Fine-grained control of randomly entering and exiting things in D3.js, for impeccable object constancy. Adapted from an example co-authored with Mike Bostock.
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February 12, 2017 15:39
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Advanced object constancy.
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<!DOCTYPE html> | |
<html> | |
<head> | |
<script src="http://d3js.org/d3.v3.min.js"></script> | |
<style> | |
html, body { | |
width: 100%; | |
height: 100%; | |
overflow: hidden; | |
margin: 0; | |
padding: 0; | |
} | |
circle { | |
fill: black; | |
stroke: none; | |
} | |
circle.saved { | |
fill: green; | |
} | |
</style> | |
</head> | |
<body> | |
<script> | |
var w = 900, | |
h = 500, | |
svg = d3.select('body').append('svg') | |
.attr('width',w) | |
.attr('height',h); | |
var data = [], | |
removed = []; | |
function render() { | |
var circles = svg.selectAll('circle') | |
.data(data, function(d){ | |
return d.id; | |
}); | |
// the enter() selection needs representation: | |
circles.enter().append('circle') | |
.classed('entering',true) | |
.attr('cx',function(d){ return d.center.x; }) | |
.attr('cy',function(d){ return d.center.y; }) | |
.attr('r',100) | |
.style('opacity',1e-6); | |
// the exit() selection needs removing | |
circles.exit().filter(':not(.exiting)') // but only if we didn't already | |
.classed('exiting',true) | |
.transition().duration(1000) | |
.attr('r',100) | |
.style('opacity',1e-6) | |
.remove(); | |
// just for debugging this demo, show which things were saved | |
// circles.classed('saved',function(d){ return d.saved; }); | |
// two things here: | |
// - if something is currently exiting (but in this selection), | |
// we should cancel its exiting transition and restore it | |
// - if something is currently entering (it was *just* added), | |
// we need to trigger a brand new transition | |
circles.filter('.exiting, .entering') | |
.classed('exiting',false) | |
.classed('entering',false) | |
.transition().duration(1000) | |
.attr('r',function(d){ return d.radius; }) | |
.style('opacity',1.0); | |
console.log(data.length) | |
} | |
setInterval(function(){ | |
// remove a random element ever other tick (or so) | |
if (data.length > 20 && Math.random() > 0.5) { | |
var index = Math.floor(Math.random() * data.length); | |
var item = data[index]; | |
data.splice(index,1); | |
// save 1 in 4 removed thing for later restoration | |
if (Math.random() < 0.25) { | |
item.saved = true; | |
removed.push(item); | |
} | |
} else { | |
// if we have something to save, save it: | |
if (removed.length) { | |
data.push(removed.pop()); | |
} else { | |
// otherwise create a new one | |
data.push({ | |
id: new Date().getTime(), | |
center: { | |
x: Math.random() * w, | |
y: Math.random() * h | |
}, | |
radius: 2 + Math.random() * 10 | |
}); | |
} | |
} | |
render(); | |
}, 30); | |
</script> |
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