I could see why you might not want to fill under the terrain in a game that features things like underground caves, but thin terrain seems to be present in a huge majority of 3D games (even those without underground features) and is not engine-specific. Why is terrain almost always a fragile piece of origami that’s so easily punctured?
In: Technology
Usually, collisions are handled between the surfaces of objects. This is relatively simple and boils down to answering the question “Do these two shapes intersect at this time?” Time, however, has finite precison and is considered in finite steps (e.g. you might be checking 60 times per second). Any collision that occurs between those 1/60 second intervals wouldnt be detected until the next 1/60th of a second. If the game is not designed properly, you could have an object that moves from one side of a wall to the other side of the wall in 1/60th of a second and never actually intersects with the wall.
The solution is to either use a smaller time step (which requires much more work to simulate the same amount of time) or to make a more complicated comparison like “do these two shapes intersect at any time between the last time step and this time step?” (which also requires more work). For example, bullets in first person shooters are often treated as lines that instantly go from the barrel of the gun to the bullet’s impact point and that entire line is then compared against the world’s geometry. However, this gets much more difficult when you’re dealing with complicated objects and is too costly to be used for everything by default.
Well-designed games are able to use the appropriate collision methods in the right situations and should not allow situations where objects have properties that can break the simulation.
Latest Answers