Introduce tooltip.position callback function

spec/tooltip-spec.js

 var describe = window.describe,
     expect = window.expect,
     it = window.it,
+    jasmine = window.jasmine,
+    beforeAll = window.beforeAll,
     beforeEach = window.beforeEach;
 
 describe('c3 chart tooltip', function () {
     'use strict';
 
     var chart, d3;
-
-    var args = {
-        data: {
-            columns: [
-                ['data1', 30, 200, 100, 400, 150, 250],
-                ['data2', 50, 20, 10, 40, 15, 25],
-                ['data3', 150, 120, 110, 140, 115, 125]
-            ]
-        }
+    var tooltipConfiguration;
+
+    var args = function () {
+        return {
+            data: {
+                columns: [
+                    ['data1', 30, 200, 100, 400, 150, 250],
+                    ['data2', 50, 20, 10, 40, 15, 25],
+                    ['data3', 150, 120, 110, 140, 115, 125]
+                ],
+            },
+            tooltip: tooltipConfiguration
+        };
     };
 
     beforeEach(function (done) {
-        chart = window.initChart(chart, args, done);
+        chart = window.initChart(chart, args(), done);
         d3 = chart.internal.d3;
     });
 
     describe('tooltip position', function () {
+        beforeAll(function () {
+            tooltipConfiguration = {};
+        });
 
         describe('without left margin', function () {
 
@@ -66,4 +75,35 @@ describe('c3 chart tooltip', function () {
 
     });
 
+    describe('tooltip positionFunction', function () {
+        var topExpected = 37, leftExpected = 79;
+
+        beforeAll(function () {
+            tooltipConfiguration = {
+                position: function (data, width, height, element) {
+                    expect(data.length).toBe(args().data.columns.length);
+                    expect(data[0]).toEqual(jasmine.objectContaining({
+                        index: 2,
+                        value: 100,
+                        id: 'data1'
+                    }));
+                    expect(width).toBeGreaterThan(0);
+                    expect(height).toBeGreaterThan(0);
+                    expect(element).toBe(d3.select('.c3-event-rect-2').node());
+                    return {top: topExpected, left: leftExpected};
+                }
+            };
+        });
+
+        it('should be set to the coordinate where the function returned', function () {
+            var eventRect = d3.select('.c3-event-rect-2').node();
+            window.setMouseEvent(chart, 'mousemove', 100, 100, eventRect);
+
+            var tooltipContainer = d3.select('.c3-tooltip-container'),
+                top = Math.floor(+tooltipContainer.style('top').replace(/px/, '')),
+                left = Math.floor(+tooltipContainer.style('left').replace(/px/, ''));
+            expect(top).toBe(topExpected);
+            expect(left).toBe(leftExpected);
+        });
+    });
 });

src/arc.js

@@ -273,7 +273,7 @@ c3_chart_internal_fn.redrawArc = function (duration, durationForExit, withTransf
             var updated = $$.updateAngle(d),
                 arcData = $$.convertToArcData(updated),
                 selectedData = [arcData];
-            $$.showTooltip(selectedData, d3.mouse(this));
+            $$.showTooltip(selectedData, this);
         } : null)
         .on('mouseout', config.interaction_enabled ? function (d) {
             var updated, arcData;

src/config.js

@@ -183,6 +183,7 @@ c3_chart_internal_fn.getDefaultConfig = function () {
         tooltip_format_title: undefined,
         tooltip_format_name: undefined,
         tooltip_format_value: undefined,
+        tooltip_position: undefined,
         tooltip_contents: function (d, defaultTitleFormat, defaultValueFormat, color) {
             return this.getTooltipContent ? this.getTooltipContent(d, defaultTitleFormat, defaultValueFormat, color) : '';
         },

src/interaction.js

@@ -175,7 +175,7 @@ c3_chart_internal_fn.generateEventRectsForSingleX = function (eventRectEnter) {
             });
 
             if (config.tooltip_grouped) {
-                $$.showTooltip(selectedData, d3.mouse(this));
+                $$.showTooltip(selectedData, this);
                 $$.showXGridFocus(selectedData);
             }
 
@@ -206,7 +206,7 @@ c3_chart_internal_fn.generateEventRectsForSingleX = function (eventRectEnter) {
                         eventRect.style('cursor', 'pointer');
                     }
                     if (!config.tooltip_grouped) {
-                        $$.showTooltip([d], d3.mouse(this));
+                        $$.showTooltip([d], this);
                         $$.showXGridFocus([d]);
                         if (config.point_focus_expand_enabled) { $$.expandCircles(index, d.id, true); }
                         $$.expandBars(index, d.id, true);
@@ -289,7 +289,7 @@ c3_chart_internal_fn.generateEventRectsForMultipleXs = function (eventRectEnter)
             selectedData = sameXData.map(function (d) {
                 return $$.addName(d);
             });
-            $$.showTooltip(selectedData, mouse);
+            $$.showTooltip(selectedData, this);
 
             // expand points
             if (config.point_focus_expand_enabled) {

src/tooltip.js

@@ -49,20 +49,12 @@ c3_chart_internal_fn.getTooltipContent = function (d, defaultTitleFormat, defaul
     }
     return text + "</table>";
 };
-c3_chart_internal_fn.showTooltip = function (selectedData, mouse) {
-    var $$ = this, config = $$.config;
-    var tWidth, tHeight, svgLeft, tooltipLeft, tooltipRight, tooltipTop, chartRight;
+c3_chart_internal_fn.tooltipPosition = function (dataToShow, tWidth, tHeight, element) {
+    var $$ = this, config = $$.config, d3 = $$.d3;
+    var svgLeft, tooltipLeft, tooltipRight, tooltipTop, chartRight;
     var forArc = $$.hasArcType(),
-        dataToShow = selectedData.filter(function (d) { return d && isValue(d.value); });
-    if (dataToShow.length === 0 || !config.tooltip_show) {
-        return;
-    }
-    $$.tooltip.html(config.tooltip_contents.call($$, selectedData, $$.getXAxisTickFormat(), $$.getYFormat(forArc), $$.color)).style("display", "block");
-
-    // Get tooltip dimensions
-    tWidth = $$.tooltip.property('offsetWidth');
-    tHeight = $$.tooltip.property('offsetHeight');
-    // Determin tooltip position
+        mouse = d3.mouse(element);
+  // Determin tooltip position
     if (forArc) {
         tooltipLeft = ($$.width / 2) + mouse[0];
         tooltipTop = ($$.height / 2) + mouse[1] + 20;
@@ -90,10 +82,28 @@ c3_chart_internal_fn.showTooltip = function (selectedData, mouse) {
     if (tooltipTop < 0) {
         tooltipTop = 0;
     }
+    return {top: tooltipTop, left: tooltipLeft};
+};
+c3_chart_internal_fn.showTooltip = function (selectedData, element) {
+    var $$ = this, config = $$.config;
+    var tWidth, tHeight, position;
+    var forArc = $$.hasArcType(),
+        dataToShow = selectedData.filter(function (d) { return d && isValue(d.value); }),
+        positionFunction = config.tooltip_position || c3_chart_internal_fn.tooltipPosition;
+    if (dataToShow.length === 0 || !config.tooltip_show) {
+        return;
+    }
+    $$.tooltip.html(config.tooltip_contents.call($$, selectedData, $$.getXAxisTickFormat(), $$.getYFormat(forArc), $$.color)).style("display", "block");
+
+    // Get tooltip dimensions
+    tWidth = $$.tooltip.property('offsetWidth');
+    tHeight = $$.tooltip.property('offsetHeight');
+
+    position = positionFunction.call(this, dataToShow, tWidth, tHeight, element);
     // Set tooltip
     $$.tooltip
-        .style("top", tooltipTop + "px")
-        .style("left", tooltipLeft + 'px');
+        .style("top", position.top + "px")
+        .style("left", position.left + 'px');
 };
 c3_chart_internal_fn.hideTooltip = function () {
     this.tooltip.style("display", "none");