add CoilOptions.electronsVisible for use by screen icons, #28

js/common/model/Coil.ts

@@ -66,6 +66,9 @@ type SelfOptions = {
   // Horizontal spacing between loops in the coil. Zero is tightly packed.
   loopSpacing?: number;
 
+  // Initial value of electronsVisibleProperty.
+  electronsVisible?: boolean;
+
   // Initial value of electronSpeedScaleProperty, a developer control.
   electronSpeedScale?: number;
 };
@@ -124,6 +127,7 @@ export default class Coil extends PhetioObject {
       wireWidth: 16,
       loopSpacing: 8,
       electronSpeedScale: 1,
+      electronsVisible: true,
 
       // PhetioObjectOptions
       phetioState: false
@@ -173,7 +177,7 @@ export default class Coil extends PhetioObject {
     this.loopRadiusProperty = new DerivedProperty( [ this.loopAreaProperty ],
       loopArea => Math.sqrt( loopArea / Math.PI ) );
 
-    this.electronsVisibleProperty = new BooleanProperty( true, {
+    this.electronsVisibleProperty = new BooleanProperty( options.electronsVisible, {
       tandem: options.tandem.createTandem( 'electronsVisibleProperty' ),
       phetioFeatured: true
     } );

js/common/view/FELScreenIconFactory.ts

@@ -125,17 +125,14 @@ const FELScreenIconFactory = {
  */
 function createCoilNode( numberOfLoops: number, loopSpacing: number ): Node {
 
-  const currentAmplitudeProperty = new NumberProperty( 0 );
-  const currentAmplitudeRange = FELConstants.CURRENT_AMPLITUDE_RANGE;
-
-  const coil = new Coil( currentAmplitudeProperty, currentAmplitudeRange, {
+  const coil = new Coil( new NumberProperty( 0 ), FELConstants.CURRENT_AMPLITUDE_RANGE, {
     numberOfLoopsRange: new RangeWithValue( numberOfLoops, numberOfLoops, numberOfLoops ),
     loopSpacing: loopSpacing,
     maxLoopArea: 7000,
     loopAreaPercentRange: new RangeWithValue( 100, 100, 100 ),
+    electronsVisible: false,
     tandem: Tandem.OPT_OUT
   } );
-  coil.electronsVisibleProperty.value = false;
 
   // We must have a subclass of FELMovable associated with a coil's background layer. This one will do.
   const movable = new BarMagnet( { tandem: Tandem.OPT_OUT } );