added helper function that calulates graph element position in 2d space

lib/helper/calculatePosition.js

@@ -0,0 +1,19 @@
+"use strict";
+if (typeof define !== 'function') { var define = require('amdefine')(module) }
+
+/**
+ * Helper function used to calculate the pixel position of a graph vertex
+ * (identified by its numerical id, starting at 1) on a 2D plane
+ */
+
+define([], function() {
+  var calculatePosition = function(id, options) {
+    var position = {};
+    var rowsize = options.width / options.rows;
+    var colsize = options.height / options.columns;
+    position.x = ((id - 1) % options.rows) * rowsize;
+    position.y = Math.floor((id - 1) / options.columns) * colsize;
+    return position;
+  };
+  return calculatePosition;
+});

spec/helper/calculatePosition.spec.js

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+"use strict";
+
+var calculatePosition = require("../../lib/helper/calculatePosition");
+
+describe("calculatePosition", function() {
+  it("places item 8 at 448,0", function() {
+    var options = {
+      width: 640,
+      height: 500,
+      rows: 10,
+      columns: 10
+    };
+    var position = calculatePosition(8, options);
+    expect(position.x).toEqual(448);
+    expect(position.y).toEqual(0);
+  });
+
+  it("places item 10 at 576,0", function() {
+    var options = {
+      width: 640,
+      height: 500,
+      rows: 10,
+      columns: 10
+    };
+    var position = calculatePosition(10, options);
+    expect(position.x).toEqual(576);
+    expect(position.y).toEqual(0);
+  });
+
+  it("places item 11 at 0,50", function() {
+    var options = {
+      width: 640,
+      height: 500,
+      rows: 10,
+      columns: 10
+    };
+    var position = calculatePosition(11, options);
+    expect(position.x).toEqual(0);
+    expect(position.y).toEqual(50);
+  });
+});