Add barycentric demo
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cg/barycentric/barycentric.js
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132
cg/barycentric/barycentric.js
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(function () {
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function fillCanvas (element, draw) {
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var canvas = document.createElement("canvas");
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var ctx = canvas.getContext("2d");
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var windowToCanvas;
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function resize () {
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var vw = element.clientWidth;
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var vh = element.clientHeight;
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canvas.width = vw;
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canvas.height = vh;
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var vpMin = Math.min(vw, vh);
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// cartesion coordinates [0, 100] on both x and y axes
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ctx.setTransform(
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vpMin / 100, 0,
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0, -vpMin / 100,
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(vw - vpMin) / 2, (vh - vpMin) / 2 + vh
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);
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windowToCanvas = ctx.getTransform().inverse();
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}
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new ResizeObserver(resize).observe(element);
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resize();
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function render () {
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draw(ctx, canvas.width, canvas.height, windowToCanvas);
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requestAnimationFrame(render);
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}
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render();
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element.appendChild(canvas);
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}
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const Vec2 = {
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add: (v1, v2) => [v1[0] + v2[0], v1[1] + v2[1]],
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sub: (v1, v2) => [v1[0] - v2[0], v1[1] - v2[1]],
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scale: (s, v) => [s * v[0], s * v[1]],
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magnitude: (v) => Math.sqrt(v[0] * v[0] + v[1] * v[1]),
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distance: (v1, v2) => Vec2.magnitude(Vec2.sub(v1, v2)),
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normalize: (v) => Vec2.scale(1 / Vec2.magnitude(v), v),
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transform: (m, v) => {
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return [
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m.a * v[0] + m.c * v[1] + m.e,
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m.b * v[1] + m.d * v[1] + m.f
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];
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},
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dot: (v1, v2) => [v1[0] * v2[0] + v1[1] * v2[1]],
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triangleArea: (p1, p2, p3) => {
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// Cramers rule for signed area (necessary to get negative lambdas)
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var [x1, y1] = p1;
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var [x2, y2] = p2;
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var [x3, y3] = p3;
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return (x1 * y2 - x1 * y3 - x2 * y1 + x3 * y1 + x2 * y3 - x3 * y2) / 2;
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}
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};
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var p1 = [30, 20];
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var p2 = [10, 80];
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var p3 = [80, 50];
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var ptr = null;
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window.addEventListener("mousemove", function (e) {
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ptr = [e.clientX, e.clientY];
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});
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fillCanvas(document.querySelector(".canvas"), function (ctx, vw, vh, w2c) {
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var origin = Vec2.transform(w2c, [0, 0]);
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var omega = Vec2.transform(w2c, [vw, vh]);
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ctx.fillStyle = "black";
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ctx.fillRect(origin[0], origin[1], omega[0] - origin[0], omega[1] - origin[1])
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ctx.lineCap = "round";
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ctx.lineJoin = "round";
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var inside = false;
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if (ptr !== null) {
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var p = Vec2.transform(w2c, ptr);
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var a = Vec2.triangleArea(p1, p2, p3);
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var lambda1 = Vec2.triangleArea(p, p2, p3) / a;
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var lambda2 = Vec2.triangleArea(p1, p, p3) / a;
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var lambda3 = Vec2.triangleArea(p1, p2, p) / a;
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document.querySelector("#lambda1").innerHTML = formatLambda(lambda1);
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document.querySelector("#lambda2").innerHTML = formatLambda(lambda2);
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document.querySelector("#lambda3").innerHTML = formatLambda(lambda3);
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if (lambda1 > 0 && lambda2 > 0 && lambda3 > 0) {
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inside = true;
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}
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}
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ctx.beginPath();
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ctx.moveTo(p1[0], p1[1]);
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ctx.lineTo(p2[0], p2[1]);
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ctx.lineTo(p3[0], p3[1]);
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ctx.closePath();
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ctx.strokeStyle = inside ? "white" : "red";
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ctx.stroke();
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if (ptr !== null) {
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ctx.beginPath();
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ctx.arc(p[0], p[1], 10, 0, Math.PI * 2);
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ctx.strokeStyle = "green";
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ctx.stroke();
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ctx.beginPath();
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ctx.moveTo(p1[0], p1[1]);
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ctx.lineTo(p[0], p[1]);
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ctx.strokeStyle = "white";
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ctx.stroke();
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ctx.beginPath();
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ctx.moveTo(p2[0], p2[1]);
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ctx.lineTo(p[0], p[1]);
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ctx.strokeStyle = "white";
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ctx.stroke();
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ctx.beginPath();
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ctx.moveTo(p3[0], p3[1]);
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ctx.lineTo(p[0], p[1]);
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ctx.strokeStyle = "white";
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ctx.stroke();
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}
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function formatLambda (lambda) {
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return String(Math.floor(lambda * 100) / 100);
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}
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});
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})();
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43
cg/barycentric/index.html
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43
cg/barycentric/index.html
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="UTF-8">
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<title>barycentric</title>
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<style>
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body {
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margin: 0;
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overflow: hidden;
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font-family: Helvetica, Arial, sans-serif;
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}
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canvas {
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display: block;
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}
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.main {
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display: flex;
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flex-direction: column;
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height: 100vh;
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align-items: center;
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}
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.canvas {
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flex: 1;
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width: 100vw;
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overflow: hidden;
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}
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.text {
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font-size: 1.5em;
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width: 30rem;
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}
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</style>
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</head>
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<body>
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<div class="main">
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<div class="canvas"></div>
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<div class="text">
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<p>λ₁ = <span id="lambda1">...</span></p>
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<p>λ₂ = <span id="lambda2">...</span></p>
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<p>λ₃ = <span id="lambda3">...</span></p>
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</div>
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</div>
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<script src="./barycentric.js"></script>
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</body>
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</html>
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