Fix size of triangle.

Also add tests to verify symbol sizes.

package.json

@@ -30,6 +30,7 @@
     "d3-path": "~0.1.2"
   },
   "devDependencies": {
+    "d3-polygon": "~0.0.3",
     "faucet": "0.0",
     "rollup": "0.20.5",
     "tape": "4",

src/symbol/triangle.js

@@ -2,7 +2,7 @@ var sqrt3 = Math.sqrt(3);
 
 export default {
   draw: function(context, size) {
-    var y = -Math.sqrt(size * 4 / 27);
+    var y = -Math.sqrt(size / (sqrt3 * 3));
     context.moveTo(0, y * 2);
     context.lineTo(-sqrt3 * y, -y);
     context.lineTo(sqrt3 * y, -y);

test/inDelta.js

@@ -0,0 +1,10 @@
+var tape = require("tape");
+
+tape.Test.prototype.inDelta = function(actual, expected) {
+  this._assert(expected - 1e-6 < actual && actual < expected + 1e-6, {
+    message: "should be in delta",
+    operator: "inDelta",
+    actual: actual,
+    expected: expected
+  });
+};

test/polygonContext.js

@@ -0,0 +1,12 @@
+var polygon = require("d3-polygon");
+
+module.exports = function() {
+  return {
+    points: null,
+    area: function() { return Math.abs(polygon.area(this.points)); },
+    moveTo: function(x, y) { this.points = [[x, y]]; },
+    lineTo: function(x, y) { this.points.push([x, y]); },
+    rect: function(x, y, w, h) { this.points = [[x, y], [x + w, y], [x + w, y + h], [x, y + h]]; },
+    closePath: function() {}
+  };
+};

test/symbol-test.js

@@ -1,6 +1,8 @@
 var tape = require("tape"),
-    shape = require("../");
+    shape = require("../"),
+    polygonContext = require("./polygonContext");
 
+require("./inDelta");
 require("./pathEqual");
 
 tape("symbol() returns a default symbol shape", function(test) {
@@ -47,27 +49,62 @@ tape("symbol.size(size) observes the specified size constant", function(test) {
   test.end();
 });
 
+tape("symbol.type(circle) generates the expected path", function(test) {
+  var s = shape.symbol().type(shape.circle).size(function(d) { return d; });
+  test.pathEqual(s(0), "M0,0");
+  test.pathEqual(s(20), "M2.523133,0A2.523133,2.523133,0,1,1,-2.523133,0A2.523133,2.523133,0,1,1,2.523133,0");
+  test.end();
+});
+
+tape("symbol.type(cross) generates a polygon with the specified size", function(test) {
+  var p = polygonContext(), s = shape.symbol().type(shape.cross).context(p);
+  s.size(1)(); test.inDelta(p.area(), 1);
+  s.size(240)(); test.inDelta(p.area(), 240);
+  test.end();
+});
+
 tape("symbol.type(cross) generates the expected path", function(test) {
   var s = shape.symbol().type(shape.cross).size(function(d) { return d; });
   test.pathEqual(s(0), "M0,0L0,0L0,0L0,0L0,0L0,0L0,0L0,0L0,0L0,0L0,0L0,0Z");
   test.pathEqual(s(20), "M-3,-1L-1,-1L-1,-3L1,-3L1,-1L3,-1L3,1L1,1L1,3L-1,3L-1,1L-3,1Z");
   test.end();
 });
 
+tape("symbol.type(diamond) generates a polygon with the specified size", function(test) {
+  var p = polygonContext(), s = shape.symbol().type(shape.diamond).context(p);
+  s.size(1)(); test.inDelta(p.area(), 1);
+  s.size(240)(); test.inDelta(p.area(), 240);
+  test.end();
+});
+
 tape("symbol.type(diamond) generates the expected path", function(test) {
   var s = shape.symbol().type(shape.diamond).size(function(d) { return d; });
   test.pathEqual(s(0), "M0,0L0,0L0,0L0,0Z");
   test.pathEqual(s(10), "M0,-2.942831L1.699044,0L0,2.942831L-1.699044,0Z");
   test.end();
 });
 
+tape("symbol.type(star) generates a polygon with the specified size", function(test) {
+  var p = polygonContext(), s = shape.symbol().type(shape.star).context(p);
+  s.size(1)(); test.inDelta(p.area(), 1);
+  s.size(240)(); test.inDelta(p.area(), 240);
+  test.end();
+});
+
 tape("symbol.type(star) generates the expected path", function(test) {
   var s = shape.symbol().type(shape.star).size(function(d) { return d; });
   test.pathEqual(s(0), "M0,0L0,0L0,0L0,0L0,0L0,0L0,0L0,0L0,0L0,0Z");
   test.pathEqual(s(10), "M0,-2.984649L0.670095,-0.922307L2.838570,-0.922307L1.084237,0.352290L1.754333,2.414632L0,1.140035L-1.754333,2.414632L-1.084237,0.352290L-2.838570,-0.922307L-0.670095,-0.922307Z");
   test.end();
 });
 
+tape("symbol.type(square) generates a polygon with the specified size", function(test) {
+  var p = polygonContext(), s = shape.symbol().type(shape.square).context(p);
+  s.size(1)(); test.inDelta(p.area(), 1);
+  s.size(240)(); test.inDelta(p.area(), 240);
+  test.end();
+});
+
 tape("symbol.type(square) generates the expected path", function(test) {
   var s = shape.symbol().type(shape.square).size(function(d) { return d; });
   test.pathEqual(s(0), "M0,0h0v0h0Z");
@@ -76,10 +113,24 @@ tape("symbol.type(square) generates the expected path", function(test) {
   test.end();
 });
 
+tape("symbol.type(triangle) generates a polygon with the specified size", function(test) {
+  var p = polygonContext(), s = shape.symbol().type(shape.triangle).context(p);
+  s.size(1)(); test.inDelta(p.area(), 1);
+  s.size(240)(); test.inDelta(p.area(), 240);
+  test.end();
+});
+
 tape("symbol.type(triangle) generates the expected path", function(test) {
   var s = shape.symbol().type(shape.triangle).size(function(d) { return d; });
   test.pathEqual(s(0), "M0,0L0,0L0,0Z");
-  test.pathEqual(s(10), "M0,-2.434322L2.108185,1.217161L-2.108185,1.217161Z");
+  test.pathEqual(s(10), "M0,-2.774528L2.402811,1.387264L-2.402811,1.387264Z");
+  test.end();
+});
+
+tape("symbol.type(wye) generates a polygon with the specified size", function(test) {
+  var p = polygonContext(), s = shape.symbol().type(shape.wye).context(p);
+  s.size(1)(); test.inDelta(p.area(), 1);
+  s.size(240)(); test.inDelta(p.area(), 240);
   test.end();
 });