celebration.js

function celebrate(){

	const urlParams = new URLSearchParams(window.location.search);
	const name = urlParams.get('name');
	var w = c.width = window.innerWidth,
	h = c.height = window.innerHeight,
	ctx = c.getContext( '2d' ),

		hw = w / 2, // half-width
		hh = h / 2,
		
		opts = {
			strings: [ 'HAPPY', 'BIRTHDAY!',name ],
			charSize: 30,
			charSpacing: 35,
			lineHeight: 40,
			
			cx: w / 2,
			cy: h / 2,
			
			fireworkPrevPoints: 10,
			fireworkBaseLineWidth: 5,
			fireworkAddedLineWidth: 8,
			fireworkSpawnTime: 200,
			fireworkBaseReachTime: 30,
			fireworkAddedReachTime: 30,
			fireworkCircleBaseSize: 20,
			fireworkCircleAddedSize: 10,
			fireworkCircleBaseTime: 30,
			fireworkCircleAddedTime: 30,
			fireworkCircleFadeBaseTime: 10,
			fireworkCircleFadeAddedTime: 5,
			fireworkBaseShards: 5,
			fireworkAddedShards: 5,
			fireworkShardPrevPoints: 3,
			fireworkShardBaseVel: 4,
			fireworkShardAddedVel: 2,
			fireworkShardBaseSize: 3,
			fireworkShardAddedSize: 3,
			gravity: .1,
			upFlow: -.1,
			letterContemplatingWaitTime: 360,
			balloonSpawnTime: 20,
			balloonBaseInflateTime: 10,
			balloonAddedInflateTime: 10,
			balloonBaseSize: 20,
			balloonAddedSize: 20,
			balloonBaseVel: .4,
			balloonAddedVel: .4,
			balloonBaseRadian: -( Math.PI / 2 - .5 ),
			balloonAddedRadian: -1,
		},
		calc = {
			totalWidth: opts.charSpacing * Math.max( opts.strings[0].length, opts.strings[1].length )
		},
		
		Tau = Math.PI * 2,
		TauQuarter = Tau / 4,
		
		letters = [];

		ctx.font = opts.charSize + 'px Verdana';

		function Letter( char, x, y ){
			this.char = char;
			this.x = x;
			this.y = y;

			this.dx = -ctx.measureText( char ).width / 2;
			this.dy = +opts.charSize / 2;

			this.fireworkDy = this.y - hh;

			var hue = x / calc.totalWidth * 360;

			this.color = 'hsl(hue,80%,50%)'.replace( 'hue', hue );
			this.lightAlphaColor = 'hsla(hue,80%,light%,alp)'.replace( 'hue', hue );
			this.lightColor = 'hsl(hue,80%,light%)'.replace( 'hue', hue );
			this.alphaColor = 'hsla(hue,80%,50%,alp)'.replace( 'hue', hue );

			this.reset();
		}
		Letter.prototype.reset = function(){

			this.phase = 'firework';
			this.tick = 0;
			this.spawned = false;
			this.spawningTime = opts.fireworkSpawnTime * Math.random() |0;
			this.reachTime = opts.fireworkBaseReachTime + opts.fireworkAddedReachTime * Math.random() |0;
			this.lineWidth = opts.fireworkBaseLineWidth + opts.fireworkAddedLineWidth * Math.random();
			this.prevPoints = [ [ 0, hh, 0 ] ];
		}
		Letter.prototype.step = function(){

			if( this.phase === 'firework' ){

				if( !this.spawned ){

					++this.tick;
					if( this.tick >= this.spawningTime ){

						this.tick = 0;
						this.spawned = true;
					}

				} else {

					++this.tick;

					var linearProportion = this.tick / this.reachTime,
					armonicProportion = Math.sin( linearProportion * TauQuarter ),
					
					x = linearProportion * this.x,
					y = hh + armonicProportion * this.fireworkDy;

					if( this.prevPoints.length > opts.fireworkPrevPoints )
						this.prevPoints.shift();

					this.prevPoints.push( [ x, y, linearProportion * this.lineWidth ] );

					var lineWidthProportion = 1 / ( this.prevPoints.length - 1 );

					for( var i = 1; i < this.prevPoints.length; ++i ){

						var point = this.prevPoints[ i ],
						point2 = this.prevPoints[ i - 1 ];

						ctx.strokeStyle = this.alphaColor.replace( 'alp', i / this.prevPoints.length );
						ctx.lineWidth = point[ 2 ] * lineWidthProportion * i;
						ctx.beginPath();
						ctx.moveTo( point[ 0 ], point[ 1 ] );
						ctx.lineTo( point2[ 0 ], point2[ 1 ] );
						ctx.stroke();

					}

					if( this.tick >= this.reachTime ){

						this.phase = 'contemplate';

						this.circleFinalSize = opts.fireworkCircleBaseSize + opts.fireworkCircleAddedSize * Math.random();
						this.circleCompleteTime = opts.fireworkCircleBaseTime + opts.fireworkCircleAddedTime * Math.random() |0;
						this.circleCreating = true;
						this.circleFading = false;

						this.circleFadeTime = opts.fireworkCircleFadeBaseTime + opts.fireworkCircleFadeAddedTime * Math.random() |0;
						this.tick = 0;
						this.tick2 = 0;

						this.shards = [];

						var shardCount = opts.fireworkBaseShards + opts.fireworkAddedShards * Math.random() |0,
						angle = Tau / shardCount,
						cos = Math.cos( angle ),
						sin = Math.sin( angle ),
						
						x = 1,
						y = 0;

						for( var i = 0; i < shardCount; ++i ){
							var x1 = x;
							x = x * cos - y * sin;
							y = y * cos + x1 * sin;

							this.shards.push( new Shard( this.x, this.y, x, y, this.alphaColor ) );
						}
					}

				}
			} else if( this.phase === 'contemplate' ){

				++this.tick;

				if( this.circleCreating ){

					++this.tick2;
					var proportion = this.tick2 / this.circleCompleteTime,
					armonic = -Math.cos( proportion * Math.PI ) / 2 + .5;

					ctx.beginPath();
					ctx.fillStyle = this.lightAlphaColor.replace( 'light', 50 + 50 * proportion ).replace( 'alp', proportion );
					ctx.beginPath();
					ctx.arc( this.x, this.y, armonic * this.circleFinalSize, 0, Tau );
					ctx.fill();

					if( this.tick2 > this.circleCompleteTime ){
						this.tick2 = 0;
						this.circleCreating = false;
						this.circleFading = true;
					}
				} else if( this.circleFading ){

					ctx.fillStyle = this.lightColor.replace( 'light', 70 );
					ctx.fillText( this.char, this.x + this.dx, this.y + this.dy );

					++this.tick2;
					var proportion = this.tick2 / this.circleFadeTime,
					armonic = -Math.cos( proportion * Math.PI ) / 2 + .5;

					ctx.beginPath();
					ctx.fillStyle = this.lightAlphaColor.replace( 'light', 100 ).replace( 'alp', 1 - armonic );
					ctx.arc( this.x, this.y, this.circleFinalSize, 0, Tau );
					ctx.fill();

					if( this.tick2 >= this.circleFadeTime )
						this.circleFading = false;

				} else {

					ctx.fillStyle = this.lightColor.replace( 'light', 70 );
					ctx.fillText( this.char, this.x + this.dx, this.y + this.dy );
				}

				for( var i = 0; i < this.shards.length; ++i ){

					this.shards[ i ].step();

					if( !this.shards[ i ].alive ){
						this.shards.splice( i, 1 );
						--i;
					}
				}

				if( this.tick > opts.letterContemplatingWaitTime ){

					this.phase = 'balloon';

					this.tick = 0;
					this.spawning = true;
					this.spawnTime = opts.balloonSpawnTime * Math.random() |0;
					this.inflating = false;
					this.inflateTime = opts.balloonBaseInflateTime + opts.balloonAddedInflateTime * Math.random() |0;
					this.size = opts.balloonBaseSize + opts.balloonAddedSize * Math.random() |0;

					var rad = opts.balloonBaseRadian + opts.balloonAddedRadian * Math.random(),
					vel = opts.balloonBaseVel + opts.balloonAddedVel * Math.random();

					this.vx = Math.cos( rad ) * vel;
					this.vy = Math.sin( rad ) * vel;
				}
			} else if( this.phase === 'balloon' ){

				ctx.strokeStyle = this.lightColor.replace( 'light', 80 );

				if( this.spawning ){

					++this.tick;
					ctx.fillStyle = this.lightColor.replace( 'light', 70 );
					ctx.fillText( this.char, this.x + this.dx, this.y + this.dy );

					if( this.tick >= this.spawnTime ){
						this.tick = 0;
						this.spawning = false;
						this.inflating = true;	
					}
				} else if( this.inflating ){

					++this.tick;

					var proportion = this.tick / this.inflateTime,
					x = this.cx = this.x,
					y = this.cy = this.y - this.size * proportion;

					ctx.fillStyle = this.alphaColor.replace( 'alp', proportion );
					ctx.beginPath();
					generateBalloonPath( x, y, this.size * proportion );
					ctx.fill();

					ctx.beginPath();
					ctx.moveTo( x, y );
					ctx.lineTo( x, this.y );
					ctx.stroke();

					ctx.fillStyle = this.lightColor.replace( 'light', 70 );
					ctx.fillText( this.char, this.x + this.dx, this.y + this.dy );

					if( this.tick >= this.inflateTime ){
						this.tick = 0;
						this.inflating = false;
					}

				} else {

					this.cx += this.vx;
					this.cy += this.vy += opts.upFlow;

					ctx.fillStyle = this.color;
					ctx.beginPath();
					generateBalloonPath( this.cx, this.cy, this.size );
					ctx.fill();

					ctx.beginPath();
					ctx.moveTo( this.cx, this.cy );
					ctx.lineTo( this.cx, this.cy + this.size );
					ctx.stroke();

					ctx.fillStyle = this.lightColor.replace( 'light', 70 );
					ctx.fillText( this.char, this.cx + this.dx, this.cy + this.dy + this.size );

					if( this.cy + this.size < -hh || this.cx < -hw || this.cy > hw  )
						this.phase = 'done';

				}
			}
		}
		function Shard( x, y, vx, vy, color ){

			var vel = opts.fireworkShardBaseVel + opts.fireworkShardAddedVel * Math.random();

			this.vx = vx * vel;
			this.vy = vy * vel;

			this.x = x;
			this.y = y;

			this.prevPoints = [ [ x, y ] ];
			this.color = color;

			this.alive = true;

			this.size = opts.fireworkShardBaseSize + opts.fireworkShardAddedSize * Math.random();
		}
		Shard.prototype.step = function(){

			this.x += this.vx;
			this.y += this.vy += opts.gravity;

			if( this.prevPoints.length > opts.fireworkShardPrevPoints )
				this.prevPoints.shift();

			this.prevPoints.push( [ this.x, this.y ] );

			var lineWidthProportion = this.size / this.prevPoints.length;

			for( var k = 0; k < this.prevPoints.length - 1; ++k ){

				var point = this.prevPoints[ k ],
				point2 = this.prevPoints[ k + 1 ];

				ctx.strokeStyle = this.color.replace( 'alp', k / this.prevPoints.length );
				ctx.lineWidth = k * lineWidthProportion;
				ctx.beginPath();
				ctx.moveTo( point[ 0 ], point[ 1 ] );
				ctx.lineTo( point2[ 0 ], point2[ 1 ] );
				ctx.stroke();

			}

			if( this.prevPoints[ 0 ][ 1 ] > hh )
				this.alive = false;
		}
		function generateBalloonPath( x, y, size ){

			ctx.moveTo( x, y );
			ctx.bezierCurveTo( x - size / 2, y - size / 2,
				x - size / 4, y - size,
				x,            y - size );
			ctx.bezierCurveTo( x + size / 4, y - size,
				x + size / 2, y - size / 2,
				x,            y );
		}

		function anim(){

			window.requestAnimationFrame( anim );

			ctx.fillStyle = '#111';
			ctx.fillRect( 0, 0, w, h );

			ctx.translate( hw, hh );

			var done = true;
			for( var l = 0; l < letters.length; ++l ){

				letters[ l ].step();
				if( letters[ l ].phase !== 'done' )
					done = false;
			}

			ctx.translate( -hw, -hh );

			if( done )
				for( var l = 0; l < letters.length; ++l )
					letters[ l ].reset();
			}

			for( var i = 0; i < opts.strings.length; ++i ){
				for( var j = 0; j < opts.strings[ i ].length; ++j ){
					letters.push( new Letter( opts.strings[ i ][ j ], 
						j * opts.charSpacing + opts.charSpacing / 2 - opts.strings[ i ].length * opts.charSize / 2,
						i * opts.lineHeight + opts.lineHeight / 2 - opts.strings.length * opts.lineHeight / 2 ) );
				}
			}

			anim();

			window.addEventListener( 'resize', function(){

				w = c.width = window.innerWidth;
				h = c.height = window.innerHeight;

				hw = w / 2;
				hh = h / 2;

				ctx.font = opts.charSize + 'px Verdana';
			})

		}