| 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.

left view | create spotlight

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°.)

front view | clone spotlight

Now you have an arch made out of spotlights.

front view | arch 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°.

top view | clone spotlights

Bingo! You now have a dome made out of spotlights.

front view | dome 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).

top view | objects to illuminate

Finally create a camera to give you a nice view of
the torus-knot. Okay, now hit the render button!

camera view | torus-knot

Step 6 | So this is how the first rendering looks like. Diffuse
light is coming from all angles illuminating the scene.

rendering #1

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.

front view | creating a directional target light

Step 7 | Now this looks nice, don't you think?

rendering #2

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.

front view | mirroring spotlights

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.

final rendering



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