Add d3.geom.hull to d3.v3.js

Makefile

@@ -115,6 +115,7 @@ D3_FILES = \
 	node_modules/d3/src/geo/path.js \
 	node_modules/d3/src/geo/stream.js \
 	node_modules/d3/src/geom/polygon.js \
+	node_modules/d3/src/geom/hull.js \
 	node_modules/d3/src/selection/index.js \
 	node_modules/d3/src/transition/index.js \
 	node_modules/d3/src/xhr/index.js \

js/lib/d3.v3.js

@@ -4370,6 +4370,131 @@ function d3_geom_polygonClosed(coordinates) {
       b = coordinates[coordinates.length - 1];
   return !(a[0] - b[0] || a[1] - b[1]);
 }
+function d3_geom_pointX(d) {
+  return d[0];
+}
+
+function d3_geom_pointY(d) {
+  return d[1];
+}
+
+/**
+ * Computes the 2D convex hull of a set of points using Graham's scanning
+ * algorithm. The algorithm has been implemented as described in Cormen,
+ * Leiserson, and Rivest's Introduction to Algorithms. The running time of
+ * this algorithm is O(n log n), where n is the number of input points.
+ *
+ * @param vertices [[x1, y1], [x2, y2], …]
+ * @returns polygon [[x1, y1], [x2, y2], …]
+ */
+d3.geom.hull = function(vertices) {
+  var x = d3_geom_pointX,
+      y = d3_geom_pointY;
+
+  if (arguments.length) return hull(vertices);
+
+  function hull(data) {
+    if (data.length < 3) return [];
+
+    var fx = d3_functor(x),
+        fy = d3_functor(y),
+        n = data.length,
+        vertices, // TODO use parallel arrays
+        plen = n - 1,
+        points = [],
+        stack = [],
+        d,
+        i, j, h = 0, x1, y1, x2, y2, u, v, a, sp;
+
+    if (fx === d3_geom_pointX && y === d3_geom_pointY) vertices = data;
+    else for (i = 0, vertices = []; i < n; ++i) {
+      vertices.push([+fx.call(this, d = data[i], i), +fy.call(this, d, i)]);
+    }
+
+    // find the starting ref point: leftmost point with the minimum y coord
+    for (i = 1; i < n; ++i) {
+      if (vertices[i][1] < vertices[h][1]
+          || vertices[i][1] == vertices[h][1]
+          && vertices[i][0] < vertices[h][0]) h = i;
+    }
+
+    // calculate polar angles from ref point and sort
+    for (i = 0; i < n; ++i) {
+      if (i === h) continue;
+      y1 = vertices[i][1] - vertices[h][1];
+      x1 = vertices[i][0] - vertices[h][0];
+      points.push({angle: Math.atan2(y1, x1), index: i});
+    }
+    points.sort(function(a, b) { return a.angle - b.angle; });
+
+    // toss out duplicate angles
+    a = points[0].angle;
+    v = points[0].index;
+    u = 0;
+    for (i = 1; i < plen; ++i) {
+      j = points[i].index;
+      if (a == points[i].angle) {
+        // keep angle for point most distant from the reference
+        x1 = vertices[v][0] - vertices[h][0];
+        y1 = vertices[v][1] - vertices[h][1];
+        x2 = vertices[j][0] - vertices[h][0];
+        y2 = vertices[j][1] - vertices[h][1];
+        if (x1 * x1 + y1 * y1 >= x2 * x2 + y2 * y2) {
+          points[i].index = -1;
+          continue;
+        } else {
+          points[u].index = -1;
+        }
+      }
+      a = points[i].angle;
+      u = i;
+      v = j;
+    }
+
+    // initialize the stack
+    stack.push(h);
+    for (i = 0, j = 0; i < 2; ++j) {
+      if (points[j].index > -1) {
+        stack.push(points[j].index);
+        i++;
+      }
+    }
+    sp = stack.length;
+
+    // do graham's scan
+    for (; j < plen; ++j) {
+      if (points[j].index < 0) continue; // skip tossed out points
+      while (!d3_geom_hullCCW(stack[sp - 2], stack[sp - 1], points[j].index, vertices)) {
+        --sp;
+      }
+      stack[sp++] = points[j].index;
+    }
+
+    // construct the hull
+    var poly = [];
+    for (i = sp - 1; i >= 0; --i) poly.push(data[stack[i]]);
+    return poly;
+  }
+
+  hull.x = function(_) {
+    return arguments.length ? (x = _, hull) : x;
+  };
+
+  hull.y = function(_) {
+    return arguments.length ? (y = _, hull) : y;
+  };
+
+  return hull;
+};
+
+// are three points in counter-clockwise order?
+function d3_geom_hullCCW(i1, i2, i3, v) {
+  var t, a, b, c, d, e, f;
+  t = v[i1]; a = t[0]; b = t[1];
+  t = v[i2]; c = t[0]; d = t[1];
+  t = v[i3]; e = t[0]; f = t[1];
+  return (f - b) * (c - a) - (d - b) * (e - a) > 0;
+}
 
 var d3_ease_default = function() { return d3_identity; };