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@mbostock /.block
Last active Jul 20, 2017

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Circle-Polygon Intersection
license: gpl-3.0

Drag the control points of the polygon to see whether the polygon intersects with the circle.

<!DOCTYPE html>
<meta charset="utf-8">
<style>
.circle {
fill: red;
fill-opacity: .3;
}
.circle.intersects {
fill: green;
}
.polygon path {
fill: #000;
fill-opacity: .3;
}
.polygon circle {
fill: #000;
stroke: #fff;
cursor: move;
}
</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>
var width = 960,
height = 500;
var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height);
var circle = svg.append("circle")
.attr("class", "circle intersects")
.datum([width / 2, height / 2, 120])
.call(positionCircle)
.attr("r", function(d) { return d[2]; });
var polygon = svg.append("g")
.attr("class", "polygon")
.datum([[500, 300], [600, 300], [600, 400], [500, 400]]);
polygon.append("path")
.call(positionPath);
polygon.selectAll("circle")
.data(function(d) { return d; })
.enter().append("circle")
.call(positionCircle)
.attr("r", 4.5)
.call(d3.behavior.drag()
.origin(function(d) { return {x: d[0], y: d[1]}; })
.on("drag", function(d) {
d[0] = d3.event.x, d[1] = d3.event.y;
d3.select(this).call(positionCircle);
polygon.select("path").call(positionPath);
circle.classed("intersects", intersects(circle.datum(), polygon.datum()));
}));
function positionCircle(circle) {
circle
.attr("cx", function(d) { return d[0]; })
.attr("cy", function(d) { return d[1]; });
}
function positionPath(path) {
path
.attr("d", function(d) { return "M" + d.join("L") + "Z"; });
}
function intersects(circle, polygon) {
return pointInPolygon(circle, polygon)
|| polygonEdges(polygon).some(function(line) { return pointLineSegmentDistance(circle, line) < circle[2]; });
}
function polygonEdges(polygon) {
return polygon.map(function(p, i) {
return i ? [polygon[i - 1], p] : [polygon[polygon.length - 1], p];
});
}
function pointInPolygon(point, polygon) {
for (var n = polygon.length, i = 0, j = n - 1, x = point[0], y = point[1], inside = false; i < n; j = i++) {
var xi = polygon[i][0], yi = polygon[i][1],
xj = polygon[j][0], yj = polygon[j][1];
if ((yi > y ^ yj > y) && (x < (xj - xi) * (y - yi) / (yj - yi) + xi)) inside = !inside;
}
return inside;
}
function pointLineSegmentDistance(point, line) {
var v = line[0], w = line[1], d, t;
return Math.sqrt(pointPointSquaredDistance(point, (d = pointPointSquaredDistance(v, w))
? ((t = ((point[0] - v[0]) * (w[0] - v[0]) + (point[1] - v[1]) * (w[1] - v[1])) / d) < 0 ? v
: t > 1 ? w
: [v[0] + t * (w[0] - v[0]), v[1] + t * (w[1] - v[1])])
: v));
}
function pointPointSquaredDistance(v, w) {
var dx = v[0] - w[0], dy = v[1] - w[1];
return dx * dx + dy * dy;
}
</script>
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