10-06-2015, 06:27 PM
I believe it's mostly due to the caches.
Take the biome cache, for example. By default it stores up to 4 * 64 chunks worth of biomes. When the spawn generator goes from left to right for the first time, it primes the cache. When it goes back from right to left, it re-uses most of the values in the cache, adding only those that are one chunk below. However, that only works as long as the values from the first pass stay in the cache. When the left-to-right pass is too long, the values from the start of the run get pushed off out of the cache before the left-to-right pass is completed, so the following right-to-left pass has to generate them again. In my opinion that's what happens at the first drop in the graph, at around 40 % of the X axis.
First the biome cache gets depleted like this, because it's the most heavily used one. Then the composition cache gets depleted, and that's when the line starts going all wiggly.
Take the biome cache, for example. By default it stores up to 4 * 64 chunks worth of biomes. When the spawn generator goes from left to right for the first time, it primes the cache. When it goes back from right to left, it re-uses most of the values in the cache, adding only those that are one chunk below. However, that only works as long as the values from the first pass stay in the cache. When the left-to-right pass is too long, the values from the start of the run get pushed off out of the cache before the left-to-right pass is completed, so the following right-to-left pass has to generate them again. In my opinion that's what happens at the first drop in the graph, at around 40 % of the X axis.
First the biome cache gets depleted like this, because it's the most heavily used one. Then the composition cache gets depleted, and that's when the line starts going all wiggly.