Corrupted/Exploding/fan looking fake stones...

[reck]

...or whatever you want to call them. Anyone who has used the fake stone shader for a while will have seen them. It's a problem that's been around for a long time now and is something that occurs by just using the shader, it's not some obscure bug that hardly anyone has seen and only happens under unusual circumstances.

Has this been fixed for the final release?

[Seth]

I am not sure it is a bug...
it looks like bad value on powerfractal shaders (bad scale or bad dsiplacement)
The only bad looking stones i got these days are flat ones, but it's been a while i didn't get exploding ones...

[reck]

Really! I get this problem a lot so if I know its user error and I can fix it myself without affecting the look of the 99.9% "good" stones I'll be a happy person. But if I have to alter the values that I've entered into the scale/displacement etc to fix 1 bad stone while altering the look of the good stones it's not really a good fix.

In the past I've fixed it by randomly hitting the seed button (without altering the scale/displacement values) until I get stones that don't suffer from this issue. The problem is that if you get a nice distribution/look of stones you lose this when you hit the seed button.

[Seth]

IMHO it really is user's wrong values.
check some of my renders with a lot of fake stones... no exploding ones...
maybe it's luck but i checked hitting random seed button on one of them more than 10 times and doing preview renders each times and, as i already said, the only issue i get is one or two flat stones sometimes.

[MF_Erwan]

Me I have a question: how do you guess the good values to put for displacement on fake stones?

Erwan

[cyphyr]

VERY small values together with HIGH contrast make exploding stones. Try lowering the contrast of your displacing fractal and making its scale a little bigger. Also if you happy with the displacement on most of your stones try putting a transform shader after your displacement fractal and simply move the fractal to a place where you cant see any exploded stones.

richard

[Seth]

Me I have a question: how do you guess the good values to put for displacement on fake stones?

Erwan

I'll do a little something about Fake Stones as soon as I will have some free time
but basically I use the same scale value for my powerfractal than the stone's scale, then my displacement is usually smaller let's say maximum 80% of the powerfractal value...
And i play a lot with the colours (contrast, offset, roughness) to have smooth displacement and avoid bright white spots...
let's say that's the beginning of my way to achieve fake stones...

[MF_Erwan]

Try lowering the contrast

Correct me if I'm wrong, but won't decreasing the "displacement multiplier" make the same thing?

Erwan

[cyphyr]

Sure, if your going through a default shader
richard

[Oshyan]

I don't think this is technically considered a "bug". It is basically due to a coincidental alignment of particularly strong displacement, likely with a small "fake stone" or one whose shape is not conducive to being displaced in that way. One possible approach to fixing it would be to use a painted shader to mask out the area where the "exploding" stone is from the displacement being applied.

- Oshyan

[reck]

OK so it sounds like I need to spend some more time on tweaking my settings. I've never touched contrast/offset/rougness before when creating fake stones.

Even though not technically a bug I see this problem a lot, not only with my renders but with other peoples renders that I see on here and over at Ashundar.

[reck]

I've been spending the last few days trying to understand what makes fake stones explode. I've read what was posted on this thread and spent a lot of time with the power fractal which is used as the fake stones surface shader, changing different values. I've changed the scale, displacement values, the roughness and the contrast, none of these make any difference. Then I realised that none of these things are causing the stones to explode, in fact it's got nothing to do with the surface shader/powerfractal at all. The reason I know this is because I deleted the surface shader so i'm left with just the fake stones and the exploding stones are still there! If you look at the node network you can see the only two nodes i've added to the standard node network is the fake stone shader and a distribution shader to restrict the stones to flat surfaces. 

So the exploding stone problem is related to some setting in the fake stone or the distribution shader. The distribution shader restricts the stones based on angle, i've made sure not to use really low values and in this render it was set to 15 metres for the max slope and 20 metres for the fuzzy zone. The fake stone shader has 8 for the stone scale and 0.5 for the stone density. These values don't seem extreme to me and seeing as i'm not using any power fractals I don't know what's causing this problem. All I do know is I always get exploding stones, I wish I had the same luck as Seth in this regard as his images seem great.

Any idea?

[rcallicotte]

What happens when you remove the distribution shader?

[reck]

I get a lot of white blobs everywhere 

But looking around the landscape I don't see any exploding rocks, so why is the distribution shader blowing them up I wonder?

I really only wanted a 5 metre fuzzy zone but I increased it to 15 in case this was the cause of the problem. I still get the exploding rocks and the rocks go higher than I would like now so maybe I will lower it back down to 5.

[Oshyan]

I don't know for sure, but this sounds like the maybe the "exploding" stones in this case are actually *cut off* stones, from the distribution shader, and it's just that the cut-off is sharper than you want it to be when it intersects a "stone". I'm not sure if this is a limitation of the Fake Stones shader, or of your setup. Unfortunately it's a difficult time to get input from the rest of the team but I'll try to have this thread revisited in the near future.

- Oshyan