4.3: BSP is ... not a BSP?

(Still) having an awesome time following along the tutorial, thank you so much for writing it!

Section 4.3 got me confused. For context: I've heard of BSP before, but never implemented one / looked at it very closely.

The first thing that confused me was that the "B" in BSP stands for "binary", but the algorithm in the tutorial seems to subdivide each region into 4 parts, so this would be more like ... quaternary? Given that confusion, I did some quick searching and read http://www.roguebasin.com/index.php?title=Basic_BSP_Dungeon_generation. Based on that, there seem to be (at least) two major differences between the algorithm in 4.3 and BSP as described on roguebasin:

Dividing each region into 2 vs 4 subregions
The roguebasin description uses the tree of regions to generate corridors: it connects sister regions. The algorithm in the tutorial "just" directly connects rooms in an almost-arbitrary order. One notable difference is that the roguebasin approach allows connections between corridors, not just rooms (effectively creating junctions in corridors), providing a slightly more organic feel.

I'm pretty new to procedural generation, so first, a question: do I just have a too-narrow idea of what BSP is? If not, it may be good to note how exactly the algorithm given deviates from "canonical" BSP. And second: I've directly implemented the roguebasin flavor of BSP at https://github.com/abesto/rktrl/blob/f923a14d1f00216f807768c43c402fa5e11d91b4/src/mapgen/bsp_dungeon.rs within the framework set up by the previous chapters. If useful, feel free to use / share.

bsp

Addendum: the BSP implementation above (which, yes, I forget the stairs, obviously) was somewhat easy to make configurable, such that the exact same map builder, given different inputs, can generate either a dungeon or a castle interior (as in chapter 4.4):

impl BspConfig {
    pub fn dungeon() -> Self {
        BspConfig {
            subdivision_variance: 0.2,
            depth: 6,
            min_room_width: 6,
            max_room_width: 10,
            min_room_height: 6,
            max_room_height: 10,
            max_padding: 9000, // Arbitrarily large number. Not maxint because that leads to overflow.
            min_padding: 2,
        }
    }

    pub fn interior() -> Self {
        BspConfig {
            subdivision_variance: 0.2,
            depth: 5,
            min_room_width: 6,
            max_room_width: 9000,
            min_room_height: 6,
            max_room_height: 9000,
            max_padding: 0, // this is what gives us the "interior" look
            min_padding: 0,
        }
    }
// ... SNIP ...
}

Implementation: https://github.com/abesto/rktrl/blob/4360f791e930679ae7f46896916703c7104772d0/src/mapgen/bsp_dungeon.rs

amethyst / rustrogueliketutorial

4.3: BSP is ... not a BSP? #156