What
is gMil? gMil is a surface shader
for LW that simulates radiosity.
After hearing about gMil in the
LW7.x feature list I've wondered
what use can it give me. This paper
shows some of my trial and errors
to test the use of this surface
shader. This paper also has a collection
of thoughts and insight of other
people using gMil.
After
Searching the Forum on Newtek I
came across a post where a LWer
posted this:
"gMil
is a surface shader which simulates
global illumination, based on the
backdrop on a surface by surface
basis. It adds color or illumination
to the surfaces normal shading received
by scene lights. The shadow it receives
by other objects is calculated by
sampling an imaginary lighting sphere
around your scene (probably area
lights), either random (which results
again in noizy changes when calculating
anims) or ordered (which results
clearly in shadow lines cast by
the area? lights). Objects that
cast shadow on the (gMil)surface
can optionally occlude diffuse and/or
specular lighting and reflection,
this either in a additive(ON) or
negative(INV) fashion.
By
using gMil in combination with BRDF
you can put up a relation between
your scene lighting (also put some
ambient lighting) and global illumination
to change the shadow appearance.
Hope
this helps... ",(By Rick C.)
Wow,
that all sounds great. Lets give it
a try now.
Here's
my model with some basic surface
attributes. Rendered with one distant
light.
Now
I
tried to get a nice render using
backdrop radiosity. The backdrop
settings are shown to the left.
9sec render.
Next
I added gMil to the surface and
turned off backdrop radiosity.
When
you first add gMil these are the
default settings you get something
similar to what's seen on the right.
My
interpretations of the settings
are:
Colour
Add: Adds color from the back drop.
Luminous
Add: Adds some luminosity (brightness).
Falloff:
Doubles the shading for the diffusion/darkens
the shadows.
Sample
Style:
Changes the type of shadow from
dithered noise to a smooth smudged
like.
Occlusion:
Lets you turn on/off each attribute
affected by gMil.
To closely
match the radiosity render I did I
added 0.9 to Colour Add too get some
color from the backdrop.Then changed
the Luminous Add to 0.
My
first render is shown to
the left.
3
Sec render.
Sample
Rate was left at 10.
Shading
noise reduction enabled.
12.8
Sec render.
Sample
Rate was set to 75.
Shading
noise
reduction enabled.
3.1
Sec render.
Sample
Rate was set to 10.
Sample
Style changed to Ordered.
Shading
noise reduction enabled.
Even
though the sample rate is low there's
no noise like the render I got with
it set to random.
This
could work as a dirt shader!
14.5
Sec render
Sample
Rate was set to 75
Sample
Style changed to Ordered.
Shading
noise reduction enabled.
A
lot longer then our prettier radiosity
render that took 9sec. This could
work as a dirt shader. But is it
worth the rendertime?
15.9
Sec render.
Sample
Rate was set to 75.
Sample
Style changed to Ordered.
Falloff
is set to y=x^2
Shading
noise reduction enabled.
Occlusion
Diffusion is turned on
A
lot more dirtier. Looks like it needs
a wet rag.
My
tests with gMil have come to an
end. Turns out to be a kinda neat
surface shader with tons of settings.
I still don't know gMils purpose,
but I consider gMil more of a dirt
shader then a fake radiosity shader.
Although I didn't get the nice warm
render I got with the radiosity
render, I find it has its alternative
uses. Good thing about gMil is you
can apply it on a surface by surface
basic which has its advantages.
In all, gMil is just another weapon
in my LW arsenal.
I
hope this paper/tutorial shines a
little more light on the uses of gMil.
If you
want to download the scene you can
do so here.
