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depth pass for volumetric shader, and flickering problems

 
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Bazilikum



Joined: 17 Jun 2011
Posts: 2

PostPosted: Fri Jun 17, 2011 3:51 pm    Post subject: depth pass for volumetric shader, and flickering problems Reply with quote

Hello Holger!

Thank you for your time,
Im not sure if this has anything to do with you, but from what i figured, the softimage particle volume shader is your making?
Im using the Softimage 2011 particle volume cloud shader, and have some questions please,maybe you know:
Im only using the Ambient color, no illumination, and no Occlusion, just plain white, with a particle shaper conected to the density.
Currently, to get the depth of the particles, im connecting a raylength to the ambient color, rendering it in 32bit, then subdividing it by the alpha to get pure depth and using the alpha for the actual shading. its not perfect but its working. Is there a better way to get a depth map of the volume? i Tried using the built in buffer writer, but it either crashes softimage or just doesnt render.
Another thing is that sometimes i get flickering of particles on\off. (no warnings of data limit breach).
There seems to be a problem if the particles are initialized - if the scene is closed and then reopened then softimage spits the "no data found" on the density, and the simulation needs to be reinitialized every time, also if i partition the cloud and give that partition a different shader it will render only if i resimulate, and then i have to resimulate again if i want to switch to the volume shader.

Thanks again anyway,
Amit
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schoenberger
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Joined: 02 Mar 2005
Posts: 3786

PostPosted: Fri Jun 17, 2011 4:58 pm    Post subject: Reply with quote

Hi

The raylength into the ambient color should work, but I am not sure if you need to divide it with the alpha (as the default render is already premultiplied).
The framebuffer should be right way, this is the first time I hear that it crashes Softimage.
Perhaps I can to a test with a simple sim in the next time.

The resimulation issue is not my part. The ICE particle export is done before my shader or even MRay is started.
Seems to be a Softimage bug.

Particles flickering should not happen, perhaps if you have too many at the exact same location in space. But then you would not see it as all particles would require a very very low density/alpha for that case.
You are not using multiple volume shaders, are you? If the flickering is squared, then perhaps descrease the cell size.

Sorry that I cannot help you much.
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Holger Schönberger
Binary Alchemy - digital materialization
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Bazilikum



Joined: 17 Jun 2011
Posts: 2

PostPosted: Sat Jun 18, 2011 11:26 am    Post subject: Reply with quote

Hi Holger!

Thanks for the fast replay!
what i did with the built in buffer writer is assign it to one of the options (like the refraction buffer) and give that buffer a 32bit file like openEXR in the pass options. Is that the right approach? Should i do something else?

I need to unpremultiply the depth from the raylength because if not i get depth blending where the point clouds alpha is not 100% opaque. Its not 100% correct but its sufficient for pass depth blending later.

The flickering is not squre like, and i dont think its from the shadow lookup table, its just areas of particles suddenly disappearing and showing up the next frame, if i reduce the number of particles it doesnt happen, so currently im just rendering 2 different clouds and merging them later. Im not using more then one volumetric shader in the scene, and its connected to only one point cloud.

Again thank you very much!
Amit
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schoenberger
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Joined: 02 Mar 2005
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PostPosted: Sat Jun 18, 2011 3:00 pm    Post subject: Reply with quote

The depth pass is setup right. It should work that way.

I checked, the limit for particles in one location is 500!
So if you have 500 particles in one space, you should definately reduce them and increase the density instead.
I would also assume the rendering is pretty slow if you have more than 500 particles at one location.
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