zoom at center

ChartingSpace/Viewport.js

@@ -30,6 +30,7 @@ function newViewport () {
     mousePosition: undefined,
     margins: MARGINS,
     payload: undefined,
+    zoomAtCenter: zoomAtCenter,
     changeZoom: changeZoom,
     onMouseWheel: onMouseWheel,
     transformThisPoint: transformThisPoint,
@@ -62,6 +63,8 @@ function newViewport () {
   thisObject.zoomTargetLevel = MIN_ZOOM_LEVEL
   INITIAL_TIME_PERIOD = recalculatePeriod(thisObject.zoomLevel)
 
+  let overrideMousePositionCounter = 0
+
   return thisObject
 
   function finalize () {
@@ -263,6 +266,11 @@ function newViewport () {
     thisObject.eventHandler.raiseEvent('Position Changed', event)
   }
 
+  function zoomAtCenter (level) {
+    thisObject.zoomTargetLevel = level
+    overrideMousePositionCounter = 10
+  }
+
   function changeZoom (oldLevel, newLevel) {
     if (thisObject.visible === false) { return }
     let oldMouse = unTransformThisPoint(thisObject.mousePosition, oldLevel)