学会做一个烟花HTML5画布和JavaScript。在这个演示,像素大小的火箭发射自动从底部的屏幕,通过鼠标的点击。您还可以单击并拖动来启动多个焰火。
本教程介绍了跟踪和对象包含在数组循环,跟踪鼠标点击和坐标,动画烟花特定目标坐标,使美丽的粒子爆炸通过使用随机生成的值
HTML
<canvas id="canvas">Canvas is not supported in your browser.</canvas>
CSS
/* basic styles for black background and crosshair cursor */
body {
background: #000;
margin: 0;
}
canvas {
cursor: crosshair;
display: block;
}
JS
// 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 = 5,
limiterTick = 0,
// this will time the auto launches of fireworks, one launch per 80 loop ticks
timerTotal = 80,
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 ) );
}
// 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 a trail effect, increase the coordinate count to 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 ) {
Particles( 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();
}
// particle
function Particle( x, y ) {
this.x = x;
this.y = y;
// track the past coordinates of each particle to a trail effect, increase the coordinate count to 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();
}
// particle group/explosion
function Particles( 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 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 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 s 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;
