I have been working my way through the legacy material. I have made my way to rendering which so far seems to be the most difficult for me to get working. First trying to find where the old button or field is in the new interface or trying to finds its newer counterpart is a little frustrating. I have been able to get most all the concepts, but I just can not get the atmosphere object to render. I have tried the user guide example, intro_shops, and rendering_01. I must be doing something wrong. Is there anyway to get a simple proof of concept scene so that I may debug what I am doing wrong. Maybe the userguide file setup. I think that I almost have the user guide file, but I am unclear how Houdini references

/temp/$OS.pic.

What is the $OS variable. Could I render the $OS.pic to say
ctemp,
or say
dsomearbitrary_directory/$OS.pic.

Does Houdini keep track of the path entered in the z_depth file field?


What are the crucial elements that make atmosphere objects render in Mantra?

Do I need to switch anything in the output settings? I really want to beat this problem.

Thanks in Advance

todd dufour
I have been working my way through the legacy material. I have made my way to rendering which so far seems to be the most difficult for me to get working. First trying to find where the old button or field is in the new interface or trying to finds its newer counterpart is a little frustrating. I have been able to get most all the concepts, but I just can not get the atmosphere object to render. I have tried the user guide example, intro_shops, and rendering_01. I must be doing something wrong. Is there anyway to get a simple proof of concept scene so that I may debug what I am doing wrong. Maybe the userguide file setup. I think that I almost have the user guide file, but I am unclear how Houdini references

/temp/$OS.pic.

What is the $OS variable. Could I render the $OS.pic to say
ctemp,
or say
dsomearbitrary_directory/$OS.pic.

From the ExpressionLang.fmk.pdf file, pg 2:

OS Operator String. Contains the current OP?fs name.

Yes, you can render “$OS.pic” to “ctemp” or any directory you choose. Of course, you can use any filename for the .pic file instead of “$OS.pic”.

Does Houdini keep track of the path entered in the z_depth file field?

Yes.

What are the crucial elements that make atmosphere objects render in Mantra?

VEX Fog shader & assign the shader to the Atmosphere Object. Try the VEX Uniform Fog & then render.

Tip: Move the light & the Atmosphere object to 0,0,0 then parent the Atmosphere Object to the light.

Do I need to switch anything in the output settings? I really want to beat this problem.

Nope, there isn't anything to switch.

Please let me know if you have more questions.

Cheers!
steven

Thanks so much for the reply. I can not try out your suggestions until I get home tonight. I realy want to crack this nut. I have tried off and on for a couple of days. An hour here an hour there.. Thanks Shops and character are the only legacy stuff I have left… Thanks.

I want to thank you for your help… I definately got a “hello world” with the atmosphere object… Very cool and quite simple now that I understand the basics… I still have some questsions though…

It seems that version 5.5 is a transition version from 4 to 6. Therefore I am assuming that this version sometimes has two different workflow models overlapping certain task. For example the legacy material assumes that tweeking the atmosphere parameters will get results without a VEX_(atmosphere) shader. In the atmosphere object there was a context switch from uniform to light halo. I am now assuming that this is the same difference between VEX_uniformfog shader and VEX_litfog shader. Would I be correct in assuming this?

Also, the lights contain an atmosphere tag… I did some experiments with changeing these values but could not determine their intended controls… Could anyone explain how the atmosphere field in a light is intended to control results?


I have one more observation. I assigned a projection map to the lights in my scene and notice a camera obscura with the light volume. It was stated that the light volumes do not respect the cone light parameters. In order to mimic this, assign a circle or a noisey circle hicon matte as a projector map. (Does this projector map have to be grayscale or can I project rgb values through an atmosphere object to mimic a movie projector?) When I dolly out the camera I notice a light ball volume that looks a little like

O><

Where O is the location of the light. > comes from the ball to a point. < is the light beam coming out of the point. This is not what I expected. How can I control this shape of the light. I was expecting a light volume that looked more like

O< or o< or <

If you have read this far you are very brave…I any comments or suggestions would be greatly appreciated.

Hey Todd,

todd dufour
I want to thank you for your help… I definately got a “hello world” with the atmosphere object… Very cool and quite simple now that I understand the basics… I still have some questsions though…

It seems that version 5.5 is a transition version from 4 to 6. Therefore I am assuming that this version sometimes has two different workflow models overlapping certain task. For example the legacy material assumes that tweeking the atmosphere parameters will get results without a VEX_(atmosphere) shader. In the atmosphere object there was a context switch from uniform to light halo. I am now assuming that this is the same difference between VEX_uniformfog shader and VEX_litfog shader. Would I be correct in assuming this?

Yes, you're correct about the using VEX Uniform For & VEX Lit Fog.

Also, the lights contain an atmosphere tag… I did some experiments with changeing these values but could not determine their intended controls… Could anyone explain how the atmosphere field in a light is intended to control results?

The Atmosphere parameter is meant for Mantra3 so I'll recommend you to use a VEX shader solution instead.

I have one more observation. I assigned a projection map to the lights in my scene and notice a camera obscura with the light volume. It was stated that the light volumes do not respect the cone light parameters. In order to mimic this, assign a circle or a noisey circle hicon matte as a projector map. (Does this projector map have to be grayscale or can I project rgb values through an atmosphere object to mimic a movie projector?) When I dolly out the camera I notice a light ball volume that looks a little like

O><

Where O is the location of the light. > comes from the ball to a point. < is the light beam coming out of the point. This is not what I expected. How can I control this shape of the light. I was expecting a light volume that looked more like

O< or o< or <

If you have read this far you are very brave…I any comments or suggestions would be greatly appreciated.

Yes, you can use a RGB image as the Projection map. Type “Mandril.pic” (without the quotes) into the Light's Projection Map parameter & render. Together with the VEX Z-Map Fog shader, you can have the movie projector effect.

With regards to your light beam/volume problems, do you mind posting the setup here? Which shader you're using, values of the parameters, position of the light etc.

Alternatively, please send me a private message and we can arrange for the hip file to be emailed.

Thanks!

Cheers!
steven