Use Util.roundSymmetric, see #191

js/common/model/Lattice.js

@@ -12,6 +12,7 @@ define( require => {
   const Bounds2 = require( 'DOT/Bounds2' );
   const Emitter = require( 'AXON/Emitter' );
   const Matrix = require( 'DOT/Matrix' );
+  const Util = require( 'DOT/Util' );
   const waveInterference = require( 'WAVE_INTERFERENCE/waveInterference' );
 
   // constants
@@ -127,7 +128,7 @@ define( require => {
       if ( array.length !== samplingWidth ) {
         array.length = 0;
       }
-      const samplingVerticalLocation = Math.round( this.height / 2 );
+      const samplingVerticalLocation = Util.roundSymmetric( this.height / 2 );
       for ( let i = 0; i < this.width - this.dampX * 2; i++ ) {
         array[ i ] = this.getCurrentValue( i + this.dampX, samplingVerticalLocation );
       }

js/common/model/Scene.js

@@ -22,6 +22,7 @@ define( require => {
   const SceneType = require( 'WAVE_INTERFERENCE/common/model/SceneType' );
   const StringUtils = require( 'PHETCOMMON/util/StringUtils' );
   const Vector2 = require( 'DOT/Vector2' );
+  const Util = require( 'DOT/Util' );
   const waveInterference = require( 'WAVE_INTERFERENCE/waveInterference' );
   const WaveInterferenceConstants = require( 'WAVE_INTERFERENCE/common/WaveInterferenceConstants' );
   const WaveSpatialType = require( 'WAVE_INTERFERENCE/common/model/WaveSpatialType' );
@@ -299,7 +300,7 @@ define( require => {
 
           const frontTime = this.timeProperty.value - this.button1PressTime;
           const frontPosition = this.modelToLatticeTransform.modelToViewX( this.waveSpeed * frontTime );
-          const barrierLatticeX = Math.round( this.modelToLatticeTransform.modelToViewX( this.getBarrierLocation() ) );
+          const barrierLatticeX = Util.roundSymmetric( this.modelToLatticeTransform.modelToViewX( this.getBarrierLocation() ) );
 
           // if the wave had passed by the barrier, then repropagate from the barrier.  This requires back-computing the
           // time the button would have been pressed to propagate the wave to the barrier.  Hence this is the inverse of
@@ -342,13 +343,13 @@ define( require => {
           // assumes a square lattice
           const sourceSeparation = this.sourceSeparationProperty.get();
           const separationInLatticeUnits = sourceSeparation / this.waveAreaWidth * this.lattice.visibleBounds.width;
-          const distanceAboveAxis = Math.round( separationInLatticeUnits / 2 );
+          const distanceAboveAxis = Util.roundSymmetric( separationInLatticeUnits / 2 );
 
           // Named with a "J" suffix instead of "Y" to remind us we are working in integral (i,j) lattice coordinates.
           // To understand why we subtract 1 here, imagine for the sake of conversation that the lattice is 5 units wide
           // so the cells are indexed 0,1,2,3,4.  5/2 === 2.5, rounded up that is 3, so we must subtract 1 to find the
           // center of the lattice.
-          const latticeCenterJ = Math.round( this.lattice.height / 2 ) - 1;
+          const latticeCenterJ = Util.roundSymmetric( this.lattice.height / 2 ) - 1;
 
           // Point source
           if ( this.continuousWave1OscillatingProperty.get() || this.pulseFiringProperty.get() ) {
@@ -371,14 +372,14 @@ define( require => {
         const lattice = this.lattice;
 
         // Round this to make sure it appears at an integer cell column
-        let barrierLatticeX = Math.round( this.modelToLatticeTransform.modelToViewX( this.getBarrierLocation() ) );
+        let barrierLatticeX = Util.roundSymmetric( this.modelToLatticeTransform.modelToViewX( this.getBarrierLocation() ) );
         const slitSeparationModel = this.slitSeparationProperty.get();
 
         const frontTime = time - this.button1PressTime;
         const frontPosition = this.modelToLatticeTransform.modelToViewX( this.waveSpeed * frontTime );
 
         const slitWidthModel = this.slitWidthProperty.get();
-        const slitWidth = Math.round( this.modelToLatticeTransform.modelToViewDeltaY( slitWidthModel ) );
+        const slitWidth = Util.roundSymmetric( this.modelToLatticeTransform.modelToViewDeltaY( slitWidthModel ) );
         const latticeCenterY = this.lattice.height / 2;
 
         // Take the desired frequency for the water scene, or the specified frequency of any other scene

js/common/model/SoundParticle.js

@@ -29,10 +29,10 @@ define( require => {
       // @public {number} - vertical lattice coordinate of the particle
       this.j = j;
 
-      // @public - x coordinate
+      // @public {number} - x coordinate
       this.x = x;
 
-      // @public - y coordinate
+      // @public {number} - y coordinate
       this.y = y;
 
       // @private

js/common/model/SoundScene.js

@@ -29,7 +29,7 @@ define( require => {
     constructor( showSoundParticles, config ) {
       super( config );
 
-      // @public (read-only) true if SoundParticles should be created and displayed.  They are not displayed
+      // @public (read-only) {boolean} - true if SoundParticles should be created and displayed.  They are not displayed
       // on the Slits screen, see https://github.com/phetsims/wave-interference/issues/109
       this.showSoundParticles = showSoundParticles;
 
@@ -82,8 +82,8 @@ define( require => {
 
           // Find the lattice coordinate of the current location of the particle
           const latticeCoordinate = this.modelToLatticeTransform.modelToViewXY( soundParticle.x, soundParticle.y );
-          const latticeX = Math.round( latticeCoordinate.x );
-          const latticeY = Math.round( latticeCoordinate.y );
+          const latticeX = Util.roundSymmetric( latticeCoordinate.x );
+          const latticeY = Util.roundSymmetric( latticeCoordinate.y );
 
           // Estimate the numerical gradient in the neighborhood of the particle
           // https://en.wikipedia.org/wiki/Pressure-gradient_force

js/common/view/LightScreenNode.js

@@ -55,10 +55,16 @@ define( require => {
       // Use a single column of pixels, then stretch them to the right (since that is a constant)
       const width = 1;
       const height = this.lattice.height - this.lattice.dampY * 2;
+
+      // @private
       this.directCanvas = document.createElement( 'canvas' );
       this.directCanvas.width = width;
       this.directCanvas.height = height;
+
+      // @private
       this.directContext = this.directCanvas.getContext( '2d' );
+
+      // @private
       this.imageData = this.directContext.createImageData( width, height );
 
       // Invalidate paint when model indicates changes

js/diffraction/view/DiffractionScreenView.js

@@ -380,7 +380,7 @@ define( require => {
           const idxInPixels = 4 * ( dims[ 0 ] * k + l );
           currImageData.data[ idxInPixels + 3 ] = 255; // full alpha
           let color = Math.log( cc * $h( l, k ).magnitude() + 1 );
-          color = Math.round( 255 * ( color / logOfMaxMag ) );
+          color = Util.roundSymmetric( 255 * ( color / logOfMaxMag ) );
           // RGB are the same -> gray
           for ( let c = 0; c < 3; c++ ) { // lol c++
             currImageData.data[ idxInPixels + c ] = color;