Coroutines in Lua

[Zhen]

Hello
I was playing with coroutines in Lua, And using it to implement cooperative multitasking. I got the idea from Game Programming Gems 6.

I post the code and one example so everyone can test it, and play with it too.

I think it's very funny. And coroutines is an powerful tool of Lua.

Also, I post it, because I can't think usefull applications for coroutines in a game. I think that it can be useful for animations, gameplay of sprites,..and so on. I will be pleased for every comment.

Zhen

There is more information in http://en.wikipedia.org/wiki/Coroutines

[waruwaru]

Cool!  I was playing with coroutines example from Lua's online reference a little bit.  It's pretty neat.  I havn't really read up on it to see what it's capable of yet.  The usecase that I was thinking of (not sure if this will work) was one function polling wifi (which is searching for AP/wifi-clients), while another function to update the UI/getting inputs.  Kinda like when you try Download n' Play.  It would be really cool to be able to have something like that.

Waruwaru

[Zhen]

One think awesome if this system is that you can create several scheduler and asign diffente task to each. e.g: one scheduler for the polling task that you say. Other scheduler for the gameplay tasks and another for play music, animations,.. etc. And you can create a top level scheduler to exectute all other schedulers in a concurrent way.

A problem that i have now, and I was looking for is when tasks end, sometimes lua crash. You can try it changing the  ( while true do ) sentence with a ( while health >= 0 do ) sentence in the player function.

Zhen

[Zhen]

I just fixed the end problem,

with a check before execute the actual task.

Code:

function Scheduler:Execute( task )
if coroutine.status( task.co ) == "dead" then
self.tasks[ task.name ] = nil
return
end

self.active = task
--.....

[daltonlaffs]

ooooooooooooh. Nice one. This is an interesting program. I have learned stuff now, and this is cool. Player never dies, though. 

[Zhen]

  yes is true, the player remains alive at 1 HP. Well is easy to fix.

The die of entities with coroutines is a difficult task. I was thinking about have two or more task per entity. One task to execute the behaviour and another task to control the messages. One example of behaviour task can be:

Code:

-------------------------------------------------------------------------------
function MoveTo( scheduler, entity, x, y )
    local incx, incy
    if ( x - entity.x ) > 0 then
        incx = 1
    else
        incx = -1
    end

    if ( y - entity.y ) > 0 then
        incy = 1
    else
        incy = -1
    end
   
    while entity.x ~= x or entity.y ~= y do
        if entity.x ~= x then
            entity.x = entity.x + incx
        end
        if entity.y ~= y then
            entity.y = entity.y + incy
        end
        scheduler.Transfer()
    end
end

-------------------------------------------------------------------------------
function Boss()
    local fun = function( scheduler )
        local entity = {}
        entity.x = 0
        entity.y = 0
        while true do
            MoveTo( scheduler, entity, 0, 10 )
            MoveTo( scheduler, entity, 10, 10 )
            --Shot()
            MoveTo( scheduler, entity, 10, 0 )
            MoveTo( scheduler, entity, 0, 0 )
            scheduler:Sleep( 20 )
        end
    end

    return fun
end

The MoveTo function is a generic one, all entities can use it. We can have generic functions like PlayAnimation, MoveTo, gfx effects..etc. The main function of the 'boss' only use the generic functions.

Zhen.