Add linear-closed interpolation. Fixes #610.

d3.v2.js

@@ -3332,6 +3332,7 @@ var d3_svg_lineInterpolatorDefault = "linear";
 // The various interpolators supported by the `line` class.
 var d3_svg_lineInterpolators = d3.map({
   "linear": d3_svg_lineLinear,
+  "linear-closed": d3_svg_lineLinearClosed,
   "step-before": d3_svg_lineStepBefore,
   "step-after": d3_svg_lineStepAfter,
   "basis": d3_svg_lineBasis,
@@ -3349,6 +3350,10 @@ function d3_svg_lineLinear(points) {
   return points.join("L");
 }
 
+function d3_svg_lineLinearClosed(points) {
+  return d3_svg_lineLinear(points) + "Z";
+}
+
 // Step interpolation; generates "H" and "V" commands.
 function d3_svg_lineStepBefore(points) {
   var i = 0,

examples/area/area-radial.html

@@ -33,7 +33,7 @@ var angle = d3.scale.linear()
     .range([0, 2 * Math.PI]);
 
 var line = d3.svg.line.radial()
-    .interpolate("basis-closed")
+    .interpolate("linear-closed")
     .radius(radius)
     .angle(function(d, i) { return angle(i); });
 

src/svg/line.js

@@ -86,6 +86,7 @@ var d3_svg_lineInterpolatorDefault = "linear";
 // The various interpolators supported by the `line` class.
 var d3_svg_lineInterpolators = d3.map({
   "linear": d3_svg_lineLinear,
+  "linear-closed": d3_svg_lineLinearClosed,
   "step-before": d3_svg_lineStepBefore,
   "step-after": d3_svg_lineStepAfter,
   "basis": d3_svg_lineBasis,
@@ -103,6 +104,10 @@ function d3_svg_lineLinear(points) {
   return points.join("L");
 }
 
+function d3_svg_lineLinearClosed(points) {
+  return d3_svg_lineLinear(points) + "Z";
+}
+
 // Step interpolation; generates "H" and "V" commands.
 function d3_svg_lineStepBefore(points) {
   var i = 0,