why-cant-we-deploy-today/js/playback.js

/**
 * Constructor for the playback component, which displays
 * play/pause/progress controls.
 *
 * @param {HTMLElement} container The component will append
 * itself to this
 * @param {function} progressCheck A method which will be
 * called frequently to get the current progress on a range
 * of 0-1
 */
export default class Playback {

	constructor( container, progressCheck ) {

		// Cosmetics
		this.diameter = 100;
		this.diameter2 = this.diameter/2;
		this.thickness = 6;

		// Flags if we are currently playing
		this.playing = false;

		// Current progress on a 0-1 range
		this.progress = 0;

		// Used to loop the animation smoothly
		this.progressOffset = 1;

		this.container = container;
		this.progressCheck = progressCheck;

		this.canvas = document.createElement( 'canvas' );
		this.canvas.className = 'playback';
		this.canvas.width = this.diameter;
		this.canvas.height = this.diameter;
		this.canvas.style.width = this.diameter2 + 'px';
		this.canvas.style.height = this.diameter2 + 'px';
		this.context = this.canvas.getContext( '2d' );

		this.container.appendChild( this.canvas );

		this.render();

	}

	setPlaying( value ) {

		const wasPlaying = this.playing;

		this.playing = value;

		// Start repainting if we weren't already
		if( !wasPlaying && this.playing ) {
			this.animate();
		}
		else {
			this.render();
		}

	}

	animate() {

		const progressBefore = this.progress;

		this.progress = this.progressCheck();

		// When we loop, offset the progress so that it eases
		// smoothly rather than immediately resetting
		if( progressBefore > 0.8 && this.progress < 0.2 ) {
			this.progressOffset = this.progress;
		}

		this.render();

		if( this.playing ) {
			requestAnimationFrame( this.animate.bind( this ) );
		}

	}

	/**
	 * Renders the current progress and playback state.
	 */
	render() {

		let progress = this.playing ? this.progress : 0,
			radius = ( this.diameter2 ) - this.thickness,
			x = this.diameter2,
			y = this.diameter2,
			iconSize = 28;

		// Ease towards 1
		this.progressOffset += ( 1 - this.progressOffset ) * 0.1;

		const endAngle = ( - Math.PI / 2 ) + ( progress * ( Math.PI * 2 ) );
		const startAngle = ( - Math.PI / 2 ) + ( this.progressOffset * ( Math.PI * 2 ) );

		this.context.save();
		this.context.clearRect( 0, 0, this.diameter, this.diameter );

		// Solid background color
		this.context.beginPath();
		this.context.arc( x, y, radius + 4, 0, Math.PI * 2, false );
		this.context.fillStyle = 'rgba( 0, 0, 0, 0.4 )';
		this.context.fill();

		// Draw progress track
		this.context.beginPath();
		this.context.arc( x, y, radius, 0, Math.PI * 2, false );
		this.context.lineWidth = this.thickness;
		this.context.strokeStyle = 'rgba( 255, 255, 255, 0.2 )';
		this.context.stroke();

		if( this.playing ) {
			// Draw progress on top of track
			this.context.beginPath();
			this.context.arc( x, y, radius, startAngle, endAngle, false );
			this.context.lineWidth = this.thickness;
			this.context.strokeStyle = '#fff';
			this.context.stroke();
		}

		this.context.translate( x - ( iconSize / 2 ), y - ( iconSize / 2 ) );

		// Draw play/pause icons
		if( this.playing ) {
			this.context.fillStyle = '#fff';
			this.context.fillRect( 0, 0, iconSize / 2 - 4, iconSize );
			this.context.fillRect( iconSize / 2 + 4, 0, iconSize / 2 - 4, iconSize );
		}
		else {
			this.context.beginPath();
			this.context.translate( 4, 0 );
			this.context.moveTo( 0, 0 );
			this.context.lineTo( iconSize - 4, iconSize / 2 );
			this.context.lineTo( 0, iconSize );
			this.context.fillStyle = '#fff';
			this.context.fill();
		}

		this.context.restore();

	}

	on( type, listener ) {
		this.canvas.addEventListener( type, listener, false );
	}

	off( type, listener ) {
		this.canvas.removeEventListener( type, listener, false );
	}

	destroy() {

		this.playing = false;

		if( this.canvas.parentNode ) {
			this.container.removeChild( this.canvas );
		}

	}

}