Modeling “Sky-Sensitive” Leaves and Phototropism with SpeedTree®

As a lead into this new feature I’d like to present a common interaction I have with people at SIGGRAPH every year . . .

Random Attendee: “So what is this, an L-system?” (referring to formal Lindenmayer systems)

Me: “No, SpeedTree is much closer to an art tool than it is a biology simulator.”

That’s when I launch into my spiel about how that makes it easier to model . . . the tool feels more like running a typical modeling app, etc.  I certainly believe that and the conversation quickly turns to how they might use SpeedTree® and we move on.  In fact, when challenged to simulate a particular biological phenomenon it’s typically pretty easy to do.  For example, phototropism can be modeled with direction and magnet forces.  Another example is this forum user attempting to recreate various forms of Phyllotaxis, which can be read here.

That being said, we’ve been dinged (rightfully so) for leaf orientations that are difficult to get right.  I’ve always kind of pushed it aside with the thought that you can achieve any orientations you want if you just fiddle with the numbers and curves enough.  While that is true, it’s just too time-consuming for a lot of users.  At SIGGRAPH this year we had a long-time customer stop by our booth and we got to chatting about this very subject.  Between that conversation, reading some criticism of our software regarding this issue online, and just looking at some trees, we decided to do something about it.

We added a new orientation style to leaf meshes called “Sky sensitive”.  The existing algorithm is still an option, but this now provides three sliders that make leaf orientation a little easier.  These sliders allow you to orient leaves, based on the structure of the model (parent and angle sensitivity) and the natural tendency for leaves to face the light (sky sensitivity).

Sky Sensitive Setting

These options make it much easier to get natural leaf placements like those shown in the image above.  Leaf orientation on this model is governed entirely by the options in the “Meshes” group, pictured above in the GUI section.  The “Up”, “Out”, and “Right” rotations are each given a 20% variance to prevent the look from being to “computed”.

This is a new feature in 6.2.3 and is available as a free upgrade for all 6.x users.  Enjoy!