An example of using built-in svg path properties (.getTotalLength() and .getPointAtLength()) to iterate through svg paths. Uses precomputed TopoJSON from Census Bureau data. breathe.js provides animation.
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March 1, 2017 21:06
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Drawing United States Counties
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| height: 600 |
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset="utf-8" /> | |
| <style> | |
| #draw-canvas{ | |
| width: 100%; | |
| height: auto; | |
| } | |
| </style> | |
| </head> | |
| <body> | |
| <svg id="map-svg" style='display:none'></svg> | |
| <canvas id="draw-canvas"></canvas> | |
| <script src="https://d3js.org/d3.v4.min.js"></script> | |
| <script src="https://d3js.org/topojson.v2.min.js"></script> | |
| <script src="https://unpkg.com/breathejs@0.2.0/breathe.js"></script> | |
| <script> | |
| var svg = d3.select("#map-svg"); | |
| var canvas = document.getElementById('draw-canvas'); | |
| var ctx = canvas.getContext('2d'); | |
| var scale = 1; | |
| var width = 960 * scale; | |
| var height = 600 * scale; | |
| canvas.width = width; | |
| canvas.height = height; | |
| var path = d3.geoPath(); | |
| var drawPaths = function (paths, lineWidth) { | |
| var chains = []; | |
| return breathe.withId().times(paths.length, function (i) { | |
| var path = paths[i]; | |
| var s = 0; | |
| var length = path.getTotalLength(); | |
| // if you add `return` before breathe.loop, it draws only one at a time | |
| var chain = breathe.withId().loop(function () { return s < length; }, function () { | |
| point = path.getPointAtLength(s); | |
| ctx.fillRect(point.x*scale, point.y*scale, lineWidth, lineWidth); | |
| s += 0.25; | |
| }); | |
| chains.push(chain); | |
| }).then(function(){ | |
| return Promise.all(chains); | |
| }); | |
| }; | |
| d3.json('https://d3js.org/us-10m.v1.json', function(mapData){ | |
| var counties = svg.append('g') | |
| .selectAll('path') | |
| .data(topojson.feature(mapData, mapData.objects.counties).features) | |
| .enter() | |
| .append('path') | |
| .attr('d', path); | |
| var states = svg.append('g') | |
| .selectAll('path') | |
| .data(topojson.feature(mapData, mapData.objects.states).features) | |
| .enter() | |
| .append('path') | |
| .attr('d', path); | |
| var paths; | |
| breathe.animationMode(); | |
| ctx.fillStyle = 'black'; | |
| breathe.chain().then(function(){ | |
| return drawPaths(counties.nodes(), 0.5); | |
| }).then(function(){ | |
| return drawPaths(states.nodes(), 4); | |
| }); | |
| }); | |
| </script> | |
| </body> | |
| </html> |
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