Tiling Physics using Farseer

Question

I'm having a problem with the Farseer Physics Engine, where in a tiled environment, my object will at times interact with corners of others objects, even if they align perfectly.

You can try it here. Controls are A for Left, D for Right. Don't mind the tile textures have rounding, the objects are still perfectly square in the simulation.

I've read about people suggesting that you calculate and create one larger object, using Marching Squares or something similar. This is not an option however, as I'd like each tile to have different physical qualities, like different friction and restitution.

My question is, what exactly is causing it, is it float precision issues or something else? And is there a way to fix it, without breaking the whole physics engine?

Answer 1

Farseer uses an iterative solver, so when your wheel starts colliding with another rectangle at high velocity, from time to time you'll see bumps since it's a "perfect align" to us, not to a physics simulation, with iterations things like these will never be "pixel-perfect".

You will have to convert rectangles to Edge/Loop shapes and then model different physical qualities with hacks like creating artificial tile bounds and then changing properties when character enters a bounding box, but not every physical quality can be emulated that way.

Sooner or later you'll end up writing your own tile-based physics instead of Farseer. If your game doesn't have lots of complex physics puzzles, it will be simpler to abandon Farseer completely and roll your own tile-based physics.

Answer 2

you can optimize your collisions shapes, this scene can be done with only four rectangles.

you can join correlative boxes to make one bigger.

this video shows it http://www.youtube.com/watch?v=eyhGckHgkkE

when it is adding boxes you can see a light blue rectangle with the optimized shape.

Answer 3

Hmm... I suspect it might have something to do with your circle and not the tiles beneath it. Try making the ground using a single hull and see if you get the same results. If not, it's the tiles like you suspect. If so, your circle isn't as round as you might think it is.