放烟花
- Published on
- //趣玩前端
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset="UTF-8" />
<title>放烟花</title>
<style>
/* basic styles for black background and crosshair cursor */
body {
background: #000;
margin: 0;
}
canvas {
cursor: crosshair;
display: block;
}
</style>
</head>
<body>
<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 = 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));
}
// 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>
</body>
</html>