modify hover default to change opacity rather than set everything to grey

Author: Michael Potter

src/traces/sankey/attributes.js

@@ -200,8 +200,8 @@ var attrs = module.exports = overrideAll({
             arrayOk: true,
             description: [
                 'Sets the `link` hover color. It can be a single value, or an array for specifying hover colors for',
-                'each `link`. If `link.hovercolor` is omitted, then by default, links will become solid grey when',
-                'hovered over.'
+                'each `link`. If `link.hovercolor` is omitted, then by default, links will become slightly more',
+                'opaque when hovered over.'
             ].join(' ')
         },
         customdata: {

src/traces/sankey/defaults.js

@@ -63,16 +63,31 @@ module.exports = function supplyDefaults(traceIn, traceOut, defaultColor, layout
     handleHoverLabelDefaults(linkIn, linkOut, coerceLink, hoverlabelDefault);
     coerceLink('hovertemplate');
 
-    var defaultLinkColor = tinycolor(layout.paper_bgcolor).getLuminance() < 0.333 ?
-                'rgba(255, 255, 255, 0.6)' :
-                'rgba(0, 0, 0, 0.2)';
+    var darkBG = tinycolor(layout.paper_bgcolor).getLuminance() < 0.333;
+    var defaultLinkColor = darkBG ? 'rgba(255, 255, 255, 0.6)' : 'rgba(0, 0, 0, 0.2)';
+    var linkColor = coerceLink('color', defaultLinkColor);
+
+    function makeDefaultHoverColor(_linkColor) {
+        var tc = tinycolor(_linkColor);
+        if (!tc.isValid()) {
+            // hopefully the user-specified color is valid, but if not that can be caught elsewhere
+            return _linkColor;
+        }
+        var alpha = tc.getAlpha();
+        if (alpha <= 0.8) {
+            tc.setAlpha(alpha + 0.2);
+        }
+        else {
+            tc = darkBG ? tc.brighten() : tc.darken();
+        }
+        return tc.toRgbString();
+    }
 
-    var defaultHoverColor = tinycolor(layout.paper_bgcolor).getLuminance() < 0.333 ?
-                'rgba(128, 128, 128, 1.0)' :
-                'rgba(128, 128, 128, 1.0)';
+    coerceLink('hovercolor', Array.isArray(linkColor) ? 
+        linkColor.map(makeDefaultHoverColor) :
+        makeDefaultHoverColor(linkColor)
+    );
 
-    coerceLink('color', Lib.repeat(defaultLinkColor, linkOut.value.length));
-    coerceLink('hovercolor', Lib.repeat(defaultHoverColor, linkOut.value.length));
     coerceLink('customdata');
 
     handleArrayContainerDefaults(linkIn, linkOut, {

test/jasmine/tests/sankey_test.js

@@ -1087,7 +1087,7 @@ describe('sankey tests', function() {
                         .filter(function(obj) {
                             return obj.link.label === 'stream 1';
                         })[0].forEach(function(l) {
-                            expect(l.style.fillOpacity).toEqual('1');
+                            expect(l.style.fillOpacity).toEqual('0.4');
                         });
                 }).then(function() {
                     mouseEvent('mouseout', 200, 250);

test/plot-schema.json

@@ -44150,7 +44150,7 @@
      "editType": "calc",
      "hovercolor": {
       "arrayOk": true,
-      "description": "Sets the `link` hover color. It can be a single value, or an array for specifying hover colors for each `link`. If `link.hovercolor` is omitted, then by default, links will become solid grey when hovered over.",
+      "description": "Sets the `link` hover color. It can be a single value, or an array for specifying hover colors for each `link`. If `link.hovercolor` is omitted, then by default, links will become slightly more opaque when hovered over.",
       "editType": "calc",
       "valType": "color"
      },