Hi.

I am wondering about this. I was not satisfied with my previous system for doing this, which seemed kind of ugly or limited, and I was wondering what would be the most efficient and elegant solution.

What I have is a cell-based, turn-based game with a discrete game world, that is, it's a raster of tiles, not a space with (approximately) continuous (floating point) coordinates, with each object in one time. And I was wondering how you deal with collisions. In particular, each object can move but it can, obviously, only move from tile to tile, never be in between two tiles.

This means that when we get collisions, we have a number of cases to consider, and I'd preferably like something better than a casewise approach. Moving one cell at a time, we could have, e.g. that two objects move at each other, their coordinates would change by 1 cell each in opposing directions, causing them to swap places if they were right next to each other. They'd go through each other, so that should be a collision. Another way a collision can occur is that two objects try to rush each other for the same cell. A situation that might look like it would be a collision, but isn't, is two objects moving in the same direction, in the same line, one just behind the other. If you look at only the one in behind, one could think it will collide with the one ahead unless you also look to see which way that is moving, which adds more complicated, tricky programming to make it work on a computer. Things are further complicated by that some objects may move different velocities, crossing multiple squares in a turn (like a shot arrow).

Almost all the collision-handling stuff I've seen deals with continuous space and (approximate) continuous time, e.g. checking overlap, etc. and so does not seem obvious how to apply to a discrete space and maybe also discrete time.

One way I thought to handle it would be to just use a continuous simulation space which is "rounded" to discrete, but then we get a computationally-intensive simulation, as it seems that given the discrete character of the world space, we should be able to simplify/optimize things considerably.

What do you do?