带交互功能的HTML5+JS烟花特效-阿里云开发者社区

<!DOCTYPE html>
<html dir="ltr" lang="zh-CN">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width" />
<title>带交互功能的HTML5+JS烟花特效</title> 
<style>
/* basic styles for black background and crosshair cursor */
body {
  background: #000;
  margin: 0;
}
canvas {
  cursor: crosshair;
  display: block;
}
</style>
</head>
<canvas id="canvas">Canvas is not supported in your browser.</canvas>
<script>
// when animating on canvas, it is best to use requestAnimationFrame instead of setTimeout or setInterval
// not supported in all browsers though and sometimes needs a prefix, so we need a shim
window.requestAnimFrame = ( function() {
  return window.requestAnimationFrame ||
        window.webkitRequestAnimationFrame ||
        window.mozRequestAnimationFrame ||
        function( callback ) {
          window.setTimeout( callback, 1000 / 60 );
        };
})();
// now we will setup our basic variables for the demo
var canvas = document.getElementById( 'canvas' ),
    ctx = canvas.getContext( '2d' ),
    // full screen dimensions
    cw = window.innerWidth,
    ch = window.innerHeight,
    // firework collection
    fireworks = [],
    // particle collection
    particles = [],
    // starting hue
    hue = 120,
    // when launching fireworks with a click, too many get launched at once without a limiter, one launch per 5 loop ticks
    limiterTotal = 10,
    limiterTick = 0,
    // this will time the auto launches of fireworks, one launch per 80 loop ticks
    timerTotal = 200,
    timerTick = 0,
    mousedown = false,
    // mouse x coordinate,
    mx,
    // mouse y coordinate
    my;
// set canvas dimensions
canvas.width = cw;
canvas.height = ch;
// now we are going to setup our function placeholders for the entire demo
// get a random number within a range
function random( min, max ) {
  return Math.random() * ( max - min ) + min;
}
// calculate the distance between two points
function calculateDistance( p1x, p1y, p2x, p2y ) {
  var xDistance = p1x - p2x,
      yDistance = p1y - p2y;
  return Math.sqrt( Math.pow( xDistance, 2 ) + Math.pow( yDistance, 2 ) );
}
// create firework
function Firework( sx, sy, tx, ty ) {
  // actual coordinates
  this.x = sx;
  this.y = sy;
  // starting coordinates
  this.sx = sx;
  this.sy = sy;
  // target coordinates
  this.tx = tx;
  this.ty = ty;
  // distance from starting point to target
  this.distanceToTarget = calculateDistance( sx, sy, tx, ty );
  this.distanceTraveled = 0;
  // track the past coordinates of each firework to create a trail effect, increase the coordinate count to create more prominent trails
  this.coordinates = [];
  this.coordinateCount = 3;
  // populate initial coordinate collection with the current coordinates
  while( this.coordinateCount-- ) {
    this.coordinates.push( [ this.x, this.y ] );
  }
  this.angle = Math.atan2( ty - sy, tx - sx );
  this.speed = 2;
  this.acceleration = 1.05;
  this.brightness = random( 50, 70 );
  // circle target indicator radius
  this.targetRadius = 1;
}
// update firework
Firework.prototype.update = function( index ) {
  // remove last item in coordinates array
  this.coordinates.pop();
  // add current coordinates to the start of the array
  this.coordinates.unshift( [ this.x, this.y ] );
  // cycle the circle target indicator radius
  if( this.targetRadius < 8 ) {
    this.targetRadius += 0.3;
  } else {
    this.targetRadius = 1;
  }
  // speed up the firework
  this.speed *= this.acceleration;
  // get the current velocities based on angle and speed
  var vx = Math.cos( this.angle ) * this.speed,
      vy = Math.sin( this.angle ) * this.speed;
  // how far will the firework have traveled with velocities applied?
  this.distanceTraveled = calculateDistance( this.sx, this.sy, this.x + vx, this.y + vy );
  // if the distance traveled, including velocities, is greater than the initial distance to the target, then the target has been reached
  if( this.distanceTraveled >= this.distanceToTarget ) {
    createParticles( this.tx, this.ty );
    // remove the firework, use the index passed into the update function to determine which to remove
    fireworks.splice( index, 1 );
  } else {
    // target not reached, keep traveling
    this.x += vx;
    this.y += vy;
  }
}
// draw firework
Firework.prototype.draw = function() {
  ctx.beginPath();
  // move to the last tracked coordinate in the set, then draw a line to the current x and y
  ctx.moveTo( this.coordinates[ this.coordinates.length - 1][ 0 ], this.coordinates[ this.coordinates.length - 1][ 1 ] );
  ctx.lineTo( this.x, this.y );
  ctx.strokeStyle = 'hsl(' + hue + ', 100%, ' + this.brightness + '%)';
  ctx.stroke();
  ctx.beginPath();
  // draw the target for this firework with a pulsing circle
  ctx.arc( this.tx, this.ty, this.targetRadius, 0, Math.PI * 2 );
  ctx.stroke();
}
// create particle
function Particle( x, y ) {
  this.x = x;
  this.y = y;
  // track the past coordinates of each particle to create a trail effect, increase the coordinate count to create more prominent trails
  this.coordinates = [];
  this.coordinateCount = 5;
  while( this.coordinateCount-- ) {
    this.coordinates.push( [ this.x, this.y ] );
  }
  // set a random angle in all possible directions, in radians
  this.angle = random( 0, Math.PI * 2 );
  this.speed = random( 1, 10 );
  // friction will slow the particle down
  this.friction = 0.95;
  // gravity will be applied and pull the particle down
  this.gravity = 1;
  // set the hue to a random number +-20 of the overall hue variable
  this.hue = random( hue - 20, hue + 20 );
  this.brightness = random( 50, 80 );
  this.alpha = 1;
  // set how fast the particle fades out
  this.decay = random( 0.015, 0.03 );
}
// update particle
Particle.prototype.update = function( index ) {
  // remove last item in coordinates array
  this.coordinates.pop();
  // add current coordinates to the start of the array
  this.coordinates.unshift( [ this.x, this.y ] );
  // slow down the particle
  this.speed *= this.friction;
  // apply velocity
  this.x += Math.cos( this.angle ) * this.speed;
  this.y += Math.sin( this.angle ) * this.speed + this.gravity;
  // fade out the particle
  this.alpha -= this.decay;
  // remove the particle once the alpha is low enough, based on the passed in index
  if( this.alpha <= this.decay ) {
    particles.splice( index, 1 );
  }
}
// draw particle
Particle.prototype.draw = function() {
  ctx. beginPath();
  // move to the last tracked coordinates in the set, then draw a line to the current x and y
  ctx.moveTo( this.coordinates[ this.coordinates.length - 1 ][ 0 ], this.coordinates[ this.coordinates.length - 1 ][ 1 ] );
  ctx.lineTo( this.x, this.y );
  ctx.strokeStyle = 'hsla(' + this.hue + ', 100%, ' + this.brightness + '%, ' + this.alpha + ')';
  ctx.stroke();
}
// create particle group/explosion
function createParticles( x, y ) {
  // increase the particle count for a bigger explosion, beware of the canvas performance hit with the increased particles though
  var particleCount = 30;
  while( particleCount-- ) {
    particles.push( new Particle( x, y ) );
  }
}
// main demo loop
function loop() {
  // this function will run endlessly with requestAnimationFrame
  requestAnimFrame( loop );
  // increase the hue to get different colored fireworks over time
  hue += 0.5;
  // normally, clearRect() would be used to clear the canvas
  // we want to create a trailing effect though
  // setting the composite operation to destination-out will allow us to clear the canvas at a specific opacity, rather than wiping it entirely
  ctx.globalCompositeOperation = 'destination-out';
  // decrease the alpha property to create more prominent trails
  ctx.fillStyle = 'rgba(0, 0, 0, 0.5)';
  ctx.fillRect( 0, 0, cw, ch );
  // change the composite operation back to our main mode
  // lighter creates bright highlight points as the fireworks and particles overlap each other
  ctx.globalCompositeOperation = 'lighter';
  // loop over each firework, draw it, update it
  var i = fireworks.length;
  while( i-- ) {
    fireworks[ i ].draw();
    fireworks[ i ].update( i );
  }
  // loop over each particle, draw it, update it
  var i = particles.length;
  while( i-- ) {
    particles[ i ].draw();
    particles[ i ].update( i );
  }
  // launch fireworks automatically to random coordinates, when the mouse isn't down
  if( timerTick >= timerTotal ) {
    if( !mousedown ) {
      // start the firework at the bottom middle of the screen, then set the random target coordinates, the random y coordinates will be set within the range of the top half of the screen
      fireworks.push( new Firework( cw / 2, ch, random( 0, cw ), random( 0, ch / 2 ) ) );
      timerTick = 0;
    }
  } else {
    timerTick++;
  }
  // limit the rate at which fireworks get launched when mouse is down
  if( limiterTick >= limiterTotal ) {
    if( mousedown ) {
      // start the firework at the bottom middle of the screen, then set the current mouse coordinates as the target
      fireworks.push( new Firework( cw / 2, ch, mx, my ) );
      limiterTick = 0;
    }
  } else {
    limiterTick++;
  }
}
// mouse event bindings
// update the mouse coordinates on mousemove
canvas.addEventListener( 'mousemove', function( e ) {
  mx = e.pageX - canvas.offsetLeft;
  my = e.pageY - canvas.offsetTop;
});
// toggle mousedown state and prevent canvas from being selected
canvas.addEventListener( 'mousedown', function( e ) {
  e.preventDefault();
  mousedown = true;
});
canvas.addEventListener( 'mouseup', function( e ) {
  e.preventDefault();
  mousedown = false;
});
// once the window loads, we are ready for some fireworks!
window.onload = loop;
</script>
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