This article explains the principles behind the terrain generator in MCServer. It is not strictly +specific to MCServer, though, it can be viewed as a generic guide to various terrain-generating algorithms, +with specific implementation notes regarding MCServer.
+ +The nature has many complicated geological, physical and biological processes working on all scales from +microscopic to planet-wide scale, that have shaped the terrain into what we see today. The tectonic plates +collide, push mountain ranges up and ocean trenches down. Erosion dulls the sharp shapes. Plantlife takes +over to further change the overall look of the world.
+Generally speaking, the processes take what's there and change it. Unlike computer generating, which +usually creates a finished terrain from scratch, or maybe with only a few iterations. It would be unfeasible +for software to emulate all the natural processes in enough detail to provide world generation for a game, +mainly because in the nature everything interacts with everything. If a mountain range rises, it changes the +way that the precipitation is carried by the wind to the lands beyond the mountains, thus changing the +erosion rate there and the vegetation type.
+ +For a MineCraft-like game terrain generator we need the generator to have several properties: +
As already mentioned, the nature works basically by generating raw terrain composition, then "applying" +erosion, vegetation and finally this leads to biomes being formed. Let's now try a somewhat inverse +approach: First generate biomes, then fit them with appropriate terrain, and finally cover in vegetation +and all the other stuff.
+Splitting the parts like this suddenly makes it possible to create a generator with the required +properties. We can generate a reasonable biome map chunk-wise, independently of all the other data. Once we +have the biomes, we can compose the terrain for the chunk by using the biome data for the chunk, and +possibly even for neighboring chunks. Note that we're not breaking the first property, the biomes can be +generated separately so a neighboring chunk's biome map can be generated without the need for the entire +neighboring chunk to be present. Similarly, once we have the terrain composition for a chunk, we can +generate all the vegetation and structures in it, and those can again use the terrain composition in +neighboring chunks.
+ +This leads us directly to the main pipeline that is used for generating terrain in MCServer. For +technical reasons, the terrain composition step is further subdivided into Height generation and Composition +generation, and the structures are really called Finishers. For each chunk the generator generates, in this +sequence: +
+
+
+
+The beautiful thing about this is that the individual components can be changed independently. You can +have 5 biome generators and 3 height generators and you can let the users mix'n'match. +
+ +For a great tutorial on coherent noise, see the LibNoise +documentation.
+Coherent noise is a type of noise that has three important properties that we can use to our advantage: +
We'll be mostly using Perlin noise in this article. It is the easiest one to visualise and use and is one +of the most useful kinds of coherent noises. Here's an example of a Perlin noise generated in 2 dimensions:
+
+It comes only naturally that such a 2D noise can be used as a terrain height map directly:
+
+However, this is not the only use for this noise, and 2 dimensions is not the limit - this noise can be +generated for any number of dimensions.
+ +The easiest way to generate biomes is to not generate at all - simply assign a single constant biome to +everywhere. And indeed there are times when this kind of "generator" is useful - for the MineCraft's Flat +world type, or for testing purposes, or for tematic maps. In MCServer, this is exactly what the Constant +biome generator does.
+Of course, there are more interesting test scenarios for which multiple biomes must be generated as easy +as possible. For these special needs, there's a CheckerBoard biome generator. As the name suggests, it +generates a grid of biomes.
+These two generators are more of a technicality, we need to make something more interesting if we're +going for a natural look. The Voronoi generator is the first step towards such a change. Recall that a +Voronoi diagram is a construct that creates a +set of areas where each point in an area is closer to the appropriate seed of the area than the seeds of any +other area:
+
+The overall shape of a Voronoi diagram is governed by the placement of the seeds. In extreme cases, a +seed could affect the entire diagram, which is what we don't want - we need our locality, so that we can +generate a chunk's worth of biome data. We also don't want the too much irregular diagrams that are produced +when the seeds are in small clusters. We need our seeds to come in random, yet somewhat uniform fashion.
+Luckily, we have just the tool: Grid with jitter. Originally used in antialiasing techniques, they can be +successfully applied as a source of the seeds for a Voronoi diagram. Simply take a regular 2D grid of seeds +with the grid distance being N, and move each seed along the X and Y axis by a random distance, usually in +the range [-N / 2, +N / 2]:
+
+Such a grid is the ideal seed source for a Voronoi biome generator, because not +only are the Voronoi cells "reasonable", but the seed placement's effect on the diagram is localized - each +pixel in the diagram depends on at most 5 x 5 seeds around it:
+
+
+