Use axis.y.tick.values for y grids if it's set - #680

c3.js

@@ -3335,9 +3335,10 @@
     };
 
     c3_chart_internal_fn.updateYGrid = function () {
-        var $$ = this, config = $$.config;
+        var $$ = this, config = $$.config,
+            gridValues = $$.yAxis.tickValues() || $$.y.ticks(config.grid_y_ticks);
         $$.ygrid = $$.main.select('.' + CLASS.ygrids).selectAll('.' + CLASS.ygrid)
-            .data($$.y.ticks(config.grid_y_ticks));
+            .data(gridValues);
         $$.ygrid.enter().append('line')
             .attr('class', CLASS.ygrid);
         $$.ygrid.attr("x1", config.axis_rotated ? $$.y : 0)

spec/grid-spec.js

+var describe = window.describe,
+    expect = window.expect,
+    it = window.it,
+    beforeEach = window.beforeEach;
+
+describe('c3 chart grid', function () {
+    'use strict';
+
+    var chart, d3;
+
+    var args = {
+        data: {
+            columns: [
+                ['data1', 30, 200, 100, 400, 150, 250]
+            ]
+        },
+        axis: {
+            y: {
+                tick: {
+                }
+            }
+        },
+        grid: {
+            y: {
+                show: false
+            }
+        }
+    };
+
+    beforeEach(function (done) {
+        chart = window.initChart(chart, args, done);
+        d3 = chart.internal.d3;
+    });
+
+    describe('y grid', function () {
+
+        it('should not show y grids', function () {
+            expect(chart.internal.main.select('.c3-ygrids').size()).toBe(0);
+        });
+
+        it('should update args to show y grids', function () {
+            args.grid.y.show = true;
+            expect(true).toBeTruthy();
+        });
+
+        it('should show y grids', function () {
+            var ygrids = chart.internal.main.select('.c3-ygrids');
+            expect(ygrids.size()).toBe(1);
+            expect(ygrids.selectAll('.c3-ygrid').size()).toBe(9);
+        });
+
+        it('should update args to show only 3 y grids', function () {
+            args.grid.y.ticks = 3;
+            expect(true).toBeTruthy();
+        });
+
+        it('should show only 3 y grids', function () {
+            var ygrids = chart.internal.main.select('.c3-ygrids');
+            expect(ygrids.size()).toBe(1);
+            expect(ygrids.selectAll('.c3-ygrid').size()).toBe(3);
+        });
+
+        it('should update args to show y grids depending on y axis ticks', function () {
+            args.axis.y.tick.count = 5;
+            expect(true).toBeTruthy();
+        });
+
+        it('should show grids depending on y axis ticks', function () {
+            var ygrids = chart.internal.main.select('.c3-ygrids'),
+                expectedYs = [];
+            ygrids.selectAll('.c3-ygrid').each(function (d, i) {
+                expectedYs[i] = +d3.select(this).attr('y1');
+            });
+            expect(ygrids.size()).toBe(1);
+            expect(ygrids.selectAll('.c3-ygrid').size()).toBe(5);
+            chart.internal.main.select('.c3-axis-y').selectAll('.tick').each(function (d, i) {
+                var t = d3.transform(d3.select(this).attr('transform'));
+                expect(t.translate[1]).toBe(expectedYs[i]);
+            });
+        });
+
+    });
+});

src/grid.js

@@ -55,9 +55,10 @@ c3_chart_internal_fn.updateXGrid = function (withoutUpdate) {
 };
 
 c3_chart_internal_fn.updateYGrid = function () {
-    var $$ = this, config = $$.config;
+    var $$ = this, config = $$.config,
+        gridValues = $$.yAxis.tickValues() || $$.y.ticks(config.grid_y_ticks);
     $$.ygrid = $$.main.select('.' + CLASS.ygrids).selectAll('.' + CLASS.ygrid)
-        .data($$.y.ticks(config.grid_y_ticks));
+        .data(gridValues);
     $$.ygrid.enter().append('line')
         .attr('class', CLASS.ygrid);
     $$.ygrid.attr("x1", config.axis_rotated ? $$.y : 0)