Html5 Canvas背光文字动画特效代码

//把站长天下修改为自己需要显示的名称
var txt = "站长天下";
var txtH = 100;
var font = "sans-serif";
var bg = "#000";
var rayColor1 = "#e0f7fa";
var rayColor2 = "#18ffff";
var fade = 1000;

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var cw = canvas.width = window.innerWidth;
var ch = canvas.height = window.innerHeight;

var w2 = cw/2;
var h2 = ch/2;
var pi = Math.PI;
var pi2 = pi*.5;

var txtCanvas = document.createElement("canvas");
var txtCtx = txtCanvas.getContext("2d");
txtCtx.font = txtH + "px " + font;
txtCtx.textBaseline = "middle";
var txtW = Math.floor(txtCtx.measureText(txt).width);
txtCanvas.width = txtW;
txtCanvas.height = txtH*1.5;

var gradient = ctx.createRadialGradient(w2, h2, 0, w2, h2, txtW);
gradient.addColorStop(0, rayColor2);
gradient.addColorStop(1, rayColor1);
ctx.strokeStyle = gradient;

txtCtx.fillStyle = gradient;
txtCtx.font = txtH + "px " + font;
txtCtx.textBaseline = "middle";
txtCtx.fillText(txt,0,txtH*.5);

//dirty adjust for descends
txtH *= 1.5;

var bufferCanvas = document.createElement("canvas");
bufferCanvas.width = txtW;
bufferCanvas.height = txtH;
var buffer = bufferCanvas.getContext("2d");

//text start position
var sx = (cw-txtW)*0.5
var sy = (ch-txtH)*0.5

////generate data
var rays = [];
var txtData = txtCtx.getImageData(0,0,txtW,txtH);
for (var i = 0; i < txtData.data.length; i+=4) {
  var ii = i/4;
  var row = Math.floor(ii/txtW)
  var col = ii%txtW
  var alpha = txtData.data[i+3]
  if(alpha !== 0){
    var c = "rgba("
    c += [txtData.data[i],txtData.data[i+1],txtData.data[i+2], alpha/255 ]
    c += ")";
    rays.push(new Ray(Math.floor(ii/txtW), ii%txtW, c));  
  }
}

var current = 1;
//start animation
tick();

function tick() {
  ctx.clearRect(0,0,cw,ch)
  ctx.drawImage(bufferCanvas, 0, 0, current, txtH, sx, sy, current, txtH)
  ctx.save()
  ctx.globalAlpha = .07;
  ctx.globalCompositeOperation = "lighter";
  if(drawRays(current)){
    current++;
    current = Math.min(current, txtW)
    window.requestAnimationFrame(tick)  
  }else{
    fadeOut()
  }
  ctx.restore()
}

function fadeOut(){
  ctx.clearRect(0,0,cw,ch)
  ctx.globalAlpha *= .95;
  ctx.drawImage(bufferCanvas, 0, 0, current, txtH, sx, sy, current, txtH)
  if(ctx.globalAlpha > .01){
   window.requestAnimationFrame(fadeOut)
  }else{
    window.setTimeout(restart, 500)
  }
}
function restart(){
  for(var i = 0; i < rays.length; i++){
    rays[i].reset()
  }
  ctx.globalAlpha = 1
  buffer.clearRect(0,0,txtW,txtH)
  current = 1;
  tick();
}
function drawRays(c){
  var count = 0;
  ctx.beginPath()
  for(var i = 0; i < rays.length; i++){
    var ray = rays[i];
    if(ray.col < c){
      count += ray.draw()
    }
  }
  ctx.stroke()
  return count !== rays.length;
}

function filterRays(r){
  return Boolean(r);
}

function Ray(row, col, f){
  this.col = col;
  this.row = row;
 
  var xp = sx + col;
  var yp = sy + row;
  var fill = f;
 
  var ath = (txtH/1.5)
 
  var a = pi2 * (this.row - ath*.5) / ath;
  if(a === 0){
    a = (Math.random() - .5) * pi2;
  }
  var da = .02 * Math.sign(a);
  da += (Math.random() - .5) * .005;
  var l = 0;
  var dl = Math.random()*2 + 2;
 
  var buffered = false;
  this.reset = function(){
    a = pi2 * (this.row - ath*.5) / ath;
    if(a === 0){
      a = -pi2*.5;
    }
    l = 0;
    buffered = false
  }
  this.draw = function(){
    if(l < 0){
      if(!buffered){
        buffer.fillStyle = fill;
        buffer.fillRect(this.col, this.row, 1, 1);
        buffered = true
      }
      return 1;
    }else{
      ctx.moveTo(xp, yp)
      ctx.lineTo(xp + Math.cos(a) * l, yp + Math.sin(a) * l);
      a += da;
      l += Math.cos(a)*dl;
      return 0;
    }
  }
}