31:T878,function* poissonDiscSampler(width, height, radius) { const k = 30; // maximum number of samples before rejection const radius2 = radius * radius; const radius2_3 = 3 * radius2; const cellSize = radius * Math.SQRT1_2; const gridWidth = Math.ceil(width / cellSize); const gridHeight = Math.ceil(height / cellSize); const grid = new Array(gridWidth * gridHeight); const queue = []; // Pick the first sample. yield {add: sample(width / 2 + Math.random() * radius, height / 2 + Math.random() * radius, null)}; // Pick a random existing sample from the queue. pick: while (queue.length) { const i = Math.random() * queue.length | 0; const parent = queue[i]; // Make a new candidate between [radius, 2 * radius] from the existing sample. for (let j = 0; j < k; ++j) { const a = 2 * Math.PI * Math.random(); const r = Math.sqrt(Math.random() * radius2_3 + radius2); const x = parent[0] + r * Math.cos(a); const y = parent[1] + r * Math.sin(a); // Accept candidates that are inside the allowed extent // and farther than 2 * radius to all existing samples. if (0 <= x && x < width && 0 <= y && y < height && far(x, y)) { yield {add: sample(x, y), parent}; continue pick; } } // If none of k candidates were accepted, remove it from the queue. const r = queue.pop(); if (i < queue.length) queue[i] = r; yield {remove: parent}; } function far(x, y) { const i = x / cellSize | 0; const j = y / cellSize | 0; const i0 = Math.max(i - 2, 0); const j0 = Math.max(j - 2, 0); const i1 = Math.min(i + 3, gridWidth); const j1 = Math.min(j + 3, gridHeight); for (let j = j0; j < j1; ++j) { const o = j * gridWidth; for (let i = i0; i < i1; ++i) { const s = grid[o + i]; if (s) { const dx = s[0] - x; const dy = s[1] - y; if (dx * dx + dy * dy < radius2) return false; } } } return true; } function sample(x, y, parent) { const s = grid[gridWidth * (y / cellSize | 0) + (x / cellSize | 0)] = [x, y]; queue.push(s); return s; } }32:[] 2f:{"title":"Bridson’s Algorithm","cells":[{"id":1,"value":"md`# Bridson’s Algorithm\n\nThis algorithm efficiently generates [poisson-disc samples](https://dl.acm.org/citation.cfm?id=1278807).`","pinned":false,"hidden":false,"mode":"ojs"},{"id":236,"value":"viewof replay = html``","pinned":false,"hidden":false,"mode":"ojs"},{"id":9,"value":"chart = {\n const height = 600;\n const svg = d3.create(\"svg\").attr(\"viewBox\", [0, 0, width, height]);\n \n replay;\n \n for (const event of poissonDiscSampler(width, height, 10)) {\n if (event.add) {\n event.parent && svg.insert(\"line\", \"circle\")\n .attr(\"x1\", event.parent[0])\n .attr(\"y1\", event.parent[1])\n .attr(\"x2\", event.add[0])\n .attr(\"y2\", event.add[1])\n .attr(\"stroke\", \"#999\");\n\n svg.append(\"circle\")\n .attr(\"id\", `point-${event.add.map(Math.round).join(\"-\")}`)\n .attr(\"r\", 0)\n .attr(\"cx\", event.add[0])\n .attr(\"cy\", event.add[1])\n .transition()\n .ease(d3.easeLinear)\n .attr(\"r\", 3)\n .transition()\n .attr(\"fill\", \"#f00\");\n } else if (event.remove) {\n svg.select(`#point-${event.remove.map(Math.round).join(\"-\")}`)\n .transition()\n .ease(d3.easeLinear)\n .attr(\"fill\", \"#999\")\n .attr(\"r\", 2);\n }\n \n yield svg.node();\n }\n}","pinned":true,"hidden":false,"mode":"ojs"},{"id":3,"value":"$31","pinned":true,"hidden":false,"mode":"ojs"},{"id":118,"value":"d3 = require(\"d3@5\")","pinned":true,"hidden":false,"mode":"ojs"}],"files":"$W32","stdlib":"1","titling":"auto"}