Optional parameters to interpolators.

Related d3/d3-scale#39.

README.md

@@ -163,30 +163,31 @@ Returns an HCL color space interpolator between the two colors *a* and *b*. The
 
 Like [hcl](#hcl), but does not use the shortest path between hues.
 
-<a name="cubehelix" href="#cubehelix">#</a> d3_interpolate.<b>cubehelix</b>(<i>a</i>, <i>b</i>)
+<a name="cubehelix" href="#cubehelix">#</a> d3_interpolate.<b>cubehelix</b>(<i>a</i>, <i>b</i>[, <i>gamma</i>])
 
 <img src="https://raw.githubusercontent.com/d3/d3-interpolate/master/img/cubehelix.png" width="100%" height="80" alt="cubehelix">
 
-Returns a Cubehelix color space interpolator between the two colors *a* and *b* using the default *gamma* of 1.0. The colors *a* and *b* need not be in Cubehelix; they will be converted to Cubehelix using [color.cubehelix](https://github.com/d3/d3-color#cubehelix). If either color’s hue or saturation is NaN, the opposing color’s channel value is used. The shortest path between hues is used. The return value of the interpolator is a hexadecimal RGB string.
+Or, with a gamma of 3.0 to emphasize high-intensity values:
 
-<a name="cubehelixLong" href="#cubehelixLong">#</a> d3_interpolate.<b>cubehelixLong</b>(<i>a</i>, <i>b</i>)
+<img src="https://raw.githubusercontent.com/d3/d3-interpolate/master/img/cubehelixGamma.png" width="100%" height="80" alt="cubehelixGamma">
 
-<img src="https://raw.githubusercontent.com/d3/d3-interpolate/master/img/cubehelixLong.png" width="100%" height="80" alt="cubehelixLong">
+Returns a Cubehelix color space interpolator between the two colors *a* and *b* using the specified *gamma*. If *gamma* is not specified, it defaults to 1.0. The colors *a* and *b* need not be in Cubehelix; they will be converted to Cubehelix using [color.cubehelix](https://github.com/d3/d3-color#cubehelix). If either color’s hue or saturation is NaN, the opposing color’s channel value is used. The shortest path between hues is used. The return value of the interpolator is a hexadecimal RGB string.
 
-Like [cubehelix](#cubehelix), but does not use the shortest path between hues.
+<a name="cubehelixLong" href="#cubehelixLong">#</a> d3_interpolate.<b>cubehelixLong</b>(<i>a</i>, <i>b</i>[, <i>gamma</i>])
 
-<a name="cubehelixGamma" href="#cubehelixGamma">#</a> d3_interpolate.<b>cubehelixGamma</b>(<i>gamma</i>)
+<img src="https://raw.githubusercontent.com/d3/d3-interpolate/master/img/cubehelixLong.png" width="100%" height="80" alt="cubehelixLong">
 
-<img src="https://raw.githubusercontent.com/d3/d3-interpolate/master/img/cubehelixGamma.png" width="100%" height="80" alt="cubehelixGamma">
+Or, with a gamma of 3.0 to emphasize high-intensity values:
 
-Returns a Cubehelix color space interpolator factory using the specified *gamma*. A gamma value less than one emphasizes low intensity values, while a gamma value greater than one emphasizes high intensity values. For example:
+<img src="https://raw.githubusercontent.com/d3/d3-interpolate/master/img/cubehelixGammaLong.png" width="100%" height="80" alt="cubehelixGammaLong">
 
-```js
-var i = d3_interpolate.cubehelixGamma(3)("purple", "orange");
-```
+Like [cubehelix](#cubehelix), but does not use the shortest path between hues.
 
-<a name="cubehelixGammaLong" href="#cubehelixGammaLong">#</a> d3_interpolate.<b>cubehelixGammaLong</b>(<i>gamma</i>)
+<a name="bind" href="#bind">#</a> d3_interpolate.<b>bind</b>(<i>type</i>[, <i>parameters…</i>])
 
-<img src="https://raw.githubusercontent.com/d3/d3-interpolate/master/img/cubehelixGammaLong.png" width="100%" height="80" alt="cubehelixGammaLong">
+A convenience function for binding zero or more *parameters* to the specified interpolation function *type*. If no *parameters* are specified, this function simply returns *type*. The returned function takes two arguments *a* and *b* and passes any optional *parameters* to the underlying function *type*. For example, the following statements are equivalent:
 
-Like [cubehelixGamma](#cubehelixGamma), but does not use the shortest path between hues.
+```js
+d3_interpolate.bind(d3_interpolate.cubehelix, 3)("purple", "orange");
+d3_interpolate.cubehelix("purple", "orange", 3);
+```

index.js

@@ -13,9 +13,6 @@ export {default as hslLong} from "./src/hslLong";
 export {default as lab} from "./src/lab";
 export {default as hcl} from "./src/hcl";
 export {default as hclLong} from "./src/hclLong";
-
-import cubehelixGamma from "./src/cubehelixGamma";
-import cubehelixGammaLong from "./src/cubehelixGammaLong";
-export var cubehelix = cubehelixGamma(1);
-export var cubehelixLong = cubehelixGammaLong(1);
-export {cubehelixGamma, cubehelixGammaLong};
+export {default as cubehelix} from "./src/cubehelix";
+export {default as cubehelixLong} from "./src/cubehelixLong";
+export {default as bind} from "./src/bind";

package.json

@@ -1,11 +1,12 @@
 {
   "name": "d3-interpolate",
-  "version": "0.2.1",
+  "version": "0.3.0",
   "description": "Interpolate numbers, colors, strings, arrays, objects, whatever!",
   "keywords": [
     "d3",
     "interpolate",
-    "interpolation"
+    "interpolation",
+    "color"
   ],
   "homepage": "https://github.com/d3/d3-interpolate",
   "license": "BSD-3-Clause",

src/bind.js

@@ -0,0 +1,16 @@
+var slice = Array.prototype.slice;
+
+function bindN(type, args) {
+  args = slice.call(args);
+  args[0] = null;
+  args.unshift(null);
+  return function(a, b) {
+    args[0] = a;
+    args[1] = b;
+    return type.apply(null, args);
+  };
+}
+
+export default function(type) {
+  return arguments.length === 1 ? type : bindN(type, arguments);
+};

src/cubehelix.js

@@ -0,0 +1,20 @@
+import {cubehelix} from "d3-color";
+import deltaHue from "./deltaHue";
+
+export default function(a, b, gamma) {
+  if (arguments.length < 3) gamma = 1;
+  a = cubehelix(a);
+  b = cubehelix(b);
+  var ah = isNaN(a.h) ? b.h : a.h,
+      as = isNaN(a.s) ? b.s : a.s,
+      al = a.l,
+      bh = isNaN(b.h) ? 0 : deltaHue(b.h, ah),
+      bs = isNaN(b.s) ? 0 : b.s - as,
+      bl = b.l - al;
+  return function(t) {
+    a.h = ah + bh * t;
+    a.s = as + bs * t;
+    a.l = al + bl * Math.pow(t, gamma);
+    return a + "";
+  };
+};

src/cubehelixLong.js

@@ -0,0 +1,19 @@
+import {cubehelix} from "d3-color";
+
+export default function(a, b, gamma) {
+  if (arguments.length < 3) gamma = 1;
+  a = cubehelix(a);
+  b = cubehelix(b);
+  var ah = isNaN(a.h) ? b.h : a.h,
+      as = isNaN(a.s) ? b.s : a.s,
+      al = a.l,
+      bh = isNaN(b.h) ? 0 : b.h - ah,
+      bs = isNaN(b.s) ? 0 : b.s - as,
+      bl = b.l - al;
+  return function(t) {
+    a.h = ah + bh * t;
+    a.s = as + bs * t;
+    a.l = al + bl * Math.pow(t, gamma);
+    return a + "";
+  };
+};

test/bind-test.js

@@ -0,0 +1,15 @@
+var tape = require("tape"),
+    interpolate = require("../");
+
+tape("bind(type) returns type", function(test) {
+  test.equal(interpolate.bind(interpolate.cubehelix), interpolate.cubehelix);
+  test.equal(interpolate.bind(interpolate.rgb), interpolate.rgb);
+  test.end();
+});
+
+tape("bind(type, parameter) binds the specified parameter to the given type", function(test) {
+  test.equal(interpolate.bind(interpolate.cubehelix, 3)("purple", "orange")(0.5), interpolate.cubehelix("purple", "orange", 3)(0.5));
+  test.equal(interpolate.bind(interpolate.cubehelixLong, 3)("purple", "orange")(0.5), interpolate.cubehelixLong("purple", "orange", 3)(0.5));
+  test.equal(interpolate.bind(interpolate.rgb, 3)("purple", "orange")(0.5), interpolate.rgb("purple", "orange", 3)(0.5)); // ignored
+  test.end();
+});