Make quadtrees generic

[eschweic]

Rewrite quadtrees to store generic types rather than store points.
r? @pcwalton

[pcwalton]

So I think instead of using an @mut here it might be better to have an &mut f32 threaded through each method call, and to remove scale from the Quadtree<T> datastructure.

[pcwalton]

Actually, I noticed that the Quadtree doesn't mutate the scale at all. So you don't need a pointer at all, I don't think. Just have the caller of each method pass the scale as a plain old f32.

[pcwalton]

OK, I see. Since you're making multiple Quadtree instances for each child, it seems like a waste to have max_tile_size duplicated. I think what you want is something like this:

pub struct Quadtree<T> {
    root: QuadtreeNode<T>,
    scale: f32,
    max_tile_size: uint,
}

struct QuadtreeNode<T> {
    tile: Option<T>,
    origin: Point2D<f32>,
    size: f32,
    quadrants: [Option<~QuadtreeNode<T>>, ..4],
}

For each method on each QuadtreeNode, have it take fields of its parent like so:

impl<T> QuadtreeNode<T> {
    fn munge(&mut self, scale: f32, max_tile_size: uint, ...) {
        ...
    }
}

[pcwalton]

I take it this the scale factor of each tile? Please add a comment :)

[eschweic]

See #557 .