Wind animation is controlled by editing the properties on the Fan object and the wind properties of each generator in the model (e.g., branches and leaves). The recommended procedure is to run the Wind Wizard (“Tools→Wind wizard…”) and then fine tune the results.
When wind is enabled ('8' hotkey or “Enabled” property on the Fan) the model will animate continuously in the window (unless it's under timeline control as described below). If the model is too complex to run fluidly, consider focusing on a section to improve performance.
When wind is enabled an overlay appears under the Fan object in the upper right section of the window as pictured to the right. Set the direction of the wind by rotating the Fan (hold 'G', press the left mouse button, and drag the cursor as a shortcut for fan rotation).
Set the strength by clicking the blue arrow and dragging it between the “min” and “max” markings. The actual strength is indicated by the blue bar. Notice that it does not react immediately to strength changes. Models do not react instantly to strength changes; rather, they react at a speed governed by their strength response time. Wind strength will gradually reach the desired setting as the model reacts. Direction changes are handled in a similar fashion.
Gusting can be controlled by moving the green sections on the overlay. Drag the green arrow pointing left to a location between the “min” and “max” markings to set the frequency of gusts. Drag the green arrow pointing to the right at the gust range box and drag it up and down to set the gust strength. Click and drag in the gust range box (faded green rectangle) to set the limits of each gust.
Note: The blue strength bar will always indicated the effective strength of the wind based on your strength setting, the strength response time of the model, and the current gusting state.
The best way to get started tuning wind on a new model is to run the Wind Wizard (“Tools→Wind wizard…”). You will see the dialog pictured below.
Answer the questions on the dialog and press “Ok”. SpeedTree will analyze your model and set wind properties on the generators and Fan object based on your model's structure and your wizard selections. The model will recompute and wind will enabled in the window when the wizard is finished. Feel free to edit the results as described below.
Branch motion is controlled by five groups of properties: one for the motion shared by the entire model (like a tall pine rocking back and forth) and then four groups corresponding to each of the four discrete wind levels in the model. Wind levels are determined by starting from the Tree generator and incrementing the wind level by one for every generator encountered on each path to the leaves that has wind enabled. When you enable wind the Generation Editor displays the wind level on each generator where wind is enabled. Conisder the example below:
The “Trunk” has no number indicator because wind is not enabled on that generator (it usually isn't on trunks, “Shared” wind gets it). Similarly, wind is not enabled for the “Roots” generator or it's child labelled “Branch”). “Branch 1, 2, & 3” and “Twig 1, 2, & 3” all have wind enabled. Notice how the wind level indicator starts at one, goes up to four, and then sticks at four for the last two twigs. You can only have four discrete wind levels no matter how many generators have wind enabled. It is okay to have fewer than four, and it is okay to have gaps in the number sequence as you see fit (sometimes it is better to concentrate the control near the trunk and twigs and leave middle sections alone).
The wind level indicator corresponds to the levels in the “VFX Branch Motion” group on the Fan. Edit these properties to control the behavior of each wind level. Edit the wind properties on each Branch generator to control weights and weight distribution along each branch.
When editing wind curves, the left hand side of the curve corresponds to no wind (“Calm”) and the right hand side corresponds to maximum wind (“Stormy”). The black line indicates the current wind strength is pictured below:
Use the curve to set low and high wind conditions and control how each level makes the transition. Strength changes and gusts will cause the wind algorithm to look up this curve at various points to define the motion for a given simulation.
Leaf wind animation is broken into two groups. Assign a group and wind weight by editing the properties on Batched Leaf or Leaf Mesh generators. Typically, leaf group 1 corresponds to the leaves of the model while leaf group 2 corresponds to more rigid things like fruit.
Edit the properties in the “VFX Leaf Motion” group to control leaf behavior.
Frond wind is not broken into groups or levels. All fronds share the same wind attributes. Edit the properties in the “VFX Frond Motion” group to control frond behavior in general and edit the wind properties on each frond generator to fine tune behavior.
Gusting provides a mechanism to have the wind strength periodically rise and fall simulating gusty conditions. Edit the gusting properties of the Fan or use the overlay as described above to control gusting behavior.
The “Set conditions” menu option on the fan and wind toolbar menu provide shortcuts for setting common conditions like breezy and stormy. These choices set the nominal wind strength and gusting parameters to best match the named conditions. Use these settings to help guide wind tuning for models that will be in the same scene. The Wind Wizard will attempt to set all wind properties such that the model behaves appropriately under all of the preset conditions.
You can force a gust to happen by double clicking on the gust area of the wind overlay.
Note: “Duration” values of 0.0 still have an effect on gusting since the time to rise to the value and fall from it are not counted against the duration. Use 0.0 and low scalars to simulate turbulent conditions.
Wind can be exported either as a point cache for FBX files or as an Alembic file. If you're exporting FBX files, simply check “Wind” (and “Wind gusting” if you want it) on the export dialog then select your cache format and select “OK”. Gusting and other randomness in the algorithm mean exporting wind in this manner is not necessarily the same in two separate exports of the same model.
If you're exporting to Alembic you have the option to use the Timeline Bar to control the wind. Check the “Wind” box on the timeline and use the strength curve to explicitly control the wind strength. This mechanism disables gusting and provides consistent, controllable wind strength on export.
Note: Wind animation does not loop. You must export enough frames to cover your shot.
The following list outlines a few things to keep in mind when tuning wind.