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CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.2.18
+
+- `Rune.Polygon` method `centroid()` now calculates centroid as closed shape.
+
 ## 0.2.17
 
 - Publish failed. Republishing.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "rune.js",
-  "version" : "0.2.17",
+  "version" : "0.2.18",
   "description": "A JavaScript library for programming graphic design systems with SVG",
   "repository": {
     "type": "git",

src/shapes/polygon.js

@@ -56,6 +56,16 @@ class Polygon {
     return this.vectorAtLength(this.length() * scalar);
   }
 
+  area() {
+    var area = 0;
+    for(var i = 0; i < this.vars.vectors.length-1; i++)
+    {
+      area += this.vars.vectors[i].x * this.vars.vectors[i+1].y - this.vars.vectors[i+1].x * this.vars.vectors[i].y;
+    }
+    area /= 2;
+    return Math.abs(area);
+  }
+
   bounds() {
     var xmax = undefined;
     var ymax = undefined;
@@ -78,22 +88,19 @@ class Polygon {
   }
 
   centroid() {
-    var ps = this.vars.vectors;
     var areaAcc = 0.0;
     var xAcc = 0.0;
     var yAcc = 0.0;
-
-    for(var i = 0; i < ps.length-1; i++)
-    {
-      areaAcc += ps[i].x * ps[i+1].y - ps[i+1].x * ps[i].y;
-      xAcc += (ps[i].x + ps[i+1].x) * (ps[i].x * ps[i+1].y - ps[i+1].x * ps[i].y);
-      yAcc += (ps[i].y + ps[i+1].y) * (ps[i].x * ps[i+1].y - ps[i+1].x * ps[i].y);
+    for(var i = 0; i < this.vars.vectors.length; i++) {
+      var start = this.vars.vectors[i];
+      var stop = this.vars.vectors[(i+1)%this.vars.vectors.length];
+      areaAcc += start.x * stop.y - stop.x * start.y;
+      xAcc += (start.x + stop.x) * (start.x * stop.y - stop.x * start.y);
+      yAcc += (start.y + stop.y) * (start.x * stop.y - stop.x * start.y);
     }
-
     areaAcc /= 2.0;
     var x = xAcc/(6.0*areaAcc);
     var y = yAcc/(6.0*areaAcc);
-
     return new Vector(x, y);
   }
 

test/shared/shapes/polygon.js

@@ -48,6 +48,13 @@ describe("Rune.Polygon", function() {
     });
   });
 
+  describe("area()", function() {
+    it("should return area of polygon", function() {
+      var area = s.area();
+      expect(area).toEqual(3600);
+    });
+  });
+
   describe("bounds()", function() {
 
     it("should return internal bounds", function() {