Using linear interpolation (lerping) to smooth d3.drag
behavior.
Last active
July 3, 2016 04:27
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Smooth drag with linear interpolation
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<!DOCTYPE html> | |
<meta charset="utf-8"> | |
<style> | |
body { | |
text-align: center; | |
font: 16px sans-serif; | |
} | |
circle { | |
stroke: #000; | |
stroke-width: 2px; | |
fill: #f0f; | |
cursor: -webkit-grab; | |
cursor: grab; | |
} | |
circle.dragging { | |
fill: lime; | |
} | |
.dragging { | |
cursor: -webkit-grabbing; | |
cursor: grabbing; | |
} | |
</style> | |
<body> | |
<script src="//cdnjs.cloudflare.com/ajax/libs/d3/3.5.14/d3.min.js"></script> | |
<script> | |
var margin = {top: 32, right: 32, bottom: 32, left: 32}, | |
width = 960 - margin.left - margin.right, | |
height = 500 - margin.top - margin.bottom, | |
alpha = 0.2; | |
var svg = d3.select("body").append("svg") | |
.attr("width", width + margin.left + margin.right) | |
.attr("height", height + margin.top + margin.bottom) | |
.append("g") | |
.attr("transform", "translate(" + margin.left + "," + margin.top + ")"); | |
var drag = d3.behavior.drag() | |
.origin(ƒ()); | |
var dots = svg.selectAll("circle") | |
.data(d3.range(16).map(function(d){ | |
return { | |
x: Math.random() * width, | |
y: Math.random() * height | |
}; | |
})) | |
.enter() | |
.append("circle") | |
.attr("r",31) | |
.attr("cx",ƒ("x")) | |
.attr("cy",ƒ("y")) | |
.each(function(d){ | |
d.x2 = d.x; | |
d.y2 = d.y; | |
}) | |
.call(drag); | |
drag.on("dragstart",function(d,i){ | |
this.parentNode.appendChild(this); | |
var dot = d3.select(this); | |
dot.classed("dragging",true); | |
d3.select("body").classed("dragging",true); | |
d3.timer(function(t){ | |
return lerp(dot); | |
}); | |
}); | |
drag.on("drag",function(d){ | |
var dragged = d3.select(this); | |
dragged.datum().x2 = d3.event.x; | |
dragged.datum().y2 = d3.event.y; | |
}); | |
drag.on("dragend",function(){ | |
d3.selectAll(".dragging").classed("dragging",false); | |
}); | |
function lerp(dot) { | |
var d = dot.datum(); | |
if (!dot.classed("dragging") && Math.abs(d.x2 - d.x) < 0.01 && Math.abs(d.y2 - d.y) < 0.01) { | |
// It's not being dragged and it's roughly caught up | |
return true; | |
} | |
// Constrain to bounds | |
d.x = Math.max(Math.min(width,d.x + (d.x2 - d.x) * alpha),0); | |
d.y = Math.max(Math.min(height,d.y + (d.y2 - d.y) * alpha),0); | |
dot.attr("cx",d.x) | |
.attr("cy",d.y); | |
return false; | |
} | |
function ƒ(key) { | |
return function (d){ | |
return key ? d[key] : d; | |
}; | |
} | |
</script> |
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