I'm working on a Minecraft-style game, and I need a way to reduce the amount of the world rendered. Currently, I'm using a naive, render-everything approach, which is having obvious scaling problems. I need a way to take an array of blocks, and in some way find out which ones are touching air, water, or any other translucent block.
I'm open to using external modules like NumPy or SciPy, though some of their documentation is a bit over my head. Alternatively, it would also be acceptable to iterate through each block and get a list of neighbors, though the performance cost of doing these calculations in Python instead of C would be pretty hefty.
For the record, I've already tried looking at NetworkX, but it seems to be more for scientific analysis or pathfinding than visibility checking.
If you only need to do this once, performance should not be an issue. If you also incrementally update the .isBoundary property of blocks whenever the world is changed, you will never have to do it again.
However you still run into issues if your world is too large or full of holes and caverns and transparent-interleaved-with-nontransparent. If you need to dynamically determine what is visible, you can keep an octree ( http://en.wikipedia.org/wiki/Octree ) where you can have giant expanses of air/water/etc. as a single node (giant block), labeled as "transparent". Then use the "paintbucket" algorithm (modified to perform Dijkstra's algorithm, so it is easy to detect when you've "gone around a corner" by checking to see if blocks exist between the current block and the origin) to quickly figure out which blocks are in sight. Updates for things far in the distance can be delayed significantly if the player is moving slowly.