Demonstrates how to use the getTotalLength and getPointAtLength methods on SVG path elements to interpolate a point along an existing path, and how to animate the stroke using the stroke-dasharray style. Built with D3. Forked (and tweaked) from Mike Bostock's original.
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Point-Along-Path Interpolation
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta http-equiv="Content-Type" content="text/html;charset=utf-8"/> | |
| <title>Point-Along-Path Interpolation</title> | |
| <script type="text/javascript" src="http://mbostock.github.com/d3/d3.js?2.4.6"></script> | |
| <style type="text/css"> | |
| path { | |
| cursor: pointer; | |
| fill: #eee; | |
| stroke: #666; | |
| stroke-width: 1.5px; | |
| } | |
| circle { | |
| fill: steelblue; | |
| stroke: white; | |
| stroke-width: 1.5px; | |
| } | |
| </style> | |
| </head> | |
| <body> | |
| <script type="text/javascript"> | |
| var w = 960, | |
| h = 500; | |
| var svg = d3.select("body").append("svg:svg") | |
| .attr("width", w) | |
| .attr("height", h) | |
| .append("svg:g") | |
| .attr("transform", "translate(" + w / 2 + "," + h / 2 + ")"); | |
| var path = svg.append("svg:path") | |
| .attr("d", d3.svg.arc() | |
| .innerRadius(h / 4) | |
| .outerRadius(h / 3) | |
| .startAngle(0) | |
| .endAngle(Math.PI)); | |
| var circle = svg.append("svg:circle") | |
| .attr("r", 6.5) | |
| .attr("transform", "translate(0," + -h / 3 + ")"); | |
| var draw = 0; | |
| function transition() { | |
| circle.transition() | |
| .duration(5000) | |
| .attrTween("transform", translateAlong(path.node())); | |
| path.transition() | |
| .duration(5000) | |
| .styleTween("stroke-dasharray", strokeAlong(path.node())) | |
| .each("end", transition); | |
| draw = 1 - draw; | |
| } | |
| transition(); | |
| // Returns an attrTween for translating along the specified path element. | |
| function translateAlong(path) { | |
| var l = path.getTotalLength(); | |
| return function(d, i, a) { | |
| return function(t) { | |
| var p = path.getPointAtLength(t * l); | |
| return "translate(" + p.x + "," + p.y + ")"; | |
| }; | |
| }; | |
| } | |
| // Returns an attrTween for stroking along the specified path element. | |
| function strokeAlong(path) { | |
| var l = path.getTotalLength(); | |
| return function(d, i, a) { | |
| return function(t) { | |
| var stroked = t * l, not = l - stroked; | |
| return (draw ? '' : '0,') + stroked + "," + not; | |
| }; | |
| }; | |
| } | |
| </script> | |
| </body> | |
| </html> |
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