Small Values for Fractal

Started by nikita, September 02, 2007, 12:26:05 pm

Previous topic - Next topic

nikita

Quote from: Matt link=topic=2174.msg21131#msg21131Power Fractal V3:
    Safely handles very small or negative values for smallest scale.


I attached a screenshot. It seems it doesn't handle small values safely enough yet. :)

Tangled-Universe

Your smallest scale is 0,00000366... wouldn't surprise me it can't be handled safely.
What's the point of using micrometer scale displacement?  ???

Regards,
Martin

nikita

I just wanted to reproduce the effect in the most simple way possible.
I'll render some more realistic renders that suffer from this bug and post them later.

Tangled-Universe

I doubt if you can speak about it as being really a bug, but that thought isn't really relevant in this case.
What more relevant is what the use/point is of using such small scale displacement? When do you use it?
I don't think anybody is going to render a microscopic image with a landscaperenderer...see what I mean?  ;)

nikita

I know what you mean. But if those values aren't intended to be used, I'd suggest to not let the user chose them using the slider or popping up a warning. :)
Anyway: Here are two different examples, which, I think, suffer from at least a related problem and don't make use of micrometer values  ;D

The first one is a simple rock object. Adding a power fractal to its surface results in a black rock, no matter what color, displacement amplitude etc you choose. The scale values are at default.

The other example is a more complex scene. The min-scale is at about 0.5 cm... which is a perfectly sane value if you ask me. What really surprised me is, that it affects the sky too.

Also, I'd expect to have some weird polygons or something similar... not the colour changing.

Volker Harun

What is the displacement amplitude you are using? Can it be that those tiny displacements are very long and thus cause the sky's darkening?

Volker

nikita

No, its at 0.1.
I wondered whether the combination of small smallest scale and relatively large amplitude would cause the light to be "trapped" between near-parallel spikes. But smaller values that fit the smallest scale don't make the effect disappear either.

Volker Harun

I attached a screenshot where I used an amplitude of 0.1, too.
The fractal's setting are shown in the image.

Is there anything else, you are doing?

nikita

My lead-in scale is much lower (but still not below any of the other scale values).
It works when I raise it to a much higher value.

But the render (see attachment) looks like there's still something wrong.

Volker Harun

I was not able to reproduce the effect.
Feature scale 0.0005m
Lead in scale 0.0015m
Smallest scale 0.0001m
were the smallest I tried.
The displacement amplitude (aka multiplier in the surface shader's displacement) was set to 0.1, 0.05, 0.01

Do you have a scene to check?

Volker

Oshyan

Is it possible you're inside the terrain? Providing a .tgd would help a lot in diagnosing this as it isn't easy to reproduce with just the settings you've specified.

- Oshyan

Cyber-Angel

Question: is some form of collision detection planed for the final release of TG2 which would solve the camera inside the terrain issue and may also solve many of the terrain geometry tearing issues that are seen at the moment seen when you change some thing like displacement offset or similar and the terrain breaks apart along the terrain edges and/ or when you move the camera to a different POV parts of the terrain seem to be broken off.

Regards to you

Cyber-Angel   

nikita

September 10, 2007, 11:30:47 am #12 Last Edit: September 10, 2007, 11:47:52 am by nikita
@Volker/Oshyan Oops, I forgot to post the file last time I read this thread.  :-\
(@Oshyan Welcome back  :) edit: oh.. 5 days late ^^)

I attached the file (one of those with non-insane values).
I only removed some image maps.

Volker Harun

I can verify this problem. It seems to be the feature scale (values below ~0.93 seem to be the cause).