relative-stack bars within the same trace that would otherwise be hidden

... under barmode:'group'

src/traces/bar/cross_trace_calc.js

@@ -198,6 +198,10 @@ function setGroupPositionsInGroupMode(gd, pa, sa, calcTraces) {
     // set bar offsets and widths, and update position axis
     setOffsetAndWidthInGroupMode(gd, pa, sieve);
 
+    // relative-stack bars within the same trace that would otherwise
+    // be hidden
+    unhideBarsWithinTrace(gd, sa, sieve);
+
     // set bar bases and sizes, and update size axis
     if(barnorm) {
         sieveBars(gd, sa, sieve);
@@ -578,6 +582,36 @@ function sieveBars(gd, sa, sieve) {
     }
 }
 
+function unhideBarsWithinTrace(gd, sa, sieve) {
+    var calcTraces = sieve.traces;
+
+    for(var i = 0; i < calcTraces.length; i++) {
+        var calcTrace = calcTraces[i];
+        var fullTrace = calcTrace[0].trace;
+
+        if(fullTrace.base === undefined) {
+            var inTraceSieve = new Sieve([calcTrace], {
+                separateNegativeValues: true,
+                dontMergeOverlappingData: true
+            });
+
+            for(var j = 0; j < calcTrace.length; j++) {
+                var bar = calcTrace[j];
+
+                if(bar.p !== BADNUM) {
+                    // stack current bar and get previous sum
+                    var barBase = inTraceSieve.put(bar.p, bar.b + bar.s);
+
+                    // if previous sum if non-zero, this means:
+                    // multiple bars have same starting point are potentially hidden,
+                    // shift them vertically so that all bars are visible by default
+                    if(barBase) bar.b = barBase;
+                }
+            }
+        }
+    }
+}
+
 // Note:
 //
 // normalizeBars requires that either sieveBars or stackBars has been

test/image/mocks/bar_unhidden.json

@@ -0,0 +1,27 @@
+{
+  "data": [
+    {
+      "type": "bar",
+      "x": [ 0, 0, 0 ],
+      "y": [ 1, 1, -1 ],
+      "marker": {
+        "color": [ "red", "green", "blue" ]
+      }
+    },
+    {
+      "type": "bar",
+      "x": [ 0, 0, 0 ],
+      "y": [ 1, 1, -1 ],
+      "marker": {
+        "color": [ "cyan", "magenta", "yellow" ]
+      }
+    }
+  ],
+  "layout": {
+    "margin": { "t": 30, "b": 30, "l": 30, "r": 30 },
+    "width": 400,
+    "height": 400,
+    "showlegend": false,
+    "hovermode": "closest"
+  }
+}

test/jasmine/tests/bar_test.js

@@ -926,6 +926,67 @@ describe('Bar.crossTraceCalc (formerly known as setPositions)', function() {
         expect(gd._fullLayout.xaxis.type).toBe('multicategory');
         assertPointField(gd.calcdata, 'b', [[0, 0, 0, 0]]);
     });
+
+    describe('should relative-stack bar within the same trace that overlap under barmode=group', function() {
+        it('- base case', function() {
+            var gd = mockBarPlot([{
+                x: [0, 0, 0],
+                y: [1, -2, -1]
+            }]);
+
+            assertPointField(gd.calcdata, 'b', [[0, 0, -2]]);
+            assertPointField(gd.calcdata, 'y', [[1, -2, -3]]);
+        });
+
+        it('- with blank positions', function() {
+            var gd = mockBarPlot([{
+                x: [0, null, 0, null, 0],
+                y: [1, null, -2, null, -1]
+            }]);
+
+            assertPointField(gd.calcdata, 'b', [[0, 0, 0, 0, -2]]);
+            assertPointField(gd.calcdata, 'y', [[1, NaN, -2, NaN, -3]]);
+        });
+
+        it('- with barnorm set', function() {
+            var gd = mockBarPlot([{
+                x: [0, 0, 0],
+                y: [1, -2, -1],
+            }], {
+                barnorm: 'fraction'
+            });
+
+            assertPointField(gd.calcdata, 'b', [[0, 0, -0.5]]);
+            assertPointField(gd.calcdata, 'y', [[0.25, -0.5, -0.75]]);
+        });
+
+        it('- skipped when base is set', function() {
+            var gd = mockBarPlot([{
+                x: [0, 0, 0],
+                y: [1, -2, -1],
+                base: 10
+            }, {
+                x: [0, 0, 0],
+                y: [1, -2, -1],
+                base: [1, 2, 1]
+            }]);
+
+            assertPointField(gd.calcdata, 'b', [[10, 10, 10], [1, 2, 1]]);
+            assertPointField(gd.calcdata, 'y', [[11, 8, 9], [2, 0, 0]]);
+        });
+
+        it('- skipped when barmode=overlay', function() {
+            var gd = mockBarPlot([{
+                x: [0, 0, 0],
+                y: [1, -2, -1]
+            }], {
+                barmode: 'overlay'
+            });
+
+            assertPointField(gd.calcdata, 'b', [[0, 0, 0]]);
+            assertPointField(gd.calcdata, 'y', [[1, -2, -1]]);
+        });
+    });
 });
 
 describe('A bar plot', function() {