diff --git a/README.md b/README.md
index 08bee8e..a7e7232 100644
--- a/README.md
+++ b/README.md
@@ -31,13 +31,13 @@ Note that the generic value interpolator detects not only nested objects and arr
 
 ## Installing
 
-If you use NPM, `npm install d3-interpolate`. Otherwise, download the [latest release](https://github.com/d3/d3-interpolate/releases/latest). You can also load directly from [d3js.org](https://d3js.org), either as a [standalone library](https://d3js.org/d3-interpolate.v1.min.js) or as part of [D3](https://github.com/d3/d3). AMD, CommonJS, and vanilla environments are supported. 
+If you use NPM, `npm install d3-interpolate`. Otherwise, download the [latest release](https://github.com/d3/d3-interpolate/releases/latest). You can also load directly from [d3js.org](https://d3js.org), either as a [standalone library](https://d3js.org/d3-interpolate.v2.min.js) or as part of [D3](https://github.com/d3/d3). AMD, CommonJS, and vanilla environments are supported. 
 
 In vanilla, a `d3` global is exported. (If using [color interpolation](#color-spaces), also load [d3-color](https://github.com/d3/d3-color).)
 
 ```html
-<script src="https://d3js.org/d3-color.v1.min.js"></script>
-<script src="https://d3js.org/d3-interpolate.v1.min.js"></script>
+<script src="https://d3js.org/d3-color.v2.min.js"></script>
+<script src="https://d3js.org/d3-interpolate.v2.min.js"></script>
 <script>
 
 var interpolate = d3.interpolateRgb("steelblue", "brown");
@@ -133,6 +133,10 @@ Returns an interpolator between the two views *a* and *b* of a two-dimensional p
 
 The returned interpolator exposes a *duration* property which encodes the recommended transition duration in milliseconds. This duration is based on the path length of the curved trajectory through *x,y* space. If you want a slower or faster transition, multiply this by an arbitrary scale factor (<i>V</i> as described in the original paper).
 
+<a name="interpolate_rho" href="#interpolate_rho">#</a> *interpolateZoom*.<b>rho</b>(<i>rho</i>) · [Source](https://github.com/d3/d3-interpolate/blob/master/src/zoom.js)<!-- , [Examples](https://observablehq.com/@d3/interpolatezoom-rho) -->
+
+Given a [zoom interpolator](#interpolateZoom), returns a new zoom interpolator using the specified curvature *rho*. When *rho* is close to 0, the interpolator is almost linear. The default curvature is sqrt(2).
+
 <a name="interpolateDiscrete" href="#interpolateDiscrete">#</a> d3.<b>interpolateDiscrete</b>(<i>values</i>) · [Source](https://github.com/d3/d3-interpolate/blob/master/src/discrete.js), [Examples](https://observablehq.com/@d3/d3-interpolatediscrete)
 
 Returns a discrete interpolator for the given array of *values*. The returned interpolator maps *t* in [0, 1 / *n*) to *values*[0], *t* in [1 / *n*, 2 / *n*) to *values*[1], and so on, where *n* = *values*.length. In effect, this is a lightweight [quantize scale](https://github.com/d3/d3-scale/blob/master/README.md#quantize-scales) with a fixed domain of [0, 1].
@@ -243,10 +247,12 @@ Returns a uniform nonrational B-spline interpolator through the specified array
 
 ### Piecewise
 
-<a name="piecewise" href="#piecewise">#</a> d3.<b>piecewise</b>(<i>interpolate</i>, <i>values</i>) · [Source](https://github.com/d3/d3-interpolate/blob/master/src/piecewise.js), [Examples](https://observablehq.com/@d3/d3-piecewise)
+<a name="piecewise" href="#piecewise">#</a> d3.<b>piecewise</b>([<i>interpolate</i>, ]<i>values</i>) · [Source](https://github.com/d3/d3-interpolate/blob/master/src/piecewise.js), [Examples](https://observablehq.com/@d3/d3-piecewise)
 
 Returns a piecewise interpolator, composing interpolators for each adjacent pair of *values*. The returned interpolator maps *t* in [0, 1 / (*n* - 1)] to *interpolate*(*values*[0], *values*[1]), *t* in [1 / (*n* - 1), 2 / (*n* - 1)] to *interpolate*(*values*[1], *values*[2]), and so on, where *n* = *values*.length. In effect, this is a lightweight [linear scale](https://github.com/d3/d3-scale/blob/master/README.md#linear-scales). For example, to blend through red, green and blue:
 
 ```js
 var interpolate = d3.piecewise(d3.interpolateRgb.gamma(2.2), ["red", "green", "blue"]);
 ```
+
+If  *interpolate* is not specified, defaults to [d3.interpolate](#interpolate).
diff --git a/package.json b/package.json
index a5e9fca..d84b972 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,9 @@
 {
   "name": "d3-interpolate",
-  "version": "1.4.0",
+  "version": "2.0.0-rc.1",
+  "publishConfig": {
+    "tag": "next"
+  },
   "description": "Interpolate numbers, colors, strings, arrays, objects, whatever!",
   "keywords": [
     "d3",
@@ -34,7 +37,7 @@
     "postpublish": "git push && git push --tags && cd ../d3.github.com && git pull && cp ../${npm_package_name}/dist/${npm_package_name}.js ${npm_package_name}.v${npm_package_version%%.*}.js && cp ../${npm_package_name}/dist/${npm_package_name}.min.js ${npm_package_name}.v${npm_package_version%%.*}.min.js && git add ${npm_package_name}.v${npm_package_version%%.*}.js ${npm_package_name}.v${npm_package_version%%.*}.min.js && git commit -m \"${npm_package_name} ${npm_package_version}\" && git push && cd - && zip -j dist/${npm_package_name}.zip -- LICENSE README.md dist/${npm_package_name}.js dist/${npm_package_name}.min.js"
   },
   "dependencies": {
-    "d3-color": "1"
+    "d3-color": ">=2.0.0-rc.1"
   },
   "sideEffects": false,
   "devDependencies": {
diff --git a/rollup.config.js b/rollup.config.js
index 804bba8..1991e64 100644
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -1,6 +1,11 @@
 import {terser} from "rollup-plugin-terser";
 import * as meta from "./package.json";
 
+function onwarn(message, warn) {
+  if (message.code === "CIRCULAR_DEPENDENCY") return;
+  warn(message);
+}
+
 const config = {
   input: "src/index.js",
   external: Object.keys(meta.dependencies || {}).filter(key => /^d3-/.test(key)),
@@ -13,7 +18,8 @@ const config = {
     banner: `// ${meta.homepage} v${meta.version} Copyright ${(new Date).getFullYear()} ${meta.author.name}`,
     globals: Object.assign({}, ...Object.keys(meta.dependencies || {}).filter(key => /^d3-/.test(key)).map(key => ({[key]: "d3"})))
   },
-  plugins: []
+  plugins: [],
+  onwarn
 };
 
 export default [
diff --git a/src/constant.js b/src/constant.js
index b7d42e7..3487c0d 100644
--- a/src/constant.js
+++ b/src/constant.js
@@ -1,5 +1 @@
-export default function(x) {
-  return function() {
-    return x;
-  };
-}
+export default x => () => x;
diff --git a/src/piecewise.js b/src/piecewise.js
index 41f76ae..8b568c5 100644
--- a/src/piecewise.js
+++ b/src/piecewise.js
@@ -1,4 +1,7 @@
+import {default as value} from "./value.js";
+
 export default function piecewise(interpolate, values) {
+  if (values === undefined) values = interpolate, interpolate = value;
   var i = 0, n = values.length - 1, v = values[0], I = new Array(n < 0 ? 0 : n);
   while (i < n) I[i] = interpolate(v, v = values[++i]);
   return function(t) {
diff --git a/src/transform/parse.js b/src/transform/parse.js
index ef7b95f..c62088e 100644
--- a/src/transform/parse.js
+++ b/src/transform/parse.js
@@ -1,18 +1,11 @@
 import decompose, {identity} from "./decompose.js";
 
-var cssNode,
-    cssRoot,
-    cssView,
-    svgNode;
+var svgNode;
 
+/* eslint-disable no-undef */
 export function parseCss(value) {
-  if (value === "none") return identity;
-  if (!cssNode) cssNode = document.createElement("DIV"), cssRoot = document.documentElement, cssView = document.defaultView;
-  cssNode.style.transform = value;
-  value = cssView.getComputedStyle(cssRoot.appendChild(cssNode), null).getPropertyValue("transform");
-  cssRoot.removeChild(cssNode);
-  value = value.slice(7, -1).split(",");
-  return decompose(+value[0], +value[1], +value[2], +value[3], +value[4], +value[5]);
+  const m = new (typeof DOMMatrix === "function" ? DOMMatrix : WebKitCSSMatrix)(value + "");
+  return m.isIdentity ? identity : decompose(m.a, m.b, m.c, m.d, m.e, m.f);
 }
 
 export function parseSvg(value) {
diff --git a/src/zoom.js b/src/zoom.js
index 3368b01..f275602 100644
--- a/src/zoom.js
+++ b/src/zoom.js
@@ -1,7 +1,4 @@
-var rho = Math.SQRT2,
-    rho2 = 2,
-    rho4 = 4,
-    epsilon2 = 1e-12;
+var epsilon2 = 1e-12;
 
 function cosh(x) {
   return ((x = Math.exp(x)) + 1 / x) / 2;
@@ -15,50 +12,60 @@ function tanh(x) {
   return ((x = Math.exp(2 * x)) - 1) / (x + 1);
 }
 
-// p0 = [ux0, uy0, w0]
-// p1 = [ux1, uy1, w1]
-export default function(p0, p1) {
-  var ux0 = p0[0], uy0 = p0[1], w0 = p0[2],
-      ux1 = p1[0], uy1 = p1[1], w1 = p1[2],
-      dx = ux1 - ux0,
-      dy = uy1 - uy0,
-      d2 = dx * dx + dy * dy,
-      i,
-      S;
+export default (function zoomRho(rho, rho2, rho4) {
 
-  // Special case for u0 ≅ u1.
-  if (d2 < epsilon2) {
-    S = Math.log(w1 / w0) / rho;
-    i = function(t) {
-      return [
-        ux0 + t * dx,
-        uy0 + t * dy,
-        w0 * Math.exp(rho * t * S)
-      ];
+  // p0 = [ux0, uy0, w0]
+  // p1 = [ux1, uy1, w1]
+  function zoom(p0, p1) {
+    var ux0 = p0[0], uy0 = p0[1], w0 = p0[2],
+        ux1 = p1[0], uy1 = p1[1], w1 = p1[2],
+        dx = ux1 - ux0,
+        dy = uy1 - uy0,
+        d2 = dx * dx + dy * dy,
+        i,
+        S;
+
+    // Special case for u0 ≅ u1.
+    if (d2 < epsilon2) {
+      S = Math.log(w1 / w0) / rho;
+      i = function(t) {
+        return [
+          ux0 + t * dx,
+          uy0 + t * dy,
+          w0 * Math.exp(rho * t * S)
+        ];
+      }
     }
-  }
 
-  // General case.
-  else {
-    var d1 = Math.sqrt(d2),
-        b0 = (w1 * w1 - w0 * w0 + rho4 * d2) / (2 * w0 * rho2 * d1),
-        b1 = (w1 * w1 - w0 * w0 - rho4 * d2) / (2 * w1 * rho2 * d1),
-        r0 = Math.log(Math.sqrt(b0 * b0 + 1) - b0),
-        r1 = Math.log(Math.sqrt(b1 * b1 + 1) - b1);
-    S = (r1 - r0) / rho;
-    i = function(t) {
-      var s = t * S,
-          coshr0 = cosh(r0),
-          u = w0 / (rho2 * d1) * (coshr0 * tanh(rho * s + r0) - sinh(r0));
-      return [
-        ux0 + u * dx,
-        uy0 + u * dy,
-        w0 * coshr0 / cosh(rho * s + r0)
-      ];
+    // General case.
+    else {
+      var d1 = Math.sqrt(d2),
+          b0 = (w1 * w1 - w0 * w0 + rho4 * d2) / (2 * w0 * rho2 * d1),
+          b1 = (w1 * w1 - w0 * w0 - rho4 * d2) / (2 * w1 * rho2 * d1),
+          r0 = Math.log(Math.sqrt(b0 * b0 + 1) - b0),
+          r1 = Math.log(Math.sqrt(b1 * b1 + 1) - b1);
+      S = (r1 - r0) / rho;
+      i = function(t) {
+        var s = t * S,
+            coshr0 = cosh(r0),
+            u = w0 / (rho2 * d1) * (coshr0 * tanh(rho * s + r0) - sinh(r0));
+        return [
+          ux0 + u * dx,
+          uy0 + u * dy,
+          w0 * coshr0 / cosh(rho * s + r0)
+        ];
+      }
     }
+
+    i.duration = S * 1000 * rho / Math.SQRT2;
+
+    return i;
   }
 
-  i.duration = S * 1000;
+  zoom.rho = function(_) {
+    var _1 = Math.max(1e-3, +_), _2 = _1 * _1, _4 = _2 * _2;
+    return zoomRho(_1, _2, _4);
+  };
 
-  return i;
-}
+  return zoom;
+})(Math.SQRT2, 2, 4);
diff --git a/test/inDelta.js b/test/inDelta.js
index f3def21..9df0b7f 100644
--- a/test/inDelta.js
+++ b/test/inDelta.js
@@ -1,10 +1,26 @@
 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",
+tape.Test.prototype.inDelta = function(actual, expected, delta) {
+  delta = delta || 1e-6;
+  this._assert(inDelta(actual, expected, delta), {
+    message: "should be in delta " + delta,
     operator: "inDelta",
     actual: actual,
     expected: expected
   });
 };
+
+function inDelta(actual, expected, delta) {
+  return (Array.isArray(expected) ? inDeltaArray : inDeltaNumber)(actual, expected, delta);
+}
+
+function inDeltaArray(actual, expected, delta) {
+  var n = expected.length, i = -1;
+  if (actual.length !== n) return false;
+  while (++i < n) if (!inDelta(actual[i], expected[i], delta)) return false;
+  return true;
+}
+
+function inDeltaNumber(actual, expected, delta) {
+  return actual >= expected - delta && actual <= expected + delta;
+}
diff --git a/test/piecewise-test.js b/test/piecewise-test.js
new file mode 100644
index 0000000..5b149d8
--- /dev/null
+++ b/test/piecewise-test.js
@@ -0,0 +1,38 @@
+var tape = require("tape"),
+    interpolate = require("../");
+
+tape("piecewise(interpolate, values)(t) returns the expected values", function(test) {
+  var i = interpolate.piecewise(interpolate.interpolate, [0,2,10]);
+  test.strictEqual(i(-1), -4);
+  test.strictEqual(i(0), 0);
+  test.strictEqual(i(0.19), 0.76);
+  test.strictEqual(i(0.21), 0.84);
+  test.strictEqual(i(0.5), 2);
+  test.strictEqual(i(0.75), 6);
+  test.strictEqual(i(1), 10);
+  test.end();
+});
+
+tape("piecewise(values) uses the default interpolator", function(test) {
+  var i = interpolate.piecewise([0,2,10]);
+  test.strictEqual(i(-1), -4);
+  test.strictEqual(i(0), 0);
+  test.strictEqual(i(0.19), 0.76);
+  test.strictEqual(i(0.21), 0.84);
+  test.strictEqual(i(0.5), 2);
+  test.strictEqual(i(0.75), 6);
+  test.strictEqual(i(1), 10);
+  test.end();
+});
+
+tape("piecewise(values) uses the default interpolator/2", function(test) {
+  var i = interpolate.piecewise(["a0","a2","a10"]);
+  test.strictEqual(i(-1), "a-4");
+  test.strictEqual(i(0), "a0");
+  test.strictEqual(i(0.19), "a0.76");
+  test.strictEqual(i(0.21), "a0.84");
+  test.strictEqual(i(0.5), "a2");
+  test.strictEqual(i(0.75), "a6");
+  test.strictEqual(i(1), "a10");
+  test.end();
+});
diff --git a/test/transformCss-test.js b/test/transformCss-test.js
new file mode 100644
index 0000000..4fe0e2f
--- /dev/null
+++ b/test/transformCss-test.js
@@ -0,0 +1,26 @@
+var tape = require("tape"),
+    interpolate = require("../");
+
+/*
+
+// see https://github.com/d3/d3-interpolate/pull/83
+// and https://github.com/Automattic/node-canvas/issues/1313
+global.DOMMatrix = require("Canvas").DOMMatrix;
+
+tape("interpolateTransformCss(a, b) transforms as expected", function(test) {
+  test.equal(interpolate.interpolateTransformCss(
+    "translateY(12px) scale(2)",
+    "translateX(3em) rotate(5deg)"
+  )(0.5), "translate(24px, 6px) rotate(2.5deg) scale(1.5,1.5)");
+  test.deepEqual(interpolate.interpolateTransformCss(
+    "matrix(1.0, 2.0, 3.0, 4.0, 5.0, 6.0)",
+    "translate(3px,90px)"
+  )(0.5), "translate(4px, 48px) rotate(-58.282525588538995deg) skewX(-39.847576765616985deg) scale(-0.6180339887498949,0.9472135954999579)");
+  test.deepEqual(interpolate.interpolateTransformCss(
+    "skewX(-60)",
+    "skewX(60) translate(280,0)"
+  )(0.5), "translate(140, 0) skewX(0)");
+  test.end();
+});
+
+*/
diff --git a/test/zoom-test.js b/test/zoom-test.js
index dcb9692..a4c19c5 100644
--- a/test/zoom-test.js
+++ b/test/zoom-test.js
@@ -5,3 +5,32 @@ tape("interpolateZoom(a, b) handles nearly-coincident points", function(test) {
   test.deepEqual(interpolate.interpolateZoom([324.68721096803614, 59.43501602433761, 1.8827137399562621], [324.6872108946794, 59.43501601062763, 7.399052110984391])(0.5), [324.68721093135775, 59.43501601748262, 3.7323313186268305]);
   test.end();
 });
+
+tape("interpolateZoom returns the expected duration", function(test) {
+  test.inDelta(interpolate.interpolateZoom([0, 0, 1], [0, 0, 1.1]).duration, 67, 1);
+  test.inDelta(interpolate.interpolateZoom([0, 0, 1], [0, 0, 2]).duration, 490, 1);
+  test.inDelta(interpolate.interpolateZoom([0, 0, 1], [10, 0, 8]).duration, 2872.5, 1);
+  test.end();
+});
+
+tape("interpolateZoom parameter rho() defaults to sqrt(2)", function(test) {
+  test.inDelta(
+    interpolate.interpolateZoom([0,0,1], [10, 10, 5])(0.5),
+    interpolate.interpolateZoom.rho(Math.sqrt(2))([0,0,1], [10, 10, 5])(0.5),
+  );
+  test.end();
+});
+
+tape("interpolateZoom.rho(0) is (almost) linear", function(test) {
+  const interp = interpolate.interpolateZoom.rho(0)([0, 0, 1], [10, 0, 8]);
+  test.inDelta(interp(0.5), [1.111, 0, Math.sqrt(8)], 1e-3);
+  test.equal(Math.round(interp.duration), 1470);
+  test.end();
+});
+
+tape("interpolateZoom parameter rho(2) has a high curvature and takes more time", function(test) {
+  const interp = interpolate.interpolateZoom.rho(2)([0, 0, 1], [10, 0, 8]);
+  test.inDelta(interp(0.5), [1.111, 0, 12.885], 1e-3);
+  test.equal(Math.round(interp.duration), 3775);
+  test.end();
+});