So, we use a depth first shortest path algorithm. It's pretty complex. We use it to find paths from one location to another in a localized fashion (rooms are pretty close to each other) and we use the same algorithm when rooms are far away, using waypoints.
I was watching some videos today about how this algorithm works, hoping to find places we could optimize ours. I stumbled on something that we thought we were doing, but we weren't.
First, a bit of an explanation on how the depth first shortest path works.
We take a starting location, we take an ending location. We then find a bunch of different paths from starting point to ending point while at the same time keeping track of the shortest one that's found. We don't know which one is shortest until we're doing making our calculations. When we're all done, we use the shortest path to move NPCs and vehicles and stuff like that, throughout the game.
Sometimes this causes lag because NPCs move from one location to another and it's far away so it takes lots of calculations, or a taxi needs to drive from red to blue and that is a lot of moves, even with waypoints, and so it takes awhile. Sometimes a bunch of NPCs are moving at the same time or in quick succession in an automated manner. All these things lag the MOO intermittently because they all are calculation heavy.
The optimization I made today, was for each step in each calculation of a path, to check and see if the path it was currently calculating was already longer than the shortest path found. If it turns out it's longer, we just stop checking that path because it's garbage, we don't care. We have no reason to continue checking a path that will turn out to be 10 or more moves long when we already have a path that takes 9 moves to get from point a to point b.
This results in some dramatically increased performance detailed here:
Before Optimization, calculating the path from the 1st Floor Landing of New Rose, to Withmore Savings Bank: 6.86 seconds.
After optimization, making the same calculation: 0.36 seconds.
This optimization, coupled with our pathing cache, reduces the overhead that pathing has on the overall health of the MOO a large amount. This makes me very happy, but as with any change like this-- if you notice wonkiness, please let me know.