Simple fog is the basic environment fog settings
used when creating fog effects in Maya. As with any environment
fog type, Maya creates a volumetric material. In the case of simple
fog attributes, the clipping distance can be adjusted as well
as the height, saturation point and color.
(click on images for larger pop-ups)
 To
the left is a scene created primarily from polygonal surfaces
with textures taken from a library. The environment fog has
not been added yet so that you can reference changes with
Simple Fog. To add the environment fog go the the Render Options
within the Render Globals and click on the box to the right
of the Environment Fog field. |
 When
examining the fog layout in the Hypershade notice that the
envFogMaterial is connected as a Volume Material. This is
rendered as a volume within the scene and is not assigned
to a surface. In addition a envFogLight node is created which
is light linked to the envFogSE. The envFogLight does not
illuminate the geometry within the scene, it is used to exclusively
link the EnvFogSE to the light object. If the fog requires
an illumination source, the light can be activated by turning
on "Illuminates by Default" in the lights attributes. |
 The
image to the left shows the basic results of Simple Fog. The
Saturation Distance is the only thing modified to control
where the fog is the most dense. The Saturation Distance is
expressed in terms of grid units from the rendered camera
view. For example this scene is approximately 26 cm from camera
to the buildings at the end of the street and the Saturation
Distance is 8 cm or ~1/3 the depth. |
 Using
the same setting as the last image the Saturation Distance
is set to 30 cm or just behind the buildings at the end of
the street. |
 Clipping
planes are also useful for giving fog a distance start and
end point. In the envFog attributes there are two modes for
clipping. Fog Near/Far adjusts the fog clip distance locally
offset from the camera. The Camera Near/Far uses the cameras
clipping plane values as set by the camera attribute editor.
In the above example the Fog Near/Far is set just before the
overpass for the Near and to 200 cm for the Far. The Saturation
Distance is set to the same depth as the Near clip to create
a sharp wall of fog. |
 Use
Height -ON enables the fog to grade from a top to bottom height
within a scene. The Min/Max value is set to the working grid
units so that is determines exactly where the fog deminishes.
The Blend Range controls how quickly the fog grades as it
approaches the boundary of the Min/Max Height. In the above
scene the fog Min is at the ground level 0 and the max is
set just above the height of the camera. Additionally, a Fog
Near/Far value clips the start of the fog to be a few units
from the camera with the Saturation Distance also a few units
from camera.. |
 Once
the camera moves above or below the Min/Max Height, a sharp
boundary exists for the height clip. In this example the Fog
Max Height is below the camera.
|
 Color
Based Transparency by default is ON which makes darker color
values more transparent. This is the opposite of transparency
in shaders which darker colors are more opaque. If you wanted
to create a smoggy scene or have the appearance of light being
blocked by thick smoke, turn OFF Color Based Transparency.
The image above uses this idea to create a low smog bank.
The Height Min/Max is set closely below and above the camera
with a high Blend Range (6) to soften the outer limits..
|
 This
example uses a very dark color value with Color Based Transparency
unpicked. The Use Height is OFF and the Saturation Distance
is just before the bridge to create a dark gloom. Use Layer
is the last option in the Simple Fog Attributes.
When writing the tutorial I was unable to get results claimed
to be achieved in the manuals. Namely the ability to map the
fog with a 3D volume texture to break up the density of fog.
If I am able to solve this mystery it will be added to the
tutorial..
|
Tutorial
written by:
Darrin Krumweide
