[Ohrrpgce] SVN: james/8760 Add an A* pathfinding for maps. NPCs can be set to chase the hero around

[Ralph Versteegen]

On 27 May 2017 at 11:35, <subversion at hamsterrepublic.com> wrote:

> james
> 2017-05-26 16:35:19 -0700 (Fri, 26 May 2017)
> 346
> Add an A* pathfinding for maps. NPCs can be set to chase the hero around
> obstacles.
>
> Currently only supports wallmap checking, I will be adding zone-checking
> and NPC-collision checking soon.
>
> You can test this already, but the NPC movement type is marked
> "EXPERIMENTAL" because the behavior will definitely change a bit before I
> am done with it.
> ---
> U   wip/SConscript
> U   wip/customsubs.rbas
> U   wip/game.bas
> A   wip/pathfinding.bas
> A   wip/pathfinding.bi
> U   wip/util.bas
> U   wip/util.bi
> U   wip/walkabouts.bas
> U   wip/walkabouts.bi
>

Excellent!
I was going to remind you about one-way walls, but looking quickly at the
code, it looks like they would just work automatically.

How will you handle tiles blocked by other NPCs? Just give them a high
cost? I don't know a good solution for this. If the cost isn't high enough,
then the NPC won't go a different way while there's an NPC in the way if
the other way is an extra X files.
Really, any stationary NPC should be treated more like a wall. But so
should NPCs that are just stuck in a corridor.
Maaaaybe this could be handled by giving each NPC a dynamic path cost. For
every tick that another NPC is trying to get past it (its path goes
straight through the blocking NPC), its cost increases. Finally the pathing
NPC gets so sick of waiting that it goes another way. This could happen
before the pathing NPC ever reaches the blocking NPC, since the cost can be
updated for each tick that the pathing NPC moves. I don't know what the
condition would be for decreasing the dynamic cost. Maybe something like
when the NPC moves off someone's path. If an NPC gains a really high cost,
then computed paths across the map with fluctuate wildly when the high-cost
NPC steps in and out of a corridor.

Have you tried running this on larger maps? In particular when you place
some NPC that can't reach the hero? I image that in that case the NPC would
try to repath every tick. We're going to have to stop that from happening.
Maybe delay for half a second before trying again. It's also possible to
cancel further pathing attempts until either the map changes or the hero
crosses a one-way wall (approximation: when the hero/target changes).

I notice that how you determine the 'best' node of the openlist is very
inefficient. Instead, you should keep openlist sorted so you can pop off
the end (popping off the front is slow). You can use v_sort to sort the
list, but first you need to define a compare function. See vector.bas for
examples.
Using v_sort on an almost-sorted array is still less efficient than it
could be (linear instead of logarithm time). I have some C code for a
priority queue, so I could add a couple functions for using a vector as a
priority queue, and we can switch to that later.
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