Add midpoint attr to color scales

src/components/colorscale/attributes.js

@@ -87,6 +87,8 @@ module.exports = function colorScaleAttrs(context, opts) {
     var auto = cLetter + 'auto';
     var min = cLetter + 'min';
     var max = cLetter + 'max';
+    var mid = cLetter + 'mid';
+    var autoFull = code(contextHead + auto);
     var minFull = code(contextHead + min);
     var maxFull = code(contextHead + max);
     var minmaxFull = minFull + ' and ' + maxFull;
@@ -160,6 +162,21 @@ module.exports = function colorScaleAttrs(context, opts) {
         ].join('')
     };
 
+    attrs[mid] = {
+        valType: 'number',
+        role: 'info',
+        dflt: null,
+        editType: 'calc',
+        impliedEdits: autoImpliedEdits,
+        description: [
+            'Sets the mid-point of the color domain by scaling ', minFull,
+            ' and/or ', maxFull, ' to be equidistant to this point.',
+            effectDesc,
+            ' Value should have the same units as ', colorAttrFull, '. ',
+            'Has no effect when ', autoFull, ' is `false`.'
+        ].join('')
+    };
+
     attrs.colorscale = {
         valType: 'colorscale',
         role: 'style',

src/components/colorscale/calc.js

@@ -23,9 +23,11 @@ module.exports = function calc(gd, trace, opts) {
     var autoAttr = cLetter + 'auto';
     var minAttr = cLetter + 'min';
     var maxAttr = cLetter + 'max';
+    var midAttr = cLetter + 'mid';
     var auto = container[autoAttr];
     var min = container[minAttr];
     var max = container[maxAttr];
+    var mid = container[midAttr];
     var scl = container.colorscale;
 
     if(auto !== false || min === undefined) {
@@ -36,6 +38,15 @@ module.exports = function calc(gd, trace, opts) {
         max = Lib.aggNums(Math.max, null, vals);
     }
 
+    if(auto !== false && mid !== undefined) {
+        if(max - mid > mid - min) {
+            min = mid - (max - mid);
+        }
+        else if(max - mid < mid - min) {
+            max = mid + (mid - min);
+        }
+    }
+
     if(min === max) {
         min -= 0.5;
         max += 0.5;

src/components/colorscale/defaults.js

@@ -33,9 +33,14 @@ module.exports = function colorScaleDefaults(traceIn, traceOut, layout, coerce,
     var minIn = containerIn[cLetter + 'min'];
     var maxIn = containerIn[cLetter + 'max'];
     var validMinMax = isNumeric(minIn) && isNumeric(maxIn) && (minIn < maxIn);
-    coerce(prefix + cLetter + 'auto', !validMinMax);
-    coerce(prefix + cLetter + 'min');
-    coerce(prefix + cLetter + 'max');
+    var auto = coerce(prefix + cLetter + 'auto', !validMinMax);
+
+    if(auto) {
+        coerce(prefix + cLetter + 'mid');
+    } else {
+        coerce(prefix + cLetter + 'min');
+        coerce(prefix + cLetter + 'max');
+    }
 
     // handles both the trace case (autocolorscale is false by default) and
     // the marker and marker.line case (autocolorscale is true by default)

src/traces/scattermapbox/attributes.js

@@ -93,6 +93,7 @@ module.exports = overrideAll({
         cauto: markerAttrs.cauto,
         cmax: markerAttrs.cmax,
         cmin: markerAttrs.cmin,
+        cmid: markerAttrs.cmid,
         autocolorscale: markerAttrs.autocolorscale,
         reversescale: markerAttrs.reversescale,
         showscale: markerAttrs.showscale,

test/image/mocks/cmid-zmid.json

@@ -0,0 +1,43 @@
+{
+  "data": [{
+    "y": [1, 2, 1],
+    "mode": "markers",
+    "marker": {
+      "size": 20,
+      "color": [-1, 1, 10],
+      "cmid": "0",
+      "colorbar": {
+        "len": 0.3,
+        "y": "1",
+        "yanchor": "top",
+        "title": {"text": "marker.cmid=0", "side": "right"}
+      }
+    }
+  }, {
+    "type": "heatmap",
+    "z": [[1,2], [2, 3]],
+    "zmid": -1,
+    "colorbar": {
+      "len": 0.3,
+      "y": "0.5",
+      "yanchor": "middle",
+      "title": {"text": "zmid=-1", "side": "right"}
+    }
+  }, {
+    "type": "bar",
+    "y": [0.5, 1, 0.5],
+    "name": "marker.line.cmid=2",
+    "hoverlabel": {"namelength": -1},
+    "marker": {
+      "line": {
+          "width": 2,
+          "color": [-1, -1, -10],
+          "cmid": 2
+      }
+    }
+  }],
+  "layout": {
+    "title": {"text": "Traces with set <b>cmid</b> / <b>zmid</b>"},
+    "showlegend": false
+  }
+}

test/jasmine/tests/plot_api_test.js

@@ -1195,6 +1195,77 @@ describe('Test plot api', function() {
             .then(done);
         });
 
+        it('turns on cauto when cmid is edited', function(done) {
+            function _assert(msg, exp) {
+                return function() {
+                    var mk = gd._fullData[0].marker;
+                    for(var k in exp) {
+                        expect(mk[k]).toBe(exp[k], [msg, k].join(' - '));
+                    }
+                };
+            }
+
+            function _restyle(arg) {
+                return function() { return Plotly.restyle(gd, arg); };
+            }
+
+            Plotly.plot(gd, [{
+                mode: 'markers',
+                y: [1, 2, 1],
+                marker: { color: [1, -1, 4] }
+            }])
+            .then(_assert('base', {
+                cauto: true,
+                cmid: undefined,
+                cmin: -1,
+                cmax: 4
+            }))
+            .then(_restyle({'marker.cmid': 0}))
+            .then(_assert('set cmid=0', {
+                cauto: true,
+                cmid: 0,
+                cmin: -4,
+                cmax: 4
+            }))
+            .then(_restyle({'marker.cmid': -2}))
+            .then(_assert('set cmid=-2', {
+                cauto: true,
+                cmid: -2,
+                cmin: -8,
+                cmax: 4
+            }))
+            .then(_restyle({'marker.cmid': 2}))
+            .then(_assert('set cmid=2', {
+                cauto: true,
+                cmid: 2,
+                cmin: -1,
+                cmax: 5
+            }))
+            .then(_restyle({'marker.cmin': 0}))
+            .then(_assert('set cmin=0', {
+                cauto: false,
+                cmid: undefined,
+                cmin: 0,
+                cmax: 5
+            }))
+            .then(_restyle({'marker.cmax': 10}))
+            .then(_assert('set cmin=0 + cmax=10', {
+                cauto: false,
+                cmid: undefined,
+                cmin: 0,
+                cmax: 10
+            }))
+            .then(_restyle({'marker.cauto': true, 'marker.cmid': null}))
+            .then(_assert('back to cauto=true', {
+                cauto: true,
+                cmid: undefined,
+                cmin: -1,
+                cmax: 4
+            }))
+            .catch(failTest)
+            .then(done);
+        });
+
         it('turns off autobin when you edit bin specs', function(done) {
             // test retained (modified) for backward compat with new autobin logic
             var start0 = 0.2;

test/jasmine/tests/scattergeo_test.js

@@ -90,7 +90,7 @@ describe('Test scattergeo defaults', function() {
 describe('Test scattergeo calc', function() {
 
     function _calc(opts) {
-        var base = { type: 'scattermapbox' };
+        var base = { type: 'scattergeo' };
         var trace = Lib.extendFlat({}, base, opts);
         var gd = { data: [trace] };