.inc/r/glass-tube-border-feature-card-in-webgl-with-a-warm-bead-of-light-that-runs-the-edge-and-warms-the-sunlit-table.json
The text is not in the WebGL picture. Each frame the four corners of the card's writing area are projected through the same camera the shader uses, and a CSS `matrix3d` maps the HTML block onto that four-sided shape. `mix-blend-mode: multiply` lets the sun, the shade and the bead's glow show through the ink.
A glass cylinder acts like a lens. The shadow test records how deep a sun ray passes through the tube: rays near its edge are bent away and leave a darker outline, while rays near its axis are focused, so the shader adds a narrow bright band there. It is a cheap stand-in for a real caustic, and it is what makes the glass read as glass.
No. The edge is divided into 24 places that each hold an amount of warmth. The bead adds to the places it crosses, faster laps add more, and every place fades on its own. The shader treats each one as a small warm lamp sitting in the tube, lighting the paper and the planks with distance falloff.
The picture is limited to about 1.1 million pixels and a device pixel ratio of 1.5, and the loop watches its own frame time and renders fewer pixels if frames start taking too long. It stops completely when the section scrolls out of view or the tab is hidden.
Yes. Replace the contents of `CardText` with any markup that fits the writing area, which is 620 by about 340 CSS pixels on desktop and 340 by about 500 on phones. The tube follows whatever card size you set in the layouts, so a square card only needs new `hx` and `hy` values.
Related: Framed Portrait Testimonials in WebGL with a Leaning Two-Sided Frame That Swings on Its Corner and Claps Back onto a Sunlit Wall, Glass Prism That Splits a Beam Carrying One Sentence into a Homepage Made of Light.
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