fix(axis): Correct subchart x axis culling

Include subchart x axis on culling process.
Subchart x axis should be aligned with the x axis culling.

Fix #1068

spec/internals/axis-spec.js

@@ -1630,6 +1630,9 @@ describe("AXIS", function() {
 							culling: true
 						}
 					}
+				},
+				subchart: {
+					show: true
 				}
 			};
 		});
@@ -1641,13 +1644,13 @@ describe("AXIS", function() {
 				y2: [0, 100, 200, 300, 400]
 			};
 
-			["x", "y", "y2"].forEach(v => {
+			["subx", "x", "y", "y2"].forEach(v => {
 				const data = chart.internal.axes[v]
 					.selectAll(".tick text").filter(function() {
 						return this.style.display === "block";
 					}).data();
 
-				expect(data).to.be.deep.equal(expected[v]);
+				expect(data).to.be.deep.equal(expected[v === "subx" ? "x" : v]);
 			});
 		}
 

src/axis/Axis.js

@@ -750,15 +750,18 @@ export default class Axis {
 		const $$ = this.owner;
 		const config = $$.config;
 
-		["x", "y", "y2"].forEach(type => {
+		["subx", "x", "y", "y2"].forEach(type => {
 			const axis = $$.axes[type];
-			const toCull = config[`axis_${type}_tick_culling`];
+
+			// subchart x axis should be aligned with x axis culling
+			const id = type === "subx" ? "x" : type;
+			const toCull = config[`axis_${id}_tick_culling`];
 
 			if (axis && toCull) {
 				const tickText = axis.selectAll(".tick text");
 				const tickValues = sortValue(tickText.data());
 				const tickSize = tickValues.length;
-				const cullingMax = config[`axis_${type}_tick_culling_max`];
+				const cullingMax = config[`axis_${id}_tick_culling_max`];
 				let intervalForCulling;
 
 				if (tickSize) {