Merge pull request #16 from pbeshai/equal-distribution

Switch to a segment splitting approach

README.md

@@ -2,9 +2,12 @@
 
 [![npm version](https://badge.fury.io/js/d3-interpolate-path.svg)](https://badge.fury.io/js/d3-interpolate-path)
 
+d3-interpolate-path is a D3 plugin that adds an [interpolator](https://github.com/d3/d3-interpolate)
+optimized for SVG <path> elements.
+
 Blog: [Improving D3 Path Animation](https://bocoup.com/weblog/improving-d3-path-animation)
 
-Demo: http://pbeshai.github.io/d3-interpolate-path/
+Demo: http://peterbeshai.com/d3-interpolate-path/
 
 ![d3-interpolate-path demo](http://peterbeshai.com/vis/d3-interpolate-path/d3-interpolate-path-demo.gif)
 
@@ -52,7 +55,7 @@ If you use NPM, `npm install d3-interpolate-path`. Otherwise, download the [late
 ## API Reference
 
 
-<a href="#interpolatePath" name="interpolatePath">#</a> <b>interpolatePath</b>(*a*, *b*)
+<a href="#interpolatePath" name="interpolatePath">#</a> <b>interpolatePath</b>(*a*, *b*, *excludeSegment*)
 
 Returns an interpolator between two path attribute `d` strings *a* and *b*. The interpolator extends *a* and *b* to have the same number of points before using [d3.interpolateString](https://github.com/d3/d3-interpolate#interpolateString) on them.
 
@@ -62,3 +65,22 @@ pathInterpolator(0)   // 'M0,0 L10,10 L10,10'
 pathInterpolator(0.5) // 'M5,5 L15,15 L20,20'
 pathInterpolator(1)   // 'M10,10 L20,20 L30,30'
 ```
+
+You can optionally provide a function *excludeSegment* that takes two adjacent path commands and returns true if that segment should be excluded when splitting the line. A command object has form `{ type, x, y }` (with possibly more attributes depending on type). An example object:
+
+```js
+// equivalent to M0,150 in a path `d` string
+{
+  type: 'M',
+  x: 0,
+  y: 150
+}
+```
+
+This is most useful when working with d3-area. Excluding the final segment (i.e. the vertical line at the end) from being split ensures a nice transition. If you know that highest `x` value in the path, you can exclude the final segment by passing an excludeSegment function similar to:
+
+```js
+function excludeSegment(a, b) {
+  return a.x === b.x && a.x === 300; // here 300 is the max X
+}
+```