Generation Orchestration #36

Background

Generation orchestration is the single entrypoint that everything outside the core uses to ask for terrain. Both the CLI and the generation service call in here with a seed and a tile coordinate and get back a finished height grid. It does not generate anything itself, it derives the tile's seed, builds the pipeline and the region grids, and hands #4 what it needs to do the work.

Description

Given a seed and a tile coordinate, return a finished full resolution height grid.

• Work out the tile's own seed from the global seed and its coordinate
• Build the pipeline and the region grids, then hand the sampler the pipeline's patch cleaning function and those grids
• Ask the tile cache for a tile that was already generated before generating it again

This module is the only place that decides whether the blur route or the model route in #23 gets run. The sampler must not be able to tell which one it was handed, which is why it gets a function that cleans a patch rather than the pipeline itself.

For now the tile cache from #31 stays here, since nothing in #4 needs a finished tile in order to generate a region of known size.

Keep this thin. If logic about windows or patches starts showing up here then something has leaked out of #4.