const height = 600;

​

// Determines wavelength, lamba = 1 / SCALE

const SCALE = 5;

​

// y level where 'detector' is, amplitudes graphed from this level

const Y_BASE = 30;

const BAR_HEIGHT = 40;

const dx = 2;

let dt = 0;

​

let x1;

let y1;

let x2;

let y2;

​

let t = 0;

​

function setup() {

    createCanvas(width, height);

    pixelDensity(1);

    rectMode(CENTER);

    x1 = 250;

    y1 = height;

    x2 = x1 + (SCALE * TWO_PI) * 2;

    y2 = height;

    dt = PI / 8;

    frameRate(10);

    textSize(16);

}

​

function draw() {

    strokeWeight(.5);

    fill(100, 100, 255);

​

    loadPixels();

​

    for (let i = 0; i < width; i++) {

        for (let j = 0; j < height; j++) {

            let col1 = cos(dist(x1, y1, i, j) / SCALE - t);

            let col2 = cos(dist(x2, y2, i, j) / SCALE - t);

            let col = map(col1 + col2, -2, 2, 100, 150);

            setPixel(i, j, col, col, col, 255);

        }

    }

    updatePixels();

​

    plotCurrentAmp(Y_BASE);

    plotInterferenceAmp(Y_BASE);

​

    stroke(0, 255, 0);

    line(0, Y_BASE, width, Y_BASE);

    stroke(200, 200, 0, 200);

    line(0, Y_BASE + 10, width, Y_BASE + 10);

    line(0, Y_BASE - 10, width, Y_BASE - 10);

    stroke(0);

​

    writeCaptions();

    t += dt;

}

​

function setPixel(x, y, r, g, b, a) {

​

    let index = (x + y * width) * 4;

    pixels[index] = r;

    pixels[index+1] = g;

    pixels[index+2] = b;

    pixels[index+3] = a;

}

​

function getPixel(x, y) {

​

    // Return R, G, B values for pixel (x, y)

    let index = (x + y * width) * 4;

    return createVector(pixels[index], pixels[index+1], pixels[index+2])

}

​

function plotInterferenceAmp (yLevel) {

    const eps = 0.05;

​

    for (let i = 0; i < width; i += dx) {

        let r2 = dist(i, yLevel, x2, y2);

        let r1 = dist(i, yLevel, x1, y1);

        let phi = (1 / SCALE) * abs(r2 - r1);

        let E = 2 * abs(cos(phi / 2));

        fill(250, 50, 50, 80);

        rect(i, yLevel + 50, 2, map(E, 0, 2, 0, BAR_HEIGHT));

        if (E < eps)

            stroke(200, 200, 0, 100);

            line(i, 0, i, height);

            stroke(0);

    }

}

​

function plotCurrentAmp(yLevel) {

    for (let i = 0; i < width; i += dx) {

        fill(50, 50, 255, 100);

        rect(i, yLevel, 2, map(getPixel(i, yLevel).x, 100, 150, 0, BAR_HEIGHT));

    }

}

​

function keyPressed() {

    let increment = (1 / SCALE) * 50;

    switch (keyCode) {

        case RIGHT_ARROW: 

            x2 += increment;

            break;

        case LEFT_ARROW: 

            x2 -= increment;

            break;

        case 65: // 'a'

            x1 -= increment;

            break;

        case 68: // 'd'

            x1 += increment;

            break;

    }

}

​

function writeCaptions() {

    fill(255);

    text("Click anywhere to set focus", width - 200, height - 10);

    text("A and D move left source", 10, height - 30);

    text("← and → move right source", 10, height - 10);

    text("Blue graph shows current amplitude at y = 30", 10, 150);

    text("Red graph shows max amplitude of interference at y = 30", 10, 170);

}