Revert "Use mutable form of Vector2.add() instead of Vector2.plus() (…

…memory optimization) #115"

This reverts commit 55b2dd8.

js/common/model/Atom2.js

@@ -133,8 +133,8 @@ class Atom2 extends Atom {
   }
 
   translatePositionAndDestination( delta ) {
-    this.positionProperty.value = this.positionProperty.value.add( delta );
-    this.destinationProperty.value.add( delta );
+    this.positionProperty.value = this.positionProperty.value.plus( delta );
+    this.destinationProperty.value = this.destinationProperty.value.plus( delta );
   }
 
   setPositionAndDestination( point ) {

js/common/model/Kit.js

@@ -488,8 +488,8 @@ class Kit {
             foundOverlap = true;
 
             // get perturbed centers. this is so that if two molecules have the exact same centers, we will push them away
-            const aCenter = aBounds.center.add( new Vector2( phet.joist.random.nextDouble() - 0.5, phet.joist.random.nextDouble() - 0.5 ) );
-            const bCenter = bBounds.center.add( new Vector2( phet.joist.random.nextDouble() - 0.5, phet.joist.random.nextDouble() - 0.5 ) );
+            const aCenter = aBounds.center.plus( new Vector2( phet.joist.random.nextDouble() - 0.5, phet.joist.random.nextDouble() - 0.5 ) );
+            const bCenter = bBounds.center.plus( new Vector2( phet.joist.random.nextDouble() - 0.5, phet.joist.random.nextDouble() - 0.5 ) );
 
             // delta from center of A to center of B, scaled to half of our push amount.
             const delta = bCenter.minus( aCenter ).normalized().times( pushAmount );
@@ -648,7 +648,7 @@ class Kit {
     // cause all atoms in the molecule to move to that location
     const delta = bestLocation.idealLocation.minus( bestLocation.b.positionProperty.value );
     this.getMolecule( bestLocation.b ).atoms.forEach( atomInMolecule => {
-      atomInMolecule.setPositionAndDestination( atomInMolecule.positionProperty.value.add( delta ) );
+      atomInMolecule.setPositionAndDestination( atomInMolecule.positionProperty.value.plus( delta ) );
     } );
 
     // we now will bond the atom
@@ -695,7 +695,7 @@ class BondingOption {
     this.b = b;
 
     // The location the atom should be placed
-    this.idealLocation = a.positionProperty.value.add( direction.vector.times( a.covalentRadius + b.covalentRadius ) );
+    this.idealLocation = a.positionProperty.value.plus( direction.vector.times( a.covalentRadius + b.covalentRadius ) );
   }
 }
 

js/common/model/LewisDotModel.js

@@ -168,7 +168,7 @@ class LewisDotModel {
 
         // if this atom isn't excluded
         if ( otherDot.atom !== excludedAtom ) {
-          success = this.mapMolecule( coordinates.add( direction.vector ), otherDot.atom, atom, coordinateMap );
+          success = this.mapMolecule( coordinates.plus( direction.vector ), otherDot.atom, atom, coordinateMap );
 
           // if we had a failure mapping that one, bail out
           if ( !success ) {

js/common/model/Molecule.js

@@ -46,8 +46,9 @@ class Molecule extends MoleculeStructure {
    */
   shiftDestination( delta ) {
     this.atoms.forEach( atom => {
+      // TODO: memory: consider alternate mutable form atom.destination.add( delta )
       atom.isSeparatingProperty.value = true;
-      atom.destinationProperty.value.add( delta );
+      atom.destinationProperty.value = atom.destinationProperty.value.plus( delta );
     } );
   }
 }

js/common/view/MoleculeBondNode.js

@@ -150,7 +150,7 @@ class MoleculeBondNode extends Node {
       if ( orientation.magnitude > 0 ) {
         orientation.normalize();
       }
-      const location = orientation.times( this.a.covalentRadius ).add( this.a.positionProperty.value );
+      const location = orientation.times( this.a.covalentRadius ).plus( this.a.positionProperty.value );
       this.setTranslation( BAMConstants.MODEL_VIEW_TRANSFORM.modelToViewPosition( location ) );
     };
     this.a.positionProperty.link( this.positionListener );