Displacement Problems

[David Gary]

Hi,

I created a simple shader ( where displacement amount is almost constant, value=0.5 except near the crack zone, (value -->0) , but the scene doesn't render correctly

( is the displacement amount too important or did i forget to turn something on ?)

I think my topology is correct...

->UGLY RENDER

[stevenong]

Hi there,

You have to turn on Displace Bound for the object. The parameter can be found under the Object's Render tab. The value to set is equal or more than the displacement amount. A quick way will be to channel reference the displacement amount from the shader. However, please note negative value will be evaluated as zero so use an abs() function with the channel reference.

If you still see cracks after channel referencing, add small increments, e.g. 0.1, to the expression until the cracks disappear. This is to prevent an increase in render time.

Cheers!

steven

[Jason]

Acutally, I think this may not be a displacement bounds issue; those usually look like one or more of the edges of the buckets are clipped; i.e. you get perfectly horizontal or vertical edges on your artifacts.

Look below.

I can only think you should inspect your point and primitive normals and make sure they're pointing the the direction you expect for the displacement. (usually in the direction you want it to displace).

[David Gary]

Yeah, thanks Jason, if have very often the exact kind of artifacts you're talking about.

(perfectly vertical and horizontal edges).

But here, i just turned on the Displace Bound and everything worked out properly.

So, Thanks stevenong.

--> PROBLEM SOLVED.

Still some work with the shader...

[David Gary]

Getting a bit confused/angry with mantra renders.

I checked my topology.

There is still rendering artifacts

Here is the displacement shader:

each normal of the "canyon walls" is smoothly interpolated, in the displacement shader, between the geometric normal and the "up normal", with the height, so that it creates a correct transition between the walls and the plateau.

(normals are smoothly interpolated between each face of the walls but not between walls faces and plateau faces)

I tried to adjust :

-the displacement bound param. in OBJ parameter page

-the shading Quality param. in OBJ parameter page

-the Super Sample param. in MantraROP parameter page.

But still these stupid artifacts.

Where can they come from?

Division by zero?

Still uncorrect geometry?

Bugs?

insufficient displacement bound? -> increased it and either no change or never-ending renders.

Any help is welcome!

[David Gary]

forget it!

I found it at last:

it comes from specular computations within my shader. I turned to a Lambertian shader...

Noise diplacement with high octaves+vexSpecular seems to give ugly results

[mark]

glad you worked it out FrenchOP. Yesterday I noticed similar highlights when using VexSpecular, when the specular was set (too) high, but there was no displacement map. i dropped the specular level and it looks ok.