Fix tooltip position when it's on the bottom - #635

c3.js

@@ -3589,10 +3589,13 @@
             if (tooltipRight > chartRight) {
                 tooltipLeft -= tooltipRight - chartRight;
             }
-            if (tooltipTop + tHeight > $$.currentHeight && tooltipTop > tHeight + 30) {
+            if (tooltipTop + tHeight > $$.currentHeight) {
                 tooltipTop -= tHeight + 30;
             }
         }
+        if (tooltipTop < 0) {
+            tooltipTop = 0;
+        }
         // Set tooltip
         $$.tooltip
             .style("top", tooltipTop + "px")

src/tooltip.js

@@ -83,10 +83,13 @@ c3_chart_internal_fn.showTooltip = function (selectedData, mouse) {
         if (tooltipRight > chartRight) {
             tooltipLeft -= tooltipRight - chartRight;
         }
-        if (tooltipTop + tHeight > $$.currentHeight && tooltipTop > tHeight + 30) {
+        if (tooltipTop + tHeight > $$.currentHeight) {
             tooltipTop -= tHeight + 30;
         }
     }
+    if (tooltipTop < 0) {
+        tooltipTop = 0;
+    }
     // Set tooltip
     $$.tooltip
         .style("top", tooltipTop + "px")