Programmer’s Log Programmers Writing Stuff – Garry Bodsworth

Cluttered Mind

Finally, I have contributed something back to an open-source project.

The memory leak in Clutter I mentioned in a previous post has been fixed. I submitted the patches last week, and they got pushed onto master in time for Clutter 1.0.

I've been playing around with Clutter a bit more now and it is well inside the GTK+ comfort zone. I am really pleased I can contribute something useful to a project of this size because I am so used to using libraries but not actually fixing them. It's the glory of open-source.

I've been playing around a little with Clutter 1.0 and its master clock based animation and it looks really interesting. Just be careful that some parameters are floats instead of ints now and this caused me to segfault.

Intel 945GM Linux Drivers – The Good Bits

Using the latest Linux drivers for Intel 945GM are really, really good. The best drivers available for Linux displays in my humble opinion, especially since the deficiencies are more hardware related rather than the software.

Using the UXA acceleration you can even composite x-video windows in OpenGL. The 3D performance is impressive for such an old device and as of the end of last week xvmc was working as well with GEM. It uses the latest tech available in Linux display drivers like Kernel Mode Setting and DRI2 (which is a new interface for speaking to the kernel).

The latest drivers are also not only well capable of good compositing, but they are also capable of it without tearing, even with x-video surfaces. The actual rendering itself doesn't tear any more thanks to people like Jesse Barnes who have put great effort into that work.

Since computers like netbooks/nettops are coming with the 945GM chipset, good support for it is essential. This is even better when it is open-source because you can help out with hackery and diagnosis (actually editing the code is very scary, but I tried a bit attempting to backport some changes to 2.7 because master was not stable enough at the time). It was a bit frustrating trying to balance performance, features and stability when deciding which driver version to finally run with, but I can see the driver is almost there with some minor stability work.

So I must say the guys have done really good work and 2.8 looks like it will be a really good release performance/feature-wise. I think I have wedged the hardware a few times, but I suppose the 2.7.99 releases are alpha, and also it is probably down to me hammering the graphics card.

Intel 945GM Linux Drivers – UXA and Memory Leaks

One of the things I have been plugging away with at work is getting Intel 945GM graphics drivers working at their best. I was using 2.6 and 2.7 with the new UXA acceleration because it works really well with composite and xvideo.

The problem was there was a memory leak that you could drive a bus through. Because the Linux driver stack is so complex (Mesa, X Driver, X-server, kernel gubbins, the Direct Rendering Manager library) it was proving extremely difficult to find where the memory was going because it was still being used even when the process was closed.

With the code I was writing I found I could get the memory of the computer fully utilised in less than one hundred iterations. Luckily that meant I could write a small test case. The bug hit particularly hard in Moblin which relied on the Intel drivers and Clutter. At least five bugs in Freedesktop Bugzilla seem to report it, plenty in Launchpad, and several in Moblin.

As it turned out Shuang He of Intel diagnosed the root of the problem in the Mesa driver where pixmaps weren't being released properly and has submitted some patches for that. The mesa patches have been applied if you use xorg-edgers on Ubuntu which makes life a lot easier considering I spent four hours building my own fixed Mesa...

Not only this but there was a memory leak in Clutter (which I submitted patches for) which are now in their git master repository.

Now with both of those things fixed compositing windows using Clutter works brilliantly and will work for an extended period of time rather than falling over after a short time. Also if these patches are used on Moblin v2, you should get a better experience.

It’s Aliiiive!

This poor corner of the Internet has been neglected of late, and it is almost time for me to renew my domain. So I have two options - let it die or pull my finger out and actually post some content. Inbetween work and a new baby I find spare time a bit scarce (or non-existent).

But the doors won't be shutting here because at some point the baby has to sleep at some point in the future and that means I get to use my laptop.

Python Programming Dojo – Cambridge

Yesterday I ran the Python Programming Dojo in Cambridge. It was my first time running such a public speaking event. We had four people in attendance which made it a bit easier on me after four or five last minute drop-outs.

Basically, it was to cover getting started in Python development from first concepts through to more advanced ones. I can hardly believe I talked more or less continually for six hours(!) I had prepared cue cards so I didn't forget any subjects I wanted to cover and had smushed together a load of examples to go with each subject.

One of the most bizarre things was I didn't get onto the fact Python had classes until lunchtime at 1pm.... It was hard to try and cover the basics because everything relied on something else, so I was dynamically juggling the order of the subjects.

The best bit was the interaction where people were coding whilst I was talking and the discussion points and questions came out of that.

I found it really hard to explain list comprehensions because I kind of instinctively knew them, but I had managed up until now to never need to explain them.

The benefits of doing this class were many for me. First, up I had programmed in Python for a while but I just did it and didn't really think about why and how much I had used. Organising those thoughts was invaluable. Also, had to do speaking at the front of the room and I think I did okay apart from waving my hands too much and using the word "mad" too often in the description of Python features... The other benefit was I learnt some things as well.

The main Python feature I learnt was the flyweight pattern feature of Python classes. Basically if you define a variable as part of the class you maximise reuse of that object. If you defined a variable using self, it will be added to the class dictionary. We checked this by writing code which is the best way to learn.

I don't know if I will end up running one again or if it is a one-off, but I will try to update my examples and subjects to reflect what I discovered throughout the day (if I actually transfer them to digital format rather than hand-written cards I'll post it on here).

Finally, I'd like to thank Red Gate Software for supplying refreshments and somewhere to host it, Mark Dalgarno for organising it, and Clive Tong of Red Gate for making sure we could get in (and not forgetting the attendees).