GIMP Layers

Akkana Peck: Graphical Python Programming With PyGTK

2009-05-15T02:01:06+00:00

This week's Linux Planet article is another one on Python and graphical toolkits, but this time it's a little more advanced: Graphical Python Programming With PyGTK.

This one started out as a fun and whizzy screensaver sort of program that draws lots of pretty colors -- but I couldn't quite fit it all into one article, so that will have to wait for the sequel two weeks from now.

Akkana Peck: Upgrading without risk

2009-05-13T17:02:06+00:00

Someone asked on a mailing list whether to upgrade to a new OS release when her current install was working so well. I thought I should write up how I back up my old systems before attempting a risky upgrade or new install.

On my disks, I make several relatively small partitions, maybe 15G or so (pause to laugh about what I would have thought ten or even five years ago if someone told me I'd be referring to 15G as "small"), one small shared /boot partition, a swap partition, and use the rest of the disk for /home or other shared data.

Now you can install a new release, like 9.04, onto a new partition without risking your existing install.

If you prefer upgrading rather than running the installer, you can do that too. I needed a jaunty (9.04) install to test whether a bug was fixed. But my intrepid (8.10) is working fine and I know there are some issues with jaunty, so I didn't want to risk the working install. So from Intrepid, I copied the whole root partition over to one of my spare root partitions, sda5:

mkfs.ext3 /dev/sda5
mkdir /jaunty
mount /dev/sda5 /jaunty
cp -ax / /jaunty

(that last step takes quite a while: you're copying the whole system.)

Now there are a couple of things you have to do to make that /jaunty partition work as a bootable install:

1. /dev on an ubuntu system isn't a real file system, but something magically created by the kernel and udev. But to boot, you need some basic stuff there. When you're up and running, that's stored in /dev/.static, so you can copy it like this: cp -ax /dev/.static/dev/ /jaunty/dev/

2. /etc/fstab on the system you just created points to the wrong root partition, so you have to fix that. As root, edit /etc/fstab in your favorite editor (e.g. sudo vim /etc/fstab or whatever) and find the line for the root filesystem -- the one where the second entry on the line is /. It'll look something like this:

# /dev/sda1
UUID=f7djaac8-fd44-672b-3432-5afd759bc561  /  ext3  relatime,errors=remount-ro  0 1

The easy fix is to change that to point to your new disk partition:

# jaunty is now on /dev/sda5
/dev/sda5  /  ext3  relatime,errors=remount-ro  0 1

If you want to do it the "right", ubuntu-approved way, with UUIDs, you can get the UUID of your disk this way:

ls -l /dev/disk/by-uuid/ | grep sda5

Take the UUID (that's the big long hex number with the dashes) and put it after the UUID= in the original fstab line.

While you're editing /etc/fstab, be sure to look for any lines that might mount /dev/sda5 as something other than root and delete them or comment them out.

Now you should have a partition that you can boot into and upgrade. Now you just need to tell grub about it. As root, edit /boot/grub/menu.lst and find the line that's booting your current kernel. If you haven't changed the file yourself, that's probably right after a line that says:

## ## End Default Options ##

It will look something like this:

title           Ubuntu 8.10, kernel 2.6.27-11-generic
uuid            f7djaac8-fd44-672b-3432-5afd759bc561
kernel          /vmlinuz-2.6.27-11-generic root=UUID=f7djaac8-fd44-672b-3432-5afd759bc561 ro
initrd          /initrd.img-2.6.27-11-generic

Make a copy of this whole stanza, so you have two identical copies, and edit one of them. (If you edit the first of them, the new OS it will be the default when you boot; if you're not that confident, edit the second copy.) Change the two UUIDs to point to your new disk partition (the same UUID you just put into /etc/fstab) and change the Title to say 9.04 or Jaunty or My Copy or whatever you want the title to be (this is the title that shows up in the grub menu when you first boot the machine).

Now you should be able to boot into your new partition. Most things should basically work -- certainly enough to start a do-release-upgrade without risking your original install.

Akkana Peck: Making desktop recordings with recordmydesktop

2009-05-12T17:31:09+00:00

Apress asked me to make some short screencast videos illustrating GIMP tips, to help advertise the second edition of Beginning GIMP.

I've never made videos (except for putting a digital camera in video mode) so it's been an interesting learning experience, and I was surprised at how easy it was in the end.

My Apress contact suggested XVidCap and Wink as possible options. XVidCap looked quite interesting but didn't seem to work in its Ubuntu incarnation. Wink worked very nicely and produced flash videos that worked in a browser with no extra fiddling ... but unfortunately when I tried plugging in a microphone, Wink didn't seem able to read it. And it seemed to slow down all my cursor movements, rather than following my actions in real-time.

But while working with those two, I stumbled across recordmydesktop. It records mouse movements in real-time and it handles the microphone too. It has several front ends available (such as gtk-recordmydesktop) but I found the basic command-line version easiest to use.

To make a video in the upper left 1024x768 section of my screen:
recordmydesktop -width 1024 -height 768 -o layermask.ogv

Since I need to make sure all the action happens within that rectangle, I made a special desktop background that has a nice, not too distracting image in just that 1024x768 rectangle. Any other windows I'm using in that desktop (such the terminal window I'm using to control recordmydesktop) stay outside that area.

recordmydesktop starts recording right away. I run through my tutorial steps, narrating as I go, and when I'm done, I move the mouse back to the terminal window where I started the recording and hit Ctrl-C, and recordmydesktop stops recording and encodes the video (which takes a while).

It saves to ogg format, .ogv. Of course, most web surfers can't view that, and youtube doesn't accept it either (at least, ogg isn't on its list of allowed formats) so I needed to translate it into something else. Youtube suggests mpeg4, so that's what I used. Luckily, I already had a mencoder incantation that some helpful person gave me a long time ago:
mencoder movie.ogv -oac pcm -ovc lavc -lavcopts vcodec=mpeg4:vqmin=2:vlelim=-4:vcelim=9:lumi_mask=0.05:dark_mask=0.01:vhq -o movie.mp4

Only one problem: the audio came out very faint and difficult to hear. I'm sure that's a problem with the microphone I'm using, a cheap OEM model that came with some computer or other many years ago -- it's been sitting in a box since I normally have no use for a microphone. But it turns out mencoder can amplify the volume, with -af volume=X where X is decibels. A little experimentation with mplayer -af volume=X on the original ogg suggested a value around 15 or 20, so the final encoding was:
mencoder movie.ogv -af volume=19 -oac pcm -ovc lavc -lavcopts vcodec=mpeg4:vqmin=2:vlelim=-4:vcelim=9:lumi_mask=0.05:dark_mask=0.01:vhq -o movie.mp4

But Apress tells me that their Windows boxen had trouble with the mp4 and they had to run it through something called "Handbrake", so maybe some other format would have worked better. Here are two other mencoder incantations I know (without the sound amplification):
mencoder movie.ogv -oac pcm -ovc lavc -o movie.divx (divx -- Windows sometimes has trouble with this too)
mencoder movie.ogv -oac pcm -ovc lavc -lavcopts vcodec=mpeg1video -o movie.mpeg (mpeg1)

It's not great cinema, but the end result is up on the Apress page for the GIMP book.

Dave Neary: Run a marathon… check!

2009-05-11T14:02:33+00:00

Yesterday, on my second serious attempt (previously I injured myself 4 weeks before the race) I finally ran a marathon in Geneva, Switzerland.

Since getting injured in 2007, I’ve taken up running fairly seriously, joined a club, and this time round I was fairly conscientious about my training, getting in most of my long runs, speed work & pace runs as planned. I thought I was prepared, but I don’t think anything can prepare you for actually running 42.195 kilometers at race pace. Athletes will tell you that the marathon is one of the hardest events out there because it’s not just a long-distance race, it’s also a race where you have to run fast all the time. But until you’ve done it, it’s hard to appreciate what they mean.

This year, the club chose the Geneva marathon as a club outing, and around 40 club members signed up for either the marathon or the half-marathon on the banks of Lac Leman, and I couldn’t resist signing up for the marathon.

I wasn’t in perfect health, since I’ve been feeling some twinges in my right hip & hamstring for the past couple of weeks, but during taper before the race I’ve been taking it very easy, and I felt pretty good the day before. With the club we met up on Saturday 9th after lunch, and drove to Geneva to get our race numbers, and then to the hotel in Annemasse for a “special marathon runner’s” dinner (which had a little too much lardons, vinaigrette & buttery sauce to be called a true marathon runner meal), last minute preparations for the big day, and a good night’s rest.

Up early, light breakfast, back into Geneva for the race. Arrived at 7am, lots of marathon runners around, and the excitement levels are starting to climb. After the usual formalities (vaseline under armpits and between thighs, taped nipples, visit to toilet) we made our way to the starting line for the 8am start.

Nice pace from the start - a little fast, even, but by the 3rd kilometer I’d settled into my race pace, at around 4′40 per kilometer (aiming for 3h20 with a couple of minutes margin). Walked across every water station to get two or three good mouthfuls of water and banana without upsetting my tummy. Around kilometer 7, I started to feel a little twinge in the hamstring and piriformis/pyramidal muscle, and I felt like I might be in for a long day. It didn’t start affecting me for a while, but by kilometer 16, I was starting to feel muscles seize up in my hip in reaction to the pain.

First half completed on schedule, 1h38′55, and I was feeling pretty good. Not long afterwards, every step was getting painful. Around kilometer 26, I decided (or was my body deciding for me?) to ease off on the pace a little and I started running kilometers at 4′50 to 5′.

They talk about the wall, but you don’t know what they mean until you hit it. Around kilometer 32, I found out. At first, I welcomed the feeling of heavy legs - it drowned out the pain from my hip, and here was a familiar sensation I thought I could manage. But as the kilometers wore on, and my pace dropped, I was having a harder and harder time putting one foot in front of the other. Starting again after walking across a water stop at kilometers 33 and 38 was hard - it was pure will that got me going again. My pace was slipping - from 5′ to 5′30 - one kilometer I ran in 6′. It looked like I was barely going to finish in 3′30, if I made it to the end at all.

Then a club-mate who was on a slower pace caught up to me, tapped me on the shoulder, and said “Hang on to me, we’ll finish together” (”accroche toi, on termine ensemble”). A life-saver. Manna from heaven. I picked up speed to match him - if only for 100m. After that, I said to myself, I’ll try to keep this up for another kilometer. When we passed the marker for 40k, I said I’d make it to 41 with him, and let him off for the last straight. And when we got to the final straight, I summoned up everything I had left to go for the last 1200m.

In the end, I covered those last 3200m in an average of 4′35 per kilometer - which just went to teach me that those 5km when I was feeling sorry for myself were more mental blockage than anything else, and I was able to overcome my body screaming out at me to stop.

The record will show that I ran 3h26′33 for my first marathon, but that doesn’t come close to telling the story.

Afterwards, I got a massage, drank a lot of water, ate some banana, and, feeling emptied & drained, a wave of emotion overcame me when I realised what I’d done.

Congratulations to the other first-time marathon runners who ran with me yesterday, and thank you Paco, I’ll never forget that you got me to the end of my first marathon.

Update: The marathon organisers had a video camera recording everyone’s arrival during the race. I discovered this afterwards, otherwise I might have been slightly more restrained after crossing the line.

You can see me arriving here, and Paco, who arrived a few seconds after me, here - for the extended sound-track.

Carol Spears: Google Summer of Code

2009-05-10T15:16:00+00:00

I tried one software that was produced via the Google Summer of Code machine. It did not work. How many of those softwares actually do what they are supposed to?