Fractured geometry motion blur problem

[Cuprum]

Hi. I am new to Hiudini. I decided to start with quickstart tutorials from sidefx website ( the first one with modeling columns and destructing them). I did everything what was written in pdf, but my render got really ugly flickering on inside parts of fracture with motion blur. I tried to make sampling quality really high but without success. Is it even possible to get quality mblur on inside parts of fractured geometry? If yes, how?

[Tom]

You increased Pixel Samples? Around 12 samples could be enough.

If you cant fix it, drop a scene file and I will check it.

Edited December 6, 2011 by Tom

[Cuprum]

You increased Pixel Samples? Around 12 samples could be enough.

If you cant fix it, drop a scene file and I will check it.

I tried 16x16, it took very long but without success

Here is the file. It is just a tutorial scene, not a big deal really since mblur is post job usually anyways, but I am slightly discouraged to be honest. First encounter went not very well.

lesson1_4.hip

[ehsan parizi]

turn off the depth of field in your mantra renderer. that will help

[moondeer]

the flickering you see is because your normals are not correct on your columns.

add a reverse sop to your columns before your mergesop.

[ehsan parizi]

the flickering you see is because your normals are not correct on your columns.

add a reverse sop to your columns before your mergesop.

Hi Moondeer.

Can you please explain the relationship between "flickering" and reversed normals?

[Cuprum]

the flickering you see is because your normals are not correct on your columns.

add a reverse sop to your columns before your mergesop.

...and it worked out perfectly! Thank you. Seems like motion blur just exaggerated problem, it was not cause of it.

[moondeer]

Hi Moondeer.

Can you please explain the relationship between "flickering" and reversed normals?

i am sure someone else can elaborate more... the gist is that the normal is key for shading. its direction is integral to determining just how much

light and shadow should be applied to the pixel at render time. mantra will do its best even when there is no normal for a surface. when reversed or pointing

inwards, the side facing the camera does not have a proper normal with which mantra can determine proper color.

variations in 'best effort' is the flickering...

when fractured, the pieces are based on the original, so with fractured columns that have incorrect normals, you get pieces with incorrect normals.

so the pieces now also have the flickering.

i've tried to develop the habit of viewing the normals before any render. very very common to find bits that need a reverseSOP.

cheers!

[ehsan parizi]

i am sure someone else can elaborate more... the gist is that the normal is key for shading. its direction is integral to determining just how much

light and shadow should be applied to the pixel at render time. mantra will do its best even when there is no normal for a surface. when reversed or pointing

inwards, the side facing the camera does not have a proper normal with which mantra can determine proper color.

variations in 'best effort' is the flickering...

when fractured, the pieces are based on the original, so with fractured columns that have incorrect normals, you get pieces with incorrect normals.

so the pieces now also have the flickering.

i've tried to develop the habit of viewing the normals before any render. very very common to find bits that need a reverseSOP.

cheers!

Thanks. I knew that normal is the key to shading, but I wasn't aware of that attempting thing! I thought if your normals are reversed, you just get a dark side when it's supposed to get lit!(if you have only 1 light) + when I rendered his file on my computer, it was lit properly, although maybe because he has 2 lights in his scene! and I also rendered only 2 frames! anyway, seems like your solution has worked

Edited December 7, 2011 by ehsan parizi

[magneto]

This might be a little unrelated but I find it hard to tell if the normals are flipped in the viewport. I know you can use the show normals option, but I am used to seeing this very easily in other 3d apps like Max. It's immediately noticable. But in Houdini, I sometimes get a weird feeling it the normals are wrong, or right.

Is it related to the default material used for objects?

[ehsan parizi]

This might be a little unrelated but I find it hard to tell if the normals are flipped in the viewport. I know you can use the show normals option, but I am used to seeing this very easily in other 3d apps like Max. It's immediately noticable. But in Houdini, I sometimes get a weird feeling it the normals are wrong, or right.

Is it related to the default material used for objects?

Normals are not related to the material! it's a primitive(or point, depending on which normal we're talking about) attribute!

You use normals in shader writing, but I don't think you can change them! + why do you think it's hard to see them?!

Edited December 7, 2011 by ehsan parizi

[moondeer]

au contraire,

you can change your normals to your hearts desire in houdini. that is one of the most powerful moves in houdini.

change their direction or change their length can be done very easily.

see the photos. if too long then it is hard to see if they are starting at the surface moving outward, or visa versa. use the 'd' key to bring up display options and then

the scale slider to shorten them.

orient your view so that the normals are isolated or disable the floor grid.

manipulate normals tutorial

http://www.sidefx.com/index.php?option=com_content&task=view&id=1270&Itemid=261

lastly see that both balls have a simple clay shader and both render green regardless of normal direction. mantra tries to render, but with reversed normals, you will get errors

in your alpha channel sometimes and the odd flickering mentioned above... not to mention a multitude of gooy wrongness that can be very hard to figure out short of a simple normals check in wireframe display mode. 'w' key.

cheers!

[3dbeing]

another helpful trick in viewing normals is viewing with hidden line ghost... it's quite obvious in that view if the normals are incorrect. Also you can scale them up in your display options-> attributes tab..

[magneto]

Normals are not related to the material! it's a primitive(or point, depending on which normal we're talking about) attribute!

You use normals in shader writing, but I don't think you can change them! + why do you think it's hard to see them?!

I know normals are not related to materials but they use normals to define how geometry is shaded. So in the case of Max, if you have flipped/reverse normals, they will look different in the viewport. In Houdini it seems like they don't look much different either way, unless you use the display normals options or see the artifacts in the render.

au contraire,

you can change your normals to your hearts desire in houdini. that is one of the most powerful moves in houdini.

change their direction or change their length can be done very easily.

see the photos. if too long then it is hard to see if they are starting at the surface moving outward, or visa versa. use the 'd' key to bring up display options and then

the scale slider to shorten them.

orient your view so that the normals are isolated or disable the floor grid.

manipulate normals tutorial

http://www.sidefx.com/index.php?option=com_content&task=view&id=1270&Itemid=261

lastly see that both balls have a simple clay shader and both render green regardless of normal direction. mantra tries to render, but with reversed normals, you will get errors

in your alpha channel sometimes and the odd flickering mentioned above... not to mention a multitude of gooy wrongness that can be very hard to figure out short of a simple normals check in wireframe display mode. 'w' key.

cheers!

Thanks I didn't know you could modify normals that way for geometry. I knew about the display options -> normal scale though. Very useful for sure.

another helpful trick in viewing normals is viewing with hidden line ghost... it's quite obvious in that view if the normals are incorrect. Also you can scale them up in your display options-> attributes tab..

Thanks I tried it just now but couldn't tell. The shading still looked the same. Or do you mean Hidden Line only? I tried Hidden Line Ghost like you said and added a reverse SOP, toggled the result on and off but couldn't tell.

[3dbeing]

Thanks I tried it just now but couldn't tell. The shading still looked the same. Or do you mean Hidden Line only? I tried Hidden Line Ghost like you said and added a reverse SOP, toggled the result on and off but couldn't tell.

I mean hidden line ghost with normals displayed. I also use a black background, and I always verify the normals are doing what i expect them to do regardles of the opengl view.

[magneto]

I mean hidden line ghost with normals displayed. I also use a black background, and I always verify the normals are doing what i expect them to do regardles of the opengl view.

Thanks, that's a good tip. I use black too but with wireframe sometimes it's hard to tell the direction of normals.

Also I think it would be useful if the normal vectors drawn by Houdini (default pink) use a gradient instead of a solid color.

[3dbeing]

Thanks, that's a good tip. I use black too but with wireframe sometimes it's hard to tell the direction of normals.

Also I think it would be useful if the normal vectors drawn by Houdini (default pink) use a gradient instead of a solid color.

if you want to map your own normals you can do that in the display options(d in viewport)-> guides and markers tab and add a custom vector maping; in the edit menu (by right clicking the name ) Just map the attribute to N and check fade tips. . This can then be accesed in the display options tool bar-> display custom attributes...