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//==//==============//
		// canvas setup //
//==//==============//

var ctx = c.getContext( '2d' ),
    width = c.width = window.innerWidth,
    height = c.height = window.innerHeight,
    
//==//==================//
    // a few parameters //
//==//==================//
    
    particleCount = ( width / 2 ) |0,
    obstacleCount = ( ( width + height ) / 20 ) |0,
    obstacleRadius = 50,
    gravity = .1,

//==//========================//
    // other needed variables //
//==//========================//
    
		particles = [],
    obstacles = [],
    frame = 0,
    tau = Math.PI * 2,
    centerX = ( width / 2 ) |0,
    centerY = ( height / 2 ) |0,
    
//==//=========================//
    // initialization function //
//==//=========================//
    
    init = function( ) {
      
      // initial fade to cancel repaint leftover lines, pointed out by the great lemon
      ctx.fillStyle = '#222';
      ctx.fillRect( 0, 0, width, height );
      
      while( --particleCount ) particles.push( new Particle );
      while( --obstacleCount ) obstacles.push( new Obstacle );
      
      anim();
    },
    
//==//===================================//
    // animation loop and main functions //
//==//===================================//
    
    anim = function( ) {
      
      window.requestAnimationFrame( anim );
      
      step( );
      draw( );
    },
    step = function( ) {
      
      particles.map( function( particle ) { particle.step( ); } );
      obstacles.map( function( obstacle ) { obstacle.step( ); } );
    },
    draw = function( ) {
      
      ctx.save();
      ctx.globalCompositeOperation = 'destination-out';
      ctx.shadowBlur = 0;
      ctx.fillStyle = 'rgba(0, 0, 0, .1)';
      ctx.fillRect( 0, 0, width, height );
      ctx.globalCompositeOperation = 'lighter';
      
      ctx.translate( centerX, centerY );
      particles.map( function( particle ) { particle.draw( ); } );
      
      
      ctx.globalCompositeOperation = 'source-over';
      ctx.fillStyle = 'rgba(25, 25, 25, .2)';
      // purposely didn't change ctx.shadowColor
      
      obstacles.map( function( obstacle ) { obstacle.draw( ); } );
      ctx.restore();
    },
    spawnNew = function( x, y ) {
      
      var part = new Particle;
      part.x = x;
      part.y = y;
      particles.push( part );
    },

//==//===================//
    // utility functions //
//==//===================//
    
		checkDistance = function( par, obs ) {
      
      var x = par.x - obs.x,
          y = par.y - obs.y,
          d = obs.radius;
      
      return d*d >= x*x + y*y;
    },
    rand = function( min, max ) {
      
      return Math.random( ) * ( max - min ) + min;
    },
    validateObstacleResize = function( obs ) {
      obs.validateResize( );
    },
    
//==//====================================//
    // Particle and Obstacle constructors //
//==//====================================//
    
    Particle = function( ) { this.reset( ); },
    Obstacle = function( ) { this.reset( ); };

Particle.prototype = {
  
  reset: function( ) {
    
    var radiant = Math.random() * tau;
    
    this.vx = this.x = Math.cos( radiant );
    this.vy = this.y = Math.sin( radiant );
    
    this.shine = 0;
    this.last = { x: this.x, y: this.y };
    
    this.color = 'hsla(hue, 80%, 50%, alp)'
      .replace( 'hue', ( frame + 360 * radiant / tau ) |0 );
  },
  
  step: function( ) {
    
    if(this.shine) --this.shine;
    
    this.last.x = this.x;
    this.last.y = this.y;
    
    var rad = Math.atan( this.y / this.x );
    if( this.x < 0 ) rad += Math.PI;
    
    this.x += this.vx += Math.cos( rad ) * gravity;
    this.y += this.vy += Math.sin( rad ) * gravity;
      
    if( this.y < -centerY || this.y > centerY ||
        this.x < -centerX || this.x > centerX ) {
      
      frame += .3;
      this.reset( );
    }
    
    var len = obstacles.length;
    while( --len + 1 ) {
      if( checkDistance( this, obstacles[ len ] ) ) {
        
        this.hit( obstacles[ len ] );
        len = 0;
      }
    }
  },
  
  hit: function( obs ) {
    
    this.vx = ( this.x - obs.x ) * rand( .05, .01 );
    this.vy = ( this.y - obs.y ) * rand( .05, .01 );
    
    this.shine = 2;
    ++obs.toRemove;
  },
  
  draw: function( ) {
    
    ctx.strokeStyle = this.color.replace( 'alp', .4 );
    ctx.beginPath( );
    ctx.moveTo( this.last.x, this.last.y );
    ctx.lineTo( this.x , this.y );
    ctx.stroke( );
    
    if( this.shine ) {
      
      ctx.shadowColor = ctx.strokeStyle;
      ctx.shadowBlur = this.shine * 3;
      ctx.fillStyle = this.color.replace( 'alp', .05 );
      ctx.beginPath( );
      ctx.arc( this.x |0, this.y |0, this.shine * 8, 0, tau );
      ctx.fill( );
    } else ctx.shadowBlur = 0;
  }
}
Obstacle.prototype = {
  
  reset: function( ) {
    
    this.x = rand( -centerX, centerX ) |0;
  	this.y = rand( -centerY, centerY ) |0;
    
    this.maxRadius = rand( obstacleRadius / 2, obstacleRadius ) |0;
    this.radius = rand( this.maxRadius / 2, this.maxRadius );
    
    this.new = 30;
    this.toRemove = 0;
	},
  
  step: function( ) {
    
    if( this.new ) this.new -= 5;
    
    if( this.toRemove ) {
      
      --this.radius;
      --this.toRemove;
      
      if( this.radius < 0) this.reset( );
      
    } else if ( this.radius < this.maxRadius ) ++this.radius;
    
  },
  
  draw: function( ) {
    
    ctx.shadowBlur = this.new;
    ctx.beginPath( );
    ctx.arc( this.x, this.y, this.radius, 0, tau );
    ctx.fill( );
  },
  
  validateResize: function( ) {
    
    if( this.x > centerX ||-this.y > centerY ||
       -this.x > centerX || this.y > centerY ) this.reset( );
  }
}

//==//=================//
		// and here we go! //
//==//=================//

init( );

//==//================//
    // resize handler //
//==//================//

window.addEventListener( 'resize', function( ) {
  width = c.width = window.innerWidth;
  height = c.height = window.innerHeight;
  
  centerX = width / 2;
  centerY = height / 2;
  
  ctx.fillStyle = '#222';
  ctx.fillRect( 0, 0, width, height );
  
  obstacles.map( validateObstacleResize );
} );

//==//==============//
		// add on click //
//==//==============//

window.addEventListener( 'click', function( e ) {
  
  centerX = e.clientX;
  centerY = e.clientY;
  
  for( var i = 0; i < 10; ++i ) particles.push( new Particle );
} );

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