Defold what should be part of self

Question

What should I put as fields and methods of self in game objects? Should I put position and velocity as fields? What methods should I put in self? What should be fields of ob? Should I put velocity and position as

self.velocity = vmath.vector3()

or something like

go.velocity = vmath.vector3()

Answer 1

The self object is a Lua userdata storage for script instance values. What you put there is completely up to you. The nice thing about storing values in self is that the self object is passed to all of the lifecycle functions of the script (init, final, update, on_input, on_message, on_reload). This means that you have quick access to the variables in all of the functions.

Storing the velocity in self is a good example of something that you may want to access and modify in different places in your script. For instance setting the velocity to some value in on_input when a button is pressed and then use the same velocity value in update to move the object.

go.velocity = vmath.vector3()

This is not good. What you are doing there is to assign the variable velocity to the globally accessible go.* namespace containing engine provided functions to manipulate game objects.

Answer 2

Basically you have three ways of declaring variables in game object scripts:

1. name = 'Felipe' (Global variable)
2. local name = 'Felipe' (Local variable :v)
3. self.name = 'Felipe' (This one must be inside of a method (init, update, on_message...))

Are they all the same? Answer: NO.

Global variables: If you declare a global variable in a script, then you can read and modify that variable in any other script.

*hero.script* --- (component of hero.go)

power = 100

*enemy.script* --- (component of enemy.go)

print(power) -- 100
power = power + 50
print(power) -- 150

Local variables: if you declare a local variable in a script and then you assign that script to two different game objects, they will share that variable.

*hero.script*

local power = 100

function on_message(self, message_id, message, sender)
    if message_id == hash('drink_poison') then
        power = power / 2
    end
end

Now we add ./hero.script component to hero.go and knight.go

*enemy.script* --- (component of enemy.go)

print(power) -- undefined

*controller.script* --- (component of controller.go)

msg.post('hero', 'drink_poison')

-- (hero.go): power -> 50
-- but because knight and hero share the same script and power was declared locally then:
-- (knight.go): power -> 50

Self.variables: self variables create unique copies for each game object the script is assigned to.

*hero.script*

function init(self)
    self.power = 100
end

function on_message(self, message_id, message, sender)
    if message_id == hash('drink_poison') then
        self.power = self.power / 2
    end
end

Now we add ./hero.script component to hero.go and knight.go

*enemy.script* --- (component of enemy.go)

print(power) -- undefined
print(self.power) -- undefined

*controller.script* --- (component of controller.go)

msg.post('hero', 'drink_poison')

-- (hero.go): power -> 50
-- (knight.go): power -> 100