Voroblobinoids

<!DOCTYPE html>
<meta charset="utf-8">
<canvas width="960" height="500"></canvas>
<script src="//d3js.org/d3-voronoi.v0.3.min.js"></script>
<script src="//d3js.org/d3-timer.v0.1.min.js"></script>
<script>

var canvas = document.querySelector("canvas"),
    width = canvas.width,
    height = canvas.height,
    context = canvas.getContext("2d"),
    voronoi = d3_voronoi.voronoi().extent([[0.5, 0.5], [width - 0.5, height - 0.5]]);

var n = 100,
    particles = new Array(n),
    radius = 12;

for (var i = 0; i < n; ++i) particles[i] = {0: Math.random() * width, 1: Math.random() * height, vx: 0, vy: 0};

d3_timer.timer(function(elapsed) {
  for (var i = 0; i < n; ++i) {
    var p = particles[i];
    p[0] += p.vx; if (p[0] < 0) p[0] = p.vx *= -1; else if (p[0] > width) p[0] = width + (p.vx *= -1);
    p[1] += p.vy; if (p[1] < 0) p[1] = p.vy *= -1; else if (p[1] > height) p[1] = height + (p.vy *= -1);
    p.vx += 0.1 * (Math.random() - .5) - 0.01 * p.vx;
    p.vy += 0.1 * (Math.random() - .5) - 0.01 * p.vy;
  }

var cells = voronoi.polygons(particles);
  context.clearRect(0, 0, width, height);

context.beginPath();
  cells.forEach(function(cell) { drawRoundedPolygon(cell, radius); });
  context.fillStyle = "#ddd";
  context.fill();
  context.lineWidth = 5;
  context.strokeStyle = "#fff";
  context.stroke();

context.beginPath();
  cells.forEach(function(cell) { drawPolygon(cell); });
  context.lineWidth = 1;
  context.strokeStyle = "#aaa";
  context.stroke();

context.beginPath();
  particles.forEach(function(particle) { drawPoint(particle); });
  context.fillStyle = "#000";
  context.fill();
});

function drawPoint(point) {
  context.moveTo(point[0] + 1.5, point[1]);
  context.arc(point[0], point[1], 1.5, 0, 2 * Math.PI);
}

function drawPolygon(points) {
  context.moveTo(points[0][0], points[0][1]);
  for (var i = 1, n = points.length; i < n; ++i) context.lineTo(points[i][0], points[i][1]);
  context.closePath();
}

function drawRoundedPolygon(points, r) {
  var i,
      n = points.length,
      p0,
      p1,
      p2,
      p3,
      n1 = 0,
      t012,
      t123,
      x21, y21,
      x4, y4,
      x5, y5,
      moved,
      circle = polygonIncircle(points);

// Build a linked list from the array of vertices so we can splice.
  for (i = 0, p1 = points[n - 2], p2 = points[n - 1]; i < n; ++i) {
    p0 = p1, p1 = p2, p2 = points[i];
    p1.previous = p0;
    p1.next = p2;
  }

// The rounding radius can’t be bigger than the polygon’s incircle.
  // The fudge factor of 1px lets the rounded polygon get squished a bit.
  // TODO Abort the search for the incircle if one is found larger than r.
  r = Math.min(r, circle.radius - 1);
  if (r <= 0) return;

// TODO do we need to make all these extra passes?
  for (i = 0, p3 = p2.next; n1 <= n; ++n1) {
    p0 = p1, p1 = p2, p2 = p3, p3 = p3.next;
    t012 = cornerTangent(p0[0], p0[1], p1[0], p1[1], p2[0], p2[1], r);
    t123 = 1 - cornerTangent(p3[0], p3[1], p2[0], p2[1], p1[0], p1[1], r);

// If the following corner’s tangent is before this corner’s tangent,
    // replace p1 and p2 with the intersection of the lines 01 and 23.
    if (t012 >= t123) {
      p2 = p0.next = p3.previous = lineLineIntersection(p0[0], p0[1], p1[0], p1[1], p2[0], p2[1], p3[0], p3[1]);
      p2.previous = p0;
      p2.next = p3;
      p3 = p2;
      p2 = p3.previous;
      p1 = p2.previous;
      p0 = p1.previous;
      n1 = 0;
      if (--n < 3) break;
    }
  }

// If we removed too many points, just draw the previously computed incircle.
  if (n < 3) {
    context.moveTo(circle[0] + circle.radius, circle[1]);
    context.arc(circle[0], circle[1], circle.radius, 0, 2 * Math.PI);
    return;
  }

// Draw the rounded polygon, compting the corner tangents.
  for (i = 0; i <= n; ++i) {
    p0 = p1, p1 = p2, p2 = p3, p3 = p3.next;
    t012 = cornerTangent(p0[0], p0[1], p1[0], p1[1], p2[0], p2[1], r);
    t123 = 1 - cornerTangent(p3[0], p3[1], p2[0], p2[1], p1[0], p1[1], r);
    x21 = p2[0] - p1[0], y21 = p2[1] - p1[1];
    x4 = p1[0] + t012 * x21, y4 = p1[1] + t012 * y21;
    x5 = p1[0] + t123 * x21, y5 = p1[1] + t123 * y21;
    if (moved) context.arcTo(p1[0], p1[1], x4, y4, r);
    else moved = true, context.moveTo(x4, y4);
    context.lineTo(x5, y5);
  }
}

// Given a circle of radius r that is tangent to the line segments 01 and 12,
// returns the parameter t of the tangent along the line segment 12.
function cornerTangent(x0, y0, x1, y1, x2, y2, r) {
  var theta = innerAngle(x0, y0, x1, y1, x2, y2),
      x21 = x2 - x1, y21 = y2 - y1,
      l21 = Math.sqrt(x21 * x21 + y21 * y21),
      l14 = r / Math.tan(theta / 2);
  return l14 / l21;
}

// A horrible brute-force algorithm for determining the largest circle that can
// fit inside a convex polygon. For each distinct set of three sides of the
// polygon, compute the tangent circle. Then reduce the circle’s radius against
// the remaining sides of the polygon.
function polygonIncircle(points) {
  var circle = {radius: 0};

for (var i = 0, n = points.length; i < n; ++i) {
    var pi0 = points[i],
        pi1 = points[(i + 1) % n];
    for (var j = i + 1; j < n; ++j) {
      var pj0 = points[j],
          pj1 = points[(j + 1) % n],
          pij = j === i + 1 ? pj0 : lineLineIntersection(pi0[0], pi0[1], pi1[0], pi1[1], pj0[0], pj0[1], pj1[0], pj1[1]);
      search: for (var k = j + 1; k < n; ++k) {
        var pk0 = points[k],
            pk1 = points[(k + 1) % n],
            pik = lineLineIntersection(pi0[0], pi0[1], pi1[0], pi1[1], pk0[0], pk0[1], pk1[0], pk1[1]),
            pjk = k === j + 1 ? pk0 : lineLineIntersection(pj0[0], pj0[1], pj1[0], pj1[1], pk0[0], pk0[1], pk1[0], pk1[1]),
            candidate = triangleIncircle(pij[0], pij[1], pik[0], pik[1], pjk[0], pjk[1]),
            radius = candidate.radius;

for (var l = 0; l < n; ++l) {
          var pl0 = points[l],
              pl1 = points[(l + 1) % n],
              r = pointLineDistance(candidate[0], candidate[1], pl0[0], pl0[1], pl1[0], pl1[1]);
          if (r < circle.radius) continue search;
          if (r < radius) radius = r;
        }

circle = candidate;
        circle.radius = radius;
      }
    }
  }

return circle;
}

// Returns the angle between segments 01 and 12.
function innerAngle(x0, y0, x1, y1, x2, y2) {
  var x01 = x0 - x1, y01 = y0 - y1,
      x12 = x1 - x2, y12 = y1 - y2,
      x02 = x0 - x2, y02 = y0 - y2,
      l01_2 = x01 * x01 + y01 * y01,
      l12_2 = x12 * x12 + y12 * y12,
      l02_2 = x02 * x02 + y02 * y02;
  return Math.acos((l12_2 + l01_2 - l02_2) / (2 * Math.sqrt(l12_2 * l01_2)));
}

// Returns the intersection of the infinite lines 01 and 23.
function lineLineIntersection(x0, y0, x1, y1, x2, y2, x3, y3) {
  var x02 = x0 - x2, y02 = y0 - y2,
      x10 = x1 - x0, y10 = y1 - y0,
      x32 = x3 - x2, y32 = y3 - y2,
      t = (x32 * y02 - y32 * x02) / (y32 * x10 - x32 * y10);
  return [x0 + t * x10, y0 + t * y10];
}

// Returns the signed distance from point 0 to the infinite line 12.
function pointLineDistance(x0, y0, x1, y1, x2, y2) {
  var x21 = x2 - x1, y21 = y2 - y1;
  return (y21 * x0 - x21 * y0 + x2 * y1 - y2 * x1) / Math.sqrt(y21 * y21 + x21 * x21);
}

// Returns the largest circle inside the triangle 012.
function triangleIncircle(x0, y0, x1, y1, x2, y2) {
  var x01 = x0 - x1, y01 = y0 - y1,
      x02 = x0 - x2, y02 = y0 - y2,
      x12 = x1 - x2, y12 = y1 - y2,
      l01 = Math.sqrt(x01 * x01 + y01 * y01),
      l02 = Math.sqrt(x02 * x02 + y02 * y02),
      l12 = Math.sqrt(x12 * x12 + y12 * y12),
      k0 = l01 / (l01 + l02),
      k1 = l12 / (l12 + l01),
      center = lineLineIntersection(x0, y0, x1 - k0 * x12, y1 - k0 * y12, x1, y1, x2 + k1 * x02, y2 + k1 * y02);
  center.radius = Math.sqrt((l02 + l12 - l01) * (l12 + l01 - l02) * (l01 + l02 - l12) / (l01 + l02 + l12)) / 2;
  return center;
}

</script>

https://d3js.org/d3-voronoi.v0.3.min.js

https://d3js.org/d3-timer.v0.1.min.js