I'm doing some terrain generation, using the usual Perlin-style interpolated noise (although strictly speaking it's value noise, as I'm not using gradients). However rather than generating a large landmass in one go, I am generating it chunk by chunk, eg. 100m x 100m areas. Therefore it's important that the edges of each chunk line up with each other in terms of their generated height. (I think this is how Minecraft does it, but I couldn't find out exactly how the height values are calculated, especially across changing biomes. And I'm not using voxels, anyway.)
Most algorithms that I've seen for terrain generation using noise seem to assume that you're generating across the whole landmass, that you have precalculated noise values that span the entire world which you then interpolate between (and repeat with higher frequencies at lower amplitudes, etc). But since my world is unbounded I don't have this. I think the answer should be as simple as having some sort of 2D hash function that can return a noise value for any arbitrary x,y in the world, and sampling that value itself is easy. But I'm having trouble thinking about how to generalise this to the system of frequency and amplitude. If I just scale up x and y by the frequency each time then I'm sampling values from elsewhere in the world which seems logically incorrect. Can anybody clear this up for me? Maybe post some pseudocode?
I have one other aspect I am trying to implement - each chunk has itself got a height value, so that I can specify that certain parts of the world are higher than others before the noise algorithm runs. I am contemplating calculating the height at each point as basically a bilinear interpolation of the chunk height with that of its neighbours, and then add the noise value for that position. I think this should be continuous both within chunks and across chunk boundaries, but I'd be interested to hear if there are any problems with this approach, ways it could be improved, or ways to combine it with the previous step to make the algorithm simpler and/or faster.
Edited by Kylotan, 25 February 2013 - 12:10 PM.