Difference between revisions of "Dungeon-Building Algorithm"

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(Originally written by [[Mike Anderson]]. Please note that this guide only contains the essential parts about the algorithm, nothing else from his guide)
(Originally written by [[Mike Anderson]].)


Interesting random maps are one of the things that make roguelike games
unique. They add greatly to the enjoyment of the game since the player
will always be able to face fresh challenges and different problems.
But random maps are far from easy to implement. In most conventional
games, you would have a level designer who can create cunningly crafted
scenarios. In any roguelike worthy of the name, the programmer must take
on the daunting task of creating a "virtual level designer" which will be
able to build unlimited numbers of interesting dungeons and mazes with
nothing more than a [[random number generator]]......
In this article, I've documented the technique that I am developing for
use in my own little roguelike called Tyrant. I doubt it's a truly
original idea, but I have never seen this exact algorithm used for
creating dungeons before. Anyhow, it works pretty well so I've decided to
share it with the world.
== The goals of the dungeon builder ==
When writing any piece of code, it's always useful to decide on the
objectives beforehand. This can help a lot when designing an algorithm,
even if you end up making a lot of changes later.
A basic dungeon will need:
*A set of interconnected rooms, doors and tunnels
*An entrance (staircase up)
*An exit (staircase down)
*Every space must be reachable
The last condition is quite important; it's nice to know that the
player will always be able to get through the level with enough
perseverance, and it's also useful to know that when you add a unique
artifact, it's not hidden away in some impenetrable cell.


In this algorithm a "feature" is taken to mean any kind of map component
e.g. large room, small room, corridor, circular arena, vault etc.


1.  Fill the whole map with solid earth
== The Plan ==


2. Dig out a single room in the centre of the map
When I came to write my dungeon builder for Tyrant, I decided to play with
a whole host of different algorithms to see what I liked best. The one I
will present here is the best one that I came up with, which is currently
being implemented in the actual game.


3.  Pick a wall of any room
The inspiration came from the thought:


4.  Decide upon a new feature to build
"If I were a denizen of the underworld, how would I go about building my
dungeon?"


5. See if there is room to add the new feature through the chosen wall
One certain thing was that rooms wouldn't just appear in a nice uniform
fashion and then have long snaking tunnels appear to join them together.
No, when I needed more space for my goblin lunatics I'd just grab a
pickaxe and dig a big hole. Add on a few new rooms when they were needed.
Probably in a fairly haphazard way.


6. If yes, continue. If no, go back to step 3
Some dungeon lords might be a bit more imaginative with a few
portcullises, traps and suchlike to guard the more "interesting" rooms.
But the basic idea was the same. Start with a small dungeon, then add
extensions in all directions until the whole thing is finished.


7.  Add the feature through the chosen wall


8.  Go back to step 3, until the dungeon is complete
== The algorithm ==


9. Add the up and down staircases at random points in map
In this algorithm a "feature" is taken to mean any kind of map component
e.g. large room, small room, corridor, circular arena, vault etc.


10. Finally, sprinkle some monsters and items liberally over dungeon
#  Fill the whole map with solid earth
#  Dig out a single room in the centre of the map
#  Pick a wall of any room
#  Decide upon a new feature to build
#  See if there is room to add the new feature through the chosen wall
#  If yes, continue. If no, go back to step 3
#  Add the feature through the chosen wall
#  Go back to step 3, until the dungeon is complete
#  Add the up and down staircases at random points in map
# Finally, sprinkle some monsters and items liberally over dungeon




Line 29: Line 80:
useful to write a "fillRect" command that fills a rectangular map area
useful to write a "fillRect" command that fills a rectangular map area
with a specified tile type.  
with a specified tile type.  


Step 3 is trickier. You can't pick random squares to add new features
Step 3 is trickier. You can't pick random squares to add new features
Line 38: Line 88:
This is a good method, since it gives you a roughly even chance of picking
This is a good method, since it gives you a roughly even chance of picking
any particular wall square.
any particular wall square.


Step 4 isn't too hard - I just use a random switch statement to determine
Step 4 isn't too hard - I just use a random switch statement to determine
Line 45: Line 94:
dungeons will have lots of regular rooms and long straight corridors. Cave
dungeons will have lots of regular rooms and long straight corridors. Cave
complexes will tend to have jagged caverns, twisting passages etc.
complexes will tend to have jagged caverns, twisting passages etc.


Step 5 is more tricky, and the key to the whole algorithm. For each
Step 5 is more tricky, and the key to the whole algorithm. For each
Line 54: Line 102:
new feature will occupy plus a square on each side for walls, then checks
new feature will occupy plus a square on each side for walls, then checks
to see if the entire rectangle is currently filled with solid earth.
to see if the entire rectangle is currently filled with solid earth.


Step 6 decides whether or not to add the feature. If the area under
Step 6 decides whether or not to add the feature. If the area under
Line 62: Line 109:
negligible. Tyrant tries to add 300 or so features to each dungeon, but
negligible. Tyrant tries to add 300 or so features to each dungeon, but
usually only 40 or so make it past this stage.
usually only 40 or so make it past this stage.


Step 7 draws the new feature once you've decided the area is OK. In this
Step 7 draws the new feature once you've decided the area is OK. In this
stage, you can also add any interesting room features, such as
stage, you can also add any interesting room features, such as
inhabitants, traps, secret doors and treasure.
inhabitants, traps, secret doors and treasure.


Step 8 just loops back to build more rooms. The exact number of times that
Step 8 just loops back to build more rooms. The exact number of times that
you want to do this will depend on map size and various other factors.  
you want to do this will depend on map size and various other factors.  


Step 9 is pretty self-explanatory. Easiest way to do it is to write a
Step 9 is pretty self-explanatory. Easiest way to do it is to write a
routine that picks random squares until it finds an empty one where the
routine that picks random squares until it finds an empty one where the
staircases can be added.
staircases can be added.


Step 10 just creates a host of extra random monsters in random locations
Step 10 just creates a host of extra random monsters in random locations
Line 83: Line 126:
individual rooms are generated.
individual rooms are generated.


== Java example ==
(Made by [[Solarnus]])
<small>
<pre>
import java.lang.Integer; //so we can use Integer.parseInt()
import java.util.*; //and for getting today's date
public class dungen{
//max size of the map
private int xmax = 80; //80 columns
private int ymax = 25; //25 rows
//size of the map
private int xsize = 0;
private int ysize = 0;
//number of "objects" to generate on the map
private int objects = 0;
//define the %chance to generate either a room or a corridor on the map
//BTW, rooms are 1st priority so actually it's enough to just define the chance
//of generating a room
private int chanceRoom = 75;
private int chanceCorridor = 25;
//our map
private int[] dungeon_map = new int[0];
//the old seed from the RNG is saved in this one
private long oldseed = 0;
//a list over tile types we're using
final private int tileUnused = 0;
final private int tileDirtWall = 1; //not in use
final private int tileDirtFloor = 2;
final private int tileStoneWall = 3;
final private int tileCorridor = 4;
final private int tileDoor = 5;
final private int tileUpStairs = 6;
final private int tileDownStairs = 7;
final private int tileChest = 8;
//misc. messages to print
private String msgXSize = "X size of dungeon: \t";
private String msgYSize = "Y size of dungeon: \t";
private String msgMaxObjects = "max # of objects: \t";
private String msgNumObjects = "# of objects made: \t";
private String msgHelp = "";
private String msgDetailedHelp = "";
//setting a tile's type
private void setCell(int x, int y, int celltype){
dungeon_map[x + xsize * y] = celltype;
}
//returns the type of a tile
private int getCell(int x, int y){
return dungeon_map[x + xsize * y];
}
//The RNG. the seed is based on seconds from the "java epoch" ( I think..)
//perhaps it's the same date as the unix epoch
private int getRand(int min, int max){
//the seed is based on current date and the old, already used seed
Date now = new Date();
long seed = now.getTime() + oldseed;
oldseed = seed;
Random randomizer = new Random(seed);
int n = max - min + 1;
int i = randomizer.nextInt() % n;
if (i < 0)
i = -i;
//System.out.println("seed: " + seed + "\tnum:  " + (min + i));
return min + i;
}
private boolean makeCorridor(int x, int y, int lenght, int direction){
//define the dimensions of the corridor (er.. only the width and height..)
int len = getRand(2, lenght);
int floor = tileCorridor;
int dir = 0;
if (direction > 0 && direction < 4) dir = direction;
int xtemp = 0;
int ytemp = 0;
switch(dir){
case 0:
//north
//check if there's enough space for the corridor
//start with checking it's not out of the boundaries
if (x < 0 || x > xsize) return false;
else xtemp = x;
//same thing here, to make sure it's not out of the boundaries
for (ytemp = y; ytemp > (y-len); ytemp--){
if (ytemp < 0 || ytemp > ysize) return false; //oh boho, it was!
if (getCell(xtemp, ytemp) != tileUnused) return false;
}
//if we're still here, let's start building
for (ytemp = y; ytemp > (y-len); ytemp--){
setCell(xtemp, ytemp, floor);
}
break;
case 1:
//east
if (y < 0 || y > ysize) return false;
else ytemp = y;
for (xtemp = x; xtemp < (x+len); xtemp++){
if (xtemp < 0 || xtemp > xsize) return false;
if (getCell(xtemp, ytemp) != tileUnused) return false;
}
for (xtemp = x; xtemp < (x+len); xtemp++){
setCell(xtemp, ytemp, floor);
}
break;
case 2:
//south
if (x < 0 || x > xsize) return false;
else xtemp = x;
for (ytemp = y; ytemp < (y+len); ytemp++){
if (ytemp < 0 || ytemp > ysize) return false;
if (getCell(xtemp, ytemp) != tileUnused) return false;
}
for (ytemp = y; ytemp < (y+len); ytemp++){
setCell(xtemp, ytemp, floor);
}
break;
case 3:
//west
if (ytemp < 0 || ytemp > ysize) return false;
else ytemp = y;
for (xtemp = x; xtemp > (x-len); xtemp--){
if (xtemp < 0 || xtemp > xsize) return false;
if (getCell(xtemp, ytemp) != tileUnused) return false;
}
for (xtemp = x; xtemp > (x-len); xtemp--){
setCell(xtemp, ytemp, floor);
}
break;
}
//woot, we're still here! let's tell the other guys we're done!!
return true;
}
private boolean makeRoom(int x, int y, int xlength, int ylength, int direction){
//define the dimensions of the room, it should be at least 4x4 tiles (2x2 for walking on, the rest is walls)
int xlen = getRand(4, xlength);
int ylen = getRand(4, ylength);
//the tile type it's going to be filled with
int floor = tileDirtFloor; //jordgolv..
int wall = tileDirtWall; //jordv????gg
//choose the way it's pointing at
int dir = 0;
if (direction > 0 && direction < 4) dir = direction;
switch(dir){
case 0:
//north
//Check if there's enough space left for it
for (int ytemp = y; ytemp > (y-ylen); ytemp--){
if (ytemp < 0 || ytemp > ysize) return false;
for (int xtemp = (x-xlen/2); xtemp < (x+(xlen+1)/2); xtemp++){
if (xtemp < 0 || xtemp > xsize) return false;
if (getCell(xtemp, ytemp) != tileUnused) return false; //no space left...
}
}
//we're still here, build
for (int ytemp = y; ytemp > (y-ylen); ytemp--){
for (int xtemp = (x-xlen/2); xtemp < (x+(xlen+1)/2); xtemp++){
//start with the walls
if (xtemp == (x-xlen/2)) setCell(xtemp, ytemp, wall);
else if (xtemp == (x+(xlen-1)/2)) setCell(xtemp, ytemp, wall);
else if (ytemp == y) setCell(xtemp, ytemp, wall);
else if (ytemp == (y-ylen+1)) setCell(xtemp, ytemp, wall);
//and then fill with the floor
else setCell(xtemp, ytemp, floor);
}
}
break;
case 1:
//east
for (int ytemp = (y-ylen/2); ytemp < (y+(ylen+1)/2); ytemp++){
if (ytemp < 0 || ytemp > ysize) return false;
for (int xtemp = x; xtemp < (x+xlen); xtemp++){
if (xtemp < 0 || xtemp > xsize) return false;
if (getCell(xtemp, ytemp) != tileUnused) return false;
}
}
for (int ytemp = (y-ylen/2); ytemp < (y+(ylen+1)/2); ytemp++){
for (int xtemp = x; xtemp < (x+xlen); xtemp++){
if (xtemp == x) setCell(xtemp, ytemp, wall);
else if (xtemp == (x+xlen-1)) setCell(xtemp, ytemp, wall);
else if (ytemp == (y-ylen/2)) setCell(xtemp, ytemp, wall);
else if (ytemp == (y+(ylen-1)/2)) setCell(xtemp, ytemp, wall);
else setCell(xtemp, ytemp, floor);
}
}
break;
case 2:
//south
for (int ytemp = y; ytemp < (y+ylen); ytemp++){
if (ytemp < 0 || ytemp > ysize) return false;
for (int xtemp = (x-xlen/2); xtemp < (x+(xlen+1)/2); xtemp++){
if (xtemp < 0 || xtemp > xsize) return false;
if (getCell(xtemp, ytemp) != tileUnused) return false;
}
}
for (int ytemp = y; ytemp < (y+ylen); ytemp++){
for (int xtemp = (x-xlen/2); xtemp < (x+(xlen+1)/2); xtemp++){
if (xtemp == (x-xlen/2)) setCell(xtemp, ytemp, wall);
else if (xtemp == (x+(xlen-1)/2)) setCell(xtemp, ytemp, wall);
else if (ytemp == y) setCell(xtemp, ytemp, wall);
else if (ytemp == (y+ylen-1)) setCell(xtemp, ytemp, wall);
else setCell(xtemp, ytemp, floor);
}
}
break;
case 3:
//west
for (int ytemp = (y-ylen/2); ytemp < (y+(ylen+1)/2); ytemp++){
if (ytemp < 0 || ytemp > ysize) return false;
for (int xtemp = x; xtemp > (x-xlen); xtemp--){
if (xtemp < 0 || xtemp > xsize) return false;
if (getCell(xtemp, ytemp) != tileUnused) return false;
}
}
for (int ytemp = (y-ylen/2); ytemp < (y+(ylen+1)/2); ytemp++){
for (int xtemp = x; xtemp > (x-xlen); xtemp--){
if (xtemp == x) setCell(xtemp, ytemp, wall);
else if (xtemp == (x-xlen+1)) setCell(xtemp, ytemp, wall);
else if (ytemp == (y-ylen/2)) setCell(xtemp, ytemp, wall);
else if (ytemp == (y+(ylen-1)/2)) setCell(xtemp, ytemp, wall);
else setCell(xtemp, ytemp, floor);
}
}
break;
}
//yay, all done
return true;
}
//used to print the map on the screen
public void showDungeon(){
for (int y = 0; y < ysize; y++){
for (int x = 0; x < xsize; x++){
//System.out.print(getCell(x, y));
switch(getCell(x, y)){
case tileUnused:
System.out.print(" ");
break;
case tileDirtWall:
System.out.print("+");
break;
case tileDirtFloor:
System.out.print(".");
break;
case tileStoneWall:
System.out.print("O");
break;
case tileCorridor:
System.out.print("#");
break;
case tileDoor:
System.out.print("D");
break;
case tileUpStairs:
System.out.print("<");
break;
case tileDownStairs:
System.out.print(">");
break;
case tileChest:
System.out.print("*");
break;
};
}
if (xsize < xmax) System.out.print("\n");
}
}
//and here's the one generating the whole map
public boolean createDungeon(int inx, int iny, int inobj){
if (inobj < 1) objects = 10;
else objects = inobj;
//justera kartans storlek, om den ????r st????rre eller mindre ????n "gr????nserna"
//adjust the size of the map, if it's smaller or bigger than the limits
if (inx < 3) xsize = 3;
else if (inx > xmax) xsize = xmax;
else xsize = inx;
if (iny < 3) ysize = 3;
else if (iny > ymax) ysize = ymax;
else ysize = iny;
System.out.println(msgXSize + xsize);
System.out.println(msgYSize + ysize);
System.out.println(msgMaxObjects + objects);
//redefine the map var, so it's adjusted to our new map size
dungeon_map = new int[xsize * ysize];
//start with making the "standard stuff" on the map
for (int y = 0; y < ysize; y++){
for (int x = 0; x < xsize; x++){
//ie, making the borders of unwalkable walls
if (y == 0) setCell(x, y, tileStoneWall);
else if (y == ysize-1) setCell(x, y, tileStoneWall);
else if (x == 0) setCell(x, y, tileStoneWall);
else if (x == xsize-1) setCell(x, y, tileStoneWall);
//and fill the rest with dirt
else setCell(x, y, tileUnused);
}
}
/*******************************************************************************
And now the code of the random-map-generation-algorithm begins!
*******************************************************************************/
//start with making a room in the middle, which we can start building upon
makeRoom(xsize/2, ysize/2, 8, 6, getRand(0,3)); //getrand saken f????r att slumpa fram riktning p?? rummet
//keep count of the number of "objects" we've made
int currentFeatures = 1; //+1 for the first room we just made
//then we sart the main loop
for (int countingTries = 0; countingTries < 1000; countingTries++){
//check if we've reached our quota
if (currentFeatures == objects){
break;
}
//start with a random wall
int newx = 0;
int xmod = 0;
int newy = 0;
int ymod = 0;
int validTile = -1;
//1000 chances to find a suitable object (room or corridor)..
//(yea, i know it's kinda ugly with a for-loop... -_-')
for (int testing = 0; testing < 1000; testing++){
newx = getRand(1, xsize-1);
newy = getRand(1, ysize-1);
validTile = -1;
//System.out.println("tempx: " + newx + "\ttempy: " + newy);
if (getCell(newx, newy) == tileDirtWall || getCell(newx, newy) == tileCorridor){
//check if we can reach the place
if (getCell(newx, newy+1) == tileDirtFloor || getCell(newx, newy+1) == tileCorridor){
validTile = 0; //
xmod = 0;
ymod = -1;
}
else if (getCell(newx-1, newy) == tileDirtFloor || getCell(newx-1, newy) == tileCorridor){
validTile = 1; //
xmod = +1;
ymod = 0;
}
else if (getCell(newx, newy-1) == tileDirtFloor || getCell(newx, newy-1) == tileCorridor){
validTile = 2; //
xmod = 0;
ymod = +1;
}
else if (getCell(newx+1, newy) == tileDirtFloor || getCell(newx+1, newy) == tileCorridor){
validTile = 3; //
xmod = -1;
ymod = 0;
}
//check that we haven't got another door nearby, so we won't get alot of openings besides
//each other
if (validTile > -1){
if (getCell(newx, newy+1) == tileDoor) //north
validTile = -1;
else if (getCell(newx-1, newy) == tileDoor)//east
validTile = -1;
else if (getCell(newx, newy-1) == tileDoor)//south
validTile = -1;
else if (getCell(newx+1, newy) == tileDoor)//west
validTile = -1;
}
//if we can, jump out of the loop and continue with the rest
if (validTile > -1) break;
}
}
if (validTile > -1){
//choose what to build now at our newly found place, and at what direction
int feature = getRand(0, 100);
if (feature <= chanceRoom){ //a new room
if (makeRoom((newx+xmod), (newy+ymod), 8, 6, validTile)){
currentFeatures++; //add to our quota
//then we mark the wall opening with a door
setCell(newx, newy, tileDoor);
//clean up infront of the door so we can reach it
setCell((newx+xmod), (newy+ymod), tileDirtFloor);
}
}
else if (feature >= chanceRoom){ //new corridor
if (makeCorridor((newx+xmod), (newy+ymod), 6, validTile)){
//same thing here, add to the quota and a door
currentFeatures++;
setCell(newx, newy, tileDoor);
}
}
}
}
/*******************************************************************************
All done with the building, let's finish this one off
*******************************************************************************/
//sprinkle out the bonusstuff (stairs, chests etc.) over the map
int newx = 0;
int newy = 0;
int ways = 0; //from how many directions we can reach the random spot from
int state = 0; //the state the loop is in, start with the stairs
while (state != 10){
for (int testing = 0; testing < 1000; testing++){
newx = getRand(1, xsize-1);
newy = getRand(1, ysize-2); //cheap bugfix, pulls down newy to 0<y<24, from 0<y<25
//System.out.println("x: " + newx + "\ty: " + newy);
ways = 4; //the lower the better
//check if we can reach the spot
if (getCell(newx, newy+1) == tileDirtFloor || getCell(newx, newy+1) == tileCorridor){
//north
if (getCell(newx, newy+1) != tileDoor)
ways--;
}
if (getCell(newx-1, newy) == tileDirtFloor || getCell(newx-1, newy) == tileCorridor){
//east
if (getCell(newx-1, newy) != tileDoor)
ways--;
}
if (getCell(newx, newy-1) == tileDirtFloor || getCell(newx, newy-1) == tileCorridor){
//south
if (getCell(newx, newy-1) != tileDoor)
ways--;
}
if (getCell(newx+1, newy) == tileDirtFloor || getCell(newx+1, newy) == tileCorridor){
//west
if (getCell(newx+1, newy) != tileDoor)
ways--;
}
if (state == 0){
if (ways == 0){
//we're in state 0, let's place a "upstairs" thing
setCell(newx, newy, tileUpStairs);
state = 1;
break;
}
}


else if (state == 1){
That's it. Hey, it's all in pseudo-pseudo-code, but feel free to mail
me if you want a specific implementation example. Specific means Java, in
this case....


if (ways == 0){
== Example ==


//state 1, place a "downstairs"
Well, after going through the whole process in laborious detail, I guess
it's useful to do an example. Just to see how it all fits together.


setCell(newx, newy, tileDownStairs);
Key:


state = 10;
# = Floor
D = Door
W = Wall under consideration


break;


}
1: The first room


}
#####
#####
#####


}


}
2. Select a random wall


#####
#####W
#####




//all done with the map generation, tell the user about it and finish
3. Scan area for new corridor (including space on all sides)


System.out.println(msgNumObjects + currentFeatures);
#####**********
#####W*********
#####**********




return true;
4. It's clear, so add new feature


}
#####
#####D########
#####




////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
5. Pick another wall:


#####    W
#####D########
#####


public static void main(String[] args){


//initial stuff used in making the map
6. Scan area for new Room


int x = 80; int y = 25; int dungeon_objects = 0;
        ******
        ******
        ******
        ******
        ******
#####  ***W**
#####D########
#####




//convert a string to a int, if there's more then one arg
7. Area is OK, so add new room. Throw in a chest (C) for good measure


if (args.length >= 1)
        ####
        ###C
        ####
        ####
#####    D 
#####D########
#####


dungeon_objects = Integer.parseInt(args[0]);


8. Add another corridor as before


              #
              #
        #### #
        ###C #
        #### #
        #### #
#####    D  #
#####D########
#####


if (args.length >= 2)


x = Integer.parseInt(args[1]);
9. This time, we try to add corridor to the second room.


              #
              #
        #### #
        ###C*******
        ####W******
        ####*******
#####    D  #
#####D########
#####


if (args.length >= 3)


y = Integer.parseInt(args[2]);
10. This fails since the area being scanned is already used.


              #
              #
        #### #
        ###C #
        #### #
        #### #
#####    D  #
#####D########
#####




//create a new class of "dungen", so we can use all the goodies within it
11. Fancy features. Add an octagonal room


dungen generator = new dungen();
              #
              #  ###
        #### #  #####
        ###C # #######
        #### #D#######
        #### # #######
#####    D  #  #####
#####D########  ###
#####




//then we create a new dungeon map
12. A secret door hides a fiendishly trapped corridor:


if (generator.createDungeon(x, y, dungeon_objects)){
              #
              #  ###
        #### #  #####
        ###C # #######S###T##TT#T##
        #### #D#######
        #### # #######
#####    D  #  #####
#####D########  ###
#####


//always good to be able to see the results..


generator.showDungeon();
13. Hey, I could go on and on...


}
== Conclusion ==


}
Well, that's my algorithm. I hope you find it useful, or just an
interesting perspective on how to solve this particular problem.


}
== C++ example ==
</pre>
[[C++ Example of Dungeon-Building Algorithm]]
[[Category:Articles]][[Category:Maps]]


</small>
== C# example ==
[[CSharp Example of a Dungeon-Building Algorithm]]
[[Category:Articles]][[Category:Maps]]

Latest revision as of 09:18, 26 June 2014

(Originally written by Mike Anderson.)

Interesting random maps are one of the things that make roguelike games unique. They add greatly to the enjoyment of the game since the player will always be able to face fresh challenges and different problems.

But random maps are far from easy to implement. In most conventional games, you would have a level designer who can create cunningly crafted scenarios. In any roguelike worthy of the name, the programmer must take on the daunting task of creating a "virtual level designer" which will be able to build unlimited numbers of interesting dungeons and mazes with nothing more than a random number generator......

In this article, I've documented the technique that I am developing for use in my own little roguelike called Tyrant. I doubt it's a truly original idea, but I have never seen this exact algorithm used for creating dungeons before. Anyhow, it works pretty well so I've decided to share it with the world.

The goals of the dungeon builder

When writing any piece of code, it's always useful to decide on the objectives beforehand. This can help a lot when designing an algorithm, even if you end up making a lot of changes later.

A basic dungeon will need:

  • A set of interconnected rooms, doors and tunnels
  • An entrance (staircase up)
  • An exit (staircase down)
  • Every space must be reachable

The last condition is quite important; it's nice to know that the player will always be able to get through the level with enough perseverance, and it's also useful to know that when you add a unique artifact, it's not hidden away in some impenetrable cell.


The Plan

When I came to write my dungeon builder for Tyrant, I decided to play with a whole host of different algorithms to see what I liked best. The one I will present here is the best one that I came up with, which is currently being implemented in the actual game.

The inspiration came from the thought:

"If I were a denizen of the underworld, how would I go about building my dungeon?"

One certain thing was that rooms wouldn't just appear in a nice uniform fashion and then have long snaking tunnels appear to join them together. No, when I needed more space for my goblin lunatics I'd just grab a pickaxe and dig a big hole. Add on a few new rooms when they were needed. Probably in a fairly haphazard way.

Some dungeon lords might be a bit more imaginative with a few portcullises, traps and suchlike to guard the more "interesting" rooms. But the basic idea was the same. Start with a small dungeon, then add extensions in all directions until the whole thing is finished.


The algorithm

In this algorithm a "feature" is taken to mean any kind of map component e.g. large room, small room, corridor, circular arena, vault etc.

  1. Fill the whole map with solid earth
  2. Dig out a single room in the centre of the map
  3. Pick a wall of any room
  4. Decide upon a new feature to build
  5. See if there is room to add the new feature through the chosen wall
  6. If yes, continue. If no, go back to step 3
  7. Add the feature through the chosen wall
  8. Go back to step 3, until the dungeon is complete
  9. Add the up and down staircases at random points in map
  10. Finally, sprinkle some monsters and items liberally over dungeon


Step 1 and 2 are easy once you've got the map set up. I have found it very useful to write a "fillRect" command that fills a rectangular map area with a specified tile type.

Step 3 is trickier. You can't pick random squares to add new features because the rule is to always add to the existing dungeon. This makes the connections look good, and also guarantees that every square is reachable. The way Tyrant does it is to pick random squares on the map until it finds a wall square adjacent (horizontally or vertically) to a clear square. This is a good method, since it gives you a roughly even chance of picking any particular wall square.

Step 4 isn't too hard - I just use a random switch statement to determine which of a range of features to build. You can change the whole look of the map by weighting the probabilities of different features. Well-ordered dungeons will have lots of regular rooms and long straight corridors. Cave complexes will tend to have jagged caverns, twisting passages etc.

Step 5 is more tricky, and the key to the whole algorithm. For each feature, you need to know the area of the map that it will occupy. Then you need to scan outwards from the chosen wall to see if this area intersects any features that are already there. Tyrant does this in a fairly simplistic way - it just works out the rectangular space that the new feature will occupy plus a square on each side for walls, then checks to see if the entire rectangle is currently filled with solid earth.

Step 6 decides whether or not to add the feature. If the area under consideration contains anything other than solid earth already, then the routine loops back to step 3. Note that *most* new features will be rejected in this way. This isn't a problem, as the processing time is negligible. Tyrant tries to add 300 or so features to each dungeon, but usually only 40 or so make it past this stage.

Step 7 draws the new feature once you've decided the area is OK. In this stage, you can also add any interesting room features, such as inhabitants, traps, secret doors and treasure.

Step 8 just loops back to build more rooms. The exact number of times that you want to do this will depend on map size and various other factors.

Step 9 is pretty self-explanatory. Easiest way to do it is to write a routine that picks random squares until it finds an empty one where the staircases can be added.

Step 10 just creates a host of extra random monsters in random locations to add some spice. Tyrant creates about most of the monsters at this point of the map generation, although it does add a few special creatures when individual rooms are generated.


That's it. Hey, it's all in pseudo-pseudo-code, but feel free to mail me if you want a specific implementation example. Specific means Java, in this case....

Example

Well, after going through the whole process in laborious detail, I guess it's useful to do an example. Just to see how it all fits together.

Key: 

# = Floor
D = Door
W = Wall under consideration


1: The first room 

#####
#####
#####


2. Select a random wall 

#####
#####W
#####


3. Scan area for new corridor (including space on all sides) 

#####**********
#####W*********
#####**********


4. It's clear, so add new feature 

#####
#####D########
#####


5. Pick another wall: 

#####     W
#####D########
#####


6. Scan area for new Room 

       ******
       ******
       ******
       ******
       ******
#####  ***W**
#####D########
#####


7. Area is OK, so add new room. Throw in a chest (C) for good measure 

        ####
        ###C
        ####
        ####
#####     D  
#####D########
#####


8. Add another corridor as before 

             #
             #
        #### #
        ###C #
        #### #
        #### #
#####     D  #
#####D########
#####


9. This time, we try to add corridor to the second room. 

             #
             #
        #### #
        ###C*******
        ####W******
        ####*******
#####     D  #
#####D########
#####


10. This fails since the area being scanned is already used. 

             #
             #
        #### #
        ###C #
        #### #
        #### #
#####     D  #
#####D########
#####


11. Fancy features. Add an octagonal room 

             #
             #   ###
        #### #  #####
        ###C # #######
        #### #D#######
        #### # #######
#####     D  #  #####
#####D########   ###
#####


12. A secret door hides a fiendishly trapped corridor: 

             #
             #   ###
        #### #  #####
        ###C # #######S###T##TT#T##
        #### #D#######
        #### # #######
#####     D  #  #####
#####D########   ###
#####


13. Hey, I could go on and on...

Conclusion

Well, that's my algorithm. I hope you find it useful, or just an interesting perspective on how to solve this particular problem.

C++ example

C++ Example of Dungeon-Building Algorithm

C# example

CSharp Example of a Dungeon-Building Algorithm

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