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Summer Update - Video, Reflection, Model Description

Posted on 11 July 2009 by Eric Wasylishen

My summer break is about half over, and as the Étoilé "summer student" developer, I thought I should give everyone an update on what I've been working on. The past two months have been a bit unfocused:

• Inspired by Nicolas' patch to make NSSplitView resizing "live" in GNUstep, I wrote a similar patch for NSTableView. Now, when resizing or moving table columns, the table is updated in real-time. In my opinion, these small changes really make GNUstep feel more modern.
• I wrote a prototype of a movie view for MediaKit. There are two versions: one is software-only (FFMPEG handles decoding, colorspace conversion, scaling, and the resulting bitmap data is painted on an NSView), the other uses an NSOpenGLView to scale the video in hardware. This was really quite easy (a few hundred lines of code): the FFMPEG libraries do all of the hard work. This isn't in MediaKit yet - we need to improve the threading architecture a bit to handle video - but it shouldn't be too difficult to finish.
• Since last year, I've wanted to write a reflection API for Etoile based on mirrors (see Mirrors: Design Principles for Meta-level Facilities of Object-Oriented Programming Languages). I finally wrote a basic implementation: (Header, Source, Test), written using the OS X Objective-C 2.0 Runtime API - so it works on both OS X and GNUstep (thanks to David's ObjectiveC2 framework). My implementation is read-only and only reflects the runtime state of the program. The great thing about mirrors is the idea that you should be able to use the same API to examine and manipulate running code as you use to manipulate source code. In the future I would like to extend it with write access (so we can add and remove classes and methods), sub-method reflection integrated with LanguageKit (specific to each language provided by LanguageKit), and the ability to mirror source code.

Here is a simple class browser written in Smalltalk:

• At the end of the hackathon, Quentin explained the idea of model description to me, and I thought it was really cool. Similar to how mirrors separate meta-information about an object's structure (class, instance variables) in to a separate object, a model description object separates meta-information about a model object's role in the overall model. For example, the model description could list the properties of the model object, which are read-only or read-write, the type of value permitted for the property (using UTI's), whether the property is multivalued, etc. I'm working on something similar to FAME, and hope to commit a basic version of it in the next few days.

Lastly, I've been working on polishing the website. There is still more to do, but you'll notice there is now more content, and hopefully it is easier to navigate.

As for the rest of the summer, there are several projects I would like to work on:

• UI design. From my perspective, we have a consensus on the goals of Etoile, and the UI of some parts of the system. As we're getting closer to implementing more of it, I think it would be useful to continue design discussions and plan some of the smaller details.
• CoreObject development. I think the model description framework will help modularize and simplify CoreObject, and I want to investigate serialization of objects using the model description (which FAME does)
• Work with EtoileUI more; prototype better UI's for Melodie and the photo manager
• Start the messaging framework (chat, email, etc.)