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Michael Zucchi

 B.E. (Comp. Sys. Eng.)

  also known as Zed
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Friday, 23 October 2015, 07:08

Catching up

Not much going on so today here's a diary entry ...

I've added a few little things to ZCL - it's coming along quite nicely, I should probably work toward another release. I'm slowly adding the functional-like stuff into it, I decided to go with 'q.offer()' as the enqueue function, and 'ofXX()' as the factory methods. Together with the garbage collector support it does offer some interesting possibilities for code-reuse but i'm still experimenting with it in practice.

I needed to access a webcam so i added another api to jjmpeg (but i might move it) which just wraps v4l2 devices directly from the file descriptor (no library). Actually I did that a while ago but have slowly been filling it out as I needed more functionality. OTOH I started looking into the total snot-show that webcam access is on microsoft platforms and decided to give up - you can't even build the media-framework libraries with mingw-w64 as far as I can tell and you need vs of some form just to get the "system" headers. Ugh.

However I did find webcam-capture library which has already solved these problems. It's probably what i will look at as a fallback, but on linux efficiency is a bit low. The simplest webcam dump to JavaFX with my library generates almost no garbage (it provides static access directly to the driver buffers) and uses 50% less cpu time compared to using the low-level interfaces it provides despite a pretty expensive YUYV conversion step. The high level swing one is 4x the cpu overhead.

Along the way I found that was actually using videoInput "library" but I couldn't get that to link (cross compile at any rate, it should work with the ms sdk) - and in any event that just uses the directshow stuff which I had working ... i dunno, years ago. But the driver no longer works for the webcam i'm using and i'd have to buy it, ... so yeah that can wait.

And that ultimately led me to openimaj which probably would've saved me doing almost all that myself, although i would've needed to understand it anyway for OpenCL translation. And maven, ffs. But I guess I should at least have a look.

Discovery of useful software isn't that easy these days with so much noise - even if you go looking which I can't say I did ...

I've also been using a small amount of OpenGL and interoperating with OpenCL. It's become all a bit ... naff, and JOGL has been necessarily messed up to support all this nafficity. Pity I had to do this now rather than in a couple of months otherwise I would be looking at vulkan instead but with any luck that will be out soon enough to move to it before I need to get too far into GL (with the steammachines in november?). I'm sure microsoft will find some way to totally fuck-up it's cross-platform parts again though. My current thinking is that i will write a java binding for it once I have my hands on it (if only just-because) but I haven't looked into it all so far. But removing the static per-thread state should make it a lot saner.

For now I have some simple classes to do some off-screen rendering, and some OpenCL interop which is enough for what I want. Access to an output texture in JavaFX would be nice but it sounds like this is just not going to happen. Although one would expect a vulkan backend to be done at some point it will probably suffer the same hiding issues (well, with good reason I guess). If I really needed more performance i'd just use another toolkit - which is sad as that doesn't appear to be the intended vision of the javafx designers.

On that interop I had to fill out the extension mechanism in ZCL. I followed the prototype I'd created earlier. Currently each extension is provided by a different CLExtension class. It holds a pointer which in C-land is a function table resolved on the platform, and each platform object manages these. At first I was just going to use this as the mechanism for accessing extensions but it quickly becomes messy - you have to find the platform the object belongs to an in some cases this requires multiple queries (e.g. q.getDevice().getPlatform()). One approach I tried was to hide that by providing the extension methods directly on the object they extend - e.g. new CLContext or CLCommandQueue methods. These then manage looking up the extension and invoking the correct method for the given object. The details still need to be resolved but only once per object and it's all handled java-side.

There's a bit more behind the original mechanism than just code tidyiness for the extensions - they could potentially be loaded at runtime, or written separately from the core library. But on reflection how useless is that? The problem with this approach is each extension has it's own object - this is good and bad in that eventually you end up with a table required per context, queue, device, or whatever.

I think putting the extension methods on the target object is correct and after that the details don't really matter so much since it's an internal detail. But (on the fly design) I guess i should just maintain a CLPlatform reference on each object which can be extended and handle it that way. The extension objects will still be per-extension which keeps a cleaner namespace but they only need to be set per-platform which doesn't happen often. I'm pretty sure all objects have a 1:1 platform relationship, that would be the only thing to throw a spanner in the works; but the whole extension mechanism wouldn't work if that were the case.

Somewhere along this journey i came across some C++ code for something, I can't remember what it was. It was how I find most C++ code - it's been so over-engineered almost all of the actual lines of code is just boilerplate. The workings are so hidden I gave up trying to find it. It's just as bad in Java land where everyone wants to write a fucking framework before they even get started. Cut the bullshit and get to the point. C++ shows its heritage as being born from a time when "Software Engineering" was going to solve the worlds software problems by taking the programmer out of programming; using UML and CASE tools and auto-generating everything. It really shows, it is not a good language. This craziness was at it's peak just as I was going through uni and its done it's fair share of damage to the world and clearly continues to if abominations like C++ still exists.

That'll do for now.

Tagged hacking, java, opencl.
yay summer | OpenVX
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