Building Love2d with Vectors

[seeker14491]

I'm making a simple physics engine with Love2d to learn some physics. A lot of the calculations involve vectors, so I want to have vectors in Love2d. I know you can simulate vectors with just lua, but the performance isn't good. I found lua-vec http://code.google.com/p/lua-vec/ , which looks simple to use and has good performance, but I don't know how to make it work with Love2d. Can someone explain what I need to do to get it to work?

[T-Bone]

You could just use tables as vectors. The performance will then only depend on how you implement the vector operations. You should be able to get at least decent performance without too much effort.

Lua-vec seems quite tricky to use too, since it's a modification and extension of the language Lua.

[seeker14491]

Using tables is very slow, as seen here: http://code.google.com/p/lua-vec/wiki/Benchmarks . Is there a way to build a modified version of lua and then make a modified Love2d?

[ivan]

The biggest problem with vectors in my experience is the overhead on the garbage collector. If you have a function that returns a 'new' vector every frame your memory consumption can easily get out of hand and the GC cycles will become longer. Certain C implementations use a memory pool but it's still something I find quite unnecessary.
Lua has the option of returning multiple values so why not just use that to your advantage and avoid using vectors altogether:

Code: Select all

object.getPosition = function ( object )
  return self.posX, self.posY
end

Vector functionality can be implemented as a separate module, something like:

Code: Select all

x, y = object:getPosition()

vec.rotate ( x, y, math.pi )

x2, y2 = object2:getPosition()
x3, y3 = vec.add ( x, y, x2, y2 )

dist = vec.distance ( x, y, x2, y2 )

Lastly, are you sure that vectors are the bottleneck of your application or are you projecting ahead? If you are really insistent on using vectors, just implement them in Lua and if it becomes an issue you can always optimize by moving the code to a C extension later on (although I highly doubt the result will be noticeable).

[Roland_Yonaba]

I am inclined to think the same. Are you really sure that the problem is related to that built-in vector feature?
Anyway, I'd like to add that emulating vector with Lua is not really complicated. You can grab some examples you can adapt for your needs.
For instance, i have a simple implementation i am using for an on-going project.
There is also a very complete and clean emulation of vector operations inside vrld's hump (docs here). And I found any of them fast enough.

[kikito]

If you are using 2d vectors only, you can get away with using them as pairs of integers. So for example, a function that accepts two vectors looks like this:

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function sumVectors(x1,y1,x2,y2)
-- do something here
end

There's very little overhead compared to using native vectors, and the gc will perform much better.

[seeker14491]

Thanks for the suggestions, I'll try them out. I think they'll suit my needs.

[seeker14491]

If you are using 2d vectors only, you can get away with using them as pairs of integers. So for example, a function that accepts two vectors looks like this:

Code: Select all

function sumVectors(x1,y1,x2,y2)
-- do something here
end

There's very little overhead compared to using native vectors, and the gc will perform much better.

This is what I was doing. I wanted vectors because they would make my code shorter, easier to write and understand, and hopefully faster.

[miko]

Using tables is very slow, as seen here: http://code.google.com/p/lua-vec/wiki/Benchmarks . Is there a way to build a modified version of lua and then make a modified Love2d?

Did you notice that luajit is faster than lua-vec? Just use luajit-based love2d executables (as I always do).

[seeker14491]

Using tables is very slow, as seen here: http://code.google.com/p/lua-vec/wiki/Benchmarks . Is there a way to build a modified version of lua and then make a modified Love2d?

Did you notice that luajit is faster than lua-vec? Just use luajit-based love2d executables (as I always do).

Yeah, I did notice, but I didn't know it could be used with Love2D. Is everything compatible when used with Love2D?