From 5c47f1e7c4d9acb529b1e47ff8a30d607fbe4133 Mon Sep 17 00:00:00 2001
From: samreid <reids@colorado.edu>
Date: Mon, 7 Jan 2019 18:44:43 -0700
Subject: [PATCH] Increase damping coefficient and use gradual reduction for
 masking, see https://github.com/phetsims/wave-interference/issues/304

---
 js/common/model/Lattice.js      | 6 +++---
 js/common/model/Scene.js        | 2 +-
 js/common/model/TemporalMask.js | 5 +++--
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/js/common/model/Lattice.js b/js/common/model/Lattice.js
index ab1a9593..117b87fc 100644
--- a/js/common/model/Lattice.js
+++ b/js/common/model/Lattice.js
@@ -22,7 +22,7 @@ define( require => {
   const WAVE_SPEED = 0.5;
   const WAVE_SPEED_SQUARED = WAVE_SPEED * WAVE_SPEED; // precompute to avoid work in the inner loop
   const NUMBER_OF_MATRICES = 3; // The discretized wave equation algorithm requires current value + 2 history points
-  const DAMPING_COEFFICIENT = 0.999; // wave values scaled by this much at each frame to wash out numerical artifacts
+  const DAMPING_COEFFICIENT = 0.9999; // wave values scaled by this much at each frame to wash out numerical artifacts
 
   // This is the threshold for the wave value that determines if the light has visited.  If the value is higher,
   // it will track the wavefront of the light more accurately (and hence could be used for more accurate computation of
@@ -193,9 +193,9 @@ define( require => {
      * @param {number} j
      * @public
      */
-    clearCell( i, j ) {
+    reduceCell( i, j ) {
       for ( let k = 0; k < NUMBER_OF_MATRICES; k++ ) {
-        this.matrices[ k ].set( i, j, 0.0 );
+        this.matrices[ k ].set( i, j, this.matrices[ k ].get( i, j ) * 0.95 );
       }
       this.visitedMatrix.set( i, j, 0 );
     }
diff --git a/js/common/model/Scene.js b/js/common/model/Scene.js
index f32f52e3..abd58683 100644
--- a/js/common/model/Scene.js
+++ b/js/common/model/Scene.js
@@ -618,7 +618,7 @@ define( require => {
           const cameFrom2 = this.temporalMask2.matches( i, j, this.stepIndex );
 
           if ( !cameFrom1 && !cameFrom2 ) {
-            this.lattice.clearCell( i, j );
+            this.lattice.reduceCell( i, j );
           }
         }
       }
diff --git a/js/common/model/TemporalMask.js b/js/common/model/TemporalMask.js
index e4049169..96b9bbba 100644
--- a/js/common/model/TemporalMask.js
+++ b/js/common/model/TemporalMask.js
@@ -70,8 +70,9 @@ define( require => {
           const theoreticalTime = time - distance / Lattice.WAVE_SPEED;
 
           // if theoreticalDistance matches any time in this range, then we have a winner
-          const tolerance = 4;
-          if ( theoreticalTime >= startTime - tolerance && theoreticalTime <= endTime + tolerance ) {
+          const headTolerance = 4;
+          const tailTolerance = 4;
+          if ( theoreticalTime >= startTime - headTolerance && theoreticalTime <= endTime + tailTolerance ) {
 
             // Return as early as possible to improve performance
             return true;