vumeter/vumeter.html at master · martincameron/vumeter · GitHub

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<!DOCTYPE html>
<!-- Analogue VU Meter (c) 2020 mumart@gmail.com -->
<html>
	<head>
		<meta charset="UTF-8">
		<script lang="Javascript">
			function SprungMass( mass, spring, damping ) {
				var x = 0, v = 0;
				// Model a sprung mass for the specified number of milliseconds.
				this.model = function( force, xMin, xMax, millis ) {
					for( var t = 0; t < millis; t++ ) {
						if( x < xMin ) {
							x = xMin;
							if( v < 0 ) {
								v = -v;
							}
						}
						if( x > xMax ) {
							x = xMax;
							if( v > 0 ) {
								v = -v;
							}
						}
						var a = ( force - spring * x - damping * v ) / mass; // Acceleration due to force.
						v = v + a * 0.001; // Change in velocity due to acceleration.
						x = x + v * 0.001; // Change in displacement due to velocity.
					}
					return x;
				}
			}

			function init() {
				leftSpring = new SprungMass( 0.005, 1, 0.08 );
				rightSpring = new SprungMass( 0.005, 1, 0.08 );
				leftForce = 0;
				rightForce = 0;

				canvas = document.getElementById("canvas");
				context = canvas.getContext("2d");

				drawMeter( context, canvas.width / 2 );
				background = context.getImageData( 0, 0, canvas.width / 2, canvas.width / 4 );

				time = performance.now();
				requestAnimationFrame(repaint);

				navigator.mediaDevices.getUserMedia( { audio:true, video:false } ).then( openAudio );
			}

			function openAudio( mediaStream ) {
				var audioContext = new AudioContext();
				var mediaStreamSource = audioContext.createMediaStreamSource( mediaStream );
				var scriptProcessor = audioContext.createScriptProcessor( 1024, 2, 0 );
				scriptProcessor.onaudioprocess = onAudioProcess;
				mediaStreamSource.connect( scriptProcessor );
			}

			function drawMeter( context, width ) {
				// Draw background.
				var gradient = context.createLinearGradient( 0, 0, 0, canvas.height );
				gradient.addColorStop(0, '#806633');
				gradient.addColorStop(1, '#FFCC66');
				context.fillStyle = gradient;
				context.fillRect(0, 0, width, width / 2 );
				// Draw bottom box.
				context.fillStyle = 'black';
				context.fillRect( width * 5 / 16, width * 6 / 16, width * 6 / 16, 1 );
				context.fillRect( width * 5 / 16, width * 7 / 16, width * 6 / 16, 1 );
				context.fillRect( width * 5 / 16, width * 6 / 16, 1, width / 16 );
				context.fillRect( width * 11 / 16, width * 6 / 16, 1, width / 16 );
				// Draw ruler.
				var x = width / 16;
				var y = width / 8;
				var w = width * 14 / 16;
				var h = width / 16;
				var segmentWidth = Math.round( w / 7 );
				// First black segment
				context.fillRect( x, y, segmentWidth, h );
				// Ruler segments
				for( var n = x + segmentWidth; n < x + segmentWidth * 6; n += segmentWidth ){
					context.fillRect( n, y, segmentWidth, 1 );
					// Big marks
					context.fillRect( n, y, 1, h );
					// Small marks
					if( segmentWidth >= 12 ) {
						for( var v = 1; v < 6; v++ ) {
							context.fillRect( n + Math.round( segmentWidth * v / 6 ), y, 1, h / 2 );
						}
					}
				}
				// End red segment
				context.fillStyle = '#AA0000';
				context.fillRect( x + segmentWidth * 6, y, segmentWidth, h );
			}

			function drawNeedle( context, x, width, deflection ) {
				var angle = deflection * Math.PI / 2 - Math.PI / 4;
				var x1 = width / 2 + width * 8 / 16 * Math.sin( angle );
				var y1 = width * 9 / 16 - width * 8 / 16 * Math.cos( angle );
				var x2 = width / 2 + width * 3 / 16 * Math.tan( angle );
				var y2 = width * 3 / 8;
				context.beginPath();
				context.moveTo( x + x1, y1 );
				context.lineTo( x + x2, y2 );
				context.stroke();
			}

			function onAudioProcess( event ) {
				leftForce = getForce( getMaxAmplitude( event.inputBuffer.getChannelData( 0 ) ) );
				rightForce = getForce( getMaxAmplitude( event.inputBuffer.getChannelData( 1 ) ) );
			}

			function getForce( amplitude ) {
				// 6DBA = 10 ^ 0.3 ~= 1.995
				var force = ( Math.log( amplitude ) / Math.log( 1.995 ) + 7 ) / 7;
				if( force < 0 ) {
					force = 0;
				}
				// Correct for straight ruler-marks.
				return ( Math.atan( force * 2 - 1 ) * 4 / Math.PI + 1 ) / 2;
			}

			function getMaxAmplitude( audioBuf ) {
				var maxAmp = 0;
				for( var idx = 0, len = audioBuf.length; idx < len; idx++ ) {
					var absAmp = Math.abs( audioBuf[ idx ] );
					if( absAmp > maxAmp ) {
						maxAmp = absAmp;
					}
				}
				return maxAmp;
			}

			function repaint( millis ) {
				var width = canvas.width / 2;
				context.putImageData( background, 0, 0 );
				drawNeedle( context, 0, width, leftSpring.model( leftForce, 0, 1, millis - time ) );
				context.putImageData( background, width, 0 );
				drawNeedle( context, width, width, rightSpring.model( rightForce, 0, 1, millis - time ) );
				requestAnimationFrame( repaint );
				time = millis;
			}
		</script>
	</head>
	<body style="background:black" onload="init()">
		<canvas style="display:block;margin-left:auto;margin-right:auto;" id="canvas" width="640" height="160"></canvas>
	</body>
</html>