hover on subplots when they anchored to same x or y

Author: archmoj

src/components/fx/hover.js

@@ -5,6 +5,7 @@ var isNumeric = require('fast-isnumeric');
 var tinycolor = require('tinycolor2');
 
 var Lib = require('../../lib');
+var pushUnique = Lib.pushUnique;
 var strTranslate = Lib.strTranslate;
 var strRotate = Lib.strRotate;
 var Events = require('../../lib/events');
@@ -257,11 +258,37 @@ function _hover(gd, evt, subplot, noHoverEvent, eventTarget) {
     // use those instead of finding overlayed plots
     var subplots = Array.isArray(subplot) ? subplot : [subplot];
 
+    var spId;
+
     var fullLayout = gd._fullLayout;
+    var hoversameaxis = fullLayout.hoversameaxis;
     var plots = fullLayout._plots || [];
     var plotinfo = plots[subplot];
     var hasCartesian = fullLayout._has('cartesian');
 
+    var hovermode = evt.hovermode || fullLayout.hovermode;
+    var hovermodeHasX = (hovermode || '').charAt(0) === 'x';
+    var hovermodeHasY = (hovermode || '').charAt(0) === 'y';
+
+    if(hoversameaxis && hasCartesian && (hovermodeHasX || hovermodeHasY)) {
+        for(var p = 0; p < subplots.length; p++) {
+            spId = subplots[p];
+            if(plots[spId]) {
+                // 'cartesian' case
+
+                var subplotsWith = (
+                    Axes.getFromId(gd, spId, hovermodeHasX ? 'x' : 'y')
+                )._subplotsWith;
+
+                if(subplotsWith && subplotsWith.length) {
+                    for(var q = 0; q < subplotsWith.length; q++) {
+                        pushUnique(subplots, subplotsWith[q]);
+                    }
+                }
+            }
+        }
+    }
+
     // list of all overlaid subplots to look at
     if(plotinfo) {
         var overlayedSubplots = plotinfo.overlays.map(function(pi) {
@@ -277,7 +304,7 @@ function _hover(gd, evt, subplot, noHoverEvent, eventTarget) {
     var supportsCompare = false;
 
     for(var i = 0; i < len; i++) {
-        var spId = subplots[i];
+        spId = subplots[i];
 
         if(plots[spId]) {
             // 'cartesian' case
@@ -295,8 +322,6 @@ function _hover(gd, evt, subplot, noHoverEvent, eventTarget) {
         }
     }
 
-    var hovermode = evt.hovermode || fullLayout.hovermode;
-
     if(hovermode && !supportsCompare) hovermode = 'closest';
 
     if(['x', 'y', 'closest', 'x unified', 'y unified'].indexOf(hovermode) === -1 || !gd.calcdata ||

src/components/fx/hovermode_defaults.js

@@ -12,5 +12,6 @@ module.exports = function handleHoverModeDefaults(layoutIn, layoutOut) {
     }
 
     coerce('clickmode');
+    coerce('hoversameaxis');
     return coerce('hovermode');
 };

src/components/fx/layout_attributes.js

@@ -78,6 +78,15 @@ module.exports = {
             'If false, hover interactions are disabled.'
         ].join(' ')
     },
+    hoversameaxis: {
+        valType: 'boolean',
+        dflt: false,
+        editType: 'none',
+        description: [
+            'Determines expansion of hover effects to other subplots in case of sharing an axis.',
+            'Has an effect only when `hovermode` is set to *x*, *x unified*, *y* or *y unified*.',
+        ].join(' ')
+    },
     hoverdistance: {
         valType: 'integer',
         min: -1,

test/plot-schema.json

@@ -2634,6 +2634,12 @@
      "y unified"
     ]
    },
+   "hoversameaxis": {
+    "description": "Determines expansion of hover effects to other subplots in case of sharing an axis. Has an effect only when `hovermode` is set to *x*, *x unified*, *y* or *y unified*.",
+    "dflt": false,
+    "editType": "none",
+    "valType": "boolean"
+   },
    "images": {
     "items": {
      "image": {