Chapter 42 Using Atmospheric Effects 1011

Figure 42-7: You can use the Fire atmospheric effect to create clouds.

Using the Fog Effect

Fog is an atmospheric effect that obscures objects or backgrounds by introducing a hazy layer; objects farther from the view are less visible. The normal Fog effect is used without an Atmospheric Apparatus gizmo and appears between the camera’s environment range values. The camera’s Near and Far Range settings set these values.

In the Environment and Effects dialog box, the Fog Parameters rollout appears when the Fog effect is added to the Effects list. This rollout, shown in Figure 42-8, includes a color swatch for setting the fog color. It also includes an Environment Color Map button for loading a map. If a map is selected, the Use Map option turns it on or off. You can also select a map for the Environment Opacity, which affects the fog density.

The Fog Background option applies fog to the background image. The Type options include Standard and Layered fog. Selecting one of these fog background options enables its corresponding parameters.

The Standard parameters include an Exponential option for increasing density as a function of distance. If this option is disabled, the density is linear with distance. The Near and Far values are used to set the range densities.

Layered fog simulates layers of fog that move from dense areas to light areas. The Top and Bottom values set the limits of the fog, and the Density value sets its thickness. The Falloff option lets you set where the fog density goes to 0. The Horizon Noise option adds noise to the layer of fog at the horizon as determined by the Size, Angle, and Phase values.

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Figure 42-8: The Fog Parameters rollout lets you use either Standard fog or Layered fog.

Figure 42-9 shows several different fog options. The upper-left image shows the scene with no fog, the upper-right image uses the Standard option, and the lower-left image uses the Layered option with a Density of 50. The lower-right image has the Horizon Noise option enabled.

Figure 42-9: A rendered image with several different Fog effect options applied.

Chapter 42 Using Atmospheric Effects 1013

Using the Volume Fog effect

You can add the Volume Fog effect to a scene by clicking the Add button and selecting the Volume Fog selection. This effect is different from the Fog effect in that it gives you more control over the exact position of the fog. This position is set by an Atmospheric Apparatus gizmo. The Volume Fog Parameters rollout, shown in Figure 42-10, lets you select a gizmo to use with the Pick Gizmo button. The selected gizmo is included in the drop-down list to the right of the buttons. Multiple gizmos can be selected. The Remove Gizmo button removes the selected gizmo from the list.

Note	The Atmospheric Apparatus gizmo contains only a portion of the total Volume Fog effect. If the
	gizmo is moved or scaled, it displays a different cropped portion of fog.

Figure 42-10: The Volume Fog Parameters rollout includes parameters for controlling the fog.

The Soften Gizmo Edges value feathers the fog effect at each edge. This value can range from 0 to 1.

Many of the settings for Volume Fog are the same as those for the Fog effect, but Volume Fog has several settings that are unique to it. These settings help set the patchy nature of Volume Fog. Step Size determines how small the patches of fog are. The Max Steps value limits the sampling of these small steps to keep the render time in check.

The Noise section settings also help determine the randomness of Volume Fog. Noise types include Regular, Fractal, Turbulence, and Invert. The Noise Threshold limits the effect of noise. Wind settings include direction and Wind Strength. The Phase value determines how the fog moves.

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Tutorial: Creating a swamp scene

When I think of fog, I think of swamps. In this tutorial, we model a swamp scene. To use the Volume Fog effect to create the scene, follow these steps:

1.Open the Dragonfly in a foggy swamp.max file from the Chap 42 directory on the CD-ROM.

This file includes several cattail plants and a dragonfly, positioned on top of one of the cattails.

2.Select Create Helpers Atmospherics Box Gizmo and drag a box that covers the lower half of the cattails in the Top viewport.

3.Choose Rendering Environment (or press the 8 key) to open the Environment and Effects dialog box. Click the Add button to open the Add Atmospheric Effect dialog box, and then select Volume Fog. Click OK. In the Volume Fog Parameters rollout, click the Pick Gizmo button and select the BoxGizmo in a viewport.

4.Set the Density to 0.5 and the Noise Type to Turbulence. Then set the Wind Strength to 10 from the Left.

Figure 42-11 shows the finished image. Using Atmospheric Apparatus gizmos, you can position the fog in the exact place where you want it.

Figure 42-11: A rendered image that uses the Volume Fog effect