Mantra Render - Hide Voronoi Fracture Cracks?

[TobiasSteiner]

Working on a project that is just a simple break away of a fractured model.  Problem is that Mantra renders all the cracks in the shape before they are pulled apart.  Rendering the same scene in other renderers like Arnold Render does not yield this problem.  The shape is not cracked before it it pulled apart which is the desired effect.  Anyone know why this is not the case in Mantra?

Houdini 15.5, latest Arnold render.

[davpe]

isn't it just a normals issue? if you are seeing like a weird shading around the cracks then it's quite likely it. otherwise there is no difference in how mantra renders fractured geo compared to arnold or anything else.

[TobiasSteiner]

58 minutes ago, davpe said:

isn't it just a normals issue? if you are seeing like a weird shading around the cracks then it's quite likely it. otherwise there is no difference in how mantra renders fractured geo compared to arnold or anything else.

I don't think so.  Tried adding normals to the post fractured GEO and that had no effect.  See below.  The fractured mess is the Mantra render.  The perfect one is the Arnold render.  Same scene.  Same fractured sphere. 3rd photo showing breaking of same object is rendered in Arnold as well.

 

Edited January 24, 2017 by TobiasSteiner
Added photo.

[davpe]

uh, try to delete Cd attribute before rendering. or turn off a point color in the shader.

[TobiasSteiner]

16 minutes ago, davpe said:

uh, try to delete Cd attribute before rendering. or turn off a point color in the shader.

That's exactly what it was.  This is an extra step in the process though in terms of using Mantra.  There was nothing that jumped out and said this would be an issue.  The Cd attributed isn't even shown on the spreadsheet after the fracture process.  This seems a good candidate for usage improvement.  Added a "Clean" node after the voronoi fracture node to remove Cd.  Below is proof that your method worked for Mantra.  Thank you for the suggestion!

 

[TobiasSteiner]

Just for the curious.  Here's the same two frames rendered in Arnold Render for Houdini.  Each rendered in 6 seconds.  The Mantra renders you saw in the previous post were 7 seconds (first frame) and 15 seconds (second frame).  Same light type, position, and intensity.   Exposure could be bumped a bit in the Arnold render but I think this shows how good of a render engine Arnold is.  

Not meant to be a brand debate post.  Just sharing for those out there that might be curious and do not use Arnold.

[davpe]

- well I don't think it is an extra step and it is not exactly an issue. it is admittedly an odd default in Mantrasurface shader though. I recommend starting all shaders from empty vopmaterial (Material Shader Builder) to avoid things like this.

- of course Cd is shown in a geometry spreadsheet. it behaves the same as any other attribute. For coloring pieces there is a checkbox in Voronoi Fracture SOP so you can leave it unchecked.

- don't use Clean SOP to remove an attribute (it is meant to clean a geometry from invalid prims/points). use Attribute Delete SOP instead.

cheers, D.

[TobiasSteiner]

7 minutes ago, davpe said:

- well I don't think it is an extra step and it is not exactly an issue. it is admittedly an odd default in Mantrasurface shader though. I recommend starting all shaders from empty vopmaterial (Material Shader Builder) to avoid things like this.

- of course Cd is shown in a geometry spreadsheet. it behaves the same as any other attribute. For coloring pieces there is a checkbox in Voronoi Fracture SOP so you can leave it unchecked.

- don't use Clean SOP to remove an attribute (it is meant to clean a geometry from invalid prims/points). use Attribute Delete SOP instead.

cheers, D.

Good tip regarding using the Material Shader Builder as an alternative.  I will explore that more thank you. :-)

Cd is not shown in the spreadsheet in this scene for the sphere object.  Checked all tabs (point, verts, primitives, and details) prior to posting the reply and then checked again after your comment.  The checkbox you're referring to must be "visualize pieces" and checking this box on is what creates the Cd attribute.  However, this was never the case in the original problem presented.  None the less, the Cd attribute is clearly "hidden" behind the scenes in the case where the "visualize pieces" is unchecked and is removable by....

....using the Clean OR the Attribute Delete SOP.  Each method achieves the same result to no harm or foul.  

 

The joy of throwing the knife at the same target in a thousand different ways. - Houdini

[Skybar]

The fact that you say the Cd attribute is hidden after the "fracture process" (I'm guessing you mean after the sim) might mean your pieces are packed, and the attribute will be inside and not visible in the spreadsheet. Think of packed primitives like a zipfile, you can't view what's inside until you pack it up - which also Mantra does at rendertime and can use the Cd attribute.

[davpe]

1. Cd attribute - see attached pic. No attributes are ever "hidden" in Houdini (with exception of Packed geometry and geometry soups as Skybar brought up)

2. use whatever you want, I'm only suggesting that Clean SOP may modify geometry

Edited January 24, 2017 by davpe

[dimovfx]

Well there are "hidden" attributes, like @N or @nage and maybe more.  I still don't get it why

[davpe]

sasho78:

this is already beyond the original topic, but: @N is not a hidden attribute, is it? When you create @N, you can most definitely see it in the spreadsheet. If you don't create @N, then it just isn't there and is temporarily created at render time, right? don't know what @nage is so can't argue on that

[dimovfx]

@davpe that is why i put hidden in quotes, they are there just not visible in the spreadsheet. @nage is normalized age of the particles, it is not visible as well but you can use it.

[IanVE]

Hi all,

I'm having a similar problem with rendering glass that has Voronoi fracturing. Simply put when I render with Mantra with just the Cd it renders fine and the cracks don't show up pre sim.  However, when I add a PBR  Glass shader all the cracks show up from the very beginning.  I've attempted doing a lot of fixes over the past few days but I cannot get it work. The sim itself is still a work in progress, but I wanted to make sure first that the Materials are working properly (had this problem before).  I attached the hip file also. 

Wondering if anyone could lend me a hand, that would be awesome! 

 

Cheers all!

 

Glass_Shatter_Test.hiplc