Mantra - point cloud / ambient occlusion / colour bleeding

[smidur]

Hi,

As I have a bit of time on my hands I am currently looking at Mantra's point cloud abilities, trying to create a prman style rendering pipeline and came across serveral problems. Apologies in case some of the questions are a bit stupid as I am not a shading expert.

1) Point cloud occlusion

As far as I know there is nothing similar to rendermans point cloud occlusion. It is possible to use point clouds to reduce the raytracing as shown here (files from Point cloud presentation) which is nice but you still need to do raytracing.

The only thing that seems to do the same is Mario HDK solution but as I am no too familiar with HDK stuff this seems to be a bit to tricky for me to do (and I try to avoid SOP solutions - would like to do everything/most with a shader).

Is there anything I have missed? Are there any other solutions out there worth looking at?

2) Colour bleeding

Is there anything similar to rendermans indirectdiffuse (with point cloud) function.

With pcwrite() I am able to bake direct lighting into a point cloud but I am not sure what to do with it.

Is there a way to do a cheap point cloud lookup (is it possible to "trace" into a pointcloud)?

Would be very happy if anyone has some hints for me. I will provide anything I can come up with (if I can come up with something useful) as hip files.

Thanks a lot,

Martin

[brianburke]

Hi Martin,

Other than the work described here, there's no way to solve occlusion or color bleeding on the point cloud itself in Houdini.

Mantra is a really good raytracer however (much faster than PRman in my experience). So it might make the most sense to run low res, coarsely diced, renders to cache colorbleeding and/or occlusion using pcwrite, then look up these point clouds in your final renders.

Good luck dude.

Edited August 25, 2009 by brianburke

[Wolfwood]

Here is a decent introduction to the various point based rendering techniques in RenderMan.

http://graphics.pixar.com/library/PointBasedColorBleeding/

[Dennis Sedov]

Isn't there a way to do color bleed in Mantra directly in MPR?

[fred]

Well, there is a way.

here is a file

enjoy

Fred Fortin

simply toggle on the write_pc_files in the shaders that are in /obj/shop

render the frames you want...

toggle off the write_pc_files...then re-render the sequence..

on the pc file generation, color bleeding and occlusion are not displayed..it only display when you toggle off pc generation..

it is camera base off course and it should work with displacement..

Have fun

test.hipnc

[LaidlawFX]

Hey if you figure this out better that would be great...

Here is some help from my attempts;

Visually Similar-

Irradiance point caching is very similar, and with the occlusion sop on the Houdini Exchange it is very easy to load and implement into the VopSurface side of a Shader... vop displacement I can't figure out.

As for color bleeding I list most of the ways you can do it here... UberShader ... not 100% renderman style but it will get you results

Technically Similar-

Have you tried using a lattice or a cube, and raying the point into a uniform grid like area around them, but then you would have to bake your shader or color in to your objects. That would get you more inline with the .ptc files of renderman.

Another method I tried and did not go to far into was taking a a cubic camera settup with the irradiance point caching.

It really depends on what you are trying to do in the end. If you are trying to get a similar visual result or a similar technical result. Since unless you write code I think you'll have to be creative to avoid a lawsuit...

Also I do believe more in general should be done with point cloud and i3d shading methods like this... so good luck