As with biomes, the easiest way to generate terrain height is not generating at all - assigning a constant +height value to all columns. This is again useful either for internal tests, and for worlds like MineCraft's +Flat world.
+ +For a somewhat more realistic landscape, we will employ the good old 2D Perlin noise. We can use it +directly as a heightmap - each value we get from the noise is stretched into the desired range (usually from +40 to 120 blocks for regular MineCraft worlds) and used as the height value. However, this doesn't play too +well with the biomes we've just generated. If the biome says "ocean" and the Perlin noise says "mountain", +the end result will be unpleasant.
+ +So we want a height generator that is biome-aware. The easiest way of doing this is to have a separate +generator for each biome. Simply use the biome map to select which generator to use, then ask the appropriate +generator for the height value. Again, this doesn't work too well - imagine an ExtremeHills biome right next +to an Ocean biome. If no extra care is taken, the border between these two will be a high wall. The following +image shows a 2D representation (for simplification purposes) of the problem:
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+This requires some further processing. What we need is for the terrain height to be dependent not only on +the immediate biome for that column, but also on the close surroundings of the column. This is exactly the +kind of task that averaging is designed for. If we take the area of 9x9 biomes centered around the queried +column, generate height for each of the biomes therein, sum them up and divide by 81 (the number of biomes +summed), we will be effectively making a 9-long running average over the terrain, and all the borders will +suddenly become smooth. The following image shows the situation from the previous paragraph after applying +the averaging process:
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+The approach used in MCServer's Biomal generator is based on this idea, with two slight modifications. +Instead of using a separate generator for each biome, one generator is used with a different set of input +parameters for each biomes. These input parameters modify the overall amplitude and frequency of the Perlin +noise that the generator produces, thus modifying the final terrain with regards to biomes. Additionally, the +averaging process is weighted - columns closer to the queried column get a more powerful weight in the sum +than the columns further away. The following image shows the output of MCServer's Biomal terrain height +generator (each block type represents a different biome - ocean in the front (stone), plains and ice plains +behind it (lapis, whitewool), extreme hills back right (soulsand), desert hills back left (mossy +cobble)):
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+
+One key observation about this whole approach is that in order for it to work, the biomes must be +available for columns outside the currently generated chunk, otherwise the columns at the chunk's edge would +not be able to properly average their height. This requirement can be fulfilled only by biome generators that +adhere to the second Expected property - that re-generating will produce +the same data. If the biome generator returned different data for the same chunk each time it was invoked, it +would become impossible to apply the averaging.
+ +(TODO: height with variations (N/A in MCS yet)
(TODO)
(TODO)
+ + +(TODO)