AI fun times

I hate coding AI.  I really do.  It's not necessarily because it's an unpleasant task... it's because I find it annoyingly difficult.  See, it's easy to understand what you want the computer to do, but it's ridiculously hard to tell it to do that.  For instance, it's all well and good to say "this guy should go around walls."  But how exactly do you do that, code-wise?  The answer, it turns out, is quite complicated.  Far more complicated than simply adding a "go around walls" line of code somewhere in the movement routine.

Gamemaker has a very VERY easy function for simple movement planning, which is what I used in previous Gamemaker projects (although if memory serves, enemies in Pit didn't do anything to try and find their way around walls, since it was rarely necessary).  It basically will change an NPC's movement direction under-the-hood to move parallel to a  solid object if it contacts it.  This works pretty well if you're only dealing with single blocks or detached "lines" of wall objects--the NPC sometimes takes the long way around, but it doesn't get stuck.  However, when intersecting walls come into play, this routine can regularly cause NPCs to start infinitely looping in corners.  Not a huge problem when you're making a mob shooter like Nurf Nerfus, but a significantly larger problem when you need your enemies to be able to actively hunt down the player and pursue them through inside areas.

So this is why motion planning exists.  Motion planning functions let an NPC plan out the shortest, most logical path to a given point by looking at the entire layout of the area at once rather than simply moving until they hit something.  The motion planning in Gamemaker is actually pretty good, and allows for some pretty convincing "maze solvers."  The problem with them is that calculating a path takes a fair amount of time, in computing terms.  So it's not practical to just have the AI calculate a path every step.  When my NPCs are just walking around, it's works perfectly well to set a point once and let them find their way to it.  You wouldn't notice any slowdown.  But when the point is constantly changing--such as when an NPC is chasing the player, or going to the source of a noise-- the game can easily slow to a crawl.  In reality, most situations like this can be averted with some smart "cutting corners" (for instance, if the NPC can see you, he doesn't really need to find his way around walls, and most of the situations where an enemy needs to actively chase the player involve direct line of sight).  But then, the game needs to know when to use motion planning and when not to use it.  It's not exactly a Carmack-worthy problem, but it adds more code and more complexity.

Any veteran programmers reading this are probably shaking their heads and going "what... he can't handle some simple motion planning?  How does this clown ever expect to succeed as an indie game designer!  I can do motion planning in my sleep.  Now excuse me while I go back to making a mod that improves the visuals on yet another AAA commercial title."  Well I don't know if I mentioned it previously or not, but I am a thoroughly right-brained programmer.  In other words, anything that requires something resembling mathematical competence will invariably confuse me.  This is why I love the Gamemaker toolset.  Because then I don't have to worry about those niggling little annoyances like collision detection, sprite rotation, etc.  At worst, I may have to use a function or two.  At best, I can merely set a variable and the engine takes care of it for me.  However, even within the admittedly noobish environment of Gamemaker, there are still things that I would much prefer not having to do.  Things that require me to exert effort beyond simply typing in the correct sequence of functions and variable assignments.  Things that will inevitably result in woeful spaghetti code and arcane solutions.  Which is always...ALWAYS...the case with my AI.

So, this is a rather rambling post... basically, I'm working on the AI right now.  And it's predictably difficult.  It will ultimately involve some cutting of corners and implementation of different techniques.  But thus far, it's turning out pretty good.  Enemies won't be able to see you if you're hiding in shadows or are outside their FOV, they will actively hunt for food and run from danger, and they'll do a little to try and find you if they know you're around.  Next post, I'll have some screenshots of the lighting and simple little graphical effects that the game has implemented thus far.

-jefequeso