Volume Fog Environment Effect

Volume Fog provides a fog effect in which the fog density is not constant through 3D space. This plug-in provides effects such as puffy, cloudy fog that appears to drift and break up in the wind.

Volume fog added to a scene

Volume Fog renders only in Camera or Perspective views. Orthographic or User views don’t render Volume Fog effects.

Note: When a photometric light is a projector, its beams don't interact with volume lighting effects (such as Volume Fog, Volume Light, and mental ray volume shading) in the way that standard lights do.

Procedures

To use volume fog:

  1. Create a Camera or Perspective view of your scene.
  2. Choose Rendering Environment.
  3. Under Atmosphere on the Environment panel, click Add.

    The Add Atmospheric Effect dialog is displayed.

  4. Choose Volume Fog, and then click OK.
  5. Set the parameters for volume fog.
    Note: If there are no objects in your scene, rendering shows only a solid fog color. Also, with no objects and Fog Background turned on, volume fog obscures the background.

To create a volume fog gizmo:

    Volume fog gizmo surrounds the scene.

  1. In the Helpers category of the Create panel, choose Atmospheric Apparatus from the pop-up menu.
  2. Click one of the buttons to choose a gizmo shape: SphereGizmo, CylGizmo, or BoxGizmo.
  3. Drag the mouse in the viewport to create the gizmo.

    You create Gizmos in much the same way as their matching geometry types. Drag the mouse to create the initial dimensions. The Sphere gizmo has an additional Hemisphere checkbox that turns the sphere into a hemisphere.

    In addition, each gizmo has a Seed spinner and a New Seed button. Different seed values generate different patterns. Clicking the New Seed button randomly generates a new seed value for you.

To assign volume fog to a gizmo from an apparatus modify panel:

  1. Open the Modify panel of an apparatus.
  2. Open the Atmospheres & Effects rollout.
  3. Click Add.
  4. Select Volume Fog from the Add Atmospheres dialog and click OK.
  5. Highlight Volume Fog from the Atmospheres list and click setup to adjust the Volume Fog parameters.

To assign a gizmo to volume fog from the Environment panel:

  1. On the Volume Fog Parameters rollout, click the Pick Gizmo button.
  2. Click a gizmo in the viewport.

    The name of the gizmo appears in the list field at right.

    When you render, the volume fog will be confined to the shape of the gizmo.

To remove an assigned gizmo:

  1. In the Environment dialog, go to the Volume Fog Parameters rollout
  2. Select the gizmo name from the pop-up list.
  3. Click Remove Gizmo.

    This action doesn’t delete the gizmo from the scene, but simply unbinds it from the fog effect.

Interface

Gizmos group

By default, volume fog fills the entire scene. However, you can choose a gizmo (an atmospheric apparatus) to contain the fog. The gizmo can be a sphere, a box, a cylinder, or some combination of these.

Pick Gizmo
Click to enter Pick mode and click an atmospheric apparatus in the scene. The apparatus contains the volume fog when you render. The name of the apparatus is added to the apparatus list.

Multiple apparatus objects can display the same fog effect.

You can pick multiple gizmos. Click Pick Gizmo and then press H. This opens the Pick Object dialog, which lets you choose multiple objects from a list.

Changing the dimensions of a gizmo changes the region that fog affects, but doesn't change the scale of the fog and its noise. For example, reducing the radius of a spherical gizmo crops the fog, and moving the gizmo changes the fog's appearance.

Remove Gizmo
Removes a gizmo from the volume fog effect. Select the gizmo in the list, and then click Remove Gizmo.
[gizmo drop-down list]
Shows the gizmos you have picked.
Soften Gizmo Edges
Feathers the edges of the volume fog effect. The higher the value, the softer the edges. Range=0 to 1.0.
Tip: Don't set this value to 0. At 0, Soften Gizmo Edges can cause aliased edges.

Volume group

Color
Sets the color for the fog. Click the color swatch, and then select the color you want in the Color Selector.

You can animate the color effect by changing the fog color at a nonzero frame with Auto Key on.

Exponential
Increases density exponentially with distance. When turned off, density increases linearly with distance. Activate this checkbox only when you want to render transparent objects in volume fog.
Tip: If you turn on Exponential, increase the Step Size value to avoid banding.
Density
Controls the fog density. Range=0 to 20 (anything over that tends to obliterate the scene).

Left: Original scene

Right: Increased fog density

Step Size
Determines the granularity of the fog sampling; the "fineness" of the fog. A large step size creates coarse (and to some extent, aliased) fog.
Max Steps
Limits the amount of sampling so that computing the fog doesn't take forever (literally). This is especially useful when the fog is of low density.

When both Step Size and Max Steps have low values, aliasing results.

Fog Background
Applies the fog function to the background of the scene.

Noise group

Left: Original scene

Right: Noise added to the fog

Noise options for volume fog are comparable to the noise options for materials.

Type
Choose one of three types of noise to apply.
  • Regular The standard noise pattern.
  • Fractal An iterative fractal noise pattern.
  • Turbulence An iterative turbulence pattern.

Invert Reverses the noise effect. Dense fog becomes translucent and vice versa.

Noise Threshold
Limits the noise effect. Range=0 to 1.0. When the noise value is above the Low threshold and below the High threshold, the dynamic range stretches to fill 0–1. This makes for a smaller discontinuity (First order instead of 0 order) at the threshold transition, and thus produces less potential aliasing.
High
Sets the high threshold.
Low
Sets the low threshold.
Uniformity
Ranges from –1 to 1 and acts like a high-pass filter. The smaller the value, the more transparent the volume is with discrete blobs of smoke. Around -0.3 or so your image begins to look like specks of dust. Because the fog becomes thinner as this parameter gets smaller, you'll probably need to increase the density or the volume will start to disappear.

Left: Fog with noise

Right: Changing uniformity creates "blobby" fog

Levels
Sets the number of times the noise is iteratively applied. Range=1 to 6, including fractional values. Enabled only for Fractal noise or Turbulence.
Size
Determines the size of the tendrils of smoke or fog. Smaller values give smaller tendrils.

Left: Fog with noise

Right: Decreasing the size

Phase
Controls the speed of the wind. If you have Wind Strength also set to greater than 0, the fog volume animates in accordance with the wind direction. With no Wind Strength, the fog churns in place. Because there's an animation track for phase, you can use the Function Curve editor to define precisely how you want your wind "gusts" to occur.
Wind Strength
Controls how fast the smoke moves away from the wind direction, relative to phase. As mentioned above, if the phase is not animated then the smoke won’t move, regardless of the wind strength. By having the phase animate slowly with a large wind strength, the fog moves more than it is churns.
Wind from the
Defines the direction the wind is coming from.
Parent topic: Environment and Exposure Settings