Add Y axis tick culling for rotated charts

src/c3.axis.js

@@ -26,6 +26,25 @@ function c3_axis(d3, params, $$) {
         var start = domain[0], stop = domain[domain.length - 1];
         return start < stop ? [ start, stop ] : [ stop, start ];
     }
+    function shouldDrawTickText(id){
+        if(!$$.config.axis_rotated) return true;
+        var widthLimits = [
+            // Left is width, right is number of tick labels to be removed
+            [-Infinity],
+            [200, 10],
+            [300, 5],
+            [450, 2],
+            [Infinity, 1]
+        ];
+        var divisor;
+        for(var i = widthLimits.length-1; i--; ){
+            if($$.currentWidth > widthLimits[i][0]) {
+                divisor = widthLimits[i+1][1];
+                break;
+            }
+        }
+        return !(id%divisor);
+    }
     function generateTicks(scale) {
         var i, domain, ticks = [];
         if (scale.ticks) {
@@ -161,6 +180,13 @@ function c3_axis(d3, params, $$) {
             }
 
             text = tick.select("text");
+            
+            if($$.config.axis_rotated && orient === 'bottom') {
+                text.style('display', function(d, i){
+                    return shouldDrawTickText(i) ? 'block' : 'none';
+                });
+            }
+            
             tspan = text.selectAll('tspan')
                 .data(function (d, i) {
                     var splitted = params.tickMultiline ? splitTickText(d, params.tickWidth) : [].concat(textFormatted(d));