效果：
- 逼真的火焰跟随鼠标，还冒出火花，照亮背景文字
- 使用canvas绘制
- 使用javascript，但并无复杂逻辑。上手程度：简单
- 欢迎来我的博客看此文章： https://clatterrr.com/archives/1606
源码：
- 演示地址:https://clatterrr.github.io/flamecursor/index.html
- 源码已在下方给出,或者访问github代码仓库https://github.com/clatterrr/flamecursor/settings
学习笔记：
google字体
在上一篇中已讲过。好看漂亮的html5网页特效学习笔记(3)_猜猜下一个颜色是什么？
javascript分步详细解释
第一步：
很简单的初始化函数。
var oCanvas;
init = function()
{
oCanvas = new Fire();
oCanvas.run();
}
window.onload = init;
第二步：
初始化canvas，定义各种基础的东西，以及为鼠标添加事件监测。addEventListener第三个参数的意思是，若为false，则为事件处理顺序为先进先处理，为true则为先进后处理。具体请看https://www.runoob.com/jsref/met-element-addeventlistener.html
var Fire = function(){
this.canvas = document.getElementById('fire');
this.ctx = this.canvas.getContext('2d');
this.canvas.height = window.innerHeight;
this.canvas.width = window.innerWidth;
this.aFires = [];
this.aSpark = [];
this.aSpark2 = [];
this.mouse = {
x : this.canvas.width * .5,
y : this.canvas.height * .75,
}
//一旦鼠标移动，就更新this.mouse.x和this.mouse.y，因为设置了false，所以先进来的事件先处理
this.canvas.addEventListener('mousemove', this.updateMouse.bind( this ), false);
}
Fire.prototype.updateMouse = function( e ){
this.mouse.x = e.clientX;
this.mouse.y = e.clientY;
}
第三步：
使用requestAnimationFrame使下一帧重新运行一遍run函数。为什么不用setInterval呢？因为内在运行机制会让它运行速度随机器性能变化而变化，导致时间控制不精确。而requestAnimationFrame使用系统时间，保证每秒执行60次。参考：https://www.cnblogs.com/xiaohuochai/p/5777186.html
并bind()方法创建一个新的函数，在bind()被调用时，这个新函数的this被bind的第一个参数指定，其余的参数将作为新函数的参数供调用时使用。参考：https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Function/bind
Fire.prototype.run = function(){
//重新新绘制火焰和火花
this.update();
this.draw();
//稳定重绘画面
requestAnimationFrame( this.run.bind( this ) );
}
第四步：
重新绘制一个火焰（实际上是红色的圆）和两个火花（实际上是小长方形）。若有火焰或火花的生命周期完了，那么就用删除它。否则继续更新它。
注意火焰火花原本被存储在数组里，所以删除用slice就好了。
Fire.prototype.update = function(){
//绘制新的火焰（红色的圆）以及火花
this.aFires.push( new Flame( this.mouse ) );
this.aSpark.push( new Spark( this.mouse ) );
this.aSpark2.push( new Spark( this.mouse ) );
//之前元素，即新的火焰（红色的圆）以及火花的生命周期未完的话，就继续更新它，否则就删除它
for (var i = this.aFires.length - 1; i >= 0; i--) {
if( this.aFires[i].alive )
this.aFires[i].update();
else
this.aFires.splice( i, 1 );
}
for (var i = this.aSpark.length - 1; i >= 0; i--) {
if( this.aSpark[i].alive )
this.aSpark[i].update();
else
this.aSpark.splice( i, 1 );
}
for (var i = this.aSpark2.length - 1; i >= 0; i--) {
if( this.aSpark2[i].alive )
this.aSpark2[i].update();
else
this.aSpark2.splice( i, 1 );
}
}
第五步：
以火焰为粒子。部分注释在代码中。先使用构造函数确定火焰的各项参数。若火焰被更新，那么就更新它的坐标，生命周期，以及用生命周期计算颜色。这里的颜色使用的是HSLA颜色，参考：http://caibaojian.com/css3/values/color/hsla.htm。
火花的构造参数和更新参数也是一样的。
var Flame = function( mouse ){
//鼠标坐标
this.cx = mouse.x;
this.cy = mouse.y;
//随机在鼠标周围产生
this.x = rand( this.cx - 25, this.cx + 25);
this.y = rand( this.cy - 5, this.cy + 5);
//随机变量，横轴纵轴以及半径的变化
this.vy = rand( 1, 3 );
this.vx = rand( -1, 1 );
this.r = rand( 20, 30 );
//生命周期
this.life = rand( 3, 6 );
this.alive = true;
//用于绘制火焰颜色
this.c = {
h : Math.floor( rand( 2, 40) ),
s : 100,
l : rand( 80, 100 ),
a : 0,
ta : rand( 0.8, 0.9 )
}
}
Flame.prototype.update = function()
{
//y坐标变化
this.y -= this.vy;
this.vy += 0.05;
//x坐标变化
this.x += this.vx;
if( this.x < this.cx )
this.vx += 0.1;
else
this.vx -= 0.1;
//半径变化
if( this.r > 0 )
this.r -= 0.1;
if( this.r <= 0 )
this.r = 0;
//计算生命周期，根据生命周期计算火焰颜色
this.life -= 0.15;
if( this.life <= 0 ){
this.c.a -= 0.05;
if( this.c.a <= 0 )
this.alive = false;
}else if( this.life > 0 && this.c.a < this.c.ta ){
this.c.a += .08;
}
}
第六步：
canvas的主场，绘制背景，包括黑色背景，文字FIRE，以及一个跟随在火焰后的暗红色大圆。这个大圆大圆，更像是墙壁的上的投影，需要仔细一点才能发现。canvas参考https://www.w3school.com.cn/tags/html_ref_canvas.asp，自己一个函数一个函数慢慢去查才能加深印象。
注意globalCompositeOperation的参数soft-light和color-dodge似乎国内网站都没找到解释，只在英文mdn上看到了样例。参考：
https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/globalCompositeOperation
Fire.prototype.draw = function(){
//绘制背景
this.ctx.globalCompositeOperation = "source-over";
this.ctx.fillStyle = "rgba( 15, 5, 2, 1 )";
this.ctx.fillRect( 0, 0, window.innerWidth, window.innerHeight );
//定义渐变颜色样式
this.grd = this.ctx.createRadialGradient( this.mouse.x, this.mouse.y - 200,200,this.mouse.x, this.mouse.y - 100,0 );
this.grd.addColorStop(0,"rgb( 15, 5, 2 )");
this.grd.addColorStop(1,"rgb( 30, 10, 2 )");
//绘制一个圆形，并使用颜色渐变样式。这个圆是一个暗红色的大圆
//跟随在火焰后的大圆，更像是墙壁的上的投影，需要仔细一点才能发现
this.ctx.beginPath();
this.ctx.arc( this.mouse.x, this.mouse.y - 100, 200, 0, 2*Math.PI );
this.ctx.fillStyle= this.grd;
this.ctx.fill();
//绘制文字Fire
this.ctx.font = "15em Amatic SC";
this.ctx.textAlign = "center";
this.ctx.strokeStyle = "rgb(50, 20, 0)";
this.ctx.fillStyle = "rgb(120, 10, 0)";
this.ctx.lineWidth = 2;
this.ctx.strokeText("Fire",this.canvas.width/2, this.canvas.height * .72 );
this.ctx.fillText("Fire",this.canvas.width/2, this.canvas.height * .72 );
//绘制火焰
this.ctx.globalCompositeOperation = "overlay";
for (var i = this.aFires.length - 1; i >= 0; i--)this.aFires[i].draw( this.ctx );
//绘制粒子
this.ctx.globalCompositeOperation = "soft-light";
for (var i = this.aSpark.length - 1; i >= 0; i--)
if( ( i % 2 ) === 0 )
this.aSpark[i].draw( this.ctx );
//绘制粒子2
this.ctx.globalCompositeOperation = "color-dodge";
for (var i = this.aSpark2.length - 1; i >= 0; i--) this.aSpark2[i].draw( this.ctx );
}
最后一步：
最关键但也很简单的地方，就是真正的绘制火焰和火花啦。beginpath(),arc(),fillstyle()和fill()都是canvas的方法。慢慢查找资料吧。只是注意这儿的颜色用的是hsla颜色而不是rgba颜色哦。
Flame.prototype.draw = function( ctx ){
ctx.beginPath();
ctx.arc( this.x, this.y, this.r * 3, 0, 2*Math.PI );
ctx.fillStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + (this.c.a/20) + ")";
ctx.fill();
ctx.beginPath();
ctx.arc( this.x, this.y, this.r, 0, 2*Math.PI );
ctx.fillStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + this.c.a + ")";
ctx.fill();
}
完整源码：
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Canvas实现火焰跟随鼠标动画</title>
<style>
@import url(https://fonts.googleapis.com/css?family=Amatic+SC);
html, body {
margin:0;
padding:0;
height: 100%;
}
</style>
</head>
<body>
<div style="text-align:center;clear:both;">
</div>
<canvas id="fire"></canvas>
<script>
var Fire = function(){
this.canvas = document.getElementById('fire');
this.ctx = this.canvas.getContext('2d');
this.canvas.height = window.innerHeight;
this.canvas.width = window.innerWidth;
this.aFires = [];
this.aSpark = [];
this.aSpark2 = [];
this.mouse = {
x : this.canvas.width * .5,
y : this.canvas.height * .75,
}
//一旦鼠标移动，就更新this.mouse.x和this.mouse.y，因为设置了false，所以先进来的事件先处理
this.canvas.addEventListener('mousemove', this.updateMouse.bind( this ), false);
}
Fire.prototype.run = function(){
//重新新绘制火焰和
this.update();
this.draw();
//稳定重绘画面
requestAnimationFrame( this.run.bind(this));
}
Fire.prototype.update = function(){
//绘制新的火焰（红色的圆）以及火花
this.aFires.push( new Flame( this.mouse ) );
this.aSpark.push( new Spark( this.mouse ) );
this.aSpark2.push( new Spark( this.mouse ) );
//之前元素，即新的火焰（红色的圆）以及火花的生命周期未完的话，就继续更新它，否则就删除它
for (var i = this.aFires.length - 1; i >= 0; i--) {
if( this.aFires[i].alive )
this.aFires[i].update();
else
this.aFires.splice( i, 1 );
}
for (var i = this.aSpark.length - 1; i >= 0; i--) {
if( this.aSpark[i].alive )
this.aSpark[i].update();
else
this.aSpark.splice( i, 1 );
}
for (var i = this.aSpark2.length - 1; i >= 0; i--) {
if( this.aSpark2[i].alive )
this.aSpark2[i].update();
else
this.aSpark2.splice( i, 1 );
}
}
Fire.prototype.draw = function(){
//绘制背景
this.ctx.globalCompositeOperation = "source-over";
this.ctx.fillStyle = "rgba( 15, 5, 2, 1 )";
this.ctx.fillRect( 0, 0, window.innerWidth, window.innerHeight );
//定义渐变颜色样式
this.grd = this.ctx.createRadialGradient( this.mouse.x, this.mouse.y - 200,200,this.mouse.x, this.mouse.y - 100,0 );
this.grd.addColorStop(0,"rgb( 15, 5, 2 )");
this.grd.addColorStop(1,"rgb( 30, 10, 2 )");
//绘制一个圆形，并使用颜色渐变样式。这个圆是一个暗红色的大圆
//跟随在火焰后的大圆，更像是墙壁的上的投影，需要仔细一点才能发现
this.ctx.beginPath();
this.ctx.arc( this.mouse.x, this.mouse.y - 100, 200, 0, 2*Math.PI );
this.ctx.fillStyle= this.grd;
this.ctx.fill();
//绘制文字Fire
this.ctx.font = "15em Amatic SC";
this.ctx.textAlign = "center";
this.ctx.strokeStyle = "rgb(50, 20, 0)";
this.ctx.fillStyle = "rgb(120, 10, 0)";
this.ctx.lineWidth = 2;
this.ctx.strokeText("Fire",this.canvas.width/2, this.canvas.height * .72 );
this.ctx.fillText("Fire",this.canvas.width/2, this.canvas.height * .72 );
//绘制火焰
this.ctx.globalCompositeOperation = "overlay";
for (var i = this.aFires.length - 1; i >= 0; i--)this.aFires[i].draw( this.ctx );
//绘制粒子
this.ctx.globalCompositeOperation = "soft-light";
for (var i = this.aSpark.length - 1; i >= 0; i--)
if( ( i % 2 ) === 0 )
this.aSpark[i].draw( this.ctx );
//绘制粒子2
this.ctx.globalCompositeOperation = "color-dodge";
for (var i = this.aSpark2.length - 1; i >= 0; i--) this.aSpark2[i].draw( this.ctx );
}
Fire.prototype.updateMouse = function( e ){
this.mouse.x = e.clientX;
this.mouse.y = e.clientY;
}
var Flame = function( mouse ){
//鼠标坐标
this.cx = mouse.x;
this.cy = mouse.y;
//随机在鼠标周围产生
this.x = rand( this.cx - 25, this.cx + 25);
this.y = rand( this.cy - 5, this.cy + 5);
//随机变量，横轴纵轴以及半径的变化
this.vy = rand( 1, 3 );
this.vx = rand( -1, 1 );
this.r = rand( 20, 30 );
//生命周期
this.life = rand( 3, 6 );
this.alive = true;
//用于绘制火焰颜色
this.c = {
h : Math.floor( rand( 2, 40) ),
s : 100,
l : rand( 80, 100 ),
a : 0,
ta : rand( 0.8, 0.9 )
}
}
Flame.prototype.update = function()
{
//y坐标变化
this.y -= this.vy;
this.vy += 0.05;
//x坐标变化
this.x += this.vx;
if( this.x < this.cx )
this.vx += 0.1;
else
this.vx -= 0.1;
//半径变化
if( this.r > 0 )
this.r -= 0.1;
if( this.r <= 0 )
this.r = 0;
//计算生命周期，根据生命周期计算火焰颜色
this.life -= 0.15;
if( this.life <= 0 ){
this.c.a -= 0.05;
if( this.c.a <= 0 )
this.alive = false;
}else if( this.life > 0 && this.c.a < this.c.ta ){
this.c.a += .08;
}
}
Flame.prototype.draw = function( ctx ){
ctx.beginPath();
ctx.arc( this.x, this.y, this.r * 3, 0, 2*Math.PI );
ctx.fillStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + (this.c.a/20) + ")";
ctx.fill();
ctx.beginPath();
ctx.arc( this.x, this.y, this.r, 0, 2*Math.PI );
ctx.fillStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + this.c.a + ")";
ctx.fill();
}
var Spark = function( mouse ){
this.cx = mouse.x;
this.cy = mouse.y;
this.x = rand( this.cx -40, this.cx + 40);
this.y = rand( this.cy, this.cy + 5);
this.lx = this.x;
this.ly = this.y;
this.vy = rand( 1, 3 );
this.vx = rand( -4, 4 );
this.r = rand( 0, 1 );
this.life = rand( 4, 5 );
this.alive = true;
this.c = {
h : Math.floor( rand( 2, 40) ),
s : 100,
l : rand( 40, 100 ),
a : rand( 0.8, 0.9 )
}
}
Spark.prototype.update = function()
{
this.lx = this.x;
this.ly = this.y;
this.y -= this.vy;
this.x += this.vx;
if( this.x < this.cx )
this.vx += 0.2;
else
this.vx -= 0.2;
this.vy += 0.08;
this.life -= 0.1;
if( this.life <= 0 ){
this.c.a -= 0.05;
if( this.c.a <= 0 )
this.alive = false;
}
}
Spark.prototype.draw = function( ctx ){
ctx.beginPath();
ctx.moveTo( this.lx , this.ly);
ctx.lineTo( this.x, this.y);
ctx.strokeStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + (this.c.a / 2) + ")";
ctx.lineWidth = this.r * 2;
ctx.lineCap = 'round';
ctx.stroke();
ctx.closePath();
ctx.beginPath();
ctx.moveTo( this.lx , this.ly);
ctx.lineTo( this.x, this.y);
ctx.strokeStyle = "hsla( " + this.c.h + ", " + this.c.s + "%, " + this.c.l + "%, " + this.c.a + ")";
ctx.lineWidth = this.r;
ctx.stroke();
ctx.closePath();
}
rand = function( min, max ){ return Math.random() * ( max - min) + min; };
onresize = function () { oCanvas.canvas.width = window.innerWidth; oCanvas.canvas.height = window.innerHeight; };
var oCanvas;
init = function()
{
oCanvas = new Fire();
oCanvas.run();
}
window.onload = init;
</script>
</body>
</html>
学习了。