动画画布看起来像电视噪音

Question

我有一个名为的函数generateNoise(),它创建一个canvas元素并为其绘制随机的RGBA值; 这,给出了噪音的外观.

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我的问题

什么是无限制动噪音的最佳方式,以给出运动的外观.这可能会有更多的生命？

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的jsfiddle

function generateNoise(opacity) {
    if(!!!document.createElement('canvas').getContext) {
        return false;
    }
    var canvas = document.createElement('canvas'),
        ctx = canvas.getContext('2d'),
        x,y,
        r,g,b,
        opacity = opacity || .2;

        canvas.width = 55;
        canvas.height = 55;

        for (x = 0; x < canvas.width; x++){
            for (y = 0; y < canvas.height; y++){
                r = Math.floor(Math.random() * 255);
                g = Math.floor(Math.random() * 255);
                b = Math.floor(Math.random() * 255);

                ctx.fillStyle = 'rgba(' + r + ',' + b + ',' + g + ',' + opacity + ')';
                ctx.fillRect(x,y,1,1);

            }
        }
        document.body.style.backgroundImage = "url(" + canvas.toDataURL("image/png") + ")";

}
generateNoise(.8);

Answer 1

更新1/2017:我重写了整个答案,因为它开始变得相当混乱,并解决了评论中指出的一些问题.原始答案可以在这里找到.新的本质上具有相同的代码,但改进了,并且通过一些新技术,一个人利用了新的功能,因为这个答案是第一次发布的.

对于"真正的"随机外观,我们需要使用像素级渲染.我们可以使用32位无符号缓冲区而不是8位缓冲区来优化它,我们也可以在更新的浏览器中关闭alpha通道,从而加快整个过程(对于旧版浏览器,我们可以简单地设置黑色不透明背景画布元素).

我们ImageData在主循环之外创建一个可重用的对象,因此主要成本仅putImageData()在循环内部而不是两者内部.

var ctx = c.getContext("2d", {alpha: false});       // context without alpha channel.
var idata = ctx.createImageData(c.width, c.height); // create image data
var buffer32 = new Uint32Array(idata.data.buffer);  // get 32-bit view

(function loop() {
  noise(ctx);
  requestAnimationFrame(loop)
})()

function noise(ctx) {
  var len = buffer32.length - 1;
  while(len--) buffer32[len] = Math.random() < 0.5 ? 0 : -1>>0;
  ctx.putImageData(idata, 0, 0);
}

/* for browsers wo/2d alpha disable support */
#c {background:#000}

<canvas id=c width=640 height=320></canvas>

以一些内存为代价但降低CPU成本的一种非常有效的方法是使用噪声预渲染一个较大的离屏画布,然后使用随机整数偏移将该画布放入主画布中.

它需要一些额外的准备步骤,但循环可以完全在GPU上运行.

var w = c.width;
var h = c.height;
var ocanvas = document.createElement("canvas");     // create off-screen canvas
ocanvas.width = w<<1;                               // set offscreen canvas x2 size
ocanvas.height = h<<1;

var octx = ocanvas.getContext("2d", {alpha: false});
var idata = octx.createImageData(ocanvas.width, ocanvas.height);
var buffer32 = new Uint32Array(idata.data.buffer);  // get 32-bit view

// render noise once, to the offscreen-canvas
noise(octx);

// main loop draw the offscreen canvas to random offsets
var ctx = c.getContext("2d", {alpha: false});
(function loop() {
  var x = (w * Math.random())|0;                    // force integer values for position
  var y = (h * Math.random())|0;
  
  ctx.drawImage(ocanvas, -x, -y);                   // draw static noise (pun intended)
  requestAnimationFrame(loop)
})()

function noise(ctx) {
  var len = buffer32.length - 1;
  while(len--) buffer32[len] = Math.random() < 0.5 ? 0 : -1>>0;
  ctx.putImageData(idata, 0, 0);
}

/* for browsers wo/2d alpha disable support */
#c {background:#000}

<canvas id=c width=640 height=320></canvas>

请注意,尽管使用后一种技术,您可能会遇到"冻结",其中新的随机偏移类似于前一个.要解决此问题,请将随机位置的条件设置为禁止连续位置过于接近.

Answer 2

我不久前尝试过做类似的功能.我设置每个像素随机值,除此之外,我覆盖了一个随时间向上移动的正弦波,以使其看起来更逼真.您可以使用wave中的常量来获得不同的效果.

var canvas = null;
var context = null;
var time = 0;
var intervalId = 0;

var makeNoise = function() {
  var imgd = context.createImageData(canvas.width, canvas.height);
  var pix = imgd.data;

  for (var i = 0, n = pix.length; i < n; i += 4) {
      var c = 7 + Math.sin(i/50000 + time/7); // A sine wave of the form sin(ax + bt)
      pix[i] = pix[i+1] = pix[i+2] = 40 * Math.random() * c; // Set a random gray
      pix[i+3] = 255; // 100% opaque
  }

  context.putImageData(imgd, 0, 0);
  time = (time + 1) % canvas.height;
}

var setup = function() {
  canvas = document.getElementById("tv");
  context = canvas.getContext("2d");
}

setup();
intervalId = setInterval(makeNoise, 50);

<canvas id="tv" width="400" height="300"></canvas>

我用它作为网站上的预加载器.我还添加了一个音量摇杆作为加载栏,这是一个截图:

Answer 3

肯的​​回答看起来很不错,但在看了一些真正的电视静态视频之后,我有了一些想法,这就是我想出来的(两个版本):

http://jsfiddle.net/2bzqs/

http://jsfiddle.net/EnQKm/

变更摘要:

• 不是为每个像素独立分配颜色,而是多个像素的运行将获得单一颜色,因此您可以获得这些短的,可变大小的水平线.
• 我应用伽马曲线(使用Math.pow)将颜色偏向黑色.
• 我没有在"波段"区域应用伽玛来模拟条带.

这是代码的主要部分:

var w = ctx.canvas.width,
    h = ctx.canvas.height,
    idata = ctx.createImageData(w, h),
    buffer32 = new Uint32Array(idata.data.buffer),
    len = buffer32.length,
    run = 0,
    color = 0,
    m = Math.random() * 6 + 4,
    band = Math.random() * 256 * 256,
    p = 0,
    i = 0;

for (; i < len;) {
    if (run < 0) {
        run = m * Math.random();
        p = Math.pow(Math.random(), 0.4);
        if (i > band && i < band + 48 * 256) {
            p = Math.random();
        }
        color = (255 * p) << 24;
    }
    run -= 1;
    buffer32[i++] = color;
}

Answer 4

我重新编写了你的​​代码,所以每一步都是独立的,所以你可以重新使用东西,而不必每次创建和重新创建,减少循环调用,并希望它足够清晰,以便能够通过阅读它.

function generateNoise(opacity, h, w) {
    function makeCanvas(h, w) {
         var canvas = document.createElement('canvas');
         canvas.height = h;
         canvas.width = w;
         return canvas;
    }

    function randomise(data, opacity) { // see prev. revision for 8-bit
        var i, x;
        for (i = 0; i < data.length; ++i) {
            x = Math.floor(Math.random() * 0xffffff); // random RGB
            data[i] =  x | opacity; // set all of RGBA for pixel in one go
        }
    }

    function initialise(opacity, h, w) {
        var canvas = makeCanvas(h, w),
            context = canvas.getContext('2d'),
            image = context.createImageData(h, w),
            data = new Uint32Array(image.data.buffer);
        opacity = Math.floor(opacity * 0x255) << 24; // make bitwise OR-able
        return function () {
            randomise(data, opacity); // could be in-place for less overhead
            context.putImageData(image, 0, 0);
            // you may want to consider other ways of setting the canvas
            // as the background so you can take this out of the loop, too
            document.body.style.backgroundImage = "url(" + canvas.toDataURL("image/png") + ")";
        };
    }

    return initialise(opacity || 0.2, h || 55, w || 55);
}

现在您可以创建一些间隔或超时循环,以便不断重新调用生成的函数.

window.setInterval(
    generateNoise(.8, 200, 200),
    100
);

或者requestAnimationFrame像Ken的回答一样

var noise = generateNoise(.8, 200, 200);

(function loop() {
    noise();
    requestAnimationFrame(loop);
})();

DEMO

Answer 5

我碰巧编写了一个脚本来做这件事,通过从黑色画布获取像素,只是改变随机alpha值并使用putImageData

结果可以在http://mouseroot.github.io/Video/index.html找到

var currentAnimationFunction = staticScreen

var screenObject = document.getElementById("screen").getContext("2d");

var pixels = screenObject.getImageData(0,0,500,500);

function staticScreen()
        {
            requestAnimationFrame(currentAnimationFunction);
            //Generate static
            for(var i=0;i < pixels.data.length;i+=4)
            {
                pixels.data[i] = 255;
                pixels.data[i + 1] = 255;
                pixels.data[i + 2] = 255;
                pixels.data[i + 3] = Math.floor((254-155)*Math.random()) + 156;
            }
            screenObject.putImageData(pixels,0,0,0,0,500,500);
            //Draw 'No video input'
            screenObject.fillStyle = "black";
            screenObject.font = "30pt consolas";
            screenObject.fillText("No video input",100,250,500);
        }

Answer 6

我的看起来与真正的电视静态不同，但它仍然相似。我只是遍历画布上的所有像素，并将随机坐标处每个像素的 RGB 颜色分量更改为随机颜色。该演示可以在 CodePen 上找到。

代码如下：

// Setting up the canvas - size, setting a background, and getting the image data(all of the pixels) of the canvas. 
canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
canvas.width = 400;
canvas.height = 400;
canvasData = ctx.createImageData(canvas.width, canvas.height);

//Event listeners that set the canvas size to that of the window when the page loads, and each time the user resizes the window
window.addEventListener("load", windowResize);
window.addEventListener("resize", windowResize);

function windowResize(){
  canvas.style.width = window.innerWidth + 'px';
  canvas.style.height = window.innerHeight + 'px';
}

//A function that manipulates the array of pixel colour data created above using createImageData() 
function setPixel(x, y, r, g, b, a){
  var index = (x + y * canvasData.width) * 4;

  canvasData.data[index] = r;
  canvasData.data[index + 1] = g;
  canvasData.data[index + 2] = b;
  canvasData.data[index + 3] = a;
}

window.requestAnimationFrame(mainLoop);

function mainLoop(){
  // Looping through all the colour data and changing each pixel to a random colour at a random coordinate, using the setPixel function defined earlier
  for(i = 0; i < canvasData.data.length / 4; i++){
    var red = Math.floor(Math.random()*256);
    var green = Math.floor(Math.random()*256);
    var blue = Math.floor(Math.random()*256);
    var randX = Math.floor(Math.random()*canvas.width); 
    var randY = Math.floor(Math.random()*canvas.height);

    setPixel(randX, randY, red, green, blue, 255);
  }

  //Place the image data we created and manipulated onto the canvas
  ctx.putImageData(canvasData, 0, 0);

  //And then do it all again... 
  window.requestAnimationFrame(mainLoop);
}