|	Tutorial #1 / Global Illumination
Introduction |	The goal of this tutorial is to fake diffuse light coming from every direction equal to the diffuse light distributed by an overcast sky. To achieve this effect I'll show you how to create a dome made out of about 100 spotlights. Please note that this tutorial is for 3DStudio Max, it should work for other 3D packages accordingly, though.
Step 1 |	In Left-Viewport create a free spotlight by clicking somewhere in the viewport's center. Then move this light to coordinate x=-200,y=0,z=0.
Step 2 |	Go to Front-Viewport. Here you instance-clone the spotlight 10 times by rotating it 18° clockwise around the world y-axis. Make sure to use the world center (0,0,0) as center of your transformation. (Tip: use the rotation-snap tool for the 18°.) Now you have an arch made out of spotlights.
Step 3 |	Select all lights except for the top one in the middle. Go to top view and again instance-clone the lights, this time 9 times, again 18°. Bingo! You now have a dome made out of spotlights.
Step 4 |	Of course 101 lights with multiplier 1.0 are far to bright, set all lights to multiplier 0.02. This is easy because they are instances, so you need to do the changes for one of them only. Also set your spotlight's color to something resembling your sky, e.g a light blue with RGB 240,249,255. Finally set lights to "overshoot", shadowcasting "on", and adjust the shadowmap to Map Bias 0.1, Size 64 and SmpRange 4.0
Step 5 |	Now we need something to illuminate. Anything will be fine. I made a flat box (400 x 400 x -20) centered in the middle (0,0,0) and a torus-knot on top of the box (radius 20, segments 200, sectionradius 10, sides 40). Both objects where given a simple standard material with a white diffuse color (RGB 255,255,255). Finally create a camera to give you a nice view of the torus-knot. Okay, now hit the render button!
Step 6 |	So this is how the first rendering looks like. Diffuse light is coming from all angles illuminating the scene. Let's add a sun to the scene. Create a directional target light with multiplier 0.2, check "overshoot" set falloff to 84, shadowcasting "on", Map Bias 0.1, Size 1024, SmpRange 4.0. You might want to tone the spotlights down a bit to multiplier 0.018, so the next rendering won't be too bright.
Step 7 |	Now this looks nice, don't you think? There is one more little thing left to do. A tiny bit is missing, which might just make the difference. The ground (box) should bounce back a small amount of diffuse light to top off the global illumination. So just mirror the second row of spotlights and move them down below the box. Be sure to use copy-cloning this time, not instancing. As these spotlights are underneath the box we need to exclude this box from their illumination, because otherwise the box would block the lights below.
Finally |	Well, here's the final rendering. Notice the slight increase of light on the undersides of the torus in comparison to the rendering before. The effect is subtle, but worth it.
Thank you |	This completes my tutorial on Global Illumination. I hope you enjoyed reading it and found it useful, too. For questions or comment please e-mail me. tutorials@michaelscholz.de. (c) 2001 Michael Scholz www.michaelscholz.de