Implementation of pathfinding with Z levels

The following video shows an actor moving through the different levels of depth of a simple map, and then going for a while to random coordinates on the first level:

Although the actor reaches the objective, for now I haven’t managed to prevent that in two particular moments the actor decides to go through the roof as part of his route, although I had modified the code so it wouldn’t allow him to do so, at least in theory. But it’s a minor problem for what I intended implementing the pathfinding: that when I programmed new experiments in which the user moved his character, around him other actors would find their way and act according to their AI.

Movement in three dimensions tends to divide these kinds of games. Dwarf Fortress is famous in part for how it handles the different layers, allowing the user to strike the earth for a couple dozen levels to build his fortress, or raise it several levels above sea level if he wants to. On the other hand, Rimworld, programmed with Unity, sacrifices that verticality to offer better graphics and effects and a complexity limited in comparison. I was convinced that simple sprites were enough in exchange of a complex simulation and an artificial intelligence that would, hopefully, surprise often. And behave reasonably to begin with.

I programmed this experiment a few days ago, but I recall spending a couple hours trying to solve a problem. When the actor had to find his route to the inside of the house, which should force him to pass through the doorway, the actor went straight to the western wall of the house, his image passed through and stopped in the final coordinates. I was making sure that the pathfinding algorithm identified the wall as impassable, but the actor was still going through it. In the end, after a lot of testing, I revised my assumptions. Were the actor sprites being displayed according to the level they were in? Turns out I had let that for later, and the pathfinding was doing its job: instead of going through the wall, the actor jumped it and “crashed” through the roof to reach his objective. The function that had to draw the actor showed him indistinctly going through a wall that in reality existed a level below.

After that, to make sure the pathfinding algorithm worked better in three dimensions, I had to add more booleans to the tiles. Apart from whether or not they blocked the straight path, they should mark whether they blocked going upwards or downwards (days later I wrote a couple of booleans more: whether the tile blocked the path straight up and down). Otherwise the actor would go through several layers of underground tiles to reach a basement. The changes worked for the most part, shown in the video where the actor goes down the stairs to reach the basement.

To draw the different layers of depth I paid attention to how Dwarf Fortress did it. When the user went up a z level, if any tile was defined as “empty”, the program should draw the closest “real” tile below, but tinted blue to show the user that he was seeing tiles belonging to another z level. On my first try, the code copied each of those sprites and modified its RGB component according to how close they were to the current z level. That’s shown in the video. However, copying all those sprites every frame hurt the framerate too much. A couple of days later I opted for something simpler and that even works better: I draw the first “real” tile normally, but over it I draw translucent tiles for each z level in between. The translucent tiles stack up, darkening the tile below.

This experiment worked for what I intended, so I moved on to new ones.

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