[SOLVED]mantra output weird result when using volume sample in shader

[ranw0477]

Hi All,

I am trying to shading a crack on a planet based on the depth of the crack. Since the planet before cracking is just a perfect sphere,  I generated a spherical SDF bgeo and loaded it in my shader and do volume sample to get the signed distant value based on P. It all worked fine without motion blur, but when I turned on the motion blur to get camera motion blur the render result went wrong like the signed value is offseted. I am not using geo time motion blur or geometry velocity motion blur, just Xform time motion blur to get the camera motion. I have no idea how to fix that or is there a better way to color the crack without motionblur freaking out. I know it works in sop level but I need more detail so I try to move it into shader. I attached here my result render and one simple test I did to show the problem. Hope you guy could help me out and thank you in advance.

 

This is a test render without motion blur, you can see the color separation clearly:

 

This is a test render with xform motion blur, the blue color in crack invaded in the sphere also, creating an interesting but unwanted result:

 

 

Please check my hip file, just use the rop inside the geo1 to write out the sphere volume then you can render to see the problem. You can try frames between 2-48 which has camera animation. The first frame render is correct since the camera haven't moved yet.

 

I noticed if you just wrote out the volume, the attribute vop node in sop level may not update correctly, the render will be fine but you can try save and close then open the hipfile again to see the result, not sure if it is a minor bug of houdini or what. Again, any input would be helpful, thanks!

 

test_volume.hip

Edited October 6, 2015 by rGarfield

[ranw0477]

Anyone has any theory about this problem?

[Guest tar]

Use BlurP instead of Global P. Works perfectly. 

 

EDIT Set the shutter time to -1 to remove the blue.

Edited October 6, 2015 by tar

[ranw0477]

Use BlurP instead of Global P. Works perfectly. 

 

EDIT Set the shutter time to -1 to remove the blue.

Hi Marty,

Thanks so much, this thing bugs me for a while. Don't even know there is a blurP I can use.