这次给大家带来canvas怎样做出黑色背景的红色烟花，canvas做出黑色背景的红色烟花的注意事项有哪些，下面就是实战案例，一起来看一下。
html
css
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 shimwindow.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 demovar 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 dimensionscanvas.width = cw;
canvas.height = ch;// now we are going to setup our function placeholders for the entire demo// get a random number within a rangefunction random(min, max) { return Math.random() * (max - min) + min;
}// calculate the distance between two pointsfunction calculateDistance(p1x, p1y, p2x, p2y) { var xDistance = p1x - p2x,
yDistance = p1y - p2y; return Math.sqrt(Math.pow(xDistance, 2) + Math.pow(yDistance, 2));
}// create fireworkfunction 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 fireworkFirework.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 fireworkFirework.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 particlefunction 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 particleParticle.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 particleParticle.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/explosionfunction 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 loopfunction 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'; var text = "HAPPY NEW YEAR !";
ctx.font = "50px sans-serif"; var textData = ctx.measureText(text);
ctx.fillStyle = "rgba(" + parseInt(random(0, 255)) + "," + parseInt(random(0, 255)) + "," + parseInt(random(0, 255)) + ",0.3)";
ctx.fillText(text, cw / 2 - textData.width / 2, ch / 2); // 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
for (var h = 0; h < 50; h++) {
fireworks.push(new Firework(cw / 2, ch / 2, random(0, cw), random(0, ch)));
}
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 / 2, mx, my));
limiterTick = 0;
}
} else {
limiterTick++;
}
}// mouse event bindings// update the mouse coordinates on mousemovecanvas.addEventListener('mousemove', function (e) {
mx = e.pageX - canvas.offsetLeft;
my = e.pageY - canvas.offsetTop;
});// toggle mousedown state and prevent canvas from being selectedcanvas.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;相信看了本文案例你已经掌握了方法，更多精彩请关注php中文网其它相关文章！
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