Displacement cutoff between render tiles

Started by RArcher, January 15, 2009, 10:36:55 am

Previous topic - Next topic

RArcher

Here is a very simple scene I've been working on where you can see that the renderer is not correctly rendering some of the fake stones.  There is a clear cutoff between render tiles where on one tile the stone is rendered but on another tile it is not.  I know that this can be a problem when working with some extreme displacements, but there is nothing extreme about this file.  I've marked some of the main problem areas out in the attached image.  The .tgd is also attached, but there is honestly nothing strange going on in the .tgd.

Doing crop renders of all the problem areas does work to fill in the bad sports, but then there is a great deal of extra work involved, and if this was for an animation that would be a huge problem.

Rendered in Windows Vista 64 - Q9450 - 8GB Ram so I would really not expect that this would be any sort of memory issue.

Rendered at:

Detail: 1
AA: 14
GI Relative Detail: 3
GI Sample Quality: 4
Supersample prepass on
GI Surface Details on

efflux

January 30, 2009, 08:10:48 pm #1 Last Edit: January 30, 2009, 08:12:56 pm by efflux
I had a look at this. There is quite a lot of displacement but also very high render settings. The higher this is the more likelihood of displacement cut offs. I never go up to anywhere near AA 14. I didn't experiment too much but actually I had trouble getting it to cut off even when opening your file without changes at the high settings except reducing GI. The trouble is, I might not have got the buckets to chop off at the same places without rendering the whole picture. I used your crop at bottom left as well as some others.

It's a good scene. I like the stones and sand arrangement.

RArcher

Maybe it is just me, but it seems to be a fairly big problem.  Here is a better example.

640 x 400
Detail : 0.5
AA: 3
GI: 2/2

render time 1 minute 30 seconds

First image is a screen shot of the preview window where it is correct.

Second is the finished render, not correct.

Tangled-Universe

Interesting problem, shall take a look at this when I have some time, see if I can reproduce this as well.

Kevin F

I get the same result as you.
The only way I can make whole stones render is to lower their displacements to below 1. This gives a slightly different arrangement of stones, but at least they're whole!
I've never fully understood why the displacement sliders allow such high values to be applied when most of the effects can be achieved with small values, often below 1.

jo

Hi Kevin,

Quote from: Kevin F on February 03, 2009, 06:48:15 am
I've never fully understood why the displacement sliders allow such high values to be applied when most of the effects can be achieved with small values, often below 1.

Matt has a "give 'em enough rope" philosophy. We have talked about a system which would alert you when values go outside recommended ranges, which could be something we implement in the future. At the moment you have the freedom to push things as much as you want, which is why it isn't a good idea to just push things to maximum settings :-).

Regards,

Jo

Seth

an alert system could be a good idea... I had some similar problem... and noticed it after 15 hours rendering ^^

rcallicotte

Not sure if you all have seen this.  I'm sure Oshyan has.  This problem has always been something to be aware of - http://forums.planetside.co.uk/index.php?topic=2530.0 and can be quite disconcerting, when the OpenGL preview shows everything and the final render is lopped off.

Probably no fix, as I understand it.
So this is Disney World.  Can we live here?

efflux

February 06, 2009, 06:12:01 pm #8 Last Edit: February 06, 2009, 06:13:34 pm by efflux
I've had this problem endlessly because I've pushed to the limits. Not so much with fake stones but with displacements on hillsides etc. I've learnt to tweak everything to a compromise where it rarely happens but this means endless experiment to know how far to push.

I'm a bit limited with rendering power so the original file was long render. I didn't experiment much but it looks to me like the stones are quite heavily displaced.

You have to allow some headroom as well because if you do a great scene then at some time in future decide to render it huge then you get lots of cut offs.

We want the settings to allow us to do anything. No limits. A warning might be useful though.

Does a compute normal stop the cut offs? There have been cases where I've used a compute normal but mainly for other purposes rather than stop cut offs.

I'll check that second file out later. On linux system at the moment and there is an issue with TG2 and current Wine version.

Volker Harun

An approach would be to work with negative displacements instead.

I guess that the renderer will check where displacements would likely appear. So having a larger fake stone and diplacing it to the inside has a greater chance to be rendered correctly.

I think it is impossible for a renderer to guess all the possibilities of displacements coming from anywhere.
Normal raytracers only use (to simplify it) intersections with objects (and may add a fuzzy zone around objects to fetch displacements (bumbs)).
So we should always be aware that we do not have much of that outward fuzzy-zone ... but a lot when doing negetive displacements ,-)

Volker

efflux

Negative displacement does work. It's maybe not so useful with stones though.

For example, I've experimented with with big displacements of rocks on hillsides and found that instead of blowing it all out in positive displacement, if you work in at least some negative displacement then it helps stop cut offs. It can be useful to actually displace the whole area negatively before adding further displacement but I'm talking about real extremes here. You also have detail issues depending on how far you go. A positive displacement also blows out the polygons which effects detail.

efflux

I would suggest to get fake stones as near the shape you want as possible before applying displacement like make them a bit taller. There is always a tendency to rely on displacements but sometimes it's not needed as much as you'd think.

In Mojoworld, an app where you usually see huge displacements being used, you can actually make beautiful planets with no displacements at all. Here are some shots from a Mojo planet I did with absolutely no material displacements, just terrain. Because it has no material displacements it renders FAST. The clouds are not 3D either. That was more fakery. Also, I have developed a fake GI set up in Mojo - looks very convincing until you get very close. I could render this planet to giant poster size due to it's efficiency. Bear in mind that TG2's displacements are actually way better and smoother. I feel like I'm still scratching the surface of what can be done in TG2. However Mojo does have more terrain capability.

http://www.renderosity.com/mod/gallery/media/folder_173/file_1722014.jpg

http://www.renderosity.com/mod/gallery/media/folder_173/file_1721331.jpg

This was my first experiment with the faked GI and I have also developed Mojo "fake stones". Mojo fake stones is potentially very powerful due to all Mojo's fractal power but the displacement can't be as extreme as TG2's. This meant that I had to tweak the stones to have absolute minimum displacement necessary. Now I apply that in TG2 and no cut offs.



I find it very useful working with both these apps. The limitations of each app forces you to look for new ways to do things which feeds back into the other app.

rcallicotte

efflux, your stuff is always so groovy.  Your work is awesome.

Your another person who I wish would give a tutorial on lighting.  Or maybe you and Seth (Franck) can get together to make a to-the-point tutorial on clear and believable lighting.  I do not lie when I say that I think your renders (and Seth's and a few others like RArcher and TU) rival lighting I've seen accomplished with VRay.  This says a lot about Matt's skills and our good fortune.

Anyway, consider a lesson or two?
So this is Disney World.  Can we live here?

efflux

As resolved with PM. The images are of course done in Mojo. I posted that stones image at the Renderosity Mojo forum and the admin moved it to TG2 forum thinking it was a mistake. I described how to do it (qith a file) but maybe didn't make it clear that it was actually Mojoworld. As is the case with much of my stuff, I have unfinished Mojo planets with stones. I should finish one.

rcallicotte

This is MW?!  Ohhh.  I see.  Sorry for the misunderstanding.  But, is this rendered in MW?  If so, it's an awesome render.
So this is Disney World.  Can we live here?