Hi, just a couple of things.

How can I exclude objects from reflecting photons using irradiance. I'm trying to create one of those white GI deserts. I surrond my model with a sphere with a constant white shader on it and it makes everything go white. I want the sphere to render but not bounce the photons(rays) everywhere??

Does anyone bother with faking GI? I tried it using the light instancing thing using a light and shadow shader per instance and the render times are serious!! :shock:

Thanks

In the light mask of your sphere object, exclude the light that contains the GI shader.

For example, say your light object with GI shader is named “gilight”, then in the light mask of your sphere object, replace the “*” with “* ^gilight”.

I tried that. I tried exluding the name of the shader with the method you said. Only when I turn the display of the sphere off does it go away??

But, when you click on the cross and it asks you to select a pattern it offers objects to exclude. Which I thought was strange? Exclude an object from seeing an object? hmm..

Thanks

Apoogies. They're not just objects. They're only light objects. But it still doesn't work.

It seems that I can stop light from affetcing a object using the light mask but the light still bounces off the surface.

P.s. the sphere's shader has no lighting model attached to it. Its just 3 floating point values (1.0) in a vector for colour. The light and reflection mask boxes are empty and it still renders and reflects light. Whats that about?

Since your sphere is constant shaded, it will always shade regardless of any presence of lights. I think the reflection mask is probably what you wanted instead of the light mask (sorry about misleading you as I'm a lighting noob).

Are you trying to do ambient occlusion? It's much easier to simply change the background colour on a VEX Global Illumination SHOP to white than to put in a sphere object.

If you just want a white background, then why not do it in comp.

Double oops, you need to exclude the sphere from the reflection mask of your desert object. Reading the help for Reflection mask, it says,
“Defines objects to appear in reflections on this object.” So you want your desert to not be reflected by the sphere.

I'm using irradiance.

this is confusing. I removed the sphere object and set the background colour to white and it flooded the scene with white light like the sphere did?? Its more like a background light than a background colour. The help says the pixel is only shaded white if all rays miss it. I think its lying!

Have to go home now but tomorrow I'm upload the hip.

Thanks edward

just quickly,

would it be better to use ambient occulsion? I thought they were pretty similar.

Hey, this is my 100th post! Does this mean I officially dont like maya?

I created another hip that I could upload and whatever the problem was. Its stopped. Heres the hip anyway, just in case anyone else has problems with this. Its a dead simple scene. Just a sphere.

http://homepage.ntlworld.com/thehenster/Henster/irradiance.hip [homepage.ntlworld.com]

Heres how the scene renders:


p.s. How could I increase the intensity of the shadow?

So how do you want the picture? Without knowing more about what you actually want, I can only make random comments based on just looking at your file:
- Your “amb_occlusion” shop should have a background colour of white if you want it to have the same effect as your “irradiance” shop. (it's the last parameter on the first page of the shop). Remember that if you use ambient occlusion, then you have to turn off the display of your “world” object.
- Ambient occlusion is generally cheaper than doing irradiance caching. For example, I managed to get the same look as your pic much faster by using ambient occlusion (background colour of full white), and only using 64 samples.
- I have a feeling that you don't understand what is ambient occlusion. It basically mimics what you what to do by enclosing your scene in a large sphere without actually requiring a large sphere.
- Now, I'm far from know how to light, but I think you're not getting stronger shadows because of a couple of reasons. 1) You're getting light ALL around your scene, which decreases the likelihood of shadows occuring. 2) There's also a huge discrepancy between the lighting of your “model” and “floor” objects because you take out the GI influence on your “model”. 3) Your “main_light” is not casting shadows. If you want a much softer looking shadow, perhaps you should make it an area light or a light using a VEX Blur Shadow shop. stevenong has made several good suggestions on shadows either here or on the odforce forums before. You should do a search.

re: render times, tell me about it i have a p3 cpu!

if you havent already try the irradiance caching it makes a huge difference

hey mta,

im very interested in finding out about irradiance caching and how to implement it, because ive been struggleing to achieve that.

am i correct in saying that one has to activate irradiance caching in the “specific” folder of ur mantra renderer by specifying a file, and aswell as have a ambient occlusion light shop linked to a light?

because my ambient occl works really well however its sooooo slow, whats even worse is that im not even moving any geom so its a perfect opportunity for caching out occl info.

any ways, it would be great to hear how it is done :-)

thanks in advance

all the best
aracid

hey aracid, the other account got locked out for some reason.

yes you set it in a mantra ROP -> specific tab -> use irradiance caching. try settings like default error of 0.01 and 16 default samples, set your GI light to be 8 samples. just specify a file and it will create one, e.g. /tmp/ambocc.picnc. (may not need to do this, but i cant say for sure that it works without specifying a file).

the caching works with ambient occlusion - you dont need full irradiance to get benefit from it.

there maybe more info in the video tutorial, gi_irradiance - the one with a purple wall and green chair.

played around with it some more, man it chews some RAM. is that normal or a v7 bug? PC became unusable and all i had was a teapot cache file was 37mb.

heyHey al

and mark2, shot for the info, it does work, helps alot with the render times :-)

however

after playing around a bit, and then after playing around alot, i found an interesting approach to displacement and GI speed

and thats parenting ur scene to a null in obj mode and scaling it down, to something quiet smaller that the original, like (0.01)

im busy playing around with alot of polys and had a hard time displacing and using AOccl. and once i did this, render times went from a couple of min per scenes to a couple of seconds,

now this may be old news to some, but does anyone around really ever do this ??
cause its a GREAT time saver for me :-)

nyways

would love to hear what u guys think about this approach

aracid

thats pretty cool ill give it a go. i wonder if there is an explanation - the scale should not be relevant