shadowBlur（html画布）在js循环中不起作用

Question

我正在尝试改进我使用 JS 创建的天空动画中的星星。这是我发现的时候，我可以使用 shadowBlur 属性来改变围绕我的星星创建的阴影的大小，让它看起来像是在闪烁。现在的问题是 shadowBlur 上升但不会变回黑色。这是我使用的代码。对此的任何帮助将不胜感激:)。

祝你有美好的一天！

// ---- Vars for star animation
let randomStars     = [];
let starCollection  = [];
let numberofStars   = 50;
let flickeringStars = 50;

class Star{
    constructor(x,y,color,radius,shadowBlur){
        this._canvas        = document.querySelector('canvas');
        this._canvas.width  = window.innerWidth;
        this._canvas.height = window.innerHeight; 
        this._c             = this._canvas.getContext('2d');
        this._radius        = radius;

        this._x             = x;
        this._y             = y;
        this._color         = color;  

        this._shadowBlur    = 10;
        this._shadowColor   = 'white';
    }
    //drawing individual stars
    draw(){
        this._c.beginPath();
        this._c.arc(this._x,this._y,this._radius,0,Math.PI * 2,false);
        this._c.fillStyle   = this._color;
        this._c.strokeStyle = 'black';
        this._c.shadowColor = this._shadowColor;
        this._c.shadowBlur  = this._shadowBlur;
        this._c.stroke();
        this._c.fill();
        this._c.closePath();
    }

 
    //Fade in and out for stars
    flicker(){
        setTimeout(()=>{this._shadowBlur=10;},200);
        setTimeout(()=>{this._shadowBlur=8;},400);
        setTimeout(()=>{this._shadowBlur=6;},600);
        setTimeout(()=>{this._shadowBlur=4;},800);
        setTimeout(()=>{this._shadowBlur=2;},1000);

        setTimeout(()=>{this._shadowBlur=0;},1200);
        setTimeout(()=>{this._shadowBlur=2;},1400);
        setTimeout(()=>{this._shadowBlur=4;},1600);
        setTimeout(()=>{this._shadowBlur=6;},1800);
        setTimeout(()=>{this._shadowBlur=8;},2000);
        setTimeout(()=>{this._shadowBlur=10;},2200);

        setTimeout(()=>{this.draw();},200);
        setTimeout(()=>{this.draw();},400);
        setTimeout(()=>{this.draw();},600);
        setTimeout(()=>{this.draw();},800);
        setTimeout(()=>{this.draw();},1000);
        setTimeout(()=>{this.draw();},1200);
        setTimeout(()=>{this.draw();},1400);

        setTimeout(()=>{this.draw();},1600);
        setTimeout(()=>{this.draw();},1800);
        setTimeout(()=>{this.draw();},2000);
        setTimeout(()=>{this.draw();},2200);
    }

    //Clears the canvas
    clearstars(){
        this._c.clearRect(0,0,window.innerWidth, window.innerHeight);
    }

}


// ---- Functions ----

//Typing animation
const typingAnimation       = ()=>{
        if(textProgress < text.length){
            setTimeout(()=>{requestAnimationFrame(typingAnimation)}, speed);
            if(text.charAt(textProgress) === '\n')document.getElementById('animation-text').innerHTML += '</br>';
            document.getElementById('animation-text').innerHTML += text.charAt(textProgress);
            textProgress ++;
        }else{
            let event      = new CustomEvent('showStars');
            dispatchEvent(event);
        }
}
//Store stars
const storeStars            = ()=>{
    starCollection = [];
    
    for(let i=0;i<numberofStars;i++){
        let x           = Math.floor(Math.random()*window.innerWidth);
        let y           = Math.floor(Math.random()*window.innerHeight);
        starCollection.push(new Star(x,y,"white",(Math.random()+1)-0.7));
    }
}
//Show stars to the screen
const showStars             = ()=>{
    for(let i=0;i<starCollection.length;i++){
        starCollection[i].draw();
    }
}
//Store random stars
const generateRandomStars   = ()=>{
    randomStars = [];

    for(let i=0;i<flickeringStars;i++){
        let x           = Math.floor(Math.random()*window.innerWidth);
        let y           = Math.floor(Math.random()*window.innerHeight);
        randomStars.push(new Star(x,y,"white",(Math.random()+1)-0.7));
    }
}
//Show randoms stars after clearing previous set of flickering stars
const showRandomStars       = ()=>{
    let id = window.setTimeout(function () { }, 0);
    while (id--) {
        window.clearTimeout(id); 
    }

    let starHandler = new Star(0,0,"white",0);
    starHandler.clearstars();
                    
    showStars();
    flickerStars();
}
//Flickers stars and changes set of stars randomly
const flickerStars = ()=>{
    for(let i=0;i<flickeringStars;i++){
        setInterval(()=>{
            randomStars[i].flicker();
        },2200);
        setInterval(()=>{
            console.log("changing stars pattern");
            generateRandomStars();
            showRandomStars();
        },12200);
    }
}


// ---- Event Listeners ----

//Typing animation on load
window.addEventListener("load", ()=>{
    storeStars();
    generateRandomStars();
    showStars();
    flickerStars();  
});

//Handles star animation scaling on window resize
window.addEventListener("resize", ()=>{
    let id = window.setTimeout(function () { }, 0);
    while (id--) {
        window.clearTimeout(id); 
    }

    let starHandler = new Star(0,0,"white",0);
    starHandler.clearstars();

    generateRandomStars();
    storeStars();                
    showStars();
    flickerStars();
});

body{
background-color:black;
}

<html>
<body><canvas></canvas></body>
</html>

Answer 1

我无法确定您想要获得的 FX。下面是一个简单的闪烁星形动画，它使用改变大小的小矩形来模拟闪烁。

降低帧率，使闪烁更加明显。

它非常高效，不需要复杂的状态更改，或缓慢的渲染方法（如模糊）

var W = 0, H = 0; // hold canvas size. Set to zero so first frame sizes canvas
var count = 500;         // number of stars
var frame = 0;           // current frame number
const frameRate = 5;     // render stars ever 5 frames

const sizeRange = 1.5;   // max size of star us minSize + sizeRange + flickerSize
const minSize = 1;       // minimum size of star
const flickerSize = 1;   // amount of change random change to make a star brighter
const flickerRate = 0.1; // odds per rendered frame that a star flickers
const stars = [];

// Create a random set of numbers for star positions.
// Values must be larger than largest canvas you are going to use.
// This will work up to 8K display
while (count--) { stars.push(Math.random() * 1024 * 8) } 

const ctx = canvas.getContext("2d");
requestAnimationFrame(mainLoop);

function mainLoop() {
  var len = stars.length, i = 0, x = stars[i++], starSize;

  // if the window has resized change the canvas to fit
  if (W !== innerWidth || H !== innerHeight) {
    W = canvas.width = innerWidth;
    H = canvas.height = innerHeight;
    ctx.fillStyle = "#FFF";
    frame = 0;
  }
  if (frame++ % frameRate === 0) {  // only render every frameRate frames
    ctx.clearRect(0, 0, W, H);            
    ctx.beginPath();  // draw all stars with one path aas it is several orders
                      // of magnitude quicker than creating a path for each
                            
    while (i < len) {
      // draws small stars to large
      const starScale = (i / len);               // set scale from 0 to 1
      starSize = sizeRange;                      // set the range of sizes
      if (Math.random() < flickerRate) {         // on random odds of flicker
        starSize += flickerSize * Math.random(); // add random flicker size
      } 
      starSize *= starScale;   // scale the star
      starSize += minSize;     // add min size of star
      halfSize = starSize / 2; // offset to top left of star

      const y = stars[i++]; // get next random number as star y pos

      // add rect to path fitted to canvas width and height (W, H)
      ctx.rect((x % W) - halfSize , (y % H) - halfSize , starSize , starSize );
      x = y; // Use y for the next x star coordinate

    }
    ctx.fill(); // fill in all the stars
  }
  requestAnimationFrame(mainLoop);
}

canvas {
  position: absolute;
  top: 0px;
  left: 0px;
  background: #000;
}

<canvas id="canvas"></canvas>