Fix #16 - tension is cardinal-specific.

README.md

@@ -12,6 +12,6 @@ If you use NPM, `npm install d3-shape`. Otherwise, download the [latest release]
 
 ## Changes from D3 3.x:
 
-* The default tension for cardinal interpolation is now 2 / 3, not 0.7.
+* The behavior of the cardinal interpolation tension parameter has been standardized. The default tension is now 0, not 0.7.
 
 …

src/interpolate/basis-closed.js

@@ -1,10 +1,14 @@
 import {point} from "./basis";
 
 function basisClosed(context) {
+  return new BasisClosed(context);
+}
+
+function BasisClosed(context) {
   this._context = context;
-};
+}
 
-basisClosed.prototype = {
+BasisClosed.prototype = {
   lineStart: function() {
     this._x0 = this._x1 = this._x2 = this._x3 = this._x4 =
     this._y0 = this._y1 = this._y2 = this._y3 = this._y4 = null;

src/interpolate/basis-open.js

@@ -1,10 +1,14 @@
 import {point} from "./basis";
 
 function basisOpen(context) {
+  return new BasisOpen(context);
+}
+
+function BasisOpen(context) {
   this._context = context;
-};
+}
 
-basisOpen.prototype = {
+BasisOpen.prototype = {
   lineStart: function() {
     this._x0 = this._x1 =
     this._y0 = this._y1 = null;

src/interpolate/basis.js

@@ -10,10 +10,14 @@ export function point(basis, x, y) {
 };
 
 function basis(context) {
+  return new Basis(context);
+}
+
+function Basis(context) {
   this._context = context;
-};
+}
 
-basis.prototype = {
+Basis.prototype = {
   lineStart: function() {
     this._x0 = this._x1 =
     this._y0 = this._y1 = null;

src/interpolate/cardinal-open.js

@@ -1,9 +1,15 @@
-function cardinalOpen(context, tension) {
+function cardinalOpen(tension) {
+  return function(context) {
+    return new CardinalOpen(context, tension);
+  };
+}
+
+function CardinalOpen(context, tension) {
   this._context = context;
   this._k = (tension == null ? 1 : 1 - tension) / 6;
 }
 
-cardinalOpen.prototype = {
+CardinalOpen.prototype = {
   lineStart: function() {
     this._x0 = this._x1 = this._x2 =
     this._y0 = this._y1 = this._y2 = NaN;

src/interpolate/cardinal.js

@@ -1,9 +1,15 @@
-function cardinal(context, tension) {
+function cardinal(tension) {
+  return function(context) {
+    return new Cardinal(context, tension);
+  };
+}
+
+function Cardinal(context, tension) {
   this._context = context;
   this._k = (tension == null ? 1 : 1 - tension) / 6;
 }
 
-cardinal.prototype = {
+Cardinal.prototype = {
   lineStart: function() {
     this._x0 = this._x1 = this._x2 =
     this._y0 = this._y1 = this._y2 = NaN;

src/interpolate/linear-closed.js

@@ -1,8 +1,12 @@
 function linearClosed(context) {
+  return new LinearClosed(context);
+}
+
+function LinearClosed(context) {
   this._context = context;
 }
 
-linearClosed.prototype = {
+LinearClosed.prototype = {
   lineStart: function() {
     this._state = 0;
   },

src/interpolate/linear.js

@@ -1,8 +1,12 @@
 function linear(context) {
+  return new Linear(context);
+}
+
+function Linear(context) {
   this._context = context;
 }
 
-linear.prototype = {
+Linear.prototype = {
   lineStart: function() {
     this._state = 0;
   },

src/interpolate/step-after.js

@@ -1,8 +1,12 @@
 function stepAfter(context) {
+  return new StepAfter(context);
+}
+
+function StepAfter(context) {
   this._context = context;
 }
 
-stepAfter.prototype = {
+StepAfter.prototype = {
   lineStart: function() {
     this._y = NaN;
     this._state = 0;

src/interpolate/step-before.js

@@ -1,8 +1,12 @@
 function stepBefore(context) {
+  return new StepBefore(context);
+}
+
+function StepBefore(context) {
   this._context = context;
 }
 
-stepBefore.prototype = {
+StepBefore.prototype = {
   lineStart: function() {
     this._x = NaN;
     this._state = 0;

src/interpolate/step.js

@@ -1,8 +1,12 @@
 function step(context) {
+  return new Step(context);
+}
+
+function Step(context) {
   this._context = context;
-};
+}
 
-step.prototype = {
+Step.prototype = {
   lineStart: function() {
     this._x = this._y = NaN;
     this._state = 0;

src/line.js

@@ -28,25 +28,11 @@ function _true() {
   return true;
 }
 
-// TODO bundle, cardinal-closed, monotone, cubic
-var interpolates = {
-  "linear": linear,
-  "linear-closed": linearClosed,
-  "step": step,
-  "step-before": stepBefore,
-  "step-after": stepAfter,
-  "basis": basis,
-  "basis-open": basisOpen,
-  "basis-closed": basisClosed,
-  "cardinal": cardinal,
-  "cardinal-open": cardinalOpen
-};
-
 export default function() {
   var x = pointX, _x = x,
       y = pointY, _y = y,
       defined = true, _defined = _true,
-      interpolate = "linear", _interpolate = linear,
+      interpolate = linear,
       tension = null,
       context = null,
       stream = null;
@@ -55,7 +41,7 @@ export default function() {
     var defined = false,
         buffer;
 
-    if (!context) stream = new _interpolate(buffer = path(), tension);
+    if (!context) stream = interpolate(buffer = path());
 
     for (var i = 0, n = data.length, d; i < n; ++i) {
       if (!_defined(d = data[i], i) === defined) {
@@ -87,24 +73,36 @@ export default function() {
     return line;
   };
 
-  line.interpolate = function(_) {
+  line.interpolate = function(_, tension) {
     if (!arguments.length) return interpolate;
-    _interpolate = interpolates[interpolate = interpolates.hasOwnProperty(_ += "") ? _ : "linear"];
-    if (context != null) stream = new _interpolate(context, tension);
+    if (typeof _ === "function") interpolate = _;
+    else switch (_ + "") {
+      case "linear-closed": interpolate = linearClosed; break;
+      case "step": interpolate = step; break;
+      case "step-before": interpolate = stepBefore; break;
+      case "step-after": interpolate = stepAfter; break;
+      case "basis": interpolate = basis; break;
+      case "basis-open": interpolate = basisOpen; break;
+      case "basis-closed": interpolate = basisClosed; break;
+      case "cardinal": interpolate = cardinal(tension); break;
+      case "cardinal-open": interpolate = cardinalOpen(tension); break;
+      default: interpolate = linear; break;
+    }
+    if (context != null) stream = interpolate(context);
     return line;
   };
 
   line.tension = function(_) {
     if (!arguments.length) return tension;
     tension = _ == null ? _ : +_;
-    if (context != null) stream = new _interpolate(context, tension);
+    if (context != null) stream = interpolate(context);
     return line;
   };
 
   line.context = function(_) {
     if (!arguments.length) return context;
     if (_ == null) context = stream = null;
-    else stream = new _interpolate(context = _, tension);
+    else stream = interpolate(context = _);
     return line;
   };
 

test/line-test.js

@@ -6,7 +6,6 @@ tape("line() returns a default line shape", function(test) {
   test.equal(l.x()([42, 34]), 42);
   test.equal(l.y()([42, 34]), 34);
   test.equal(l.defined(), true);
-  test.equal(l.interpolate(), "linear");
   test.equal(l.tension(), null);
   test.equal(l.context(), null);
   test.equal(l([[0, 1], [2, 3], [4, 5]]), "M0,1L2,3L4,5");
@@ -39,16 +38,13 @@ tape("line.y(y)(data) observes the specified constant", function(test) {
 
 tape("line.interpolate(name) sets the interpolation method", function(test) {
   var l = shape.line().interpolate("linear-closed");
-  test.equal(l.interpolate(), "linear-closed");
   test.equal(l([]), null);
   test.equal(l([[0, 1], [2, 3]]), "M0,1L2,3Z");
   test.end();
 });
 
-tape("line.tension(value) sets the interpolation tension", function(test) {
-  var l = shape.line().interpolate("cardinal").tension(0.1);
-  test.equal(l.interpolate(), "cardinal");
-  test.equal(l.tension(), 0.1);
+tape("line.interpolate(\"cardinal\", tension) sets the cardinal interpolation tension", function(test) {
+  var l = shape.line().interpolate("cardinal", 0.1);
   test.equal(l([]), null);
   test.equal(l([[0, 1]]), "M0,1Z");
   test.equal(l([[0, 1], [1, 3]]), "M0,1L1,3");
@@ -57,29 +53,55 @@ tape("line.tension(value) sets the interpolation tension", function(test) {
   test.end();
 });
 
-tape("line.tension(value) defaults to null", function(test) {
-  var l = shape.line().interpolate("cardinal");
-  test.equal(l.tension(), null);
+tape("line.interpolate(\"cardinal\", tension) coerces the specified tension to a number", function(test) {
+  var l = shape.line().interpolate("cardinal", "0.1");
+  test.equal(l([]), null);
+  test.equal(l([[0, 1]]), "M0,1Z");
+  test.equal(l([[0, 1], [1, 3]]), "M0,1L1,3");
+  test.equal(l([[0, 1], [1, 3], [2, 1]]), "M0,1Q0.55,3,1,3Q1.45,3,2,1");
+  test.equal(l([[0, 1], [1, 3], [2, 1], [3, 3]]), "M0,1Q0.55,3,1,3C1.3,3,1.7,1,2,1Q2.45,1,3,3");
+  test.end();
+});
+
+tape("line.interpolate(\"cardinal\") implicitly uses a tension of zero", function(test) {
+  var l0 = shape.line().interpolate("cardinal"),
+      l1 = shape.line().interpolate("cardinal", 0);
+  test.equal(l1([[0, 1], [1, 3], [2, 1], [3, 3]]), l0([[0, 1], [1, 3], [2, 1], [3, 3]]));
+  test.end();
+});
+
+tape("line.interpolate(\"cardinal\", null) implicitly uses a tension of zero", function(test) {
+  var l0 = shape.line().interpolate("cardinal"),
+      l1 = shape.line().interpolate("cardinal", null);
+  test.equal(l1([[0, 1], [1, 3], [2, 1], [3, 3]]), l0([[0, 1], [1, 3], [2, 1], [3, 3]]));
   test.end();
 });
 
-tape("line.tension(null) is equivalent to 0 for cardinal interpolation", function(test) {
-  var l0 = shape.line().interpolate("cardinal").tension(null),
-      l1 = shape.line().interpolate("cardinal").tension(0);
+tape("line.interpolate(\"cardinal\", undefined) implicitly uses a tension of zero", function(test) {
+  var l0 = shape.line().interpolate("cardinal"),
+      l1 = shape.line().interpolate("cardinal", undefined);
   test.equal(l1([[0, 1], [1, 3], [2, 1], [3, 3]]), l0([[0, 1], [1, 3], [2, 1], [3, 3]]));
   test.end();
 });
 
-tape("line.tension(null) is equivalent to 0 for cardinal-open interpolation", function(test) {
-  var l0 = shape.line().interpolate("cardinal-open").tension(null),
-      l1 = shape.line().interpolate("cardinal-open").tension(0);
+tape("line.interpolate(\"cardinal-open\") implicitly uses a tension of zero", function(test) {
+  var l0 = shape.line().interpolate("cardinal-open"),
+      l1 = shape.line().interpolate("cardinal-open", 0);
   test.equal(l1([[0, 1], [1, 3], [2, 1], [3, 3]]), l0([[0, 1], [1, 3], [2, 1], [3, 3]]));
   test.end();
 });
 
-tape("line.tension(value) coerces the specified value to a number", function(test) {
-  var l = shape.line().interpolate("cardinal").tension("0.1");
-  test.equal(l.tension(), 0.1);
+tape("line.interpolate(\"cardinal-open\", null) implicitly uses a tension of zero", function(test) {
+  var l0 = shape.line().interpolate("cardinal-open"),
+      l1 = shape.line().interpolate("cardinal-open", null);
+  test.equal(l1([[0, 1], [1, 3], [2, 1], [3, 3]]), l0([[0, 1], [1, 3], [2, 1], [3, 3]]));
+  test.end();
+});
+
+tape("line.interpolate(\"cardinal-open\", undefined) implicitly uses a tension of zero", function(test) {
+  var l0 = shape.line().interpolate("cardinal-open"),
+      l1 = shape.line().interpolate("cardinal-open", undefined);
+  test.equal(l1([[0, 1], [1, 3], [2, 1], [3, 3]]), l0([[0, 1], [1, 3], [2, 1], [3, 3]]));
   test.end();
 });