Bump area VERY narrow

Started by Dune, October 27, 2019, 03:26:33 am

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Dune

When I use a bumpmap in the default shader, there's no problem, but as soon as I add very shallow extra bump, the polys are hard edged. It's only a fraction of a millimeter. The model is quite highpoly, and normals are calculated on a smooth basis. Even when I negatively offset by half the bump height, it doesn't work properly. So I wonder what can be done about this (by me... or in TG).

René

I don't know what the cause is, but it seems to me that in the image without hard polys those edges are also visible (to a lesser extent), and that the bump there as a whole is fuzzier. Maybe it's because the bumps are multiplied.

Hannes

Indeed! The less fine bump makes the edges a bit less obvious, but if you look close, the edges are there.

Dune

Yes, you may be right, but still; without any bump it's smooth.

j meyer

The displ amplitude is negative in your example, which leads me to the following
question: have you tried a positve value and an inverted bump fractal?

Dune

I don't think I did, but displacement in the displacement tab (and not by clamped color) is positive and negative anyway, so some parts of the perlin will be above 'skinlevel', others parts under it.

KyL

From the latest changelog:


Quote from: Matt on October 23, 2019, 01:56:55 pmBuild 4.4.40 (Frontier Build)

Changed how bump mapping affects the shading position. Bump mapping doesn't affect shading position anymore because this was causing incorrect rendering of transparency. However, this also means we can't use the positive bump trick to avoid sharp terminators on low-poly geometry. We'll need another solution for this in future builds.
I am facing similar issues, though unfortunately you have the worst-case scenario :/


Cool model btw. Did you make it? How do you find working with geometry for the hairs? It may not be as heavy as one might think!

WAS

Matt has mentioned in the past high poly objects don't work well with displacement, and to use low poly objects for TG to utilize those larger faces for displacement. I assume too small a face and TG can't calculate correctly or the displacement is being cut off, exaggerating seams.

Dune

Ah, that's not so good, I have to rely on subtle bumpmapping. If that is really what Matt means. I didn't use any glass shader, btw, just the default, etc.

I's a ZBrush transformed DAZ Genesis model; just divided the head a few times extra and added some wrinkles.

It's not displacement, WAS, it's bump, as the object is raytraced. But maybe you do mean that.

WAS

October 27, 2019, 01:03:09 pm #9 Last Edit: October 27, 2019, 01:06:56 pm by WAS
Quote from: Dune on October 27, 2019, 12:58:05 pmAh, that's not so good, I have to rely on subtle bumpmapping. If that is really what Matt means. I didn't use any glass shader, btw, just the default, etc.

I's a ZBrush transformed DAZ Genesis model; just divided the head a few times extra and added some wrinkles.

It's not displacement, WAS, it's bump, as the object is raytraced. But maybe you do mean that.

TG supports Normal Maps now? I don't know how it would without it being faked as that's what it's inherent goal is. I assumed we meant displacement. I'd imagine bump would inherently have issues with any realistic rendering honestly.

Normal/Bump isn't actually displacement it's faked lighting if there was displacement, so why I may be confused.

Matt

Quote from: WAS on October 27, 2019, 12:42:35 pmMatt has mentioned in the past high poly objects don't work well with displacement, and to use low poly objects for TG to utilize those larger faces for displacement. I assume too small a face and TG can't calculate correctly or the displacement is being cut off, exaggerating seams.

For objects with "Force displacement" enabled, that's true. But for ray traced objects there is no true displacement (yet), it's only bump, so this advice doesn't apply.
Just because milk is white doesn't mean that clouds are made of milk.

Matt

Regardless of whether you have bump or not, curved surfaces need lots of polygons to render smoothly along the lighting terminator. But bump mapping can make the problem more apparent as it can increase the brightness of surfaces close to the terminator. Subdividing the object before importing into Terragen is the best solution to this problem.
Just because milk is white doesn't mean that clouds are made of milk.

WAS

Quote from: Matt on October 27, 2019, 05:39:56 pm
Quote from: WAS on October 27, 2019, 12:42:35 pmMatt has mentioned in the past high poly objects don't work well with displacement, and to use low poly objects for TG to utilize those larger faces for displacement. I assume too small a face and TG can't calculate correctly or the displacement is being cut off, exaggerating seams.

For objects with "Force displacement" enabled, that's true. But for ray traced objects there is no true displacement (yet), it's only bump, so this advice doesn't apply.


Oh strange. I was never using force displacement on the shader balls or orb object for that to even be advise then in my instances. And subdividing is what I was doing. Speaking of that does force displacement still only work on individual objects or can it be used on instances in a pop?

KyL

October 27, 2019, 07:02:28 pm #13 Last Edit: October 27, 2019, 07:06:03 pm by KyL
I think there might be something else going on here. Here is a little test I did, using the same object and same texture files, both in Terragen and Maya.
terragen.jpgarnold.jpg

Even if I push the bump in Arnold to the extremes, I never noticed anything wrong. But even with the slightess amount of bump in Terragen, the terminator is faceted.
I actually even shows on the mesh itself with a default shader:
tgout-001 00m21s v4.4.40.1.jpg
  :-\

KyL

...Doing a bit more digging on that, I might be onto something. It looks like the "Use smooth normals" checkbox in the object's tab is not affecting the shadows.

This illustrates the problem:
smooth_shadows.jpghard_shadows.jpghard_noShadows.jpgsmooth_noShadows.jpg