What’s what with the Aqsis Ray-Tracer, and Qt4 project development under Linux.

One of the subjects I once wrote about was, that I had a GUI installed on a Debian 8 / Jessie computer, which was called ‘Ayam’, and that it was mainly a front-end for 3D / Perspective graphics development, using the Aqsis Ray-Tracer (v1.8). And a question which some of my readers might have by now, could be, why this feature seems to have slipped out of the hands of the Linux software repositories, and therefore, out of the hands of users, of up-to-date Linux systems. Progress is supposed to go forwards and not backwards.

In order to answer that question, I feel that I must provide information, which starts completely from the opposite end. There exists a ‘GUI Library’, i.e., a library of function-calls that can be used by application programmers, to give their applications a GUI, but without having to do much of the coding, that actually generates the GUI itself. The GUI Library in question is called “Qt”. It’s a nice library, but, as with so many other versions of software, there are noticeably the Major Qt versions 4, 5 and 6 by now. While in the world at large, Qt4 is considered to be deprecated, and Qt6 is the bleeding edge under development, Linux software development has largely still been based on Qt4 and Qt5. So, what, you may ask?

Firstly, while it is still possible to develop applications using Qt4 on a Debian 8 or Debian 9 system, switching to using it is not as easy under Linux, as it is under Windows. When using the ‘Qt SDK’ under Windows, one installs whichever ‘Kit’ one wants, and then compiles their Qt project with that Kit. There could be a Qt4, a Qt5 and a Qt6 Kit, and they’d all work. In fact, there is more than one of each…

Under Linux, if one wants to switch to compiling code that was still written with Qt4, one actually needs to switch the configuration of one entire computer to Qt4 development, by installing the package ‘qt4-default‘. This will replace the package ‘qt5-default‘ and set everything up for (backwards-oriented) Qt4 development. Yet, Qt4 code can still be written and compiled.

And So, my reader might ask, what does this have to do with Aqsis, and potentially not being able to use it anymore?

Well, there is another resource known as ‘Boost’, which is a collection of Libraries that do many sophisticated things with data, that do not necessarily involve any sort of GUI. Aqsis happens to depend on Boost. But, there was one component of Aqsis, which was the program ‘piqslr‘, the sole purpose of which was, to provide a quick preview of a small part of a 3D Scene, so that an artist could make small adjustments to this scene, without having to re-render the whole scene every time. Such features might seem minor at first glance, but in fact they’re major, just as it’s major, to have a GUI to gestalt the scene, which in turn controls a ray-tracing program in the background, which may not have a GUI.

Well, ‘piqslr‘ was one program, that requires both Boost and Qt4. And, Qt4 is no longer receiving any sort of development time. Qt4’s present version is final. And, all versions of Qt need to feed their C++ source code through what they call a “Meta-Object Compiler” (its ‘MOC’). And ‘piqslr‘ needed to have both the header files for Boost included in its source code, as well as being programmed in Qt4.

Qt4’s MOC was still able to parse the header files of Boost v1.55 (which was standard with Debian 8) without getting lost in them. But if source code includes the corresponding header files, for Boost v1.62 (which became the standard with Debian 9), the Qt4 MOC just spits out a tangled snarl of error messages. I suppose that that is what one gets, when one wanted to modify the basic way C++ behaves, even in such a minor way.

And so, what modern versions of Aqsis, which are included in the repositories, offer, are the programs that do the actual ray-tracing, but no longer, that previewer, that had the program-name ‘piqslr‘. I suppose this development next invites the question, of who is supposed to do something about it. And the embarrassing answer to that question is, that in the world of Open-Source Software, it’s not the Debian – or any other, Linux – developers who should be patching that problem, but rather, the developers of Aqsis itself. They could, if they had the time and money, just rewrite ‘piqslr‘ to use Qt5, which can handle up-to-date Boost headers just fine. But instead, the Aqsis developers have been showing the world a Web-page for the past 5 years, that simply makes the vague statement, that a completely new version is around the corner, which will then also not be compatible with the old version anymore.

(Updated 5/21/2021, 19h15… )

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A little trick needed, to get Blender to smooth-shade an object.

I was recently working on a project in Blender, which I have little experience doing, and noticing that, after my project was completed, the exported results showed flat-shading of mesh-approximations of spheres. And my intent was, to use mesh-approximations of spheres, but to have them smooth-shaded, such as, Phong-Shaded.

Because I was exporting the results to WebGL, my next suspicion was, that the WebGL platform was somehow handicapped, into always flat-shading the surfaces of its models. But a problem with this very suspicion was, that according to something I had already posted, to convert a model which is designed to be smooth-shaded, into a model which is flat-shaded, is not only bad practice in modelling, but also difficult to do. Hence, whatever WebGL malfunction might have been taking place, would also need to be accomplishing something computationally difficult.

As it turns out, when one wants an object to be smooth-shaded in Blender, there is an extra setting one needs to select, to make it so:

Screenshot_20200104_124756c

Once that setting has been clicked on for every object to be smooth-shaded, they will turn out to be so. Not only that, but the exported file-size actually got smaller, once I had done this for my 6 spheroids, than it was, when they were to be flat-shaded. And this last observation reassures me that:

  • Flat-Shading does in fact work as I had expected, and
  • WebGL is not handicapped out of smooth-shading.

 

It should be pointed out that, while Blender allows Materials to be given different methods of applying Normal Vectors, one of which is “Lambert Shading”, it will not offer the user different methods of interpolating the normal vector, between vertex-normals, because this interpolation, if there is to be one, is usually defined by an external program, or, in many cases, by the GPU, if hardware accelerated graphics is to be applied.

Dirk

 

OGRE 1.11.5 Working on ‘Phosphene’

One of the open-source software projects which has often fascinated me, is called OGRE, which stands for Open-Source Graphics Rendering Engine. It’s a very powerful set of libraries, that allows good coders to design 3D graphics applications, which take full advantage of hardware-accelerated – i.e., GPU-based – rendering, of virtual 3D scenes designed by such users, into simulated 2D camera views, within the same scene. This is one of the most common modes in which 3D Graphics is operated.

One of the things that OGRE is not, is a full-fledged game engine unto itself. This is due to:

  • Lack of sound implementation (Additionally linking applications to the SDL Library may solve that),
  • Lack of scripting support, without some sort of add-on. I think I compiled it with Python support, which would supply scripting, if my coding was good enough.

Modern builds of OGRE break with the past, in that they no longer use ‘OIS’ as their input system. Instead, at least their Sample Browser uses the ‘SDL library’ to do the same.

One of the feats which I have now accomplished on the computer named ‘Phosphene’, which is a Debian / Stretch, Debian 9 system, was to compile version 1.11.5 of this engine because I’m curious about Game Design, which I have been for a long time. And one of the reasons I feel that this software is stable on Phosphene, is due to the information which I already provided in This past posting. The past posting announced observations which I made, when this same hardware was called the computer ‘Plato’, but already running Debian Stretch.

What my observation essentially suggests is, that running 3D, OpenGL applications can in fact break the compositor because they suspend it, but that there is a work-around.

(Updated 2/20/2019, 19h00 … )

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About how I won’t be doing any ‘ASL’ computing soon.

There exists an Open-Source code library named ‘ASL’, which stands for “Advanced Simulation Library“. Its purpose is to allow application-designers who don’t have to be deep experts at writing C++ code, to perform fluid simulations, but with the volume-based simulations running on the GPU of the computer, instead of on the CPU. This can also lead people to say, that ‘ASL’ is hardware-accelerated.

Last night I figured, that ‘ASL’ should run nicely on the Debian / Stretch computer I name ‘Plato’, because that computer has a GeForce GTX460 graphics card, which was considered state-of-the-art in 2011. But unfortunately for me, ‘ASL’ will only run its simulations correctly, if the GPU delivers ‘OpenCL’, version 1.2 or greater. The GeForce 460 graphics card is only capable of OpenCL 1.1, and is therefore no longer state-of-the-art by far.

Last night, I worked until exhausted, trying various solutions, in hopes that maybe the library had not been compiled correctly – I custom-compiled it, after finding out that the simulations were not running correctly. I also looked in to the possibility, that maybe I had just not been executing the sample experiments correctly. But alas, the problem was my ‘weak’ graphics card, that is nevertheless OpenGL 4 -capable.

As an alternative to using ‘ASL’, Linux users can use the Open-Source program-set called ‘Elmer‘. They run on the CPU.

Further, there is an associated GUI-application called ‘ParaView‘, the purpose of which is to take as input, volume-based geometries and arbitrary values – i.e., fluid states – and to render those with some amount of graphics finesse. I.e., ‘ParaView’ can be used to post-process the simulations that were created with ‘ASL’ or with ‘Elmer’, into a presentable visual. The version of ‘ParaView’ that installs from the package-manager under Debian / Stretch, ‘5.1.x’ , works fine. But for a while last night, I did not know whether problems that I was running in to were actually due to ‘ASL’ or to ‘ParaView’ misbehaving. And so what I also did, was to custom-compile ‘ParaView’, to version 5.5.2 . And if one does this, then the next problem one has, is that ParaView v5.5.2 requires VTK v7, while under Debian / Stretch, all we have is VTK v6.3 . And so on my platform, version 5.5.2 of ParaView encounters problems, in addition to ‘ASL’ encountering problems. And so for a while I had difficulty, identifying what the root causes of these bugs were.

Finally, the development branch, custom-compiled version of ‘Elmer’ and package-manager-installed ‘ParaView’ v5.1.x will serve me fine.

Dirk