Fix #993; d3.geom.hull is now ccw.

src/geom/hull.js

@@ -95,7 +95,7 @@ d3.geom.hull = function(vertices) {
 
     // construct the hull
     var poly = [];
-    for (i = 0; i < sp; ++i) poly.push(data[stack[i]]);
+    for (i = sp - 1; i >= 0; --i) poly.push(data[stack[i]]);
     return poly;
   }
 

test/geom/hull-test.js

@@ -1,4 +1,5 @@
 var vows = require("vows"),
+    _ = require("../../"),
     load = require("../load"),
     assert = require("../assert");
 
@@ -26,11 +27,14 @@ suite.addBatch({
       "of two points is empty": function(h) {
         assert.deepEqual(h([[200, 200], [760, 300]]), []);
       },
-      "for three points is empty": function(h) {
-        assert.deepEqual(h([[200, 200], [760, 300], [500, 500]]), [[200, 200], [760, 300], [500, 500]]);
+      "for three points": function(h) {
+        assert.deepEqual(h([[200, 200], [760, 300], [500, 500]]), [[500, 500], [760, 300], [200, 200]]);
       },
       "for four points": function(h) {
-        assert.deepEqual(h([[200, 200], [760, 300], [500, 500], [400, 400]]), [[200, 200], [760, 300], [500, 500]]);
+        assert.deepEqual(h([[200, 200], [760, 300], [500, 500], [400, 400]]), [[500, 500], [760, 300], [200, 200]]);
+      },
+      "returns a counter-clockwise polygon": function(h) {
+        assert.greater(_.geom.polygon(h([[200, 200], [760, 300], [500, 500], [400, 400]])).area(), 0);
       }
     },
     "the hull layout with custom accessors": {
@@ -38,7 +42,7 @@ suite.addBatch({
         return hull().x(function(d) { return d.x; }).y(function(d) { return d.y; });
       },
       "of four points": function(h) {
-        assert.deepEqual(h([{x: 200, y: 200}, {x: 760, y: 300}, {x: 500, y: 500}, {x: 400, y: 400}]), [{x: 200, y: 200}, {x: 760, y: 300}, {x: 500, y: 500}]);
+        assert.deepEqual(h([{x: 200, y: 200}, {x: 760, y: 300}, {x: 500, y: 500}, {x: 400, y: 400}]), [{x: 500, y: 500}, {x: 760, y: 300}, {x: 200, y: 200}]);
       }
     },
     "the default hull layout applied directly": {
@@ -52,10 +56,10 @@ suite.addBatch({
         return h([[200, 200], [760, 300]]);
       },
       "for three points": function(h) {
-        assert.deepEqual(h([[200, 200], [760, 300], [500, 500]]), [[200, 200], [760, 300], [500, 500]]);
+        assert.deepEqual(h([[200, 200], [760, 300], [500, 500]]), [[500, 500], [760, 300], [200, 200]]);
       },
       "for four points": function(h) {
-        assert.deepEqual(h([[200, 200], [760, 300], [500, 500], [400, 400]]), [[200, 200], [760, 300], [500, 500]]);
+        assert.deepEqual(h([[200, 200], [760, 300], [500, 500], [400, 400]]), [[500, 500], [760, 300], [200, 200]]);
       }
     }
   }