As part of my first lab, we were to get a feel for the different interface builder UI objects within a single view in order to create a manipulating student profile. See below.

All was good until I got to getImageData(), where I encountered an exception in console. The crux is this: I’m getting an NS_ERROR_DOM_SECURITY_ERR error when trying to run context.getImageData()

A bit about getImageData():

To obtain an ImageData object containing a copy of the pixel data for a context, you can use the getImageData() method:

var myImageData = context.getImageData(left, top, width, height);

Ultimately, I wanted to use this function to place a image on canvas and perform some direct pixel manipulation; perhaps inverse an image by first getting the image data from a context.

window.addEventListener('load', function () {
  var canvas = document.getElementById("canvas");
  var ctx = canvas.getContext("2d");
  var img = new Image();

  img.addEventListener('load', function () {
    var x = 0,
      y = 0;

    ctx.drawImage(this, x, y);

    var imgd = ctx.getImageData(x, y, this.width, this.height);
    var imxpxl = imgd.data;

    for (var i = 0, n = imxpxl.length; i < n; i += 4) {
      imxpxl[i] = 255 - imxpxl[i]; // red
      imxpxl[i + 1] = 255 - imxpxl[i + 1] // green;
      imxpxl[i + 2] = 255 - imxpxl[i + 2] // blue;
      // i+3 is alpha
    }
    ctx.putImageData(imgd, x, y);
  },
  false);
  img.src = "http://www.google.ca/intl/en_ca/images/logo.gif";
},
false);

Running this code, I didn't get the results I expected. In fact, I did not think out of the ordinary was incorrect, until I checked the error console and found:

Error: uncaught exception: [Exception... "Security error"  code: "1000" nsresult: "0x805303e8 (NS_ERROR_DOM_SECURITY_ERR)"  location: "file:///pixeldata.html Line: 16"]

Interesting - why the need to raise privileges? Am I forgetting something here? If I toss a,

netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead");

I end up with something yucky like this

try {
  try {
    imgd = ctx.getImageData(x, y, this.width, this.height);
  } catch(e) {
    netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead");
    imgd = ctx.getImageData(x, y, this.width, this.height);
  }
} catch(e) {
  throw new Error("unable to access image data: " + e);
}

but, running the code will yield:

A script from "file://" is requesting enhanced abilities that are UNSAFE and could be used to compromise your machine or data:

In this case, the code will run - but it will leave you with an impression that what you're doing is wrong.

I'm not nefarious, I swear! No intent to do harm here. I am trying to understand the reasoning and or need for raised privileges just to extract data from a context. With a write to canvas, a nefarious user could write something nasty to context, but why with getImageData?

- Aaron

Upon reading the WebMonkey article, “After Five Years on the Web Firefox Preps for the Next Round“, I was reminded of a suppressed annoyance, or ‘beef’ I have with Firefox through reading Jonathan Nightengale’s statement.

“When a developer loses the ability to view a web page’s source code (something you can’t easily do in Flash) they can’t see how web applications and complex interactions function. And, he says, that stymies further experimentation”

Jonathan is absolutely correct. Developers need the ability to learn from each other and the only best way to do this is through viewing a web page’s source code. View Page Source is a door to undiscovered knowledge on the web.

Ah yes, ‘View Page Source’.

See, in order to boast and fully support this idea, I believe that developers need to have access to the best tools available. Developers need to harness these tools and utilize them to their fullest potential. These tools should exhibit engaging yet intuitive functionality and rewarding characteristics.

See, my ‘beef’ is with Firefox’s ‘View Page Source’. It sucks. It’s really bad. It’s archaic. In-fact, here are 200 bugs spanning multiple years pertaining to the simple view-source component in Firefox.

Here’s my personal listing of ideas to improve View Source with 5 improvements:

1. Introduce proper syntax highlighting (crucially needed with the new HTML5 parser)
2. Links should have copy link location in the context menu
3. Line numbers should appear in a side column
4. Add view-selection-source ability
5. Interface should be tabbed!

With many of those 200 (simple query search of ‘View Source’) filed as enhancements, it’s clear that the view-source component needs a complete overhaul.

I believe that Firefox needs to revamp it’s view-source component in order to supply developers with the best tools necessary to prevent a case of being stymied from experimentation and any other further barriers of innovation on the web.

Developers need the best tools out there, and I feel that they are left out of what could be an awesomely improved component and uniquely defined characteristic of the entire Firefox experience.

Currently, I dont think there is a significant drive towards prioritizing this component in the browser. In fact, I dont think it has been touched in many years. It certainly feels archaic, sluggish and lacking. Has the code been touched in years?

So I ask the community, you reading this, do you wish to collaborate to revitalize this dying dead horse?

What do you think?

As part of Toronto Open Source Week, tomorrow marks the start of the 8th annual Free Software and Open Source Symposium at Seneca College

With a vast range of academically intriguing presentations and focused based hands-on workshops to choose from, I have narrowed down a listing of presentations that I will attend to.

Bring on tomorrow – I hope to see you all there :) ]]> http://aaronmt.com/?feed=rss2&p=579 0 http://aaronmt.com/?p=502 http://aaronmt.com/?p=502#comments Thu, 01 Oct 2009 20:43:09 +0000 Aaron http://aaronmt.com/?p=502

October 24-30, 2009

Toronto Open Source Week is a celebration of Open Source technology and community throughout the Toronto area. The following events have been confirmed; additional events are being planned.