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Some point density testing

Posted by Marius Oberholster on Tuesday, December 18, 2012 Under: General
Hey all!

I have been busy these passed few days. Not super busy, but working a bit. Still a bit under the weather, but feeling a whole lot better!

Back on point. Point density is a fantastic tool to use shaped volume, without having to use the smoke simulator. While it is very limited in what it can do ito shaped explosions and so on, it is a remarkable feature and a quite fast render.

A while back, I tried making a rocket with the smoke simulator, but it didn't go so well:

I wanted to upload the OpenGL (or OpenCL, don't know the difference, lol) version, but never did. Anyway, so this morning I got around to trying it out with some point density instead and this is the result of the first test (a single frame only):

Immediately, you'll notice that the cloud is very dotty (for a lack of better term). That is because in this test particularly, I forgot to make sure the particles fade out as they die off.

The second test was more successful:

This test sports fading out, a blend texture to add indirect lighting (not really big under the glare, but compare the two tests and you will notice the difference) and of course, a longer point density box to make sure it doesn't cut out.

As a reference, I watched a launch earlier today as I was rendering test2, and I noticed that the smoke at the bottom of the craft is moving at such a pace, it almost looks liquid in some moments. Truly astonishing to watch, not to mention hearing at what speeds they travel. Didn't finish watching as the launch was what I wanted to see, but you can watch the whole thing if you want to:

There are a few problems and issues still for me personally with point density:
 - It's like I can't get it to show right when I set it up from scratch, unless I first generate a cloud using the cloud generator, set on particles. If I don't, there is always something wrong and I don't know where the problem sits.
 - There is no depth map options available for the cloud that forms like in the above. It's the same with a transparent plane with an image on it. The plain is recognized as a full object and appears as a full plane in the Z pass, whether alpha is enabled or not. It works the same here. If you have the point density object fill the camera for example, you will have a single shade of grey Z pass, regardless of how massively or little dense the cloud may be.
 - Cloud stability and flickering with fade out. If you have a cloud that fades out as it moves, such as in time lapse videos, you will notice flickering, with or without turbulence. This, as far as I know, is still a bug and one that the light cache (which is a lot faster), still doesn't have the solution to, but feels and looks improved on. If your scene is busy enough and the fade is at the right speed, it shouldn't be as much of a distraction and will still look good. This is an example of where the flickering actually adds to the scene:

 - There is no vector blur for point density. If you want it to blur it, sampled motion blur will probably work.

And here are some tests I did with point density a while back:

It does include a smoke sim test too, but make sure you keep the annotations on for more info.

Well, I hope you found this helpful and that it gives you some ideas on what you can do with it as well. I personally still have a few ideas I would like to try, but possibly more on that later.

Have a great one!!

Thank YOU!!!!!!!!!!

In : General 

Tags: experimentation  point density  add-on  youtube  video  example  testing 

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