help needed on finalRender and fRObjLight !!

[Jayk2k]

I think you need to right click on all objects, and set the mentalray attribs to GI...

It's been a while since i've used it again.... :D

[clifford]

Well .. ok ..
I succeed in lighting my scene with fRObjLight but I had to map my lighting object with a self-illuminated texture ..
Am I doing right ? 'coz as I understand it, I don't need a fRObjLight to light my scene with a self-illuminated texture!

somebody ??

Thanks

Cliff

[Chris]

I think your mixing up two important concepts with Finalrender here, Direct & Indirect light.

Final Render object light uses the material's self illumination map to work out how bright the pseudo light's that it creates will be. This creates Direct light, the same way as a spotlight or omni light creates direct light

The other kind of light is Indirect light, or Global Illumination (its buzzword time!) when you use GI the self illumination of an object also 'creates light', but at a different stage in the calculation.

It works like this:

first of all the Geometry is calculated

Then Direct Light is produced from all direct light sources in the scene, causing specular brightening on the objects in the scene. & casting shadows (or rather placing shadow shaped dark areas over the diffuse material of an object, the opposite of the speular brightening)

Next comes the GI pass, the GI engine now shoots rays from your sample points on the geometry, whenever they impact another piece of geometry it measures the relative brightness or darkness of that point, uses that to affect the original point & then spawns another x amount of rays which travel through the scene until they too intersect geometry. This happens again & again until the diffuse bounces level is met. The GI engine dosnt care whether a bright spot that a ray has 'hit' is a product of a spotlight landing on a surface, or whether that surface is inherently self illuminated or anything like that, it is just relative levels of brightness that count.

Its kind of an over simplification, there are a lot of other factors which are taken into account as well. So, yes you can light your scene without frObject light, with just a self illuminated object. BUT the GI engine will have to bounce all the way back to that object before it is able to find ANY light to illuminate the scene. If you have some direct light in there as well, there will initially be a lot more bright areas for the GI engine to detect, which means you wont need as many bounces & RH rays, which means it will render faster & with fewer artifacts, which means you can finish earlier & have a beer! :)

crikey, did I write all that?;)

[clifford]

OK OK ...
I didn't know about this two calculation steps (ie direct illum and indirect) ...
If I understand well, simple self illuminated object cannot cast specularity and shadow (even if shadows appears because of indirect illumination).
Anyway .. if object lighting allow me to reduce render times ... cool ...

Thanks for the explaination and lets start the PA challenge :)

See u
Cliff.

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