Modeling a tree (the easy way)

Like so many things in life, I have discovered after days of work that there is an easier way to do something. That's right, my irritatingly complex description of how to model a tree has been rendered obsolete in 48 short hours. Ok, it was obsolete when I started -- I just didn't do my homework before I set to modeling.

What's the easier method, you ask? It's called Arbaro. It's an open source tree generation program based on a paper by Jason Weber and Joseph Penn outlining an algorithm for computer-generated trees. It's platform-independent. It's free.

Here are some images of trees created with the same algorithm.

I downloaded Arbaro and played around with it for about 30 minutes. Parts of it that are less than intuitive, but some helpful diagrams and more-or-less hidden documentation provide a little guidance. Regardless, this is the kind of program that invites exploration, so I don't mind some healthy trial and error.

Besides generating 3D meshes for trees, it also creates automatic UV maps, which are required for texturing. The UV maps aren't perfect, but they're a good starting point.

Lest you think this is turning into a blog solely about trees, I would like to declare an end to this brief series on vegetation. Next up: rocks and stones. Just kidding. Maybe.

Modeling a tree, and (r)ambling through the woods

After some fairly tedious work on my pine tree, I have something that doesn't look half bad.

Unity's restrictions for in-game trees require that each tree include a single mesh (for my non-gamer readers, a mesh is just a 3D object composed of triangles) using two textures: one for the bark and one for the foliage. Unfortunately, I didn't know how to place two textures on a single mesh in Cheetah (my 3D modeling program). It is possible, and pretty easy to set up, but it took some time to figure it out.

Create the foliage
Armed with the requisite knowledge of Cheetah's features, I set out in earnest to fill in my tree. The process I settled on ended up being fractal-ish in a way, which seems a fitting way to create a tree:

• First, I created a small group of six polygons that would act as a small branch and a group of pine needles.
• Then I duplicated this small branch 10 or 12 times along the bottom-most big branch on the tree. I scaled and rotated each copy so the foliage would feel random.
  
• Rather than repeat this process for each of the 20 or so branches, I just did it for the first three. This gave me three distinct sets of small branches (anybody confused yet?).
• Then I used those three branch sets to fill out the rest of the large branches, copying each set several times and moving/scaling it into position.

Remove (some of) the foliage
Another one of Unity's guidelines for trees is to keep each one below 2,000 polygons. Alas, after my foliage frenzy, I was about 1K over the limit. Time to optimize. My first inclination was to remove some of the small branches that didn't add much to the density of the foliage and wouldn't be very visible from a distance. This activity, sad as it was to remove the pretty pine needles, didn't get me far enough. How could I remove more polygons without thinning out my lush tree?

Finally it occurred to me that the branches near the top of my tree would never be seen up close. What's more, the branch sets up there had been shrunk down to the point that the polygons wouldn't be visible even if you were up close.

The solution, while probably obvious to you (if you've made it this far), seems poetic somehow. At the very top of the tree, the sets of branches aren't much bigger than a single branch at the bottom of the tree, so I just removed four of the branch sets at the top and replaced them with single branches. The difference is nearly indistinguishable, and I eliminated several hundred polygons. Final polygon count: 1,970. Yeah, I'm kind of awesome.

First the trees, then the forest

I started working yesterday on my first serious tree. I've tried modeling trees before and found them to be quite tricky. Something about the thousands of tiny branches makes them a pain.

Nevertheless, nice trees are yet another a requirement for convincing game worlds, and the first area of my game is going to feature several lovely copses. Unity has some nice tools for creating the forest (there's literally a "make forest" button), but before you can have a forest, you need some trees.

After some brief research I went with a pine tree. One of those tall ones shaped like a cone. For one thing, it will fit well with the atmosphere of the game world. For another, it's shaped like a cone. How hard could it be?

The modeling process went something like this:

• I started with a cone and manipulated it around until it looked like a decent pine tree trunk.
  
• Then I created some smaller cones to use as branches and distributed them along the length of the trunk, making them smaller as I got higher on the tree.
• Then I was ready to texture the trunk and primary branches. I found a nice, free pine bark texture here and loaded it into the GIMP, the open source graphics editing program. One "make seamless" filter, some rubber stamping, and about 20 minutes later, I had a passable, tiling bark texture. Very exciting.

Unfortunately, this is where it got hard. Foliage, it turns out, is even more detailed a thing than branches. Following Unity's advice for creating trees, I tried to create a simple group of polygons that could serve as small branches and needles. The idea is to duplicate these polygons, tilt them, and scale them until they fill out the entire tree.

As you can see from the picture, I barely got started. First I had to find a suitable texture (the one I found could still use work). Then I had to figure out how to work with alpha channels in GIMP and transfer them to Unity, which is a little tricky (I'm still not sure I could do it again).

Despite the complications, I feel that progress is being made. If I'm happy with the result, maybe I'll post a more detailed tutorial about modeling a cone-shaped pine tree.