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 which appears to drift and break up in the wind.
The Volume Fog Parameters rollout appears when you select Volume Fog under Effects in the Environment dialog. It has the following controls --
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.
Tip: When you use gizmos with volume fog, you can safely use higher Max Steps settings.
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 displays a Pick Object dialog that lets you choose multiple objects from the 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.
Caution: When you SHIFT + copy a gizmo, the new gizmo isn’t bound to the volume fog. If you want to use it, you must use Pick Gizmo to add it explicitly.
Remove Gizmo: Removes a gizmo from the volume fog effect. Select the gizmo in the list, then click Remove Gizmo.
Soften Gizmo Edges: Feathers the edges of the volume fog effect. The higher the value, the softer the edges. Can range from 0 to 1.0. Default = 0.2.
Tip: Don’t set this value to zero. At 0, Soften Gizmo Edges causes aliased edges.
Color: Sets the color for the fog. Click the color swatch, then select the color you want in the Color Selector dialog. You can animate the color effect by changing the fog color at a non-zero frame with the animate button on.
Exponential: When checked, density increases exponentially with distance. When unchecked, density increases linearly with distance. Check this only when you want to render transparent objects in volume fog.
Tip: If you check Exponential, increase the Step Size value to avoid banding.
Density: Controls the fog density. The useful range here is between 0-20. Anything over that tends to obliterate the scene.
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. Default = 100.
If both Step Size and Max Steps have low values, this can cause aliasing.
Fog Background: When this box is on (the default), the fog function is applied to the background of the scene.
Noise options for volume fog are comparable to the noise options for materials.
Type: Choose the kind 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: These values limit the noise effect. Both can range from 0 to 1.0. When the noise value is above the Low threshold and below the High threshold, the dynamic range is stretched to fill 0-1. This makes for a smaller discontinuity (1st order instead of 0 order) at the threshold transition and thus produces less potential aliasing.
High Sets the high threshold. Default = 1.0.
Low: Sets the low threshold. Default = 0.0
Uniformity: Ranges from -1 to 1 and acts like a high-pass filter. The smaller the value, the more of the volume is transparent with discrete blobs of smoke. By around -0.3 or so you start to get something that looks like specks of dust. Note that since the fog becomes thinner as this parameter gets smaller, you'll probably need to increase the density or the volume will start to disappear.
Levels: Enabled only for Fractal noise or Turbulence. Sets the number of times the noise is iteratively applied. Can range from 1 to 6, including fractional values. This parameter is animatable.
Size: Determines the size of the tendrils of smoke or fog. Smaller values give smaller tendrils.
Phase: Controls the speed of the wind. If you have Wind Strength also set to greater than 0, the fog volume will animate in accordance with the wind direction. With no Wind Strength, the fog churns in place. Since there’s an animation track for phase, you can use the function curve editor to define precisely how you want your wind "gusts" to happen.
Wind moves the fog volume in the specified direction over time. Wind is tied to the phase parameter, so as the phase changes the wind moves. If Phase is not animated there will be no wind.
Wind Strength: Controls how fast the smoke moves away from the wind direction, relative to phase. As mentioned above, if phase is not animated then the smoke will not move, regardless of the wind strength. By having the phase animate slowly with a large wind strength, the fog will move more than it is churning.
Alternatively, if the phase is changing rapidly while the wind strength is relatively small, the fog will churn fast and drift slowly. If you want the fog to just churn in place, animate the phase but keep wind strength at 0.
Wind from the: Defines the direction the wind is coming from.
The Add Atmospheric Effect dialog appears.
Note: If there are no objects in your scene, rendering shows only a solid fog color. Also, with no objects and Fog Background set, volume fog obscures the background.
Gizmos are created 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.
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.
This action does not delete the gizmo from the scene, but simply unbinds it from the fog effect.