View Full Version : Global Illumination

08 August 2004, 04:50 AM
After having tried Final Gathering, i'm now ready to try something different. I want to use a dirtmap pass for shadows, so there is no need in FG. What i need now is Global Illum, so that the scene will look like in real life, plus it'll have nice shadows as a result of the dirtmap pass. The question is: what is the most efficient way of setting up a scene with GI (how to make GI work properly, so that every object in my scene will be lit up) ??? Also, i have a sphere around the scene to generate reflections (the best way by far to achieve realistic reflections).
Note: the image-based-lighting pass does not work as good as just a sphere, so don't mention it. I want to know how to set up a GI scene with just a few lights. Please, be specific in ur response.

08 August 2004, 08:03 AM
Have you bothered to check the manual on this? You keep asking these question that can easily be answered if you happen to look in the manual. Next time take the time to search before you post please.

here is your answer , you can read it on the online guide , global illumination section:

Setting Up Transmitters and Receivers

Defining which objects transmit and which receive is perhaps the most integral step in creating photon effects. The caustic or global illumination effect you’re trying to achieve greatly depends on an object’s position to the light, its position to other objects, and its surface. When defining receivers and transmitters, you’re telling the photons where they’re starting from and what their target(s) is (are).

Select an object that you want to set as a caustic transmitter or receiver.
Remember to select a geometric object and not a light. For example, in the case of a magnifying glass, you would select the glass object rather than the light source.
Click on the Selection button on the Select panel and click the Visibility icon from the explorer that appears. The Visibility property editor opens.


If you wish to make several objects (such as four walls, a floor, a ceiling and a table) receive photons, you can multi-select every object in a scene and assign them all as transmitters and/or receivers.

Alternatively, you can group them and set the transmitter/receiver property using an override (see below).

Select whether you want your object to receive or transmit global illumination photons or caustic photons, or any combination of the four.



There is no reason that an object cannot be assigned all four properties; that is, an object can be a global illumination receiver and transmitter as well as a caustic receiver and transmitter.

Defining all of your objects in this way, however, increases render times.

Before you render, you must activate global illumination and/or caustics for the render pass.
To view the caustic and global illumination effects in the render region, see Displaying Photons in the Render Region (file:///C:/Softimage/XSI_4.0/Doc/html/shade/GIcaustics.html#wp425981) and Preparing Global Illumination and Caustics for Rendering (file:///C:/Softimage/XSI_4.0/Doc/html/shade/GIcaustics.html#wp436600).


To render global illumination or caustics, you must have at least one emitter, transmitter, and receiver defined.

If you are missing one or more of these elements, the photon effect will be disabled when you try to render it. A warning will appear, telling you which element is missing.

08 August 2004, 12:17 AM
ok, ill try to figure it out on my own then.

08 August 2004, 07:21 AM
Shaddix, a couple of things:
1. learn once and for all that neither fg or dirtmap generates shadows. What you see is occlusion of nearby objects - not real direct lightsource shadows.
2. Getting rid of artifacts - you have to setup the correct radius - work in raster space and just experiment. the "flowing in the air thing" is a result of the increase of interpolation values, thus leading to loss of detail in the indirect illumination. I prefer this loss of detail, since high-resolution fg maps are prone to flickering anyway and are slooooow.
3. There is no difference whatsoever between a sphere and a enviroment shader for reflections. Still, if you want to put an environment shader for something along with a sphere for reflections here is what: put a raytype shader on your sphere. In the reflection port plug your texture, and in eye, etc a constant material with full transparency. You can put another texture in the FG port, if you want to FG sample from that texture, rather than the environment shader.
ALso, on a final note: You must use FG+Photon maps for smooth result. Which equals long-long renders. I would say - stick with FG. It gives you the most important indirect lighting component.

08 August 2004, 08:29 AM
This will help you get answers:


08 August 2004, 11:17 AM
nice post .. especially in the "before you ask" part

When you ask your question, display the fact that you have done these things first; this will help establish that you're not being a lazy sponge and wasting people's time. Better yet, display what you have learned from doing these things. We like answering questions for people who have demonstrated that they can learn from the answers.

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