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enjalot/README.md

Last active October 1, 2015 06:48
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hull padding
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index.html
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8">
<title>Alpha-Shapes</title>
<script src="http://mbostock.github.com/d3/d3.min.js"></script>
<script src="http://mbostock.github.com/d3/d3.geom.min.js"></script>
<style type="text/css">
path {
stroke: #000;
stroke-width: .5px;
}
.regular {
fill: #39c;
}
.pad {
fill: lightgreen;
}
.shrink {
fill: orange;
}
</style>
</head>
<body>
<script type="text/javascript">
var w = 960;
var h = 500;
var alpha = 50;
var padding = 15;
var vertices = [[162, 332], [182, 299], [141, 292], [158, 264], [141, 408], [160, 400], [177, 430], [151, 442], [155, 425], [134, 430], [126, 447], [139, 466], [160, 471], [167, 447], [182, 466], [192, 442], [187, 413], [173, 403], [168, 425], [153, 413], [179, 275], [163, 292], [134, 270], [143, 315], [177, 320], [163, 311], [162, 281], [182, 255], [141, 226], [156, 235], [173, 207], [187, 230], [204, 194], [165, 189], [145, 201], [158, 167], [190, 165], [206, 145], [179, 153], [204, 114], [221, 138], [243, 112], [248, 139], [177, 122], [179, 99], [196, 82], [219, 90], [240, 75], [218, 61], [228, 53], [211, 34], [197, 51], [179, 65], [155, 70], [165, 85], [134, 80], [124, 58], [153, 44], [173, 34], [192, 27], [156, 19], [119, 32], [128, 17], [138, 36], [100, 58], [112, 73], [100, 92], [78, 100], [83, 78], [61, 63], [80, 44], [100, 26], [60, 39], [43, 71], [34, 54], [32, 90], [53, 104], [60, 82], [66, 99], [247, 94], [187, 180], [221, 168]],
offset = function(a,dx,dy) {
return a.map(function(d) { return [d[0]+dx,d[1]+dy]; });
},
dsq = function(a,b) {
var dx = a[0]-b[0], dy = a[1]-b[1];
return dx*dx+dy*dy;
},
asq = alpha*alpha,
// well, this is where the "magic" happens..
mesh = d3.geom.delaunay(offset(vertices,600,0)).filter(function(t) {
return dsq(t[0],t[1]) < asq && dsq(t[0],t[2]) < asq && dsq(t[1],t[2]) < asq;
});
var svg = d3.select("body")
.append("svg")
.attr("width", w)
.attr("height", h)
.attr("class", "Blues")
.append("g")
.attr("transform", "translate(0, 0)")
svg.append("g").classed("regular", true)
.attr("transform", "translate(-600, 0)")
.selectAll("path")
.data(mesh)
.enter().append("path")
.attr("d", function(d) { return "M" + d.join("L") + "Z"; });
svg.append("g").classed("pad", true)
.attr("transform", "translate(-300, 0)")
.selectAll("path")
.data(mesh)
.enter().append("path")
.attr("d", function(d) { return "M" + d.join("L") + "Z"; });
svg.append("g").classed("shrink", true)
.attr("transform", "translate(0, 0)")
.selectAll("path")
.data(mesh)
.enter().append("path")
.attr("d", function(d) { return "M" + d.join("L") + "Z"; });
var bounds = boundary(mesh);
svg.append("g")
.attr("transform", "translate(-600, 0)")
.selectAll("path")
.data(bounds)
.enter().append("path")
.style("fill", "#fc0")
.style("fill-opacity", .5)
.style("stroke-width", 2)
.attr("d", function(d) { return "M" + d.join("L"); });
var grow = pad(bounds, padding);
console.log(bounds[0], grow[0]);
svg.append("g")
.attr("transform", "translate(-300, 0)")
.selectAll("path")
.data(grow)
.enter().append("path")
.style("fill", "#fc0")
.style("fill-opacity", .5)
.style("stroke-width", 2)
.attr("d", function(d) { return "M" + d.join("L"); });
var shrink = pad(bounds, -padding);
console.log(bounds[0], shrink[0]);
svg.append("g")
.attr("transform", "translate(0, 0)")
.selectAll("path")
.data(shrink)
.enter().append("path")
.style("fill", "#fc0")
.style("fill-opacity", .5)
.style("stroke-width", 2)
.attr("d", function(d) { return "M" + d.join("L"); });
function pad(bounds, amount) {
var result = [];
bounds.forEach(function(bound) {
var padded = [];
var area = 0;
bound.forEach(function(p, i) {
// http://forums.esri.com/Thread.asp?c=2&f=1718&t=174277
// Area = Area + (X2 - X1) * (Y2 + Y1) / 2
var im1 = i - 1;
if(i == 0) {
im1 = bound.length - 1;
}
var pm = bound[im1];
area += (p[0] - pm[0]) * (p[1] + pm[1]) / 2;
});
var handedness = 1;
if(area > 0) handedness = -1
bound.forEach(function(p, i) {
// average the tangent between
var im1 = i - 1;
if(i == 0) {
im1 = bound.length - 2;
}
//var tp = getTangent(p, bound[ip1]);
var tm = getTangent(p, bound[im1]);
//var avg = { x: (tp.x + tm.x)/2, y: (tp.y + tm.y)/2 };
//var normal = rotate2d(avg, 90);
var normal = rotate2d(tm, 90 * handedness);
padded.push([p[0] + normal.x * amount, p[1] + normal.y * amount ])
})
result.push(padded)
})
return result
}
function getTangent(a, b) {
var vector = { x: b[0] - a[0], y: b[1] - a[1] }
var magnitude = Math.sqrt(vector.x*vector.x + vector.y*vector.y);
vector.x /= magnitude;
vector.y /= magnitude;
return vector
}
function rotate2d(vector, angle) {
//rotate a vector
angle *= Math.PI/180; //convert to radians
return {
x: vector.x * Math.cos(angle) - vector.y * Math.sin(angle),
y: vector.x * Math.sin(angle) + vector.y * Math.cos(angle)
}
}
// Computes boundaries of connected triangles, given an array of triangles.
function boundary(mesh) {
var counts = {},
edges = {},
r,
result = [];
// Traverse the edges of all triangles and discard any edges that appear twice.
mesh.forEach(function(triangle) {
for (var i = 0; i < 3; i++) {
var edge = [triangle[i], triangle[(i + 1) % 3]].sort(ascendingCoords).map(String);
(edges[edge[0]] = (edges[edge[0]] || [])).push(edge[1]);
(edges[edge[1]] = (edges[edge[1]] || [])).push(edge[0]);
var k = edge.join(":");
if (counts[k]) delete counts[k];
else counts[k] = 1;
}
});
while (1) {
var k = null;
// Pick an arbitrary starting point on a boundary.
for (k in counts) break;
if (k == null) break;
result.push(r = k.split(":").map(function(d) { return d.split(",").map(Number); }));
delete counts[k];
var q = r[1];
while (q[0] !== r[0][0] || q[1] !== r[0][1]) {
var p = q,
qs = edges[p.join(",")],
n = qs.length;
for (var i = 0; i < n; i++) {
q = qs[i].split(",").map(Number);
var edge = [p, q].sort(ascendingCoords).join(":");
if (counts[edge]) {
delete counts[edge];
r.push(q);
break;
}
}
}
}
return result;
}
function ascendingCoords(a, b) {
return a[0] === b[0] ? b[1] - a[1] : b[0] - a[0];
}
</script>
</body>
</html>
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