ENH: Scale barplot lengths by max displacement

Relevant to biocore#276. The reliance on max displacement (which doesn't
seem to have an analogue in the unrooted layout? or maybe we can sort
of treat it the same way as circ layout, idk) means that this might
be too specific a solution to apply to line width thicknesses, but
it should make using barplots a lot less painful

empress/support_files/js/empress.js

@@ -215,6 +215,14 @@ define([
          */
         this._maxDisplacement = null;
 
+        /**
+         * @type {Number}
+         * A multiple of this._maxDisplacement. This is used as the unit for
+         * barplot lengths.
+         * @private
+         */
+        this._barplotUnit = null;
+
         /**
          * @type{Boolean}
          * Indicates whether or not barplots are currently drawn.
@@ -1390,10 +1398,13 @@ define([
     Empress.prototype._computeMaxDisplacement = function () {
         var maxD = -Infinity;
         var compFunc;
+        var layoutFactor;
         if (this._currentLayout === "Rectangular") {
             compFunc = "_getMaxOfXAndNumber";
+            layoutFactor = 1;
         } else if (this._currentLayout === "Circular") {
             compFunc = "_getMaxOfRadiusAndNumber";
+            layoutFactor = 2;
         } else {
             this._maxDisplacement = null;
             return;
@@ -1404,6 +1415,7 @@ define([
             }
         }
         this._maxDisplacement = maxD;
+        this._barplotUnit = (this._maxDisplacement / 1000) * layoutFactor;
     };
 
     /**
@@ -1442,7 +1454,7 @@ define([
         // start drawing barplots, and the first barplot layer. This could be
         // made into a barplot-panel-level configurable thing if desired.
         // (Note that, as with barplot lengths, the units here are arbitrary.)
-        var maxD = this._maxDisplacement + 100;
+        var maxD = 1.1 * this._maxDisplacement;
 
         // As we iterate through the layers, we'll store the "previous layer
         // max D" as a separate variable. This will help us easily work with
@@ -1620,7 +1632,8 @@ define([
                 // present in at least one sample with that value.
                 if (!_.isUndefined(freq)) {
                     var sectionColor = sm2color[smVal];
-                    var barSectionLen = layer.lengthSM * freq;
+                    var barSectionLen =
+                        layer.lengthSM * scope._barplotUnit * freq;
                     // Assign each unique sample metadata value a length
                     // proportional to its, well, proportion within the sample
                     // presence information for this tip.
@@ -1842,7 +1855,7 @@ define([
                 }
 
                 // Update maxD if needed
-                var thisLayerMaxD = prevLayerMaxD + length;
+                var thisLayerMaxD = prevLayerMaxD + length * this._barplotUnit;
                 if (thisLayerMaxD > maxD) {
                     maxD = thisLayerMaxD;
                 }