In Profundis Progress (5/22)

I'm back baby!

So, here is the thing that's been consuming my development time lately.  Cellular automation for use in real-time games frequently has to be heavily optimized.  When you're cycling though every cell of a hundreds by hundreds array every frame, then even the overhead from those cells in which you just check contents and decide nothing needs to happen is significant.

My current strategy for negating this is to not use a big loop that iterates through every cell.  Instead, I keep a list of every cell that _might_ change this frame.  I calculate those and, any that do change, I add adjacent cells to the list for the next frame.

It's much MUCH faster, but it's worth noting that this is entirely because, for most of the game world, large portions are static between each frame.  Stone is largely inert, so we don't need to worry about it except how other things react to it -- they are the initiating factors in that, so their routines handle the work.  Empty spaces (that don't contain weird gases) are similar.  These two cell types are 90% of the world.  By removing them from consideration, it's worth a huge performance gain.

A huge gain, but it turns out, not huge enough.  I remind you that, before, we kept performance under control by only updating the screen and a short distance outside of it.  Under this system we update the whole world, and factoring in all of the cells that CAN change, it's a bit too much to reliably handle.

There is a way around it.  We sort the update list, using one of the handy-dandy, heavily-optimized Python sort functions, with the sort key being a simple Cartesian distance from the player or cursor.  Then we can just pop off the first few hundred or so every frame, and leave the rest for the next frame.  If the player never goes anywhere near them they won't get handled, but as soon as he does they'll enter consideration.

It's a cheat, but real-time game development is basically a convoluted series of cheats, a set of makeshift concessions to processor speed and memory limits.  Now that we have multicore machines and multi-gigabyte memory spaces this fundamental fact is sometimes obscured, but it doesn't change it.

In Profundis progress (5/8, part 2)

Did some more work today on speeding up the simulation.  Before, the cells that were calculated were all of them within the borders of the screen plus a small area outside of it.  Current work is towards switching to a system where changed cells in a given frame mark cells adjacent to them for calculation in the next frame.  The idea is that changes don't happen randomly; they're always spurred by other changes.  So, there's no need to, say, check a boulder every frame to see if it should roll.  If it's stable on a given frame, it won't be checked again unless the space around it is disturbed.

Since most of the game world is fairly static each frame, the result is potentially much more efficient world calculations, meaning being able to simulate more of it each frame.  The biggest drawback is that gases are unsuitable for this system, since they'd be constantly spreading bit by bit regardless of whether the neighbors change.  Even so, it's a promising direction for development.