The latest dev builds (number 64 and up) now support biome groups. This feature was developed by @Timethor and me. It allows you to group biomes together. You can for example put all ice biomes in one group and all hot biomes in another group, so that it is less likely that a hot biome spawns next to a cold biome.
An example is included in the default settings:
# Syntax: BiomeGroup(Name, Size, Rarity, BiomeName[, AnotherName[, ...]])
# Name - just for clarity, choose something descriptive
# Size - layer to generate on, from 0 to GenerationDepth. All biomes in the group must have a BiomeSize
# larger than or equal to this value.
# Rarity - relative spawn chances.
# BiomeName... - names of the biome that spawn in the group. Case sensitive.
BiomeGroup(NormalBiomes, 0, 97, Forest, Roofed Forest, Extreme Hills, Plains, Birch Forest, Swampland)
BiomeGroup(IceBiomes, 3, 90, Ice Plains, Cold Taiga)
BiomeGroup(HotBiomes, 0, 97, Desert, Savanna, Plains)
BiomeGroup(ColdBiomes, 0, 97, Forest, Extreme Hills, Taiga, Plains)
As you can see, the default settings now use four different groups. The biome Plains is added to multiple groups, so it can spawn basically anywhere.
We don't want to break carefully fine-tuned worlds! We have tried to ensure that old worlds still look exactly like they did previously. It turned out that even when you limited yourself to the two old "groups", NormalBiomes and IceBiomes, the worlds looked different. This was caused by changes made to the ocean generator to support an arbitrary number of groups.
So a compatibility biome mode was necessary: one that doesn't allow an arbitrary number of groups, but does correctly simulate the old behaviour. This biome mode is called
BeforeGroups. Old worlds with
BiomeMode: Normal will automatically be put in
BiomeMode: BeforeGroups. (Worlds are considered old when the old
NormalBiomes setting is found.) This compatibility biome mode is limited to two groups:
IceBiomes, which replace the old settings with the same name. Other groups are ignored.
Emulating the vanilla biome layout
Some more tweaks are needed to the default settings to make them look exactly like vanilla. Deep oceans, mesas, jungles and mega taigas do not spawn yet. Some isle biomes also do not spawn yet.
Some work is still needed, but we're getting somewhere!