Add/calc tickmode "proportional" in cartesian/

- Create tickmode "proportional"
- Map fractional tickvals to axis values w/ axis range:
  - Set ax.(minor?).tickvals to
  - Do that right before `arrayTicks()` is called
- Every instance of `tickmode === "array"` gets `...|| "proportional"`

This works well since tickmode "proportional" really just adds a preprocess step to
tickmode "array".

TODO:

- Check if graph is reversed
- Find where ticks are redrawn on zoom and make redraw proportional (will probably fix below)
- Figure out why ticks not redrawn on double click/home
- Add docs in layout

Author: ayjayt

Diff for: src/plot_api/plot_api.js

@@ -2945,7 +2945,7 @@ function getDiffFlags(oldContainer, newContainer, outerparts, opts) {
         // so newContainer won't have them.
         if((key === 'tick0' || key === 'dtick') && outerparts[0] !== 'geo') {
             var tickMode = newContainer.tickmode;
-            if(tickMode === 'auto' || tickMode === 'array' || !tickMode) continue;
+            if(tickMode === 'auto' || tickMode === 'array' || tickMode === 'proportional' || !tickMode) continue;
         }
         // FIXME: Similarly for axis ranges for 3D
         // contourcarpet doesn't HAVE zmin/zmax, they're just auto-added. It needs them.

Diff for: src/plots/cartesian/axes.js

@@ -682,10 +682,10 @@ axes.prepTicks = function(ax, opts) {
             if(ax._name === 'radialaxis') nt *= 2;
         }
 
-        if(!(ax.minor && ax.minor.tickmode !== 'array')) {
+        if(!(ax.minor && (ax.minor.tickmode !== 'array' && ax.minor.tickmode !== 'proportional'))) {
             // add a couple of extra digits for filling in ticks when we
             // have explicit tickvals without tick text
-            if(ax.tickmode === 'array') nt *= 100;
+            if(ax.tickmode === 'array' || ax.tickmode === 'proportional') nt *= 100;
         }
 
         ax._roughDTick = Math.abs(rng[1] - rng[0]) / nt;
@@ -944,9 +944,25 @@ axes.calcTicks = function calcTicks(ax, opts) {
             axes.prepTicks(mockAx, opts);
         }
 
+        console.log("mode:" + mockAx.tickmode)
+        if (mockAx.tickmode === 'proportional') { // TODO: if we look at autorange, can we get rid of buffer
+          var distance = maxRange - minRange;
+          var vals = []
+          if(major) {
+            vals = Lib.nestedProperty(ax, "tickvals")
+          } else {
+            vals = Lib.nestedProperty(ax.minor, "tickvals")
+          }
+          var mappedVals = vals.get().map(function(x) { return minRange+(distance*x) })
+          vals.set(mappedVals)
+          // TODO: What happens if range reversed
+          // TODO: Needs to be recalculated on auto
+          // TODO: Disappears on double click
+        }
+
         // now that we've figured out the auto values for formatting
         // in case we're missing some ticktext, we can break out for array ticks
-        if(mockAx.tickmode === 'array') {
+        if(mockAx.tickmode === 'array' || mockAx.tickmode === 'proportional') {
             if(major) {
                 tickVals = [];
                 ticksOut = arrayTicks(ax);
@@ -1617,7 +1633,7 @@ axes.tickFirst = function(ax, opts) {
 // more precision for hovertext
 axes.tickText = function(ax, x, hover, noSuffixPrefix) {
     var out = tickTextObj(ax, x);
-    var arrayMode = ax.tickmode === 'array';
+    var arrayMode = (ax.tickmode === 'array' || ax.tickmode === 'proportional');
     var extraPrecision = hover || arrayMode;
     var axType = ax.type;
     // TODO multicategory, if we allow ticktext / tickvals
@@ -3333,7 +3349,7 @@ axes.drawGrid = function(gd, ax, opts) {
 
     var counterAx = opts.counterAxis;
     if(counterAx && axes.shouldShowZeroLine(gd, ax, counterAx)) {
-        var isArrayMode = ax.tickmode === 'array';
+        var isArrayMode = (ax.tickmode === 'array' || ax.tickmode === 'proportional');
         for(var i = 0; i < majorVals.length; i++) {
             var xi = majorVals[i].x;
             if(isArrayMode ? !xi : (Math.abs(xi) < ax.dtick / 100)) {

Diff for: src/plots/cartesian/layout_attributes.js

@@ -14,7 +14,7 @@ var DAY_OF_WEEK = constants.WEEKDAY_PATTERN;
 
 var minorTickmode = {
     valType: 'enumerated',
-    values: ['auto', 'linear', 'array'],
+    values: ['auto', 'linear', 'array', 'proportional'],
     editType: 'ticks',
     impliedEdits: {tick0: undefined, dtick: undefined},
     description: [