web worker 的 self

• A self object, which is the global object representing the worker in this scope.
• 对self对象的译法，未知妥否。

// Call the invertImage method when this worker receives a message from the calling script.
// The ‘self’ object contains the only methods a web worker can access apart from those it
// defines and creates itself
//当此worker收到自来于发出调用的脚本的消息时，调用invertImage方法。“self”对象所包含的web worker所能访问的方法就只有那些由web worker自己本身进行定义和创建的方法。
self.addEventListener("message", invertImage, false);

// Define a function to take an image and invert it, pixel by pixel, using its raw data
//定义一个函数，用作接收图像的原始数据，按像素来逐粒逐粒地实施反相操作。
function invertImage(e) {

    // The ‘data’ property of the ‘message’ event contains the pixel data passed from
    // the calling script
    //“message”事件的“data”属性包含着从发出调用的脚本所包含的像素数据。
    var message = e.data,

        // The ‘data’ property of the message passed contains the raw image pixel data
        //所发送过来的消息中的“data”属性包含着原始图像的像素数据。
        imagePixels = message.data,
        x = 0,
        len = imagePixels.length;

    // Loop through each pixel, inverting its value within the original pixel data array.
    // Pixel data is arranged in groups of 4 values, representing the red, green, blue, and
    // opacity values of each visible screen pixel. We therefore loop through in jumps of 4
    // on each iteration
    //循环遍历每一粒像素，使原始像素数据的数组中所保存的值反相。像素数据按4个值进行分组，分别表示屏幕上所见像素的红、绿、蓝和透明度数值。因此，循环的每轮迭代的加数为4。
    for (; x < len; x += 4) {

        // To invert a pixel’s value, subtract it from the maximum possible value, which is 255
        //要对像素值进行反相，可以用最大的可能值（即255）进行相减。
        imagePixels[x] = 255 - imagePixels[x];
        imagePixels[x + 1] = 255 - imagePixels[x + 1];
        imagePixels[x + 2] = 255 - imagePixels[x + 2];
    }

    // Finally, post a message containing the updated pixel data back to the calling script
    //最后，把包含着更新后的像素数据的消息发送回至发出调用的脚本。
    self.postMessage(message);
}