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The wind object controls the wind simulation of SpeedTree objects. The wind behaves as it was defined in Cinema. Strength and direction are variable within Clarisse.

To begin, create one SpeedTree wind object and one SpeedTree model object. Wind will only affect the model in 3D mode, not in spike or icon mode. Connect them by clicking the “Wind Source” attribute in the model object and selecting the wind object. Only one wind source can drive a model object at a time but a single wind source can drive multiple models.

The wind object supports two modes: directional and spherical.

Directional Wind

Every tree connected to a directional wind source will share the same direction. The wind source icon clearly displays the direction. As the wind source is rotated, the wind direction will rotate with it. Translation and scale have no effect. Figure 1 below illustrates.

Figure 1. An illustration of a directional wind source on multiple reed-like models in Clarisse

Spherical Wind

Spherical wind is omni-directional, just like a point light. The direction of the wind is governed by the source's position relative to each tree it's connected to.

The figure below illustrates this type of wind source.

Figure 2. A spherical/omni-directional wind source in Clarisse


Spherical wind sources also support a “Decay” parameter that controls how much the wind will weaken over a distance. The figure below illustrates an example.

Figure 3. A spherical wind source with decay value of 0.1

The graph below shows different values of decay vs distance. The X-axis represents distance from the spherical wind source and the Y-axis represents the wind strength. The higher the decay value, the more rapidly the strength drops. A value of 0.0 (default) means no decay.

Figure 4. Wind strength over distance with several example decay values


By default, the wind system begins with a strength of zero and ramps up to the set strength. By using a pre-roll of around 10 seconds, the wind system is put into a steady-state, bypassing the ramp up so that the wind will be blowing at or near the desired strength by the first frame. If a start-up animation is desired, set this value to 0.0.

Cohesive Wind

Due to the particulars of the SpeedTree wind algorithm, cohesive wind applies to directional wind only. Spherical wind will not honor the cohesive wind parameters described in this section.

Think of “cohesive wind” not as wind in an individual tree, but in a forest. It has to do with trees sharing wind patterns. If, for example, the wind is moving from left to right in a particular scene, each tree will be animated separately so that wind gusts will flow properly from left to right. We also refer to this as “rolling wind”. This is a different approach than what is commonly done in scenes where multiple trees are given generic ambient wind and each copy uses a different time offset.

Video 1 below demonstrates this rolling/cohesive wind effect with a collection of grass models.

Video 1. A demonstration of rolling wind across multiple models, forming a cohesive cluster.

Model Attribute: Cohesive Wind

Cohesive wind overlaps with memory usage and unique object/instance considerations discussed in the memory documentation. If copies of a model are already unique (they're uniquely rotated or are connected to a spherical wind source), the “Cohesive Wind” attribute will have no effect. It is useful only for models where the wind would otherwise be instanced.

In short, this attribute applies only to directional wind when the copies are not rotated. If they're not rotated, it's already happening.

In Video 2 below, three copies of the same model are shown with the same orientation. By selecting “cohesive wind” on each copy, SpeedTree will give each copy very similar but unique wind, as illustrated in the video.

Video 2. Three identical models with "cohesive wind" enabled.

Wind Attribute: Cohesive Synchronization

The user can interpolate between the synchronized and cohesive behavior by adjusting the SpeedTree wind object's “Cohesive Synchronization” attribute. Ranging from 0% to 100%, a 100% value means that all of the grass is in sync and 0% is fully cohesive. The videos below demonstrate values of 100%, 70%, and 0% using numerous simple reed-like independent models.

Video 3. Multiple single-reed SpeedTree models with several "Cohensive Synchronization" values


The wind object has several attributes that can help optimize workflow when the wind computation load gets too high:

  • Enable Wind Updates: If there are 50 5M-tri trees in a scene tied to a spherical wind source (thereby giving every tree unique wind) and drop the wind strength from 75% to 50%, it could take two minutes or longer for them to update. There are three options:
    • Suspend: Never update wind values for any object attached to the wind object.
    • Enable: Always update wind values for any object attached to the wind object.
    • By Session: Never update within a Clarisse editing/GUI session, but always update when rendering using CNode.
  • Disable Motion Blur: Every tree object has an “Enable Motion Blur” option. If disabled, wind computation is nearly twice as fast. This option will temporarily override the motion blur setting for every tree the wind source is tied to.
  • Use Fast Noise: This is the same as the production/draft noise toggle in the Modeler. It can reduce wind computation by 30% or more.
  • Report Computation Times: Reports in the log window how long each tree's wind takes to compute.