Toward a Secret Sky

Well, all this thought of asynchronicity is getting to me. But since we mentioned how to use subprocesses and Twisted, I think it is only fair to talk a bit about threads. So, what will we be doing? Create an abstraction for running threads in PyGTK Use it Now the thing which we will be wanting to run is a generator, call it "take_really_long". And it will surely block, and might be a bit intensive, and well we obviously need something asynchronous. A generator is a bit nicer to use than a single plain long-running function, because we can update the user interface every time it returns, making it much much easier to do things like Progress Bars. You must remember two things when using threads with PyGTK: 1. GTK Threads must be initialised with gtk.gdk.threads_init: import gtk gtk.gdk.threads_init() 2. Any code that modifies the UI (basically any code) that is called from outside the main thread must be pushed into the main thread and called asynchronously in the main loop, w...

Well, it is an age-old problem: How to schedule long-running tasks withing a GUI main loop (in our case PyGTK). There are a few ways: Use Python's subprocess module and select on the pipe with gobject's io_add_watch Use GTK's built in subprocess spawning abilities Use Twisted 1 & 2 are reasonable approaches, and they both work. Of course 1 won't work on Win32. The only problem with both 1 & 2 is that they use gobject's polling functions to achieve asynchronicity. This is nice when we are forced in a PyGTK main loop, but really not nice when the application wants to run in command line mode, and we really want to be able to share the execution code between different UIs, including perhaps other toolkits. Enter Twisted. We need to do two things with Twisted: Make sure Twisted knows we are running with PyGTK Launch the process Making sure Twisted knows that we are running inside PyGTK is quite easy (though I imagine the implementation was painful). To do this, ...

Well, it was a nice idea I believe, to place a video side-by-side with a Powerpoint (or one of it's inferior Open Source clones) presentation. The idea came when my boss showed me Microsoft Producer, which does exactly this (it's nice to have people who at least pay some attention to non-Open Source, especially when he pays you.). Producer is a plugin for Powerpoint, with a simple User Interface, which involves importing a presentation, and a video. Setting the timings for the slides, placing them adjacently in an output it video. It sounds simple enough, and I thought this functionality would be possible in some of the Open Source video editing equipment, but either: I knew for a fact that the software didn't have the capability, or: the software was impossibly difficult to use. So, I had a think, and a play, and another play, and I came up with the plan: Split the presentation into images: 1 slide per file Split the video into frames of png files, and save the sound for ...