Animated growth is achieved via a combination of the Timeline Bar and the properties on each of the generators that support growth (Branch, Leaf Mesh, Fin, Frond, Cap, and Knot). Caps and knots grow automatically with their parents, the rest of the generators listed have their growth governed by a series of properties in the “Growth” group.
The typical workflow for editing growth is to first get the model correct with growth disabled. Then, run the Growth Wizard (described below) to get the basics in place and then fine-tune the behavior by editing each generator's growth properties and adjusting the overall speed and timing on the Timeline Bar.
Access the Growth Wizard by selecting it from the “Tools” menu or clicking the “Wizard” button in the “Growth” group on the Timeline bar. You will be presented with the following options:
The first option, “Grow”, is suitable for most applications. It will set up all branches and leaves to start growing off their parent once the parent has grown a little (all “Timing” generator properties are set to “Parent”). The result is a continuous growth look where the tree organically grows into its final form.
The “Reveal” option is necessary for any instance where growing branches can't move without causing artifacts in the final production. The best example is any case where branches grow around each other or a mesh used as a stand-in for a scene object. All “Timing” generator properties, in this case, are set to “In place”, which means once the parent reaches the point where the child originates, the child will start growing.
Note: You can mix and match these types after the wizard has finished. Take a look at the “trellis_growth.spm” example. The vines growing around the trellis use “In place” timing, the rest of the model uses “Parent” timing.
Once the wizard has finished, use the Timeline Bar to control the timing. First, make sure your end frame matches the shot. Then use the “Speed” control and corresponding curve to adjust how fast the model grows. All “Speed” properties on the generators are scalars applied to this central speed value. Adjust the value until the model is at the stage you need it to be in on the last frame. Growth computations naturally have a lot of variation and are subject to curve edits and node edits on individual pieces. The only way to ensure your model is at the stage you need it to be in on a particular frame is to edit the speed and speed curve.
Mose generators have a series of growth properties in a group labeled “Growth”. These properties are described in detail on each generator's reference page. Use them to control the timing, speed, orientation, and all other aspects of growth for each component of the model.
Growth animations must be exported as an Alembic file; point cache formats will not work because the number of vertices changes each frame. You can use “File→Render image sequence…” to render out a sequence of frames for a preview of the animation before exporting and rendering in a third party application.
SpeedTree Modelers that support growth are installed with growth example models. Look in the “Samples” folder in the installation location to find them.
The following list outlines a few things to keep in mind when tuning growth.