Game object API documentation

Version: stable

Functions, core hooks, messages and constants for manipulation of game objects. The "go" namespace is accessible from game object script files.

Functions

final()

final(self)

This is a callback-function, which is called by the engine when a script component is finalized (destroyed). It can be used to e.g. take some last action, report the finalization to other game object instances, delete spawned objects or release user input focus (see release_input_focus).

PARAMETERS

EXAMPLES

function final(self)
    -- report finalization
    msg.post("my_friend_instance", "im_dead", {my_stats = self.some_value})
end

go.animate()

go.animate(url,property,playback,to,easing,duration,[delay],[complete_function])

This is only supported for numerical properties. If the node property is already being animated, that animation will be canceled and replaced by the new one.

If a complete_function (lua function) is specified, that function will be called when the animation has completed. By starting a new animation in that function, several animations can be sequenced together. See the examples for more information.

If you call go.animate() from a game object's final() function, any passed complete_function will be ignored and never called upon animation completion.

See the properties guide for which properties can be animated and the animation guide for how to animate them.

PARAMETERS

EXAMPLES

Animate the position of a game object to x = 10 during 1 second, then y = 20 during 1 second:

local function x_done(self, url, property)
    go.animate(go.get_id(), "position.y", go.PLAYBACK_ONCE_FORWARD, 20, go.EASING_LINEAR, 1)
end

function init(self)
    go.animate(go.get_id(), "position.x", go.PLAYBACK_ONCE_FORWARD, 10, go.EASING_LINEAR, 1, 0, x_done)
end

Animate the y position of a game object using a crazy custom easing curve:

local values = { 0, 0, 0, 0, 0, 0, 0, 0,
                 1, 1, 1, 1, 1, 1, 1, 1,
                 0, 0, 0, 0, 0, 0, 0, 0,
                 1, 1, 1, 1, 1, 1, 1, 1,
                 0, 0, 0, 0, 0, 0, 0, 0,
                 1, 1, 1, 1, 1, 1, 1, 1,
                 0, 0, 0, 0, 0, 0, 0, 0,
                 1, 1, 1, 1, 1, 1, 1, 1 }
local vec = vmath.vector(values)
go.animate("go", "position.y", go.PLAYBACK_LOOP_PINGPONG, 100, vec, 2.0)

go.cancel_animations()

go.cancel_animations(url,property)

By calling this function, all stored animations of the given property will be canceled.

See the properties guide for which properties can be animated and the animation guide for how to animate them.

PARAMETERS

EXAMPLES

Cancel the animation of the position of a game object:

go.cancel_animations(go.get_id(), "position")

go.delete()

go.delete([id],[recursive])

Delete one or more game objects identified by id. Deletion is asynchronous meaning that the game object(s) are scheduled for deletion which will happen at the end of the current frame. Note that game objects scheduled for deletion will be counted against max_instances in "game.project" until they are actually removed.

Deleting a game object containing a particle FX component emitting particles will not immediately stop the particle FX from emitting particles. You need to manually stop the particle FX using particlefx.stop(). Deleting a game object containing a sound component that is playing will not immediately stop the sound from playing. You need to manually stop the sound using sound.stop().

PARAMETERS

EXAMPLES

This example demonstrates how to delete game objects

-- Delete the script game object
go.delete()
-- Delete a game object with the id "my_game_object".
local id = go.get_id("my_game_object") -- retrieve the id of the game object to be deleted
go.delete(id)
-- Delete a list of game objects.
local ids = { hash("/my_object_1"), hash("/my_object_2"), hash("/my_object_3") }
go.delete(ids)

This example demonstrates how to delete a game objects and their children (child to parent order)

-- Delete the script game object and it's children
go.delete(true)
-- Delete a game object with the id "my_game_object" and it's children.
local id = go.get_id("my_game_object") -- retrieve the id of the game object to be deleted
go.delete(id, true)
-- Delete a list of game objects and their children.
local ids = { hash("/my_object_1"), hash("/my_object_2"), hash("/my_object_3") }
go.delete(ids, true)

go.get()

go.get(url,property)

PARAMETERS

RETURNS

EXAMPLES

Get a property "speed" from a script "player", the property must be declared in the player-script:

go.property("speed", 50)

Then in the calling script (assumed to belong to the same game object, but does not have to):

local speed = go.get("#player", "speed")

go.get_id()

go.get_id([path])

Returns or constructs an instance identifier. The instance id is a hash of the absolute path to the instance.

• If path is specified, it can either be absolute or relative to the instance of the calling script.
• If path is not specified, the id of the game object instance the script is attached to will be returned.

PARAMETERS

RETURNS

EXAMPLES

For the instance with path /my_sub_collection/my_instance, the following calls are equivalent:

local id = go.get_id() -- no path, defaults to the instance containing the calling script
print(id) --> hash: [/my_sub_collection/my_instance]

local id = go.get_id("/my_sub_collection/my_instance") -- absolute path
print(id) --> hash: [/my_sub_collection/my_instance]

local id = go.get_id("my_instance") -- relative path
print(id) --> hash: [/my_sub_collection/my_instance]

go.get_position()

go.get_position([id])

The position is relative the parent (if any). Use go.get_world_position to retrieve the global world position.

PARAMETERS

RETURNS

EXAMPLES

Get the position of the game object instance the script is attached to:

local p = go.get_position()

Get the position of another game object instance "my_gameobject":

local pos = go.get_position("my_gameobject")

go.get_rotation()

go.get_rotation([id])

The rotation is relative to the parent (if any). Use go.get_world_rotation to retrieve the global world rotation.

PARAMETERS

RETURNS

EXAMPLES

Get the rotation of the game object instance the script is attached to:

local r = go.get_rotation()

Get the rotation of another game object instance with id "x":

local r = go.get_rotation("x")

go.get_scale()

go.get_scale([id])

The scale is relative the parent (if any). Use go.get_world_scale to retrieve the global world 3D scale factor.

PARAMETERS

RETURNS

EXAMPLES

Get the scale of the game object instance the script is attached to:

local s = go.get_scale()

Get the scale of another game object instance with id "x":

local s = go.get_scale("x")

go.get_scale_uniform()

go.get_scale_uniform([id])

The uniform scale is relative the parent (if any). If the underlying scale vector is non-uniform the min element of the vector is returned as the uniform scale factor.

PARAMETERS

RETURNS

EXAMPLES

Get the scale of the game object instance the script is attached to:

local s = go.get_scale_uniform()

Get the uniform scale of another game object instance with id "x":

local s = go.get_scale_uniform("x")

go.get_world_position()

go.get_world_position([id])

Use go.get_position to retrieve the position relative to the parent.

PARAMETERS

RETURNS

EXAMPLES

Get the world position of the game object instance the script is attached to:

local p = go.get_world_position()

Get the world position of another game object instance with id "x":

local p = go.get_world_position("x")

go.get_world_rotation()

go.get_world_rotation([id])

Use go.get_rotation to retrieve the rotation relative to the parent.

PARAMETERS

RETURNS

EXAMPLES

Get the world rotation of the game object instance the script is attached to:

local r = go.get_world_rotation()

Get the world rotation of another game object instance with id "x":

local r = go.get_world_rotation("x")

go.get_world_scale()

go.get_world_scale([id])

Use go.get_scale to retrieve the 3D scale factor relative to the parent. This vector is derived by decomposing the transformation matrix and should be used with care. For most cases it should be fine to use go.get_world_scale_uniform instead.

PARAMETERS

RETURNS

EXAMPLES

Get the world 3D scale of the game object instance the script is attached to:

local s = go.get_world_scale()

Get the world scale of another game object instance "x":

local s = go.get_world_scale("x")

go.get_world_scale_uniform()

go.get_world_scale_uniform([id])

Use go.get_scale_uniform to retrieve the scale factor relative to the parent.

PARAMETERS

RETURNS

EXAMPLES

Get the world scale of the game object instance the script is attached to:

local s = go.get_world_scale_uniform()

Get the world scale of another game object instance with id "x":

local s = go.get_world_scale_uniform("x")

go.get_world_transform()

go.get_world_transform([id])

PARAMETERS

RETURNS

EXAMPLES

Get the world transform of the game object instance the script is attached to:

local m = go.get_world_transform()

Get the world transform of another game object instance with id "x":

local m = go.get_world_transform("x")

go.property()

go.property(name,value)

This function defines a property which can then be used in the script through the self-reference. The properties defined this way are automatically exposed in the editor in game objects and collections which use the script. Note that you can only use this function outside any callback-functions like init and update.

PARAMETERS

EXAMPLES

This example demonstrates how to define a property called "health" in a script. The health is decreased whenever someone sends a message called "take_damage" to the script.

go.property("health", 100)

function init(self)
    -- prints 100 to the output
    print(self.health)
end

function on_message(self, message_id, message, sender)
    if message_id == hash("take_damage") then
        self.health = self.health - message.damage
        print("Ouch! My health is now: " .. self.health)
    end
end

go.set()

go.set(url,property,value)

PARAMETERS

EXAMPLES

Set a property "speed" of a script "player", the property must be declared in the player-script:

go.property("speed", 50)

Then in the calling script (assumed to belong to the same game object, but does not have to):

go.set("#player", "speed", 100)

go.set_parent()

go.set_parent([id],[parent_id],[keep_world_transform])

Sets the parent for a game object instance. This means that the instance will exist in the geometrical space of its parent, like a basic transformation hierarchy or scene graph. If no parent is specified, the instance will be detached from any parent and exist in world space.

PARAMETERS

EXAMPLES

Attach myself to another instance "my_parent":

go.set_parent(go.get_id(),go.get_id("my_parent"))

Attach an instance "my_instance" to another instance "my_parent":

go.set_parent(go.get_id("my_instance"),go.get_id("my_parent"))

Detach an instance "my_instance" from its parent (if any):

go.set_parent(go.get_id("my_instance"))

go.set_position()

go.set_position(position,[id])

The position is relative to the parent (if any). The global world position cannot be manually set.

PARAMETERS

EXAMPLES

Set the position of the game object instance the script is attached to:

local p = ...
go.set_position(p)

Set the position of another game object instance with id "x":

local p = ...
go.set_position(p, "x")

go.set_rotation()

go.set_rotation(rotation,[id])

The rotation is relative to the parent (if any). The global world rotation cannot be manually set.

PARAMETERS

EXAMPLES

Set the rotation of the game object instance the script is attached to:

local r = ...
go.set_rotation(r)

Set the rotation of another game object instance with id "x":

local r = ...
go.set_rotation(r, "x")

go.set_scale()

go.set_scale(scale,[id])

The scale factor is relative to the parent (if any). The global world scale factor cannot be manually set.

Physics are currently not affected when setting scale from this function.

PARAMETERS

EXAMPLES

Set the scale of the game object instance the script is attached to:

local s = vmath.vector3(2.0, 1.0, 1.0)
go.set_scale(s)

Set the scale of another game object instance with id "x":

local s = 1.2
go.set_scale(s, "x")

init()

init(self)

This is a callback-function, which is called by the engine when a script component is initialized. It can be used to set the initial state of the script.

PARAMETERS

EXAMPLES

function init(self)
    -- set up useful data
    self.my_value = 1
end

on_input()

on_input(self,action_id,action)

This is a callback-function, which is called by the engine when user input is sent to the game object instance of the script. It can be used to take action on the input, e.g. move the instance according to the input.

For an instance to obtain user input, it must first acquire input focus through the message acquire_input_focus.

Any instance that has obtained input will be put on top of an input stack. Input is sent to all listeners on the stack until the end of stack is reached, or a listener returns true to signal that it wants input to be consumed.

See the documentation of acquire_input_focus for more information.

The action parameter is a table containing data about the input mapped to the action_id. For mapped actions it specifies the value of the input and if it was just pressed or released. Actions are mapped to input in an input_binding-file.

Mouse movement is specifically handled and uses nil as its action_id. The action only contains positional parameters in this case, such as x and y of the pointer.

Here is a brief description of the available table fields:

Touch input table:

PARAMETERS

RETURNS

EXAMPLES

This example demonstrates how a game object instance can be moved as a response to user input.

function init(self)
    -- acquire input focus
    msg.post(".", "acquire_input_focus")
    -- maximum speed the instance can be moved
    self.max_speed = 2
    -- velocity of the instance, initially zero
    self.velocity = vmath.vector3()
end

function update(self, dt)
    -- move the instance
    go.set_position(go.get_position() + dt * self.velocity)
end

function on_input(self, action_id, action)
    -- check for movement input
    if action_id == hash("right") then
        if action.released then -- reset velocity if input was released
            self.velocity = vmath.vector3()
        else -- update velocity
            self.velocity = vmath.vector3(action.value * self.max_speed, 0, 0)
        end
    end
end

on_message()

on_message(self,message_id,message,sender)

This is a callback-function, which is called by the engine whenever a message has been sent to the script component. It can be used to take action on the message, e.g. send a response back to the sender of the message.

The message parameter is a table containing the message data. If the message is sent from the engine, the documentation of the message specifies which data is supplied.

PARAMETERS

EXAMPLES

This example demonstrates how a game object instance, called "a", can communicate with another instance, called "b". It is assumed that both script components of the instances has id "script".

Script of instance "a":

function init(self)
    -- let b know about some important data
    msg.post("b#script", "my_data", {important_value = 1})
end

Script of instance "b":

function init(self)
    -- store the url of instance "a" for later use, by specifying nil as socket we
    -- automatically use our own socket
    self.a_url = msg.url(nil, go.get_id("a"), "script")
end

function on_message(self, message_id, message, sender)
    -- check message and sender
    if message_id == hash("my_data") and sender == self.a_url then
        -- use the data in some way
        self.important_value = message.important_value
    end
end

on_reload()

on_reload(self)

This is a callback-function, which is called by the engine when the script component is reloaded, e.g. from the editor. It can be used for live development, e.g. to tweak constants or set up the state properly for the instance.

PARAMETERS

EXAMPLES

This example demonstrates how to tweak the speed of a game object instance that is moved on user input.

function init(self)
    -- acquire input focus
    msg.post(".", "acquire_input_focus")
    -- maximum speed the instance can be moved, this value is tweaked in the on_reload function below
    self.max_speed = 2
    -- velocity of the instance, initially zero
    self.velocity = vmath.vector3()
end

function update(self, dt)
    -- move the instance
    go.set_position(go.get_position() + dt * self.velocity)
end

function on_input(self, action_id, action)
    -- check for movement input
    if action_id == hash("right") then
        if action.released then -- reset velocity if input was released
            self.velocity = vmath.vector3()
        else -- update velocity
            self.velocity = vmath.vector3(action.value * self.max_speed, 0, 0)
        end
    end
end

function on_reload(self)
    -- edit this value and reload the script component
    self.max_speed = 100
end

update()

update(self,dt)

This is a callback-function, which is called by the engine every frame to update the state of a script component. It can be used to perform any kind of game related tasks, e.g. moving the game object instance.

PARAMETERS

EXAMPLES

This example demonstrates how to move a game object instance through the script component:

function init(self)
    -- set initial velocity to be 1 along world x-axis
    self.my_velocity = vmath.vector3(1, 0, 0)
end

function update(self, dt)
    -- move the game object instance
    go.set_position(go.get_position() + dt * self.my_velocity)
end

Constants

go.EASING_INBACK

in-back

go.EASING_INBOUNCE

in-bounce

go.EASING_INCIRC

in-circlic

go.EASING_INCUBIC

in-cubic

go.EASING_INELASTIC

in-elastic

go.EASING_INEXPO

in-exponential

go.EASING_INOUTBACK

in-out-back

go.EASING_INOUTBOUNCE

in-out-bounce

go.EASING_INOUTCIRC

in-out-circlic

go.EASING_INOUTCUBIC

in-out-cubic

go.EASING_INOUTELASTIC

in-out-elastic

go.EASING_INOUTEXPO

in-out-exponential

go.EASING_INOUTQUAD

in-out-quadratic

go.EASING_INOUTQUART

in-out-quartic

go.EASING_INOUTQUINT

in-out-quintic

go.EASING_INOUTSINE

in-out-sine

go.EASING_INQUAD

in-quadratic

go.EASING_INQUART

in-quartic

go.EASING_INQUINT

in-quintic

go.EASING_INSINE

in-sine

go.EASING_LINEAR

linear interpolation

go.EASING_OUTBACK

out-back

go.EASING_OUTBOUNCE

out-bounce

go.EASING_OUTCIRC

out-circlic

go.EASING_OUTCUBIC

out-cubic

go.EASING_OUTELASTIC

out-elastic

go.EASING_OUTEXPO

out-exponential

go.EASING_OUTINBACK

out-in-back

go.EASING_OUTINBOUNCE

out-in-bounce

go.EASING_OUTINCIRC

out-in-circlic

go.EASING_OUTINCUBIC

out-in-cubic

go.EASING_OUTINELASTIC

out-in-elastic

go.EASING_OUTINEXPO

out-in-exponential

go.EASING_OUTINQUAD

out-in-quadratic

go.EASING_OUTINQUART

out-in-quartic

go.EASING_OUTINQUINT

out-in-quintic

go.EASING_OUTINSINE

out-in-sine

go.EASING_OUTQUAD

out-quadratic

go.EASING_OUTQUART

out-quartic

go.EASING_OUTQUINT

out-quintic

go.EASING_OUTSINE

out-sine

go.PLAYBACK_LOOP_BACKWARD

loop backward

go.PLAYBACK_LOOP_FORWARD

loop forward

go.PLAYBACK_LOOP_PINGPONG

ping pong loop

go.PLAYBACK_NONE

no playback

go.PLAYBACK_ONCE_BACKWARD

once backward

go.PLAYBACK_ONCE_FORWARD

once forward

go.PLAYBACK_ONCE_PINGPONG

once ping pong

Messages

acquire_input_focus

acquires the user input focus

Post this message to a game object instance to make that instance acquire the user input focus.

User input is distributed by the engine to every instance that has requested it. The last instance to request focus will receive it first. This means that the scripts in the instance will have first-hand-chance at reacting on user input, possibly consuming it (by returning true from on_input) so that no other instances can react on it. The most common case is for a script to send this message to itself when it needs to respond to user input.

A script belonging to an instance which has the user input focus will receive the input actions in its on_input callback function. See on_input for more information on how user input can be handled.

EXAMPLES

This example demonstrates how to acquire and act on user input.

function init(self)
    -- acquire input focus as soon as the instance has been initialized
    msg.post(".", "acquire_input_focus")
end

function on_input(self, action_id, action)
    -- check which input we received
    if action_id == hash("my_action") then
        -- act on the input
        self.my_action_amount = action.value
    end
end

disable

disables the receiving component

This message disables the receiving component. All components are enabled by default, which means they will receive input, updates and be a part of the simulation. A component is disabled when it receives the disable message.

Components that currently supports this message are:

• Collection Proxy
• Collision Object
• Gui
• Label
• Spine Model
• Sprite
• Tile Grid
• Model

EXAMPLES

Disable the component "my_component":

msg.post("#my_component", "disable")

enable

enables the receiving component

This message enables the receiving component. All components are enabled by default, which means they will receive input, updates and be a part of the simulation. A component is disabled when it receives the disable message.

Components that currently supports this message are:

• Collection Proxy
• Collision Object
• Gui
• Label
• Spine Model
• Sprite
• Tile Grid
• Model

EXAMPLES

Enable the component "my_component":

msg.post("#my_component", "enable")

release_input_focus

releases the user input focus

Post this message to an instance to make that instance release the user input focus. See acquire_input_focus for more information on how the user input handling works.

EXAMPLES

How to make a game object stop receiving input:

msg.post(".", "release_input_focus")

set_parent

sets the parent of the receiving instance

When this message is sent to an instance, it sets the parent of that instance. This means that the instance will exist in the geometrical space of its parent, like a basic transformation hierarchy or scene graph. If no parent is specified, the instance will be detached from any parent and exist in world space. A script can send this message to itself to set the parent of its instance.

EXAMPLES

Attach myself to another instance "my_parent":

msg.post(".", "set_parent", {parent_id = go.get_id("my_parent")})

Attach an instance "my_instance" to another instance "my_parent":

msg.post("my_instance", "set_parent", {parent_id = go.get_id("my_parent")})

Detach an instance "my_instance" from its parent (if any):

msg.post("my_instance", "set_parent")

Properties

euler

The rotation of the game object expressed in Euler angles. Euler angles are specified in degrees in the interval (-360, 360). The type of the property is vector3.

vector3 game object euler rotation

EXAMPLES

How to set a game object's rotation with euler angles, either as a vector3 or selecting a specific dimension:

function init(self)
  -- set "player" euler z rotation component to 45 degrees around z.
  local rotz = 45
  go.set("player", "euler.z", rotz)
  local rot = go.get("player", "euler")
  -- do something useful
  assert(rot.z == rotz)
end

position

The position of the game object. The type of the property is vector3.

vector3 game object position

EXAMPLES

How to query a game object's position, either as a vector3 or selecting a specific dimension:

function init(self)
  -- get position from "player"
  local pos = go.get("player", "position")
  local posx = go.get("player", "position.x")
  -- do something useful
  assert(pos.x == posx)
end

rotation

The rotation of the game object. The type of the property is quaternion.

quaternion game object rotation

EXAMPLES

How to set a game object's rotation:

function init(self)
  -- set "player" rotation to 45 degrees around z.
  local rotz = vmath.quat_rotation_z(3.141592 / 4)
  go.set("player", "rotation", rotz)
end

scale

The uniform scale of the game object. The type of the property is number.

number game object scale

EXAMPLES

How to scale a game object:

function init(self)
  -- Double the scaling on "player"
  local scale = go.get("player", "scale")
  go.set("player", "scale", scale * 2)
end