我正在编写一个Chrome扩展程序，可以屏蔽可能令人反感的内容。我正在实现的一种方法是扫描所有图像，看看有多少皮肤在显示。我创建一个新的图像对象，将crossOrigin标志设置为“”，然后创建一个onload函数，将图像绘制到画布上，从画布中读取数据，然后执行分析，为调用函数设置一个布尔标志。定义onload函数后，我将src从我的网页源列表中分配给我的图像节点。 image_scanner函数在for循环内部调用，该循环遍历网页上的每个图像节点并执行各种操作以阻止。这是我执行的最后一个操作。以下是调用image_scanner的代码：
if (image_scanner(options.scanner_sensitivity, images[i]))
{
// Replace the image with a blank white image
images[i].src = chrome.extension.getURL("replacement.png");
}
这是image_scanner函数
function image_scanner(sensitivity, image)
{
// Sensitivity is a number and image is an image node.
// Declare a variable to count the number of skin pixels
var skin_count = 0;
if (image.width == 0 && image.height ==0)
{
// This means the image has no size and we cannot block it.
return false;
} // end if
var return_value = null; // set bool flag
// Create an HTML5 canvas object.
var canvas = document.createElement('canvas');
//window.alert("Created Canvas."); // used for testing.
// Get the context for the canvas.
var context = canvas.getContext("2d"); // This is what we actually use to draw images and pull the data from them.
context.canvas.width = image.width; // Set the canvas width to the width of the image
context.canvas.height = image.height; // Set the canvas height to the height of the image
img = new Image(); // Create a new image node to circumvent cross-domain restrictions.
img.crossOrigin = " "; // Set crossOrigin flag to ' ' so we can extract data from it.
img.onload = function(){
window.alert(img.src); // This always gives the same src until Chrome ends the function
context.drawImage(this, 0,0); // Draw the image onto the canvas.
var pixels = context.getImageData(0, 0, image.width, image.height).data;
// Now pixels is an array where every four entries in the array is the RGBa for a single pixel.
// So pixels[0] is the R value for the first pixel, pixels[1] is the G value for the first pixel,
// pixels[2] is the B value for the first pixel, and pixels[3] is the a (alpha or transparency) value for the first pixel.
// This means that pixels.length/4 is the number of pixels in the image.
// Now we calculate the number of skin pixels we can have before blocking the image.
var limit = ((pixels.length)/4) * (sensitivity/100);
// Now we go through the array of pixel data, checking if each pixel is a skin colored pixel based on its RGB value (the first 3 entries for that pixel in the pixels array)
// Each time we find a skin colored pixel, we increment skin_count and check if skin_count >= limit. If so, we return true.
for (var i = 0; i < pixels.length; i += 4) // We go up by four since every four entries describes 1 pixel
{
// pixel is skin if 0 <= (R-G)/(R+G) <= .5 and B/(R+G) <= .5 pixels[i] is the R value, pixels[i+1] is the G value, and pixels[i+2] is the B value.
if ((0 <= ((pixels[i] - pixels[i+1])/(pixels[i] + pixels[i+1]))) && (((pixels[i] - pixels[i+1])/(pixels[i] + pixels[i+1])) <= 0.5) && ((pixels[i+2]/(pixels[i] + pixels[i+1])) <= 0.5))
{
skin_count++;
//window.alert("Found skin pixel."); // used for testing.
if (skin_count >= limit)
{
//window.alert("Blocking image with src: " + image.src); // used for testing.
img.onload = null; // try to clear the onload function
return_value = true;
return false;
} // end inner if
} // end outer if
} // end for loop
//var temp;
img.onload = null;
return_value = false;
return false;
}; // end onload function
img.src = image.src; // Set the new image to the same url as the old one.
return return_value;
} // end image_scanner
我不确定问题是什么，但是onload函数会运行，遍历像素，设置标志，返回，然后再次运行。我在Chrome的调试器中尝试过调试，这就是我能找到的。我已经尝试在onload函数中将onload设置为null，但它不起作用。我试过从onload函数返回false。我已经尝试在image_scanner函数中等待，直到return_value！= null，但这似乎进入了一个无限循环，我甚至从来没有从onload函数得到警报。如果有人知道为什么onload函数会重复执行，我将非常感激。
答案 0 :(得分：0)
如果您要将.src设置为空白图片，并且在加载时不希望再次调用.onload，则应在设置{之前清除.onload {1}}。
.src看起来你正在从if (image_scanner(options.scanner_sensitivity, images[i])) {
// clear our onload handler
images[i].onload = function() {};
// Replace the image with a blank white image
images[i].src = chrome.extension.getURL("replacement.png");
}
处理程序返回一个值，并期望从image_scanner函数返回该值。它不起作用。在onload已经返回很久之后很久，onload处理程序会被调用一段时间。您需要重写代码以使用image_scanner的异步处理。