Javascript获取Facebook个人资料图像像素数据

Question

I need to get the pixel data from a random user's Facebook profile image so I can pass it through Emscripten to our C++ app. That is, I need the RGB values of each pixel. I've tried lots of different ways, using the Javascript FBSDK, graph calls, downloading images, and trying to draw to a canvas I've created but I run into all sorts of issues, eg cross domain problems. I don't need it to be rendered to a visible canvas, I just need toe data to pass back to our app.

Is there a simple way please ?

Answer 1

You can get the image pixel data from Facebook, fetching the image via an Ajax request rather than an img tag.

Specifically, you can:

• Fetch the image data using an XMLHttpRequest
• Wrap up the data in a Blob
• Set the src of an Image to an object URL of the blob
• On load of the image, put the image on a canvas, using the canvas context's drawImage
• Get the pixel data using the context's getImageData

The below. code works for me, on Chrome, without any security issues

document.addEventListener('DOMContentLoaded', function() {
  var xhr = new XMLHttpRequest();
  xhr.responseType = 'arraybuffer';
  xhr.addEventListener("load", onResponse);
  xhr.open("GET", "http://graph.facebook.com/61308470/picture");
  xhr.send();

  var image = new Image();
  var canvas = document.getElementById('canvas');
  var context = canvas.getContext('2d');

  function onResponse() {
    var blob = new Blob([xhr.response], {type: 'image/jpeg'});
    var url = (window.URL || window.webkitURL).createObjectURL(blob);
    image.src = url;
  }

  image.onload = function() {
    context.drawImage(image, 0, 0);
    var data = context.getImageData(0, 0, 50, 50).data;

    // Pixel data of the image
    console.log(data);

    // Cleanup
    (window.URL || window.webkitURL).revokeObjectURL(url);
  }
});

You can see this at http://plnkr.co/edit/fEwoIQRQhaCDRHkwNdvr?p=preview

For reference, it looks like the Facebook profile pictures do set the headers for cross domain ajax. Specifically, the responses set access-control-allow-origin: * .

I based this on this answer to "Using raw image data from ajax request for data URI"