Merge pull request #7171 from plotly/new-fix7144-zorder-overlay

Fix lower zorder traces behing some gridlines on overlayed suplots

Author: archmoj

src/plots/cartesian/index.js

@@ -568,7 +568,10 @@ function makeSubplotLayer(gd, plotinfo) {
     var yLayer = constants.layerValue2layerClass[plotinfo.yaxis.layer];
     var hasOnlyLargeSploms = fullLayout._hasOnlyLargeSploms;
 
-    if(!plotinfo.mainplot || fullLayout._zindices.length > 1) {
+    var hasMultipleZ = fullLayout._zindices.length > 1;
+    var mainplotinfo = plotinfo.mainplotinfo;
+
+    if(!plotinfo.mainplot || hasMultipleZ) {
         if(hasOnlyLargeSploms) {
             // TODO could do even better
             // - we don't need plot (but we would have to mock it in lsInner
@@ -585,9 +588,15 @@ function makeSubplotLayer(gd, plotinfo) {
                 plotinfo.shapelayer = ensureSingle(backLayer, 'g', 'shapelayer');
                 plotinfo.imagelayer = ensureSingle(backLayer, 'g', 'imagelayer');
 
-                plotinfo.minorGridlayer = ensureSingle(plotgroup, 'g', 'minor-gridlayer');
-                plotinfo.gridlayer = ensureSingle(plotgroup, 'g', 'gridlayer');
-                plotinfo.zerolinelayer = ensureSingle(plotgroup, 'g', 'zerolinelayer');
+                if(mainplotinfo && hasMultipleZ) {
+                    plotinfo.minorGridlayer = mainplotinfo.minorGridlayer;
+                    plotinfo.gridlayer = mainplotinfo.gridlayer;
+                    plotinfo.zerolinelayer = mainplotinfo.zerolinelayer;
+                } else {
+                    plotinfo.minorGridlayer = ensureSingle(plotgroup, 'g', 'minor-gridlayer');
+                    plotinfo.gridlayer = ensureSingle(plotgroup, 'g', 'gridlayer');
+                    plotinfo.zerolinelayer = ensureSingle(plotgroup, 'g', 'zerolinelayer');
+                }
 
                 var betweenLayer = ensureSingle(plotgroup, 'g', 'layer-between');
                 plotinfo.shapelayerBetween = ensureSingle(betweenLayer, 'g', 'shapelayer');
@@ -622,7 +631,6 @@ function makeSubplotLayer(gd, plotinfo) {
             }
         }
     } else {
-        var mainplotinfo = plotinfo.mainplotinfo;
         var mainplotgroup = mainplotinfo.plotgroup;
         var xId = id + '-x';
         var yId = id + '-y';