kinds of occlusion

[MENOZ]

hello.

i'm trying to understand how to use pointclouds VOP, andi read the Odwiki pages, where it talks about occlusion, irradiance cache, pointclouds..

now this is what i understood:

1) for calculating occlusion i can make a vop shader with a occlusion vop (that is a function that uses ray tracing to compute the occlusion for each shading point). this give me good results, but i need a high number of samples, so high rendertimes, to avoid noise\flickering.

2) I can use the irradiance cache that i found in the mantraROP. i don't know what this exactly does, but it speeds up render times, and i think it takes a sort of point cloud and interpolate the values, so it computes ray tracing in less points, and speeds up the render.

moreover

2a) form the Odwiki http://odforce.net/wiki/index.php/IrradianceCache

The Irradiance Cache is a file that can be written out and/or read in during Irradiance or AmbientOcclusion to increase the speed of repetitive rendering

it talks about repetitive rendering. so i can store the occlusion result and read it from disk to reuse and speed up next renderings? how can i do to write the irradiance cache on the disk?

3) I can use point clouds to speed up render times. the idea behind should be that the globalillumination is calculated only in some point on the surface, the rest are interpolated.

3b) I can use the point clouds to store values of my occlusion to the disk, and read them back for subsequent renders, without the needs of recalculating the occlusion.

please correct me, where i'm wrong?

[sibarrick]

That all sounds about right to me.

For the irradiance cache I'm not 100% sure. In H8.2 there were options to set it to read and write etc.

It may handle this automatically now, but if not you can add those parameters back to the mantra rop using the edit parameter interface dialog. The little gear icon next to the rop name. Go to the For Rendering tab and look for the irradiance folder its in there.

[Jason]

You have to add the Irradiance Cache File and Mode Rendering Parameters yourself in order to render to file. (And I updated that wiki page with this info too)

[MENOZ]

You have to add the Irradiance Cache File and Mode Rendering Parameters yourself in order to render to file. (And I updated that wiki page with this info too)

thanks!

what is the difference between using irradiance cache to accelerate occlusion and using a point cloud in the shading network? they seems to be very similar, what is the difference?

[sanostol]

how does this pointcloud method work?

[rob]

This subject also interests me greatly I have done some digging around and found this on the exchange

Hip Files From Point Cloud Presentation May 11th 2005

http://www.sidefx.com/index.php?option=com...&Itemid=137

I dont know if the files will work in 9.1 , i guess i shall find out shortly

Rob

[Jason]

You're right - internally the Irradiance Cache is stored as specialized point-cloud. If you write them to disk you can "i3dconvert" them to .bgeo's and see the type of information gets stored on the points. A specialized reconstruction is made from these points. The convenience of using Irradiance Caching is it's ease-of-use, it's more intuitive controls and the results are good.

You can indeed perform AO using PointClouds as you've seen in the pcpack - and you can even use an adaptation of the NVidia point-cloud occlusion technique on raw points (ie, no raytracing involved, good for huge models - but not as fast using VEX as an C++ implementation) and now you can even write out new baked occlusion using the pcwrite() VEX function. See: http://forums.odforce.net/index.php?showtopic=2876

This subject also interests me greatly I have done some digging around and found this on the exchange

Hip Files From Point Cloud Presentation May 11th 2005

http://www.sidefx.com/index.php?option=com...&Itemid=137

I dont know if the files will work in 9.1 , i guess i shall find out shortly

Rob

[MENOZ]

rob: thanks for the link, i'll download it

jason: thanks for the explanation!

yes i've seen that article about fast ambient occlusion from nvidia, and the post on odforce about that, now i can look at it knowing what's there were before. (...mmm strange english... )

Edited May 2, 2008 by MENOZ

[hoknamahn]

There is also another one method to calculate ambient occlusion - screen space ambient occlusion. Now people use it not only for games (Crysis, S.T.A.L.K.E.R.) but also in postproduction:

http://en.wikipedia.org/wiki/Screen_Space_Ambient_Occlusion

[Jason]

There is also another one method to calculate ambient occlusion - screen space ambient occlusion. Now people use it not only for games (Crysis, S.T.A.L.K.E.R.) but also in postproduction:

http://en.wikipedia.org/wiki/Screen_Space_Ambient_Occlusion

I forgot about this one; quite nice really. It would be interesting if one day Houdini's could implement such a thing right in the viewport for a heighted sense of depth while modeling, etc.

[edward]

There's also fake screen space AO: http://graphics.uni-konstanz.de/publikatio...sking/webseite/ .... Jeff Lait reportedly did it in 7 COPs (no code) after coming back from SIGGRAPH.

[edward]

Oops, I already forgot this is how the Depth Darken COP came about. Make that 1 COP now.

[sibarrick]

Oops, I already forgot this is how the Depth Darken COP came about. Make that 1 COP now.

Cool! but who knew that was there!!!

[sibarrick]

Another good link

SSAO

If you don't mind installing plugins, there's a nice realtime demo here

Realtime ambient occlusion test

Edited May 3, 2008 by sibarrick