Added the possibility not to specify color on one axis.

Readme.md

@@ -116,15 +116,19 @@ Number or string, defaults to `null`. Seeds the random number generator to creat
 
 ### x_colors
 
-String or array of CSS-formatted colors, default is `'random'`. Specify the color gradient used on the x axis.
+False, string, or array of CSS-formatted colors, default is `'random'`. Specify the color gradient used on the x axis.
+
+If false, the colors will not vary over the x axis; this requires the y_color to have a specified value.
 
 Valid string values are 'random' or the name of a [colorbrewer palette](http://bl.ocks.org/mbostock/5577023) (i.e. 'YlGnBu' or 'RdBu'). When set to 'random', a gradient will be randomly selected from the colorbrewer library.
 
 Valid array values should specify the color stops in any CSS format (i.e. `['#000000', '#4CAFE8', '#FFFFFF']`).
 
 ### y_colors
 
-String or array of CSS-formatted colors, default is `'match_x'`. When set to 'match_x' the same gradient will be used on both axes. Otherwise, accepts the same options as x_colors.
+False, string or array of CSS-formatted colors, default is `'match_x'`. When set to 'match_x' the same gradient will be used on both axes. 
+If false, the colors will not vary over the y axis; this requires the x_color to have a specified value.
+Otherwise, accepts the same options as x_colors.
 
 ### color_space
 

lib/trianglify.js

@@ -57,6 +57,10 @@ function Trianglify(opts) {
     throw new Error("Cell size must be greater than 2.");
   }
 
+  if(!opts.x_colors && !opts.y_colors) {
+    throw new Error("X and Y colors can not be both undefined.");
+  }
+
   // Setup the color gradient function
   var gradient;
 
@@ -65,11 +69,20 @@ function Trianglify(opts) {
       return chroma(opts.color_function(x, y));
     };
   } else {
-    var x_color = chroma.scale(opts.x_colors).mode(opts.color_space);
-    var y_color = chroma.scale(opts.y_colors).mode(opts.color_space);
-    gradient = function(x, y) {
-      return chroma.interpolate(x_color(x), y_color(y), 0.5, opts.color_space);
-    };
+    // Both colors are specified: Interpolate between both.
+    if(opts.x_colors && opts.y_colors){
+      var x_color = chroma.scale(opts.x_colors).mode(opts.color_space);
+      var y_color = chroma.scale(opts.y_colors).mode(opts.color_space);
+      gradient = function(x, y) {
+        return chroma.interpolate(x_color(x), y_color(y), 0.5, opts.color_space);
+      };
+    } else {
+      // One color missing: Use only the specified one.
+      var singleColorScale = chroma.scale(opts.x_colors ? opts.x_colors : opts.y_colors).mode(opts.color_space);
+      gradient = function(x, y) {
+        return singleColorScale(opts.x_colors ? x : y);
+      };
+    }
   }
 
   // Figure out key dimensions

test/test.js

@@ -17,6 +17,10 @@ describe('Trianglify', function(){
     (function() {Trianglify({width: 100, height: 100, bad_option: true});}).should.throw(Error);
   });
 
+  it('should throw an error on unspecified colors', function() {
+    (function() {Trianglify({width: 100, height: 100, x_colors: false, y_colors: false});}).should.throw(Error);
+  });
+
   it('should throw an error on invalid dimensions', function() {
     (function() {Trianglify({width: -1, height: 100});}).should.throw(Error);
     (function() {Trianglify({width: 100, height: -1});}).should.throw(Error);