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粒子效果文字动画特效的原理

当我们拿到一段文字，可以放到ps里面放大观察，文字是由一个个很小的颜色不同的像素点绘制出来的，那么粒子效果文字动画特效需要做的就是通过降低像素数使像素点变成圆形，再拼凑出文字内容。总的来说就是通过将输入的信息转化为图片后，读取图片的像素信息，同时粗略的将图片分块，遍历每块区域中的像素点判断该块是否需要画一个粒子。

实现粒子效果文字动画特效的步骤

步骤一：文字转化为图片插入canvas

function loadCanvas(value) {
    var fontSize = 100,
        width = calWordWidth(value, fontSize), 
        canvas = document.createElement('canvas')
    canvas.id = 'b_canvas'
    canvas.width = width 
    canvas.height = fontSize
    var ctx = canvas.getContext('2d')
    ctx.font = fontSize + "px Microsoft YaHei"
    ctx.fillStyle = "orange"
    ctx.fillText(value, 0, fontSize / 5 * 4)
    getImage(canvas, ctx)
}
function getImage(canvas, ctx) {
    var image = new Image()
    image.src = canvas.toDataURL("image/jpeg")
    image.onload = function() 
}

步骤二：降低像素数

var imageData = ctx.getImageData(0, 0, this.width, this.height)
var dataLength = imageData.data.length
var diff = 4 
var newCanvas = document.getElementById('canvas')
var newCtx = newCanvas.getContext('2d')
for (var j = 0; j < this.height; j += diff) {
    for (var i = 0; i < this.width; i += diff) {
        var colorNum = 0
        for (var k = 0; k < diff * diff; k++) {
            var row = k % diff
            var col = ~~(k / diff)
            let r = imageData.data[((j + col) * this.width + i + row) * 4 + 0]
            let g = imageData.data[((j + col) * this.width + i + row) * 4 + 1]
            let b = imageData.data[((j + col) * this.width + i + row) * 4 + 2]
            if (r < 10 && g < 10 && b < 10) colorNum++ 
        }
        if (colorNum < diff * diff / 3 * 2) {
            var option = {
                x: i,
                y: j,
                radius: 6,
                color: '#fff'
            }
            var newBubble = new Bubble(option)
            newBubble.draw(newCtx)
        } 
    }
}

效果如图所示

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