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Michael Zucchi

 B.E. (Comp. Sys. Eng.)

  also known as Zed
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Friday, 31 August 2012, 07:51

JavaFX + webcam, Android n shit.

For Friday Follies I thought i'd have a look at setting up a test harness for mucking about with object detection and so on on a webcam outside of OpenCL - and for a change of pace I thought i'd try JavaFX at last - now it's included in release Java runtime for all platforms it's time I had a look.

Well, i'm not sure i'm a fan of the squashed round-cornered buttons - but it does seem nice so far. No more need to write an 'OverlayView' to draw boxes on the screen. After fighting with some arse-pain from Android for the last couple of weeks it's nice to go back to Java proper again too.

One of the big oversights in the earlier incarnations - being able to load in-memory pixmaps into the scene - has now been fixed, and the solution is simple and elegant to boot.

For example, I hooked up video 4 linux for java to display webcam output with only 1 line of code (outside the rest of the v4l4j stuff).

  writableImage.setPixels(0, 0, width, height,
      PixelFormat.getByteRgbInstance(), videoFrame.getBytes(),
      0, width);

And all I need to do is add the writableImage to the scene. (occasionally when i start the application the window doesn't refresh properly, so i'm probably missing something - but it's quite fine for testing). It would be nice to have some YUV formats, but that should be possible with the api design.

Of course, I could do something similar with Swing, but that involved poking around some internals and making some assumptions - not to mention breaking any possible acceleration - and I still had to invoke a refresh manually.

There's a new set of concurrency stuff to deal with, but at least they seem fairly straightforward.

Let Swing ... swing?

I actually quite liked Swing. It did have a lot of baggage from the awt days but it was a nice enough toolkit to write to, and almost every component was re-usable and/or sub-classable which saved a heap of development effort (now that i'm claiming it was perfect either). The first time I used it in anger i'd just come from a few years fighting with that microsoft shit (jesus, i can't even remember what it was called now, it had fx in the name/predated silverlight) and coming to a toolkit with decent documentation, fewer performance issues, fewer bugs, the ability to subclass rather than forcing you to compose, and the friggan source-code was a big relief. (Not to mention: no visual studio).

But from what little I know about it so far, JavaFX sounds pretty good and I don't think i'll be missing Swing much either. At least now they've made it a proper Java toolkit, and fixed some shortcomings. The main benefit I see is that it eschews all the nasty X and native toolkit shit and just goes straight to the close-to-hardware apis rather than having to try to hack them in after the fact (although I found Swing ok to use from a developer standpoint, I would not have enjoyed working on it's guts too much).

I'll definitely have to have more of a play with it, but so far it looks nice.

Android ...

Or rather, the shit lifecycle of an Android window ...

Until recently I just hadn't had time to investigate and implement orientation-aware applications - so all my prototypes so far were just working with a fixed orientation. Seems like an ok toolkit when used this way - sure it has some quirks but you get decent results for little effort.

But then I looked into supporting screen rotation ... oh hang on, that window object on which you were forced to write all your application code, suddenly goes away just because the user turned the phone?

Of course, the engineers at Google have come up with other solutions to work around this, but they all just add weird amounts of complication to an already complicated situation.


So when I previously thought AsyncTask was a neat solution to a simple problem, I now realise it just makes things more complicated because of the lifecycle issue. Now there's some AsyncLoader mess which can be used to replace what you might've used an AsyncTask for - but with about 5x as much boiler-plate and lots of 'I don't really get what's going on here' crap to deal with as well. Most of that 'not knowing' goes away with time, but the learning curve is unnecessarily steep.

AsyncTask is simple because it's just a bit more around Runnable, saving you having to runOnGuiThread explicitly. AsyncLoader on the other hand is a whole 'lets pretend static resources are bad unless it's part of the toolkit' framework designed to separate your application from it's source code. i.e. it adds hidden magic. Hidden magic isn't abstraction, it's dumb.

You've been fragged!

Then take fragments. Go on ... please? So as if tying application logic to user windows wasn't enough, now one does the same for individual components of windows. A large part of why they exist just seems to be to be able to support orientation changes whilst preserving live objects - but it seems a pretty round-about way of doing it (they are also purportedly for supporting layout changes, but you can already do that ...).

But one of the biggests problem is the documentation. For the few times there is any, it is way out of date - when you find an official article explaining how to do something you soon find out that way was deprecated when you go to the class doco ... Obviously google are penny pinching on this one, you'd think with their resources they could do a better job to keep everything in sync - even Sun did a much better job and Oracle are probably better again.

To be honest, I think main issue I have personally with Fragments is the name itself - I kind of get what they're for, building activities from parts - but obviously all the meaningful names were taken (hell, even 'widget' means more). But the name 'fragment' just has no useful meaning in this context - fragments are what you have left over after you've blown shit up . Fragments are what a plate becomes after dropping one on a cement floor. Or what was left of the longneck I left too long in the freezer the other night (well, fragments and beery ice).

It is not a word of which things are constructed, it's just the mess left after some catastrophic mechanical failure.

(and the fact there are UI+logic, and logic-only 'fragments' surely does not help either)

The GoogleWay(tm)

Unfortunately, this all just forces you to code exactly the way google wants you to - which is fine when the problem suits, but it's a bit of a pain to learn just what that `way' actually is in the first place ...

In the end I just had to put everything in a database, and pass around id's to keep track of the state. Although it works there are still some complications. For example if you have a fragment which maintains its state during an orientation change, you then have to presumably code your activity to only load the state if it doesn't already have one, or fuck around with some other crap in the fragment to deal with it. I think my code just ends up reloading everything anyway, but at least it's on another thread and the user doesn't notice. If you set your object id's properly in your list adapter (now there's another 'lets mix different types of code' mess) then it mostly just works.

Once you've finally done all that ... then at least it does work out more or less, and trying to implement the 'proper' lifecycle stuff (whatever that is) becomes a whole lot easier too.

Tagged android, java, javafx, rants.
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