include info about things that reset subplot layers in d3-data

- to clean what need to be cleaned up in exit selection,
  instead of using granular and brittle old vs new plotinfo logic
- axis.layer, overlays are currently include, we might want to
  include more things in it eventually,

Author: etpinard

src/plots/cartesian/index.js

@@ -358,7 +358,7 @@ exports.drawFramework = function(gd) {
     var subplotData = makeSubplotData(gd);
 
     var subplotLayers = fullLayout._cartesianlayer.selectAll('.subplot')
-        .data(subplotData, Lib.identity);
+        .data(subplotData, String);
 
     subplotLayers.enter().append('g')
         .attr('class', function(name) { return 'subplot ' + name; });
@@ -371,19 +371,9 @@ exports.drawFramework = function(gd) {
     subplotLayers.each(function(name) {
         var plotinfo = fullLayout._plots[name];
 
-        // keep ref to plot group
         plotinfo.plotgroup = d3.select(this);
-
-        // initialize list of overlay subplots
-        plotinfo.overlays = [];
-
         makeSubplotLayer(gd, plotinfo);
 
-        // fill in list of overlay subplots
-        if(plotinfo.mainplot) {
-            var mainplot = fullLayout._plots[plotinfo.mainplot];
-            mainplot.overlays.push(plotinfo);
-        }
 
         // make separate drag layers for each subplot,
         // but append them to paper rather than the plot groups,
@@ -400,27 +390,49 @@ exports.rangePlot = function(gd, plotinfo, cdSubplot) {
 
 function makeSubplotData(gd) {
     var fullLayout = gd._fullLayout;
-    var subplotData = [];
-    var overlays = [];
-
-    for(var k in fullLayout._plots) {
-        var plotinfo = fullLayout._plots[k];
-        var xa2 = plotinfo.xaxis._mainAxis;
-        var ya2 = plotinfo.yaxis._mainAxis;
+    var ids = fullLayout._subplots.cartesian;
+    var len = ids.length;
+    var subplotData = new Array(len);
+    var i, j, id, plotinfo, xa, ya;
+
+    for(i = 0; i < len; i++) {
+        id = ids[i];
+        plotinfo = fullLayout._plots[id];
+        xa = plotinfo.xaxis;
+        ya = plotinfo.yaxis;
+
+        var xa2 = xa._mainAxis;
+        var ya2 = ya._mainAxis;
         var mainplot = xa2._id + ya2._id;
+        var mainplotinfo = fullLayout._plots[mainplot];
+        plotinfo.overlays = [];
 
-        if(mainplot !== k && fullLayout._plots[mainplot]) {
+        if(mainplot !== id && mainplotinfo) {
+            // link 'main plot' ref in overlaying plotinfo
             plotinfo.mainplot = mainplot;
-            plotinfo.mainplotinfo = fullLayout._plots[mainplot];
-            overlays.push(k);
+            plotinfo.mainplotinfo = mainplotinfo;
+            // fill in list of overlaying subplots in 'main plot'
+            mainplotinfo.overlays.push(plotinfo);
         } else {
-            subplotData.push(k);
             plotinfo.mainplot = undefined;
+            plotinfo.mainPlotinfo = undefined;
         }
     }
 
-    // main subplots before overlays
-    subplotData = subplotData.concat(overlays);
+    // use info about axis layer and overlaying pattern
+    // to clean what need to be cleaned up in exit selection
+    for(i = 0; i < len; i++) {
+        id = ids[i];
+        plotinfo = fullLayout._plots[id];
+        xa = plotinfo.xaxis;
+        ya = plotinfo.yaxis;
+
+        var d = [id, xa.layer, ya.layer, xa.overlaying || '', ya.overlaying || ''];
+        for(j = 0; j < plotinfo.overlays.length; j++) {
+            d.push(plotinfo.overlays[j].id);
+        }
+        subplotData[i] = d;
+    }
 
     return subplotData;
 }