My GTK3 porting story

It is now possible to run Cheese using GTK+ 3 getting it from Cheese’s branch gtk3.

Cheese has a gtk3 branch for a while, but until very recently it only had one patch changing mostly versions in configure.ac. Then Bastien Nocera made 3 more patches changing code of CheeseWidget, CheeseFlash and um-crop-area. I wanted to use the changes, and silly me, I thought the branch was going to compile when I first tried to run it. It turns out that I spent days on it until it finally compiled and then a little more time before I was able to run it.

Most of the changes were on build system and Cheese’s vala code. I have never programmed in vala before, so this was a learning opportunity with some challenges in the way.

Funny story

Cheese was still using libunique-1.0, but in order to work with gtk3 I would have to switch to libunique-3.0. There was no vala binding for libunique 3, but I also hadn’t found one for clutter-gtk-1.0 and I was using the GObject Instrospection one instead and it seemed to work at the time.

Using gir files didn’t work so well with libunique. Vala was loading the right gir file, but it said the namespace “Unique” did not exist. So, I asked for help on the #vala channel. The first piece of advice was to switch to GApplication instead of using libunique, but I didn’t know how hard that would be and I wanted to understand why I was unable to use libunique-3.0 first. With some more help from someone else in the #vala channel I found out that the Unique-3.0.gir file had the wrong package name on it. As I didn’t know how to fix that and I didn’t even know if it was a problem in libunique or a GObject Introspection parsing problem I asked for help in #introspection.

In the #introspection channel, Emmanuele Bassi (ebassi) was the one that helped me, libunique’s maintainer. Isn’t it nice when that happens? I mean, you’re just asking for anyone less clueless than you to help, but you can actually talk with people that work on what you’re using. Anyway, continuing with the long story, ebassi told me the problem was in libunique, that he wouldn’t work on it soon, but he encouraged me to file a bug for it and I did. It turned out that the bug was easy to fix (for him at least) and something like 15 mins later he had fixed it and pushed it to master already. That was a nice surprise!

But my problems didn’t end there. After I fixed some GObject Introspection annotation in libunique for my code to work, valac started to crash with a segfault. I reported it, but I still don’t know what the exact problem was. The only way I found to fix it was to switch to GtkApplication and stop using libunique. If only I had listened to that first advice! Using clutter-gtk with GObject Introspection did not work in the end either, but turns out I was just missing the recently released vala binding for it.

I learned many things on this quest. I had never looked at gir files or vapi files before and I learned a little trying to debug and fix problems. The non-technical lessons were: it’s really painful to use stuff that is new and not widely used (yet?), you will find problems. But it’s also very nice to be able to fix the problems and work with helpful people.

By the way, to share my love for GNOME I’m organizing a GNOME 3.0 Release party in my town – Belo Horizonte, Brazil. So, if you’re in the area, save April 9th and get in touch if you want to help with organization.

Update: Patricia Santana Cruz had already made a patch to port Cheese to Gtk.Application (which is also way better than mine), so if I was any smarter I wouldn’t have half of the work I did. And now I know she is also one of the responsibles for we having the clutter-gtk-1.0 binding for vala too and she is working on some more bugs in vala and going after the warnings that affects Cheese. In short, she is awesome!

Cheese with Camerabin

So, last week I posted I started changing Cheese to use Camerabin, the high level GStreamer element that can capture video, photos and show preview. I can now say that Cheese is now working using Camerabin as its base, at least for me and two other people.

I’m a little embarrassed to say that the black preview problem I was having all along was actually because of lack of dconf installed in jhbuild. Because of that, my contrast and saturation were always set to zero when I started Cheese and I thought that was a problem with the preview, specially because I did have a problem with clutter-gst before. Thanks to Laura I discovered that.

Other problems were much easier to solve after I stopped debugging this nonexistent problem. The main problem was that Camerabin sets a lot of stuff by default, such as resolution and filtered video format. This caused a lot of negotiation problems depending on which camera was used or which size of photo or video was requested. After working around the defaults, it seems to be working ok now.

Another improvement was to use Camerabin’s signal “set-video-resolution-fps” to set resolution for photo and video, instead of using a capsfilter for that. In the future, we might be able to switch between photo-capture and video-capture modes in Cheese without turning off the camera. But, for now, I’ll leave it like it used to be, specially because it seems Camerabin doesn’t set image-capture size separate from video-capture size as it should.

I just posted a bug with the patch to add camerabin to master in Cheese. I really hope it’s working perfectly, but it would be really nice to have more people testing it. So, if you feel like it, check camerabin branch and tell me the results.

Next week I plan to work on other improvements in libcheese. Maybe I’ll try to make some improvements in the API before the API freeze for 3.0.