BOSL2/tutorials/Fractal_Tree.md

# Fractal Tree Tutorial

### Start with a Tree Trunk

Firstoff, include the BOSL2 library, then add a tapered cylinder for the tree trunk.

```openscad-example
include <BOSL2/std.scad>
cylinder(l=1500, d1=300, d2=210);
```

### Parameterize It

It's easier to adjust a model if you split out the defining parameters.

```openscad-example
include <BOSL2/std.scad>
l = 1500;
sc = 0.7;
cylinder(l=l, d1=l/5, d2=l/5*sc);
```

### Attaching Branches

You can attach branches to the top of the trunk by using `attach()` as a child of the trunk cylinder.

```openscad-example
include <BOSL2/std.scad>
l = 1500;
sc = 0.7;
cylinder(l=l, d1=l/5, d2=l/5*sc) {
    attach(TOP) yrot( 30) cylinder(l=l*sc, d1=l/5*sc, d2=l/5*sc*sc);
    attach(TOP) yrot(-30) cylinder(l=l*sc, d1=l/5*sc, d2=l/5*sc*sc);
}
```

### Replicate Branches

Instead of attaching each branch individually, you can attach multiple branch copies at once.

```openscad-example
include <BOSL2/std.scad>
l = 1500;
sc = 0.7;
cylinder(l=l, d1=l/5, d2=l/5*sc)
    attach(TOP)
        zrot_copies(n=2)  // Make multiple rotated copies
        yrot(30) cylinder(l=l*sc, d1=l/5*sc, d2=l/5*sc*sc);
```

### Make it a Module

Lets make this into a module, for convenience.

```openscad-example
include <BOSL2/std.scad>
module tree(l=1500, sc=0.7)
    cylinder(l=l, d1=l/5, d2=l/5*sc)
        attach(TOP)
            zrot_copies(n=2)
            yrot(30) cylinder(l=l*sc, d1=l/5*sc, d2=l/5*sc*sc);
tree();
```

### Use Recursion

Since branches look much like the main trunk, we can make it recursive. Don't forget the termination clause, or else it'll try to recurse forever!

```openscad-example
include <BOSL2/std.scad>
module tree(l=1500, sc=0.7, depth=10)
    cylinder(l=l, d1=l/5, d2=l/5*sc)
        attach(TOP)
            if (depth>0)  // Important!
                zrot_copies(n=2)
                yrot(30) tree(depth=depth-1, l=l*sc, sc=sc);
tree();
```

### Make it Not Flat

A flat planar tree isn't what we want, so lets bush it out a bit by rotating each level 90 degrees.

```openscad-example
include <BOSL2/std.scad>
module tree(l=1500, sc=0.7, depth=10)
    cylinder(l=l, d1=l/5, d2=l/5*sc)
        attach(TOP)
            if (depth>0)
                zrot(90)  // Bush it out
                zrot_copies(n=2)
                yrot(30) tree(depth=depth-1, l=l*sc, sc=sc);
tree();
```

### Adding Leaves

Let's add leaves. They look much like squashed versions of the standard teardrop() module, so lets use that.

```openscad-example
include <BOSL2/std.scad>
module tree(l=1500, sc=0.7, depth=10)
    cylinder(l=l, d1=l/5, d2=l/5*sc)
        attach(TOP)
            if (depth>0)
                zrot(90)
                zrot_copies(n=2)
                yrot(30) tree(depth=depth-1, l=l*sc, sc=sc);
            else
                yscale(0.67)
                teardrop(d=l*3, l=1, anchor=BOT, spin=90);
tree();
```

### Adding Color

We can finish this off with some color. The `color()` module will force all it's children and
their descendants to the new color, even if they were colored before. The `recolor()` module,
however, will only color children and decendants that don't already have a color set by a more
nested `recolor()`.

```openscad-example
include <BOSL2/std.scad>
module tree(l=1500, sc=0.7, depth=10)
    recolor("lightgray")
    cylinder(l=l, d1=l/5, d2=l/5*sc)
        attach(TOP)
            if (depth>0)
                zrot(90)
                zrot_copies(n=2)
                yrot(30)
                tree(depth=depth-1, l=l*sc, sc=sc);
            else
                recolor("springgreen")
                yscale(0.67)
                teardrop(d=l*3, l=1, anchor=BOT, spin=90);
tree();
```