Basic BSP Dungeon generation

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A simple method to generate a basic dungeon using a bsp tree

Building the BSP

We start with a rectangular dungeon filled with wall cells. We are going to split this dungeon recursively until each sub-dungeon has approximately the size of a room. The dungeon splitting uses this operation :

  • choose a random direction : horizontal or vertical splitting
  • choose a random position (x for vertical, y for horizontal)
  • split the dungeon into two sub-dungeons

dungeon_bsp1.png The first splitting iteration.

Now we have two sub-dungeons A and B. We can apply the same operation to both of them :

dungeon_bsp2.png The second splitting iteration

When choosing the splitting position, we have to take care not to be too close to the dungeon border. We must be able to place a room inside each generated sub-dungeon. We repeat until the lowest sub-dungeons have approximately the size of the rooms we want to generate.

dungeon_bsp3.png After 4 splitting iterations

Different rules on the splitting position can result in homogeneous sub-dungeons (position between 0.45 and 0.55) or heterogeneous ones (position between 0.1 and 0.9). We can also choose to use a deeper recursion level on some parts of the dungeon so that we get smaller rooms there.

Building the dungeon

Now we create a room with random size in each leaf of the tree. Of course, the room must be contained inside the corresponding sub-dungeon. Thanks to the BSP tree, we can't have two overlapping rooms.

dungeon_bsp4.png Rooms in the tree leafs

To build corridors, we loop through all the leafs of the tree, connecting each leaf to its sister. If the two rooms have face-to-face walls, we can use a straight corridor. Else we have to use a Z shaped corridor.

dungeon_bsp5.png Connecting the level 4 sub-dungeons

Now we get up one level in the tree and repeat the process for the parent sub-regions. Now, we can connect two sub-regions with a link either between two rooms, or a corridor and a room or two corridors.

dungeon_bsp6.png Connecting the level 3 sub-dungeons

We repeat the process until we have connected the first two sub-dungeons A and B :

dungeon_bsp7.png If we allow some rooms to fill the whole leaf, we can even have less boring dungeons.

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