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              <div id="root"></div>

<a href="https://s.codepen.io/jscottsmith/debug/dRBOzE" rel="noopener" target="_blank" class="fullscreen">
    <svg version="1.1" x="0px" y="0px" width="30px" height="30px" viewBox="0 0 30 30">
        <polygon fill="#FFF" points="16.5,15 23.1,8.3 26,11.2 26,4 18.8,4 21.7,6.9 15,13.5 8.3,6.9 11.2,4 4,4 4,11.2 6.9,8.3 13.5,15  6.9,21.7 4,18.8 4,26 11.2,26 8.3,23.1 15,16.5 21.7,23.1 18.8,26 26,26 26,18.8 23.1,21.7 	"/>
    </svg>
</a>
            
          
!
            
              html, body {
    width: 100%;
    height: 100%;
    overflow: hidden;
}

button {
    z-index: 1;
    font-size: 1rem;
    font-family: Futura, helvetica;
    text-transform: uppercase;
    letter-spacing: 0.1rem;
    font-weight: bold;
    color: #fff;
    border: none;
    outline: none;
    background: transparent;
    cursor: pointer;
}

.play-btn {
    position: fixed;
    top: 1rem;
    right: 50%;
    margin-right: -40px;
}

.gyro-btn {
    position: fixed;
    bottom: 1rem;
    right: 50%;
    margin-right: -40px;
}

.fullscreen {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
}

canvas {
    cursor: none;
}

            
          
!
            
              /*------------------------------*\
|* Theremin Oscillator
\*------------------------------*/

/*
 *
 * NOTES:
 *
 * Pitch on the theremin is controlled by the pointers x position.
 * Amplitude is controlled by the pointers y position.
 * Mousedown or Touch to start the Oscillator. Toggle on/off with osc UI.
 * Must view in debug mode to use the Gyroscope. Toggle on/off with gyro UI.
 *
 **/

/*------------------------------*\
|* Utils / Constants
\*------------------------------*/

const FREQ_LOW = 32.7031956625748294; // C1 in Hz
const FREQ_HIGH = 1046.502261202394538; // C6 in Hz
const DPR = window.devicePixelRatio || 1;

function scaleBetween(value, newMin, newMax, oldMin, oldMax) {
    return (newMax - newMin) * (value - oldMin) / (oldMax - oldMin) + newMin;
}

/*------------------------------*\
|* UI Icons
\*------------------------------*/

const gyroOnIcon = `
<svg version="1.1" width="60px" height="60px" x="0px" y="0px" viewBox="0 0 60 60">
    <ellipse fill="none" stroke="#FFF" stroke-width="2" cx="30" cy="30" rx="5.5" ry="18"/>
    <ellipse fill="none" stroke="#FFF" stroke-width="2" cx="30" cy="30" rx="18" ry="5.5"/>
    <circle fill="#FFF" cx="30" cy="30" r="1"/>
    <circle fill="none" stroke="#FFF" stroke-width="2" cx="30" cy="30" r="25"/>
</svg>`;

const gyroOffIcon = `
<svg version="1.1" width="60px" height="60px" x="0px" y="0px" viewBox="0 0 60 60">
    <circle fill="none" stroke="#FFF" stroke-width="2" cx="30" cy="30" r="25"/>
    <line fill="none" stroke="#FFF" stroke-width="2" x1="19" y1="19" x2="41" y2="41"/>
    <line fill="none" stroke="#FFF" stroke-width="2" x1="41" y1="19" x2="19" y2="41"/>
</svg>`;

const oscOn = `
<svg version="1.1" width="60px" height="60px" x="0px" y="0px" viewBox="0 0 60 60">
    <path fill="none" stroke="#FFF" stroke-width="2" d="M4,30c0.8,6,1.6,12,3.2,12c3.2,0,3.2-24,6.5-24c3.2,0,3.2,24,6.5,24c3.2,0,3.2-24,6.5-24c3.2,0,3.2,24,6.5,24 c3.2,0,3.2-24,6.5-24c3.2,0,3.2,24,6.5,24c3.3,0,3.3-24,6.5-24c1.6,0,2.4,6,3.3,12"/>
    <polyline fill="none" stroke="#FFF" stroke-width="2" points="4,13.7 4,4 56,4 56,13.7 "/>
    <polyline fill="none" stroke="#FFF" stroke-width="2" points="56,46.5 56,56 4,56 4,46.5 "/>
</svg>`;

const oscOff = `
<svg version="1.1" width="60px" height="60px" x="0px" y="0px" viewBox="0 0 60 60">
    <polyline fill="none" stroke="#FFF" stroke-width="2" points="4.8,13.7 4.8,4 56.8,4 56.8,13.7 "/>
    <polyline fill="none" stroke="#FFF" stroke-width="2" points="56.8,46.5 56.8,56 4.8,56 4.8,46.5 "/>
    <line fill="none" stroke="#FFF" stroke-width="2" x1="19" y1="19.8" x2="41" y2="41.8"/>
    <line fill="none" stroke="#FFF" stroke-width="2" x1="41" y1="19.8" x2="19" y2="41.8"/>
</svg>`;

/*------------------------------*\
|* Theremin Class
\*------------------------------*/

class Theremin {
    constructor(root) {
        this.root = root;

        this.setupUI();
        this.renderDom();
        this.updateDom();

        this.x = window.innerWidth / 2 * DPR;
        this.y = window.innerWidth / 1.8 * DPR;
        this.w = window.innerWidth;
        this.h = window.innerHeight;

        const AudioCtx = window.AudioContext || window.webkitAudioContext;
        this.audioCtx = new AudioCtx();
        this.visualizer = new Visualizer(this);

        this.setupGyro();
        this.setCanvasSize();
        this.setupMasterGain();
        this.addListeners();
    }

    state = {
        isPlaying: false,
        userInteracting: false, // flag for mouse or touch interaction
    };

    setState(nextState) {
        this.state = Object.assign({}, this.state, nextState);
        this.updateDom();
    }

    setupUI() {
        this.canvas = document.createElement('canvas');
        this.playButton = document.createElement('button');
        this.playButton.className = 'play-btn';
        this.gyroButton = document.createElement('button');
        this.gyroButton.className = 'gyro-btn';
    }

    setupGyro() {
        // Gyro
        const gn = new GyroNorm();

        const args = {
            frequency: 50, // ( How often the object sends the values - milliseconds )
            gravityNormalized: true, // ( If the gravity related values to be normalized )
            orientationBase: GyroNorm.GAME,
            decimalCount: 3, // ( How many digits after the decimal point will there be in the return values )
            logger: null, // ( Function to be called to log messages from gyronorm.js )
            screenAdjusted: false, // ( If set to true it will return screen adjusted values. )
        };

        gn
            .init(args)
            .then(() => {
                gn.start(this.handleGyro);
            })
            .catch(e => {
                console.warn(
                    'Error: Device does not support DeviceOrientation or DeviceMotion is not supported by the browser or device'
                );
            });
    }

    addListeners() {
        ['mousedown', 'touchstart'].forEach(event => {
            this.canvas.addEventListener(
                event,
                this.handleInteractStart,
                false
            );
        });
        ['mouseup', 'touchend'].forEach(event => {
            this.canvas.addEventListener(event, this.handleInteractEnd, false);
        });
        ['mousemove', 'touchmove'].forEach((event, touch) => {
            this.canvas.addEventListener(event, this.handleInteractMove, false);
        });

        window.addEventListener('resize', this.handlerResize, false);
        this.playButton.addEventListener('click', this.handlePlayButton, false);
        this.gyroButton.addEventListener('click', this.handleGyroButton, false);
    }

    setupMasterGain() {
        console.log('master gain setup')
        this.masterGainNode = this.audioCtx.createGain();
        this.masterGainNode.connect(this.audioCtx.destination);
        this.masterGainNode.gain.value = 0;
    }
    
    setGain(value) {
        // cancel any future value
        const currentTime = this.audioCtx.currentTime;
        this.masterGainNode.gain.cancelScheduledValues(currentTime);
        this.masterGainNode.gain.value = value;
    }

    updateGain(nextGain, cb) {
        if (typeof nextGain === "undefined") {
            nextGain = scaleBetween(this.y, 0, 1, 0, this.h);
        }
        
        const rampTime = 0.1;
        const prevGain = this.masterGainNode.gain.value;
        const currentTime = this.audioCtx.currentTime;
        const endTime = currentTime + rampTime;
        this.masterGainNode.gain.cancelScheduledValues(currentTime);
        this.masterGainNode.gain.setValueAtTime(prevGain, currentTime);
        this.masterGainNode.gain.linearRampToValueAtTime(nextGain, endTime);
        
        // probably a nicer way to do this without callback nonsense...
        if (typeof cb === 'function') {
            if (this.gainTimeout) {
                clearTimeout(this.gainTimeout);
            }
            this.gainTimeout = setTimeout(() => {
                this.gainTimeout = null;
                cb()
            }, rampTime * 1000);
        }
    }

    setFreq() {
        const frequency = scaleBetween(this.x, FREQ_LOW, FREQ_HIGH, 0, this.w);
        this.osc.frequency.value = frequency;
    }

    setCanvasSize() {
        this.w = window.innerWidth * DPR;
        this.h = window.innerHeight * DPR;

        this.canvas.width = this.w;
        this.canvas.height = this.h;
        this.canvas.style.width = window.innerWidth + 'px';
        this.canvas.style.height = window.innerHeight + 'px';
    }

    // Interaction and Event Handlers

    handlerResize = () => {
        this.setCanvasSize();
    };

    handleInteractStart = e => {
        e.stopPropagation();

        if (!this.state.userInteracting) {
            this.setState({
                userInteracting: true,
            });
        }
        
        if (this.state.isPlaying) {
            this.stop();
        } else {
            this.play();
        }
    };

    handleInteractEnd = () => {
        this.stop();
    };

    handlePlayButton = (e) => {
        e.stopPropagation();
        this.state.isPlaying ? this.stop() : this.play();
    };

    handleGyroButton = () => {
        this.setState({
            userInteracting: !this.state.userInteracting,
        });
    };

    handleGyro = data => {
        if (this.state.userInteracting) return;

        this.x = scaleBetween(data.do.gamma, 0, this.w, -90, 90);
        this.y = scaleBetween(data.do.beta, 0, this.w, -45, 45);

        this.updateOsc();
    };

    handleInteractMove = (event, touch) => {
        if (!this.state.userInteracting) {
            this.setState({
                userInteracting: !this.state.userInteracting,
            });
        }

        if (event.targetTouches) {
            event.preventDefault();
            this.x = event.targetTouches[0].clientX * DPR;
            this.y = event.targetTouches[0].clientY * DPR;
        } else {
            this.x = event.clientX * DPR;
            this.y = event.clientY * DPR;
        }

        this.updateOsc();
    };

    // Audio Playback

    play = () => {
        if (this.osc) {
            this.osc.stop();
            this.osc = null;
        }
        
        if (this.gainTimeout) return; // wait for any fading gains
        
        this.setState({
            isPlaying: true,
        });
        
        this.updateGain();
        
        // new osc
        this.osc = this.audioCtx.createOscillator();
        this.setFreq();
        this.osc.connect(this.masterGainNode);
        this.osc.start();

        return this.osc;
    };

    stop = () => {
        this.updateGain(0, () => {            
            this.setState({
                isPlaying: false,
            });
            this.osc.stop();
            this.osc = null;
        });
    };

    updateOsc() {
        if (this.osc && !this.gainTimeout) {
            this.updateGain();
            this.setFreq();
        }
    }

    // DOM View

    renderDom() {
        this.root.appendChild(this.canvas);
        this.root.appendChild(this.playButton);
        this.root.appendChild(this.gyroButton);
    }

    updateDom() {
        this.playButton.innerHTML = this.state.isPlaying ? oscOff : oscOn;
        this.gyroButton.innerHTML = this.state.userInteracting
            ? gyroOnIcon
            : gyroOffIcon;
    }
}

/*------------------------------*\
|* Visualizer
\*------------------------------*/

class Visualizer {
    constructor(theremin) {
        this.theremin = theremin;
        this.ctx = this.theremin.canvas.getContext('2d');
        this.ctx.scale(DPR, DPR);
        this.tick = 0;

        this.draw();
    }

    drawOsc() {
        const xAxis = this.theremin.h / 2;

        this.ctx.beginPath();
        this.ctx.lineJoin = 'round';
        this.ctx.lineWidth = 2 * DPR;
        this.ctx.strokeStyle = '#222';
        this.ctx.moveTo(0, xAxis);

        // Draw Oscillator or flat line
        if (this.theremin.osc) {
            const phase = this.tick * Math.PI / 180 * this.theremin.w / 8;

            const amplitude =
                this.theremin.masterGainNode.gain.value * this.theremin.h / 4;
            const frequency =
                this.theremin.osc.frequency.value /
                this.theremin.w *
                this.theremin.w /
                10;

            const step = 1;
            const c = this.theremin.w / Math.PI / (frequency * 2);

            for (let i = 0; i < this.theremin.w; i += step) {
                const y = amplitude * Math.sin(i / c + phase);
                this.ctx.lineTo(i, xAxis + y);
            }

            this.ctx.stroke();
        } else {
            this.ctx.lineTo(this.theremin.w, xAxis);
            this.ctx.stroke();
        }
    }

    drawBackground() {
        const { x, y, w, h } = this.theremin;
        const w2 = w / 2;
        const h2 = h / 2;

        // this.ctx.fillStyle = '#FFFFFF';
        // this.ctx.fillRect(0, 0, w, h);

        const r1 = Math.floor(scaleBetween(y, 50, 155, h, 0));
        const g1 = Math.floor(scaleBetween(y, 200, 50, h, 0));
        const b1 = Math.floor(scaleBetween(x, 100, 255, 0, w));

        const r2 = Math.floor(scaleBetween(y, 95, 255, 0, h));
        const g2 = Math.floor(scaleBetween(y, 155, 95, 0, h));
        const b2 = Math.floor(scaleBetween(x, 95, 255, 0, w));

        const color1 = `rgb(${r1}, ${g1}, ${b1})`;
        const color2 = `rgb(${r2}, ${g2}, ${b2})`;

        const r = Math.max(w, h) * 2;

        const grad1 = this.ctx.createRadialGradient(w2, h2, r, x, y, 0);
        grad1.addColorStop(0, color1);
        grad1.addColorStop(1, color2);
        this.ctx.fillStyle = grad1;
        this.ctx.fillRect(0, 0, w, h);
    }

    drawPoint() {
        const r1 = 16 * DPR;
        const r2 = 2 * DPR;
        this.ctx.lineWidth = 2 * DPR;
        this.ctx.strokeStyle = '#222';
        this.ctx.beginPath();
        this.ctx.arc(
            this.theremin.x,
            this.theremin.y,
            r1,
            0,
            Math.PI * 2,
            true
        );
        this.ctx.closePath();
        this.ctx.stroke();

        this.ctx.fillStyle = '#FFFFFF';
        this.ctx.beginPath();
        this.ctx.arc(
            this.theremin.x,
            this.theremin.y,
            r2,
            0,
            Math.PI * 2,
            true
        );
        this.ctx.closePath();
        this.ctx.fill();
    }

    drawText() {
        const ms = Math.min(this.theremin.w, this.theremin.h);
        const size = ms / 12;
        this.ctx.font = `900 italic ${size}px futura-pt, futura, sans-serif`;
        this.ctx.textAlign = 'center';
        this.ctx.fillStyle = 'white';
        
        const copy = 'Theremin Oscillator';
        this.ctx.fillText(copy, this.theremin.w / 2, this.theremin.h / 2 + size / 3);
    }
    
    // Animation Loop

    draw = () => {
        this.drawBackground();
        this.drawOsc();
        this.drawText();
        this.drawPoint();

        ++this.tick;

        window.requestAnimationFrame(this.draw);
    };
}

const root = document.getElementById('root');

const theremin = new Theremin(root);

            
          
!
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