前面的话
本文将从最基本的imageData对象的理论知识说开去，详细介绍canvas粒子系统的构建
imageData
关于图像数据imageData共有3个方法，包括getImageData()、putImageData()、createImageData()
【getImageData()】
2D上下文可以通过getImageData()取得原始图像数据。这个方法接收4个参数：画面区域的x和y坐标以及该区域的像素宽度和高度
例如，要取得左上角坐标为(10,5)、大小为50*50像素的区域的图像数据，可以使用以下代码：
var imageData = context.getImageData(10,5,50,50);
返回的对象是ImageData的实例，每个ImageData对象有3个属性：width/height/data
1、width：表示imageData对角的宽度
2、height：表示imageData对象的高度
3、data是一个数组，保存着图像中每一个像素的数据。在data数组中，每一个像素用4个元素来保存，分别表示red、green、blue、透明度
[注意]图像中有多少像素，data的长度就等于像素个数乘以4
//第一个像素如下var data = imageData.data;var red = data[0];var green = data[1]; var blue = data[2];var alpha = data[3];
数组中每个元素的值是在0-255之间，能够直接访问到原始图像数据，就能够以各种方式来操作这些数据
[注意]如果要使用getImageData()获取的canvas中包含drawImage()方法，则该方法中的URL不能跨域
【createImageData()】
createImageData(width,height)方法创建新的空白ImageData对象。新对象的默认像素值 transparent black，相当于rgba(0,0,0,0)
var imgData = context.createImageData(100,100);
【putImageData()】
putImageData()方法将图像数据从指定的ImageData对象放回画布上，该方法共有以下参数
imgData：要放回画布的ImageData对象(必须)x：imageData对象的左上角的x坐标(必须)y：imageData对象的左上角的y坐标(必须)dirtyX：在画布上放置图像的水平位置(可选)dirtyY：在画布上放置图像的垂直位置(可选)dirtyWidth：在画布上绘制图像所使用的宽度(可选)dirtyHeight：在画布上绘制图像所使用的高度(可选)
[注意]参数3到7要么都没有，要么都存在
context.putImageData(imgData,0,0);
context.putImageData(imgData,0,0,50,50,200,200);
粒子写入
粒子，指图像数据imageData中的每一个像素点。下面以一个简易实例来说明完全写入与粒子写入
【完全写入】
200*200的canvas1中存在文字'小火柴'，并将canvas1整个作为图像数据写入同样尺寸的canvas2中
<canvas id="drawing1" style="border:1px solid black"></canvas><canvas id="drawing2" style="border:1px solid black"></canvas><script>var drawing1 = document.getElementById('drawing1');var drawing2 = document.getElementById('drawing2');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var cxt2 = drawing2.getContext('2d'); var W = drawing1.width = drawing2.width = 200; var H = drawing1.height = drawing2.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); //写入drawing2中 cxt2.putImageData(imageData,0,0);</script>【粒子写入】
对于完全写入而言，相当于只是简单的复制粘贴，如果要对每个像素点进行精细地控制，则需要使用粒子写入。canvas1中存在着大量的空白区域，只有'小火柴'这三个字的区域是有效的。于是，可以根据图像数据imageData中的透明度对粒子进行筛选，只筛选出透明度大于0的粒子
<canvas id="drawing1" style="border:1px solid black"></canvas><canvas id="drawing2" style="border:1px solid black"></canvas><script>var drawing1 = document.getElementById('drawing1');var drawing2 = document.getElementById('drawing2');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var cxt2 = drawing2.getContext('2d'); var W = drawing1.width = drawing2.width = 200; var H = drawing1.height = drawing2.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); //写入drawing2中 cxt2.putImageData(setData(imageData),0,0); function setData(imageData){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; for(var i = 0; i < W; i++){ for(var j = 0; j < H ;j++){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); } } } //40000 2336 console.log(i*j,dots.length); //新建一个imageData，并将筛选后的粒子信息保存到新建的imageData中 var oNewImage = cxt.createImageData(W,H); for(var i = 0; i < dots.length; i++){ oNewImage.data[dots[i]+0] = imageData.data[dots[i]+0]; oNewImage.data[dots[i]+1] = imageData.data[dots[i]+1]; oNewImage.data[dots[i]+2] = imageData.data[dots[i]+2]; oNewImage.data[dots[i]+3] = imageData.data[dots[i]+3]; } return oNewImage; }}</script>虽然结果看上去相同，但canvas2只使用了canvas1中40000个粒子中的2336个
粒子筛选
当粒子完全写入时，与canvas复制粘贴的效果相同。而当粒子有所筛选时，则会出现一些奇妙的效果
【按序筛选】
由于取得粒子时，使用的是宽度值*高度值的双重循环，且都以加1的形式递增。如果不是加1，而是加n，则可以实现按序筛选的效果
<canvas id="drawing1" style="border:1px solid black"></canvas><canvas id="drawing2" style="border:1px solid black"></canvas><div id="con"> <button>1</button> <button>2</button> <button>3</button> <button>4</button> <button>5</button></div><script>var oCon = document.getElementById('con');oCon.onclick = function(e){ e = e || event; var tempN = e.target.innerHTML; if(tempN){ cxt2.clearRect(0,0,W,H); cxt2.putImageData(setData(imageData,Number(tempN)),0,0); }}var drawing1 = document.getElementById('drawing1');var drawing2 = document.getElementById('drawing2');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var cxt2 = drawing2.getContext('2d'); var W = drawing1.width = drawing2.width = 200; var H = drawing1.height = drawing2.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); //写入drawing2中 cxt2.putImageData(setData(imageData,1),0,0); function setData(imageData,n){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; for(var i = 0; i < W; i+=n){ for(var j = 0; j < H ;j+=n){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); } } } //新建一个imageData，并将筛选后的粒子信息保存到新建的imageData中 var oNewImage = cxt.createImageData(W,H); for(var i = 0; i < dots.length; i++){ oNewImage.data[dots[i]+0] = imageData.data[dots[i]+0]; oNewImage.data[dots[i]+1] = imageData.data[dots[i]+1]; oNewImage.data[dots[i]+2] = imageData.data[dots[i]+2]; oNewImage.data[dots[i]+3] = imageData.data[dots[i]+3]; } return oNewImage; }}</script>【随机筛选】
除了使用按序筛选，还可以使用随机筛选。 通过双重循环得到的粒子的位置信息，放到dots数组中。通过splice()方法进行筛选，将筛选后的位置信息放到新建的newDots数组中，然后再使用createImageData()，新建一个图像数据对象并返回
<canvas id="drawing1" style="border:1px solid black"></canvas><canvas id="drawing2" style="border:1px solid black"></canvas><div id="con"> <button>1000</button> <button>2000</button> <button>3000</button> <button>4000</button></div><script>var oCon = document.getElementById('con');oCon.onclick = function(e){ e = e || event; var tempN = e.target.innerHTML; if(tempN){ cxt2.clearRect(0,0,W,H); cxt2.putImageData(setData(imageData,1,Number(tempN)),0,0); }}var drawing1 = document.getElementById('drawing1');var drawing2 = document.getElementById('drawing2');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var cxt2 = drawing2.getContext('2d'); var W = drawing1.width = drawing2.width = 200; var H = drawing1.height = drawing2.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); //写入drawing2中 cxt2.putImageData(setData(imageData,1),0,0); function setData(imageData,n,m){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; for(var i = 0; i < W; i+=n){ for(var j = 0; j < H ;j+=n){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); } } } //筛选粒子，仅保存m个到newDots数组中。如果不传入m，则不进行筛选 var newDots = []; if(m && (dots.length > m)){ for(var i = 0; i < m; i++){ newDots.push(Number(dots.splice(Math.floor(Math.random()*dots.length),1))); } }else{ newDots = dots; } //新建一个imageData，并将筛选后的粒子信息保存到新建的imageData中 var oNewImage = cxt.createImageData(W,H); for(var i = 0; i < newDots.length; i++){ oNewImage.data[newDots[i]+0] = imageData.data[newDots[i]+0]; oNewImage.data[newDots[i]+1] = imageData.data[newDots[i]+1]; oNewImage.data[newDots[i]+2] = imageData.data[newDots[i]+2]; oNewImage.data[newDots[i]+3] = imageData.data[newDots[i]+3]; } return oNewImage; }}</script>像素显字
下面来使用粒子筛选来实现一个像素显字的效果。像素显字即从不清晰的效果逐步过渡到完全显示
【按序像素显字】
按序像素显字的实现原理非常简单，比如，共有2000个粒子，共10个程度的过渡效果。则使用10个数组，分别保存200,400,600,800,100,1200,1400,1600,1800和2000个粒子。然后使用定时器将其逐步显示出来即可
<canvas id="drawing1" style="border:1px solid black"></canvas><button id="btn">开始显字</button><script>var drawing1 = document.getElementById('drawing1');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var W = drawing1.width = 200; var H = drawing1.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); cxt.clearRect(0,0,W,H); //获得10组粒子 var imageDataArr = []; var n = 10; var index = 0; for(var i = n; i > 0; i--){ imageDataArr.push(setData(imageData,i)); } var oTimer = null; btn.onclick = function(){ clearTimeout(oTimer); showData(); } function showData(){ oTimer = setTimeout(function(){ cxt.clearRect(0,0,W,H); //写入drawing1中 cxt.putImageData(imageDataArr[index++],0,0); //迭代函数 showData(); if(index == 10){ index = 0; clearTimeout(oTimer); } },100); } function setData(imageData,n,m){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; for(var i = 0; i < W; i+=n){ for(var j = 0; j < H ;j+=n){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); } } } //筛选粒子，仅保存m个到newDots数组中。如果不传入m，则不进行筛选 var newDots = []; if(m && (dots.length > m)){ for(var i = 0; i < m; i++){ newDots.push(Number(dots.splice(Math.floor(Math.random()*dots.length),1))); } }else{ newDots = dots; } //新建一个imageData，并将筛选后的粒子信息保存到新建的imageData中 var oNewImage = cxt.createImageData(W,H); for(var i = 0; i < newDots.length; i++){ oNewImage.data[newDots[i]+0] = imageData.data[newDots[i]+0]; oNewImage.data[newDots[i]+1] = imageData.data[newDots[i]+1]; oNewImage.data[newDots[i]+2] = imageData.data[newDots[i]+2]; oNewImage.data[newDots[i]+3] = imageData.data[newDots[i]+3]; } return oNewImage; }}</script>【随机像素显字】
随机像素显字的原理类似，保存多个不同数量的随机像素的数组即可
<canvas id="drawing1" style="border:1px solid black"></canvas><button id="btn">开始显字</button><script>var drawing1 = document.getElementById('drawing1');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var W = drawing1.width = 200; var H = drawing1.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); cxt.clearRect(0,0,W,H); //获得10组粒子 var imageDataArr = []; var n = 10; var index = 0; for(var i = n; i > 0; i--){ imageDataArr.push(setData(imageData,1,i)); } var oTimer = null; btn.onclick = function(){ clearTimeout(oTimer); showData(); } function showData(){ oTimer = setTimeout(function(){ cxt.clearRect(0,0,W,H); //写入drawing1中 cxt.putImageData(imageDataArr[index++],0,0); //迭代函数 showData(); if(index == 10){ clearTimeout(oTimer); index = 0; } },100); } function setData(imageData,n,m){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; for(var i = 0; i < W; i+=n){ for(var j = 0; j < H ;j+=n){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); } } } //筛选粒子，仅保存dots.length/m个到newDots数组中 var newDots = []; var len = Math.floor(dots.length/m); for(var i = 0; i < len; i++){ newDots.push(Number(dots.splice(Math.floor(Math.random()*dots.length),1))); } //新建一个imageData，并将筛选后的粒子信息保存到新建的imageData中 var oNewImage = cxt.createImageData(W,H); for(var i = 0; i < newDots.length; i++){ oNewImage.data[newDots[i]+0] = imageData.data[newDots[i]+0]; oNewImage.data[newDots[i]+1] = imageData.data[newDots[i]+1]; oNewImage.data[newDots[i]+2] = imageData.data[newDots[i]+2]; oNewImage.data[newDots[i]+3] = imageData.data[newDots[i]+3]; } return oNewImage; }}</script>粒子动画
粒子动画并不是粒子在做动画，而是通过getImageData()方法获得粒子的随机坐标和最终坐标后，通过fillRect()方法绘制的小方块在做运动。使用定时器，不断的绘制坐标变化的小方块，以此来产生运动的效果
【随机位置】
<canvas id="drawing1" style="border:1px solid black"></canvas><button id="btn1">开始显字</button><button id="btn2">重新混乱</button><script>var drawing1 = document.getElementById('drawing1');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var W = drawing1.width = 200; var H = drawing1.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); cxt.clearRect(0,0,W,H); function setData(imageData,n,m){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; //dots的索引 var index = 0; for(var i = 0; i < W; i+=n){ for(var j = 0; j < H ;j+=n){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); dots[index++] = { 'index':index, 'x':i, 'y':j, 'red':k, 'randomX':Math.random()*W, 'randomY':Math.random()*H, } } } } //筛选粒子，仅保存dots.length/m个到newDots数组中 var newDots = []; var len = Math.floor(dots.length/m); for(var i = 0; i < len; i++){ newDots.push(dots.splice(Math.floor(Math.random()*dots.length),1)[0]); } return newDots; } //获得粒子数组 var dataArr = setData(imageData,1,1); var oTimer1 = null; var oTimer2 = null; btn1.onclick = function(){ clearTimeout(oTimer1); showData(10); } btn2.onclick = function(){ clearTimeout(oTimer2); showRandom(10); } function showData(n){ oTimer1 = setTimeout(function(){ cxt.clearRect(0,0,W,H); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; var x0 = temp.randomX; var y0 = temp.randomY; var disX = temp.x - temp.randomX; var disY = temp.y - temp.randomY; cxt.fillRect(x0 + disX/n,y0 + disY/n,1,1); } showData(n-1); if(n === 1){ clearTimeout(oTimer1); } },60); } function showRandom(n){ oTimer2 = setTimeout(function fn(){ cxt.clearRect(0,0,W,H); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; var x0 = temp.x; var y0 = temp.y; var disX = temp.randomX - temp.x; var disY = temp.randomY - temp.y; cxt.fillRect(x0 + disX/n,y0 + disY/n,1,1); } showRandom(n-1); if(n === 1){ clearTimeout(oTimer2); } },60); } }</script>【飘入效果】
飘入效果与随机显字的原理相似，不再赘述
<canvas id="drawing1" style="border:1px solid black"></canvas><button id="btn1">左上角飘入</button><script>var drawing1 = document.getElementById('drawing1');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var W = drawing1.width = 200; var H = drawing1.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); cxt.clearRect(0,0,W,H); function setData(imageData,n,m){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; //dots的索引 var index = 0; for(var i = 0; i < W; i+=n){ for(var j = 0; j < H ;j+=n){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); dots[index++] = { 'index':index, 'x':i, 'y':j, 'red':k, 'randomX':Math.random()*W, 'randomY':Math.random()*H, } } } } //筛选粒子，仅保存dots.length/m个到newDots数组中 var newDots = []; var len = Math.floor(dots.length/m); for(var i = 0; i < len; i++){ newDots.push(dots.splice(Math.floor(Math.random()*dots.length),1)[0]); } return newDots; } //获得粒子数组 var dataArr = setData(imageData,1,1); var oTimer1 = null; btn1.onclick = function(){ clearTimeout(oTimer1); showData(10); } function showData(n){ oTimer1 = setTimeout(function(){ cxt.clearRect(0,0,W,H); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; var x0 = 0; var y0 = 0; var disX = temp.x - 0; var disY = temp.y - 0; cxt.fillRect(x0 + disX/n,y0 + disY/n,1,1); } showData(n-1); if(n === 1){ clearTimeout(oTimer1); } },60); } }</script>鼠标交互
一般地，粒子的鼠标交互都与isPointInPath(x,y)方法有关
【移入变色】
当鼠标接近粒子时，该粒子变红。实现原理很简单。鼠标移动时，通过isPointInPath(x,y)方法检测，有哪些粒子处于当前指针范围内。如果处于，绘制1像素的红色矩形即可
<canvas id="drawing1" style="border:1px solid black"></canvas><script>var drawing1 = document.getElementById('drawing1');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var W = drawing1.width = 200; var H = drawing1.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); function setData(imageData,n,m){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; //dots的索引 var index = 0; for(var i = 0; i < W; i+=n){ for(var j = 0; j < H ;j+=n){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); dots[index++] = { 'index':index, 'x':i, 'y':j, 'red':k, 'randomX':Math.random()*W, 'randomY':Math.random()*H, } } } } //筛选粒子，仅保存dots.length/m个到newDots数组中 var newDots = []; var len = Math.floor(dots.length/m); for(var i = 0; i < len; i++){ newDots.push(dots.splice(Math.floor(Math.random()*dots.length),1)[0]); } return newDots; } //获得粒子数组 var dataArr = setData(imageData,1,1); //鼠标移动时，当粒子距离鼠标指针小于10时，则进行相关操作 drawing1.onmousemove = function(e){ e = e || event; var x = e.clientX - drawing1.getBoundingClientRect().left; var y = e.clientY - drawing1.getBoundingClientRect().top; cxt.beginPath(); cxt.arc(x,y,10,0,Math.PI*2); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; if(cxt.isPointInPath(temp.x,temp.y)){ cxt.fillStyle = 'red'; cxt.fillRect(temp.x,temp.y,1,1); } } }}</script>【远离鼠标】
鼠标点击时，以鼠标指针为圆心的一定范围内的粒子需要移动到该范围以外。一段时间后，粒子回到原始位置
实现原理并不复杂，使用isPointInPath(x,y)方法即可，如果粒子处于当前路径中，则沿着鼠标指针与粒子坐标组成的直线方向，移动到路径的边缘
<canvas id="drawing1" style="border:1px solid black"></canvas><script>var drawing1 = document.getElementById('drawing1');if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var W = drawing1.width = 200; var H = drawing1.height = 200; var str = '小火柴'; cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } //渲染文字 cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); //获取imageData var imageData = cxt.getImageData(0,0,W,H); cxt.clearRect(0,0,W,H); function setData(imageData,n,m){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; //dots的索引 var index = 0; for(var i = 0; i < W; i+=n){ for(var j = 0; j < H ;j+=n){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); dots[index++] = { 'index':index, 'x':i, 'y':j, 'red':k, 'randomX':Math.random()*W, 'randomY':Math.random()*H, 'mark':false } } } } //筛选粒子，仅保存dots.length/m个到newDots数组中 var newDots = []; var len = Math.floor(dots.length/m); for(var i = 0; i < len; i++){ newDots.push(dots.splice(Math.floor(Math.random()*dots.length),1)[0]); } return newDots; } //获得粒子数组 var dataArr = setData(imageData,2,1); //将筛选后的粒子信息保存到新建的imageData中 var oNewImage = cxt.createImageData(W,H); for(var i = 0; i < dataArr.length; i++){ for(var j = 0; j < 4; j++){ oNewImage.data[dataArr[i].red+j] = imageData.data[dataArr[i].red+j]; } } //写入canvas中 cxt.putImageData(oNewImage,0,0); //设置鼠标检测半径为r var r = 20; //鼠标移动时，当粒子距离鼠标指针小于20时，则进行相关操作 drawing1.onmousedown = function(e){ e = e || event; var x = e.clientX - drawing1.getBoundingClientRect().left; var y = e.clientY - drawing1.getBoundingClientRect().top; cxt.beginPath(); cxt.arc(x,y,r,0,Math.PI*2); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; if(cxt.isPointInPath(temp.x,temp.y)){ temp.mark = true; var angle = Math.atan2((temp.y - y),(temp.x - x)); temp.endX = x - r*Math.cos(angle); temp.endY = y - r*Math.sin(angle); var disX = temp.x - temp.endX; var disY = temp.y - temp.endY; cxt.fillStyle = '#fff'; cxt.fillRect(temp.x,temp.y,1,1); cxt.fillStyle = '#000'; cxt.fillRect(temp.endX,temp.endY,1,1); dataRecovery(10); }else{ temp.mark = false; } } var oTimer = null; function dataRecovery(n){ clearTimeout(oTimer); oTimer = setTimeout(function(){ cxt.clearRect(0,0,W,H); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; if(temp.mark){ var x0 = temp.endX; var y0 = temp.endY; var disX = temp.x - x0; var disY = temp.y - y0; cxt.fillRect(x0 + disX/n,y0 + disY/n,1,1); }else{ cxt.fillRect(temp.x,temp.y,1,1); } } dataRecovery(n-1); if(n === 1){ clearTimeout(oTimer); } },17); } } }</script>综合实例
下面将上面的效果制作为一个可编辑的综合实例
<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title></head><body><canvas id="drawing1" style="border:1px solid black"></canvas><br><div style="margin-bottom:10px"> <span>粒子设置：</span> <input type="text" id="textValue" value="小火柴的蓝色理想"> <button id="btnSetText">文字设置确认</button> <button id="btnchoose2">按序筛选</button> <button id="btnchoose3">随机筛选</button> <button id="btnchoose1">不筛选</button> </div><div style="margin-bottom:10px"> <span>粒子效果：</span> <button id="btn1">按序显字</button> <button id="btn2">随机显字</button> <button id="btn3">混乱聚合</button> <button id="btn4">重新混乱</button></div><div> <span>鼠标效果：</span> <span>1、鼠标移到文字上时，文字颜色变红；</span> <span>2、鼠标在文字上点击时，粒子远离鼠标指针</span></div><script>if(drawing1.getContext){ var cxt = drawing1.getContext('2d'); var W = drawing1.width = 300; var H = drawing1.height = 200; var imageData; var dataArr; btnSetText.onclick = function(){ fnSetText(textValue.value); } function fnSetText(str){ cxt.clearRect(0,0,W,H); cxt.textBaseline = 'top'; var sh = 60; cxt.font = sh + 'px 宋体' var sw = cxt.measureText(str).width; if(sw > W){ sw = W; } cxt.fillText(str,(W - sw)/2,(H - sh)/2,W); imageData = cxt.getImageData(0,0,W,H); dataArr = setData(imageData,1,1); } fnSetText('小火柴'); btnchoose1.onclick = function(){ dataArr = setData(imageData,1,1); saveData(dataArr); } btnchoose2.onclick = function(){ dataArr = setData(imageData,2,1); saveData(dataArr); } btnchoose3.onclick = function(){ dataArr = setData(imageData,1,2); saveData(dataArr); } //筛选粒子 function setData(imageData,n,m){ //从imageData对象中取得粒子，并存储到dots数组中 var dots = []; //dots的索引 var index = 0; for(var i = 0; i < W; i+=n){ for(var j = 0; j < H ;j+=n){ //data值中的红色值 var k = 4*(i + j*W); //data值中的透明度 if(imageData.data[k+3] > 0){ //将透明度大于0的data中的红色值保存到dots数组中 dots.push(k); dots[index++] = { 'index':index, 'x':i, 'y':j, 'red':k, 'green':k+1, 'blue':k+2, 'randomX':Math.random()*W, 'randomY':Math.random()*H, 'mark':false } } } } //筛选粒子，仅保存dots.length/m个到newDots数组中 var newDots = []; var len = Math.floor(dots.length/m); for(var i = 0; i < len; i++){ newDots.push(dots.splice(Math.floor(Math.random()*dots.length),1)[0]); } return newDots; } function saveData(dataArr){ //将筛选后的粒子信息保存到新建的imageData中 var oNewImage = cxt.createImageData(W,H); for(var i = 0; i < dataArr.length; i++){ for(var j = 0; j < 4; j++){ oNewImage.data[dataArr[i].red+j] = imageData.data[dataArr[i].red+j]; } } //写入canvas中 cxt.putImageData(oNewImage,0,0); } //显示粒子 function showData(arr,oTimer,index,n){ oTimer = setTimeout(function(){ cxt.clearRect(0,0,W,H); //写入canvas中 saveData(arr[index++]); if(index == n){ clearTimeout(oTimer); }else{ //迭代函数 showData(arr,oTimer,index,n); } },60); } //重新混乱 function showDataToRandom(dataArr,oTimer,n){ oTimer = setTimeout(function fn(){ cxt.clearRect(0,0,W,H); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; var x0 = temp.x; var y0 = temp.y; var disX = temp.randomX - temp.x; var disY = temp.randomY - temp.y; cxt.fillRect(x0 + disX/n,y0 + disY/n,1,1); } n--; if(n === 0){ clearTimeout(oTimer); }else{ showDataToRandom(dataArr,oTimer,n); } },60); } //混乱聚合 function showRandomToData(dataArr,oTimer,n){ oTimer = setTimeout(function(){ cxt.clearRect(0,0,W,H); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; var x0 = temp.randomX; var y0 = temp.randomY; var disX = temp.x - temp.randomX; var disY = temp.y - temp.randomY; cxt.fillRect(x0 + disX/n,y0 + disY/n,1,1); } n--; if(n === 0){ clearTimeout(oTimer); }else{ showRandomToData(dataArr,oTimer,n); } },60); } btn1.onclick = function(){ btn1.arr = []; for(var i = 10; i > 1; i--){ btn1.arr.push(setData(imageData,i,1)); } showData(btn1.arr,btn1.oTimer,0,9); } btn2.onclick = function(){ btn2.arr = []; for(var i = 10; i > 0; i--){ btn2.arr.push(setData(imageData,2,i)); } showData(btn2.arr,btn2.oTimer,0,10); } btn3.onclick = function(){ clearTimeout(btn3.oTimer); showRandomToData(dataArr,btn3.oTimer,10); } btn4.onclick = function(){ clearTimeout(btn4.oTimer); showDataToRandom(dataArr,btn4.oTimer,10); } //鼠标移动 drawing1.onmousemove = function(e){ e = e || event; var x = e.clientX - drawing1.getBoundingClientRect().left; var y = e.clientY - drawing1.getBoundingClientRect().top; cxt.beginPath(); cxt.arc(x,y,10,0,Math.PI*2); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; if(cxt.isPointInPath(temp.x,temp.y)){ cxt.fillStyle = 'red'; cxt.fillRect(temp.x,temp.y,1,1); } } cxt.fillStyle = 'black'; } //鼠标点击 drawing1.onmousedown = function(e){ var r = 20; e = e || event; var x = e.clientX - drawing1.getBoundingClientRect().left; var y = e.clientY - drawing1.getBoundingClientRect().top; cxt.beginPath(); cxt.arc(x,y,r,0,Math.PI*2); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; if(cxt.isPointInPath(temp.x,temp.y)){ temp.mark = true; var angle = Math.atan2((temp.y - y),(temp.x - x)); temp.endX = x - r*Math.cos(angle); temp.endY = y - r*Math.sin(angle); var disX = temp.x - temp.endX; var disY = temp.y - temp.endY; cxt.fillStyle = '#fff'; cxt.fillRect(temp.x,temp.y,1,1); cxt.fillStyle = '#f00'; cxt.fillRect(temp.endX,temp.endY,1,1); cxt.fillStyle="#000"; dataRecovery(10); }else{ temp.mark = false; } } var oTimer = null; function dataRecovery(n){ clearTimeout(oTimer); oTimer = setTimeout(function(){ cxt.clearRect(0,0,W,H); for(var i = 0; i < dataArr.length; i++){ var temp = dataArr[i]; if(temp.mark){ var x0 = temp.endX; var y0 = temp.endY; var disX = temp.x - x0; var disY = temp.y - y0; cxt.fillRect(x0 + disX/n,y0 + disY/n,1,1); }else{ cxt.fillRect(temp.x,temp.y,1,1); } } dataRecovery(n-1); if(n === 1){ clearTimeout(oTimer); } },17); } } }</script> </body></html>以上这篇基于canvas粒子系统的构建详解就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持武林网。
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