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| // Copyright 2019, University of Colorado Boulder | ||
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| /** | ||
| * Records on and off times of a single source, so that we can determine whether it could have contributed to the value | ||
| * on the lattice at a later time. | ||
| * | ||
| * @author Sam Reid (PhET Interactive Simulations) | ||
| */ | ||
| define( require => { | ||
| 'use strict'; | ||
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| // modules | ||
| const waveInterference = require( 'WAVE_INTERFERENCE/waveInterference' ); | ||
| const WaveInterferenceConstants = require( 'WAVE_INTERFERENCE/common/WaveInterferenceConstants' ); | ||
|
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| // constants | ||
| // I expected the wave speed on the lattice to be 1 or sqrt(2)/2, and was surprised to see that this value | ||
| // worked much better empirically. This is a speed in lattice cells per time step, which is the same | ||
| // for each scene | ||
| const waveSpeed = Math.sqrt( 2 ) / 3; | ||
| const I = WaveInterferenceConstants.POINT_SOURCE_HORIZONTAL_COORDINATE; | ||
|
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| class TemporalMask { | ||
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| /** | ||
| */ | ||
| constructor() { | ||
|
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| // @private - record of {on, time,j} of changes in wave disturbance sources. | ||
| this.deltas = []; | ||
| } | ||
|
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| /** | ||
| * Set the current state of the model. If this differs from the prior state type (in position or whether it is on) | ||
| * a delta is generated. | ||
| * @param {boolean} on - true if the source is on, false if the source is off | ||
| * @param {number} time - integer number of times the wave has been stepped on the lattice | ||
| * @param {number} j - vertical lattice coordinate | ||
| * @public | ||
| */ | ||
| set( on, time, j ) { | ||
| const lastDelta = this.deltas.length > 0 ? this.deltas[ this.deltas.length - 1 ] : null; | ||
| if ( this.deltas.length === 0 || lastDelta.on !== on || lastDelta.j !== j ) { | ||
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| // record a delta | ||
| this.deltas.push( { | ||
| on: on, | ||
| time: time, | ||
| j: j | ||
| } ); | ||
| } | ||
| } | ||
|
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| /** | ||
| * Determines if the wave source was turned on at a time that contributed to the cell value | ||
| * @param {number} i - horizontal coordinate on the lattice | ||
| * @param {number} j - vertical coordinate on the lattice | ||
| * @param {number} time - integer number of times the wave has been stepped on the lattice | ||
| * @returns {boolean} | ||
| * @public | ||
| */ | ||
| matches( i, j, time ) { | ||
|
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| // search back through time to see if the source contributed to the value at (i,j) at the current time | ||
| for ( let k = 0; k < this.deltas.length; k++ ) { | ||
| const delta = this.deltas[ k ]; | ||
| if ( delta.on ) { | ||
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| const di = I - i; | ||
| const dj = delta.j - j; | ||
| const distance = Math.sqrt( di * di + dj * dj ); | ||
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| // Find out when this delta is in effect | ||
| const startTime = delta.time; | ||
| const endTime = this.deltas[ k + 1 ] ? this.deltas[ k + 1 ].time : time; | ||
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| const theoreticalTime = time - distance / waveSpeed; | ||
|
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| // if theoreticalDistance matches any time in this range, then we have a winner | ||
| if ( theoreticalTime >= startTime && theoreticalTime <= endTime ) { | ||
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| // Return as early as possible to improve performance | ||
| return true; | ||
| } | ||
| } | ||
| } | ||
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| return false; | ||
| } | ||
|
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| /** | ||
| * Remove delta values that are so old they can no longer impact the model, to avoid memory leaks. | ||
| * @param {number} maxDistance - the furthest a point can be from a source | ||
| * @param {number} time - integer number of times the wave has been stepped on the lattice | ||
| * @public | ||
| */ | ||
| prune( maxDistance, time ) { | ||
| for ( let k = 0; k < this.deltas.length; k++ ) { | ||
| const delta = this.deltas[ k ]; | ||
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| const time = this.time - delta.time; | ||
|
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| // max time is across the diagonal of the lattice | ||
| if ( time > maxDistance / waveSpeed ) { // d = vt, t=d/v | ||
| this.deltas.splice( k, 1 ); | ||
| k--; | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| return waveInterference.register( 'TemporalMask', TemporalMask ); | ||
| } ); |