add ScatterTernary.eventData method

- 🔪 is select method, reuse Scatter.select instead
- using same event-data pipeline for hover and select revealed
  an inconsistency: hover data includes the raw input coords whereas
  selection data includes the scaled coords (as in calcdata).

Author: etpinard

src/traces/scatterternary/event_data.js

@@ -0,0 +1,37 @@
+/**
+* Copyright 2012-2017, Plotly, Inc.
+* All rights reserved.
+*
+* This source code is licensed under the MIT license found in the
+* LICENSE file in the root directory of this source tree.
+*/
+
+'use strict';
+
+module.exports = function eventData(out, pt, trace, cd, pointNumber) {
+    if(pt.xa) out.xaxis = pt.xa;
+    if(pt.ya) out.yaxis = pt.ya;
+
+    if(cd[pointNumber]) {
+        var cdi = cd[pointNumber];
+
+        // N.B. These are the scale coordinates !!!
+        //
+        // On master, hover events get the non-scaled coordinates
+        // whereas selection events get the scaled version.
+        // Note also that the hover labels show the scaled version.
+        //
+        // What about the 'raw' input coordinates?
+        // Should we include them in parallel here or replace a/b/c with them?
+        out.a = cdi.a;
+        out.b = cdi.b;
+        out.c = cdi.c;
+    } else {
+        // for fill-hover only
+        out.a = pt.a;
+        out.b = pt.b;
+        out.c = pt.c;
+    }
+
+    return out;
+};

src/traces/scatterternary/index.js

@@ -17,7 +17,8 @@ ScatterTernary.calc = require('./calc');
 ScatterTernary.plot = require('./plot');
 ScatterTernary.style = require('./style');
 ScatterTernary.hoverPoints = require('./hover');
-ScatterTernary.selectPoints = require('./select');
+ScatterTernary.selectPoints = require('../scatter/select');
+ScatterTernary.eventData = require('./event_data');
 
 ScatterTernary.moduleType = 'trace';
 ScatterTernary.name = 'scatterternary';