2d top down wind simulation, how?
2d top down wind simulation, how?
I'm working on a simulation toy, and I want to model wind on my world/levels.
I'm currently using playrho (a box2d fork) with gravity set to 0 to model a top down view.
I assume the wind will be represented as a vector field. But I'm unsure what method to use to get this field.
Could someone point me in the right direction? Should I be looking at the navier-stokes equation? Does anybody know of any relevant tutorials?
Thanks in advance!
Well, firstly you need to decide how accurate you want your wind modeling to be, but generally, the less complicated an equation you can use for your desired level of accuracy, the better. It'll end up being a vector field, but I would probably make simple rules for how the wind interacts with objects in a given tile and the tiles around it, rather than trying to model fluid dynamics precisely.
Another approach might be a ray-tracing style approach, where the rays can bounce off object geometry and lose some momentum, objects can respond to ray impacts and gain momentum, and you do some vector math to figure out what happens when rays and moving objects intersect.
The exact approach depends on the specifics of your game, and the "right" answer might be neither of these.
If you want to write it as a fluid sim, you can take a look at "Real-Time Fluid Dynamics for Games" by Jos Stam.
There was also a series of articles by Michael J. Gourlay on Intel's website (maybe about a decade ago?) called "Fluid Simulation for Video Games". I'm having trouble finding an index of it, but individual PDFs for some of the entries show up in Google -- you might need to go digging around archive.org for that one, but it had a lot of interesting info in it. I think there were somewhere around 20-ish parts and some of the later entries discussed things like modeling heat.
That might be more detailed than what you're interested in, though; the rabbit hole on this subject goes deep...
I forgot most of my simulation subject, but we did a 2D particle simulator and yes, you will need Navier-Stokes if you want the effect to be physically correct. You will need to solve a numerical problem each frame to compute turbulences. Wind is a force with a source that will propagate depending on its parameters (like viscosity)
If you don't implement that, you won't be able to implement things like walls that block wind and such, which I guess is something you might had in mind. Also, having a changing environment is probably pretty hard, so prepare yourself.
I just took a look at the source code of The Powder Toy, and the class Air (src/simulation/Air.hpp/cpp) seems to implement what you need. Sadly it is not very well documented, so you'd have to work out the relation between code and physical formulation.
Sometimes physically incorrect simulations are easier to implement, have lighter computations, give the designer more control of the game, and makes the player able to better predict how the game will behave and have more fun.