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On 23rd of April 2015, Mihai Șucan passed away due to metastatic cancer caused by RDEB.

My name is Mihai and I work on the Firefox developer tools. When it comes to web development, I like both server-side and client-side work. I am mainly interested in web browsers, web standards and related technologies.

Web Console changes in Aurora (Firefox 15)

Hello Mozillians!

For the Aurora update that's happening this week we have some major changes under the hood for the Web Console.

Async Web Console

Work on making the Web Console UI async, decoupled from all the error and network listeners, started in July last year (bug 673148). Even if it took almost one year to get this bug fixed, I worked on these patches for about 3 months (loosely summing up the total days of work spent on this specific bug).

 Back in those months we strongly pushed for various developer tools to land and get enabled by default in Firefox. I've been working a lot on the source editor which was needed for the Style Editor, the JS debugger and Scratchpad. Work on the Web Console was on and off. 

 There was modest to good progress for the Web Console async work until around September - October when Mozilla's electrolysis project was re-prioritized. The initial work on the patch started out with the goal of making the Web Console ready for e10s. When priorities changed, I went back to source editor work which was higher priority at that point. 

In January - February a really brave and courageous contributor, Sonny Piers, took the huge patch and rebased it. His efforts were commendable given the size and complexity of the work that was going on. Thank you Sonny!

 In March I resumed work and I strongly focused on completing the async patches. Last week the last patch landed in the nightly builds of Firefox. 

What changed? Most of the Web Console was implemented in a single file, HUDService.jsm. It had everything - from UI code to all the error and network listeners and stuff for the window.console API. We have now broken that code into separate scripts with the goal to leave HUDService.jsm as the script that implements only the UI. The new HUDService-content.js script implements all the listeners, all the "backend stuff". The UI code must no longer directly access the content window and objects from the content document.

Why? This work allows us to move to the remote debug protocol and to have the Web Console UI connect to your Firefox Mobile or B2G device where all the error and network listeners are instanced. This work paves the way to a remotable Web Console.

The added benefit is that the async-ness had some modest performance benefits to content scripts (pages) that used the window.console API - a call to any method no longer had to wait for the Web Console UI parts to update.

In the future other Firefox components and extensions can build different UIs on top of the data collected by the HUDService-content.js script.

Lessons learned:

  • Focus, focus and focus! Given big projects one must not try to do everything else.
  • Do not underestimate the time it takes to polish working code, to make it ready for review. I had working code in September-October, but getting it "done" took quite more.
  • Make sure your manager is aware there's a ton of work to do on your project. There's high temptation to be nice and be helpful and do a lot of other work in between. ;)
  • Aggressively split your work into smaller chunks.
  • Be lazy - avoid doing work you don't need to do for the given goal project.

Thanks go to Rob Campbell, Dave Camp, Felipe Gomez, Ms2ger, Joe Walker, Sonny Piers and everyone else who contributed to getting these patches to be ready to land.

Improved performance

Building on top of the async Web Console work we've also made some really nice output performance improvements (bug 722685). In bug 746869 Boris Zbarsky analyzed the performance issues in our code and he made a number of valuable suggestions on how we can make it faster. Thank you Boris!

Our first attempt to make the Web Console output faster has landed in Firefox. Let's go straight for the numbers:

  • Opera 12 (post-beta, latest snapshot, with "cutting-edge" Dragonfly):

    • Closed console:

      • Simple string: 4 ms
      • Interpolation: 1 ms
    • Open console:

      • Simple string: 17 ms
      • Interpolation: 12 ms

      Display performance is sufficiently good. However, it becomes slow to very slow after several runs. No message pruning happens.

  • Chromium 18 (beta):

    • Closed console:

      • Simple string: 21 ms
      • Interpolation: 11 ms
    • Open console:

      • Simple string: 66 ms  
      • Interpolation: 68 ms  

      Performance in content pages is very good. However, display performance is actually poor. First run is fast. Subsequent runs take far more. The web inspector tool UI is frozen for many seconds when the second and third runs happen. Content process separation helps a lot. Even if Web Inspector's display is frozen, web pages continue to run smoothly.

  • Firefox 13 (without the async patches):

    • Closed console:

      • Simple string: 135 ms
      • Interpolation: 128 ms
    • Open console:

      • Simple string: 6941 ms
      • Interpolation: 7376 ms

      Firefox locks up badly, turns gray (frozen). Subsequent runs take the same amount of time - not slower. We prune old messages.

  • Firefox 15 nightly (with the async patches landed): 

    • Closed console:

      • Simple string: 139 ms
      • Interpolation: 134 ms
    • Open console:

      • Simple string: 235 ms
      • Interpolation: 240 ms

      Firefox freezes for less time, it doesn't turn gray on Ubuntu and content script impact is reduced. Subsequent runs are not slower.

  • Firefox 15 Aurora (with the performance patch landed):

    • Closed console:

      • Simple string: 50 ms
      • Interpolated string: 48 ms
    • Open console:

      • Simple string: 51 ms
      • Interpolated string: 48 ms

      For comparison: do note that 1000 dump() calls take around 10-20 ms in Firefox. (dump() is a dumb method we use to output messages to STDOUT.)

      Having the Web Console open or closed no longer directly impacts console API calls. Now the UI no longer freezes and results show up quickly.

      I tried with 5000 calls and we now do better than Opera's Dragonfly and Chrome's Web Inspector - in terms of UI updates. Still, console API calls finish faster, for some reason, in those two browsers.

Please do note that I used the simple test attached to bug 722685 for testing. These numbers are not meant to be "scientific" or anything like that - they are based on my machine setup.

We will continue to do further work in improving the output performance (bug 761257). At this point we still need to avoid doing some unneeded work when a lot of messages end up in the queue to be displayed. We also need to better balance how often and how many messages we display during "heavy fire" - during the execution of content scripts that invoke the console API methods many, many times for an extended period of time.

What's next?

We have plans to move the Web Console UI into its own <iframe>, change the UI to match the other developer tools theme, add the option to move the UI into a real window, make a global console that could replace the Error Console and, obviously, switch to the remote debug protocol so you can use the Web Console with remote Firefox instances. All this and many other improvements, of course!

You may wonder "when?" and the answer to that is that all the improvements will come gradually when we get to implement them.

File bugs, find regressions and let us know what you like and dislike! Thank you!

API reference and packaging for PaintWeb

Hello everyone!

Since my last blog post I have completed the user interface polishing for PaintWeb: the Color Mixer and the Color Picker are both working fine now.

Today I have completed work on packaging. I also generated the complete API reference documentation from the source code.

You can go and play with the PaintWeb demo at the usual location.

For packaging I use a Makefile, YUICompressor, jsdoc-toolkit, PHP and some bash scripts. First of all, I merge all the JavaScript files into a single file. I also merge the XHTML interface layout inside the JavaScript - for this I use a small PHP script which encodes the string using json_encode(). Once I have the hefty script, I use the YUICompressor tool to make it a lot smaller.

For the PaintWeb interface stylesheet I use the YUICompressor in combination with a simple PHP script I wrote. The PHP script inlines the PNG images using data URIs. This helps a lot in reducing the number of elements being downloaded.

Here are the numbers, for those curious of the packaging results. Before packaging:

  • 18 JavaScript files, 426.6 KB;
  • Three JSON files, 33.9 KB;
  • One XHTML file, 14.9 KB;
  • One CSS file, 21.8 KB;
  • 47 images (PNGs), 206.5 KB;
  • A total of 70 files, 703.7 KB.

That's quite much. Here's what the current level of packaging gives us:

  • Two JavaScript files, 130.7 KB - one of them, json2.js, is only 3 KB and is not always loaded;
  • Three JSON files, 33.9 KB. The JSON files are left untouched, the configuration example stays the same - with all the comments in it. It's up to the integrator to choose what he/she does with the file (at the moment).
  • One CSS file, 297.1 KB - with all the images inlined;
  • A total of only 6 files, worth of 461.7 KB.

That's better, but there's room for more. You should always enable gzip compression on your Apache server. Here's what a properly configured server can give you:

  • Two JavaScript files, 35 KB;
  • Three JSON files, 8 KB;
  • One CSS file, 99 KB;
  • A total of six files, and only 142 KB.

That's much better now. To properly configure your server, make sure you enable gzip compression in your .htaccess file:

<IfModule mod_deflate.c>
  <FilesMatch "\.(js|css|json|html)$">
    SetOutputFilter DEFLATE

If you are curious how fast PaintWeb loads, I added a timer in the demo script - you can take a look in a JavaScript console in your Web browser. On my local system it takes less than a second, depending on the browser I use. Go ahead and try PaintWeb yourself. Also make sure you check out the API reference.

In the coming days I will be publishing guides on PaintWeb development, extensibility and general code overview. This means Moodle integration is ready to begin!

PaintWeb performance

Hello everyone!

This week I have completed my work on performance testing and improvements for PaintWeb on the OLPC XO laptop.

During testing it became obvious that something other than the actual Canvas painting was very slow on the XO. The main performance culprit is that the default Gecko-based browser is configured to render pages using 134 DPI instead of the default 96 DPI. Generally web browsers render pages using 96 DPI. If the XO web browser would do the same the texts and the images would be far too small - the XO display is an odd 200 DPI screen perceived as 134 DPI.

PaintWeb's drawing performance was hugely affected by the bilinear scaling of the Canvas elements being done by the browser on the XO. When I configured the browser to render the page using 96 DPI, the web application became a lot more responsive.

Martin Langhoff, my mentor, got in contact with Robert O'Callahan from Mozilla. He provided us with lots of help in finding a solution for the performance issue.

We did think about having a CSS property to change the DPI only for the Canvas elements, or a different CSS property to disable scaling, or some proprietary API for changing the DPI on a single page. None of these are good ideas, because they allow web developers to start coding for specific DPIs - this is not desired.

Gecko scales pages using integer scaling factors - that's 1, 2, 3, etc - it doesn't use floating point numbers. In a normal Gecko build the scaling factor for 134 DPI is 1 - because 134 / 96 = 1, so you do not get any scaling. You can have a scaling factor of 2 or higher if you go above 192 DPI.

Gecko is patched on the XO in a way that it forces the browser to scale pages using floating-point scaling factors as well. Therefore, for 134 DPI the pages are scaled and they look really good on the XO screen.

The final solution which I implemented into PaintWeb is to simply scale down the Canvas elements in my document. If I accurately scale down the elements, Gecko is sufficiently optimized to cancel any scaling and you do not notice any performance impact. This works really great.

In Gecko 1.9.1 (Firefox 3.5) I can detect the DPI used for rendering the page with CSS 3 Media Queries. I use this in PaintWeb. However, the XO only has Gecko 1.9.0 for now, so I cannot determine the DPI. I am forced to do user agent sniffing to check if the browser runs on the OLPC XO. If it does, then I scale down the Canvas elements using a different way of calculating the scale-down factor - because Gecko is patched - and I always consider the page is render using 134 DPI. Fun, huh? ;)

On Opera, on the XO, I did all my testing using 100% zoom level. It ran much better than Gecko, for obvious reasons (no scaling, yay). Once I fixed the Gecko scaling issue, Opera came second. For some reason Canvas draws much faster in Gecko than in Opera on the OLPC XO.

Opera cannot render pages using different DPI values other than 96. People use zoom, so, for consistency, I use an old trick to measure the zoom level (thanks Arve). Based on this I scale down the Canvas elements. For some zoom levels, like 200%, the scaling is cancelled and PaintWeb works better. Unfortunately, Opera does not allow non-integer pixel values, thus the scaling-down is generally not effective...

Another important performance improvement in PaintWeb is the use of timer-based canvas drawing. This means that mouse move events are either cancelled or coalesced into one. For example, redrawing a polygon with a lot of points for every mouse move is very slow. The tools in PaintWeb use timers to update the canvas every few milliseconds. This approach makes PaintWeb feel faster.

Lastly, I now avoid going into the global scope, for things like Math.round or such. The importance of this change is reduced by the fact the JavaScript that runs is not very intensive - not too much code is executed for each mouse move event. Such changes become more important the more code you run. This will be important for the color space visualization I have.  

The loading performance will improve greatly once I will make a packager for PaintWeb. Additionally, I will continue to constantly check the overall performance of the web application on the OLPC XO.

Go ahead and try PaintWeb from SVN trunk. Lots of thanks to Robert for his great help and to Martin for his assistance and for finding the Gecko patches.

Currently I am working on the new user interface, stay tuned!

Update May 31, 2009: Just published a page on the OLPC wiki about the HTML Canvas performance on the OLPC XO laptops. The page includes code snippets explaining how to work-around the scaling issue.

PaintWeb code refactoring and more

Hello everyone!

I have been working on the PaintWeb code refactoring and now I am nearing completion. The initial PaintWeb 0.5 alpha code was more of a demo - it was all in a single big script. I have now added jsdoc comments almost everywhere and I did split the code into multiple files - per tools, per extensions, per language, and more. I have also made important changes to the API. Now any external code can easily add/remove tools, extensions and keyboard shortcuts.

For more developer-related information please read the latest forum thread I posted on the Moodle forums.

For teachers and potential users of PaintWeb inside Moodle, I have prepared a list of questions on how you would use the paint tool in Moodle.

Martin, my mentor, suggested early in my GSOC application process to also apply for the OLPC Contributors program. So I did, and my project was accepted.

Even if the OLPC XO has a slow CPU by today's expectations, it's only 400 Mhz, the system works quite nicely. It has 256 MB of RAM and 1GB of disk capacity. The Sugar interface and the activities provided are amazing. People who hear about these laptops do not know to appreciate the numerous doors such laptops open, doors to knowledge, for all those children who receive them. They help a lot in learning about computing, maths, music, and more.

The Sugar interface is quite well thought-out. I like the concept of having the neighbourhood, group, home and activity views.

The default browser, is some Python application embedding Gecko - on par with Firefox 3.0. The performance of the browser is lacking. Opera 10 alphas start much faster and feel snappier. The paint tool feels sluggish as well.

The Gnash plugin is more of a problem rather than a solution. I installed Flash Player 10, which is sluggish, but at least it works. The system can play Youtube high-quality videos and even uncompressed DVD videos, with Mplayer over the wireless connection. Flash Player cannot play Youtube videos.

Battery life is good - I can use it about three hours without any problems.

Since last week I have been working on the performance of the PaintWeb application, with the OLPC XO-1 laptop. After several tests, I have managed to improve things sufficiently such that the paint tool is now usable in Opera 10 on the XO. Unfortunately, in Browse.xo it's not, at least not by default.

The main performance culprit affecting PaintWeb on the XO is their use of layout.css.dpi. Gecko allows users to change the DPI used for rendering Web pages, in order to makes fonts and images smaller or bigger. So, on the XO the browser is set to use DPI 134, instead of DPI 96. This makes the fonts and images render bigger - with DPI 96 they would all be way too small. PaintWeb and all the pages feel much slower because Gecko performs bilinear image resampling.

When I set layout.css.dpi to 96, drawing in PaintWeb becomes real-time. I was amazed to see it works so well. It's like on my desktop computer. And ... it's even faster than in Opera 10. ;)

If you want, check out the performance tests yourself. Spoiler: Webkit is the fastest and Gecko is the slowest when running synthetic tests. Obviously, more performance tests will come - these are only limited to the pencil tool and to the main ev_canvas() event handler from PaintWeb.

Next on my of list things to do is a new GUI and a packager for the entire code. Loading PaintWeb is now slower due to the amount of code comments and the increasing number of files. The packager will compress/minify all the files into a single one.

That's all for now. Any feedback is welcome!

Opera and Firefox: speed


Yesterday I had to install Windows 98 on a really slow computer by "today's standards", a Pentium I, with only 32 MB.

The computer is a bit unstable. During system installation had some BSODs (probably corrupted RAM and/or damaged mother board).

This guy will have a broadband Internet connection.

As a browser, I, of course, excluded Internet Explorer as an option.

I got Opera 8.5 with all settings to the minimum (no skin, no smooth zoom, no smooth scrolling, no special effects, nothing). Booted and worked really fast, loved it ;). I wasn't expecting that. Yet, it causes BSODs on Opera's own site and some other sites (told you the computer is unstable!).

Now, I had to give Firefox 1.0 a try, hoping it's not slower and won't cause as many BSODs as Opera.

Yet, yesterday I finally saw for the first time the true speed difference in start-up times between Opera and Firefox. Starting Opera takes less than 3 seconds ... yet with Firefox ... you wait and wait more :), from double to triple more time. Page rendering, scrolling and overall browser usage is also slower (menus, preferences, etc).

Sadly, there's nothing to configure in Firefox to really make it faster. Also, Firefox crashed on few starts and on some sites (like mine).


  1. Firefox is not more stable than Opera (nor vice-versa). The stability issues have been caused by the hardware.
  2. Opera is a lot faster. Really usable on such a slow computer.

The only problem of Opera is PNG rendering. On my site Firefox was a tad faster :).

I actually managed to browse my site with Opera ... but Firefox crashed :).

P.S. This is not an "Opera fan rant". It's clear to me now which browser is faster: Opera. Those who really want to know which browser is faster got to try them with a really slow computer.