Collision object physics API documentation

Version: stable

Functions and messages for collision object physics interaction with other objects (collisions and ray-casting) and control of physical behaviors.

Functions

physics.create_joint()

physics.create_joint(joint_type,collisionobject_a,joint_id,position_a,collisionobject_b,position_b,[properties])

Create a physics joint between two collision object components.

Note: Currently only supported in 2D physics.

PARAMETERS

physics.destroy_joint()

physics.destroy_joint(collisionobject,joint_id)

Destroy an already physics joint. The joint has to be created before a destroy can be issued.

Note: Currently only supported in 2D physics.

PARAMETERS

physics.get_gravity()

physics.get_gravity()

Get the gravity in runtime. The gravity returned is not global, it will return the gravity for the collection that the function is called from.

Note: For 2D physics the z component will always be zero.

PARAMETERS

RETURNS

EXAMPLES

function init(self)
    local gravity = physics.get_gravity()
    -- Inverse gravity!
    gravity = -gravity
    physics.set_gravity(gravity)
end

physics.get_joint_properties()

physics.get_joint_properties(collisionobject,joint_id)

Get a table for properties for a connected joint. The joint has to be created before properties can be retrieved.

Note: Currently only supported in 2D physics.

PARAMETERS

RETURNS

physics.get_joint_reaction_force()

physics.get_joint_reaction_force(collisionobject,joint_id)

Get the reaction force for a joint. The joint has to be created before the reaction force can be calculated.

Note: Currently only supported in 2D physics.

PARAMETERS

RETURNS

physics.get_joint_reaction_torque()

physics.get_joint_reaction_torque(collisionobject,joint_id)

Get the reaction torque for a joint. The joint has to be created before the reaction torque can be calculated.

Note: Currently only supported in 2D physics.

PARAMETERS

RETURNS

physics.raycast()

physics.raycast(from,to,groups)

Ray casts are used to test for intersections against collision objects in the physics world. Collision objects of types kinematic, dynamic and static are tested against. Trigger objects do not intersect with ray casts. Which collision objects to hit is filtered by their collision groups and can be configured through groups.

PARAMETERS

RETURNS

EXAMPLES

How to perform a ray cast synchronously:

function init(self)
    self.my_groups = {hash("my_group1"), hash("my_group2")}
end

function update(self, dt)
    -- request ray cast
    local result = physics.raycast(my_start, my_end, self.my_groups)
    if result ~= nil then
        -- act on the hit (see 'ray_cast_response')
    end
end

physics.raycast_async()

physics.raycast_async(from,to,groups,[request_id])

Ray casts are used to test for intersections against collision objects in the physics world. Collision objects of types kinematic, dynamic and static are tested against. Trigger objects do not intersect with ray casts. Which collision objects to hit is filtered by their collision groups and can be configured through groups. The actual ray cast will be performed during the physics-update.

• If an object is hit, the result will be reported via a ray_cast_response message.
• If there is no object hit, the result will be reported via a ray_cast_missed message.

PARAMETERS

EXAMPLES

How to perform a ray cast asynchronously:

function init(self)
    self.my_groups = {hash("my_group1"), hash("my_group2")}
end

function update(self, dt)
    -- request ray cast
    physics.raycast_async(my_start, my_end, self.my_groups)
end

function on_message(self, message_id, message, sender)
    -- check for the response
    if message_id == hash("ray_cast_response") then
        -- act on the hit
    elseif message_id == hash("ray_cast_missed") then
        -- act on the miss
    end
end

physics.set_gravity()

physics.set_gravity(gravity)

Set the gravity in runtime. The gravity change is not global, it will only affect the collection that the function is called from.

Note: For 2D physics the z component of the gravity vector will be ignored.

PARAMETERS

EXAMPLES

function init(self)
    -- Set "upside down" gravity for this collection.
    physics.set_gravity(vmath.vector3(0, 10.0, 0))
end

physics.set_hflip()

physics.set_hflip(url,flip)

Flips the collision shapes horizontally for a collision object

PARAMETERS

EXAMPLES

function init(self)
    self.fliph = true -- set on some condition
    physics.set_hflip("#collisionobject", self.fliph)
end

physics.set_joint_properties()

physics.set_joint_properties(collisionobject,joint_id,properties)

Updates the properties for an already connected joint. The joint has to be created before properties can be changed.

Note: Currently only supported in 2D physics.

PARAMETERS

physics.set_vflip()

physics.set_vflip(url,flip)

Flips the collision shapes vertically for a collision object

PARAMETERS

EXAMPLES

function init(self)
    self.flipv = true -- set on some condition
    physics.set_vflip("#collisionobject", self.flipv)
end

Constants

physics.JOINT_TYPE_FIXED

fixed joint type

The following properties are available when connecting a joint of JOINT_TYPE_FIXED type:

physics.JOINT_TYPE_HINGE

hinge joint type

The following properties are available when connecting a joint of JOINT_TYPE_HINGE type:

physics.JOINT_TYPE_SLIDER

slider joint type

The following properties are available when connecting a joint of JOINT_TYPE_SLIDER type:

physics.JOINT_TYPE_SPRING

spring joint type

The following properties are available when connecting a joint of JOINT_TYPE_SPRING type:

Messages

apply_force

applies a force on a collision object

Post this message to a collision-object-component to apply the specified force on the collision object. The collision object must be dynamic.

EXAMPLES

Assuming the instance of the script has a collision-object-component with id "co":

-- apply a force of 1 Newton towards world-x at the center of the game object instance
msg.post("#co", "apply_force", {force = vmath.vector3(1, 0, 0), position = go.get_world_position()})

collision_response

reports a collision between two collision objects

This message is broadcasted to every component of an instance that has a collision object, when the collision object collides with another collision object. For a script to take action when such a collision happens, it should check for this message in its on_message callback function.

This message only reports that a collision actually happened and will only be sent once per colliding pair and frame. To retrieve more detailed information, check for the contact_point_response instead.

EXAMPLES

How to take action when a collision occurs:

function on_message(self, message_id, message, sender)
    -- check for the message
    if message_id == hash("collision_response") then
        -- take action
    end
end

contact_point_response

reports a contact point between two collision objects

This message is broadcasted to every component of an instance that has a collision object, when the collision object has contact points with respect to another collision object. For a script to take action when such contact points occur, it should check for this message in its on_message callback function.

Since multiple contact points can occur for two colliding objects, this message can be sent multiple times in the same frame for the same two colliding objects. To only be notified once when the collision occurs, check for the collision_response message instead.

EXAMPLES

How to take action when a contact point occurs:

function on_message(self, message_id, message, sender)
    -- check for the message
    if message_id == hash("contact_point_response") then
        -- take action
    end
end

ray_cast_missed

reports a ray cast miss

This message is sent back to the sender of a ray_cast_request, if the ray didn't hit any collision object. See physics.raycast_async for examples of how to use it.

ray_cast_response

reports a ray cast hit

This message is sent back to the sender of a ray_cast_request, if the ray hit a collision object. See physics.raycast_async for examples of how to use it.

trigger_response

reports interaction (enter/exit) between a trigger collision object and another collision object

This message is broadcasted to every component of an instance that has a collision object, when the collision object interacts with another collision object and one of them is a trigger. For a script to take action when such an interaction happens, it should check for this message in its on_message callback function.

This message only reports that an interaction actually happened and will only be sent once per colliding pair and frame. To retrieve more detailed information, check for the contact_point_response instead.

EXAMPLES

How to take action when a trigger interaction occurs:

function on_message(self, message_id, message, sender)
    -- check for the message
    if message_id == hash("trigger_response") then
        if message.enter then
            -- take action for entry
        else
            -- take action for exit
        end
    end
end

Properties

angular_damping

The angular damping value for the collision object. Setting this value alters the damping of angular motion of the object (rotation). Valid values are between 0 (no damping) and 1 (full damping).

number collision object angular damping

EXAMPLES

How to decrease a collision object component's angular damping:

-- get angular damping from collision object "collisionobject" in gameobject "floater"
local target = "floater#collisionobject"
local damping = go.get(target, "angular_damping")
-- decrease it by 10%
go.set(target, "angular_damping", damping * 0.9)

angular_velocity

READ ONLY Returns the current angular velocity of the collision object component as a vector3. The velocity is measured as a rotation around the vector with a speed equivalent to the vector length in radians/s.

vector3 collision object angular velocity

EXAMPLES

How to query a collision object component's angular velocity:

-- get angular velocity from collision object "collisionobject" in gameobject "boulder"
-- this is a 2d game so rotation around z is the only one available.
local velocity = go.get("boulder#collisionobject", "angular_velocity.z")
-- do something interesting
if velocity < 0 then
    -- clockwise rotation
    ...
else
    -- counter clockwise rotation
    ...
end

linear_damping

The linear damping value for the collision object. Setting this value alters the damping of linear motion of the object. Valid values are between 0 (no damping) and 1 (full damping).

number collision object linear damping

EXAMPLES

How to increase a collision object component's linear damping:

-- get linear damping from collision object "collisionobject" in gameobject "floater"
local target = "floater#collisionobject"
local damping = go.get(target, "linear_damping")
-- increase it by 10% if it's below 0.9
if damping <= 0.9 then
    go.set(target, "linear_damping", damping * 1.1)
end

linear_velocity

READ ONLY Returns the current linear velocity of the collision object component as a vector3. The velocity is measured in units/s (pixels/s).

vector3 collision object linear velocity

EXAMPLES

How to query a collision object component's linear velocity:

-- get linear velocity from collision object "collisionobject" in gameobject "ship"
local source = "ship#collisionobject"
local velocity = go.get(source, "linear_velocity")
-- apply the velocity on target game object "boulder"'s collision object as a force
local target = "boulder#collisionobject"
local pos = go.get_position(target)
msg.post(target, "apply_force", { force = velocity, position = pos })

mass

READ ONLY Returns the defined physical mass of the collision object component as a number.

number collision object mass

EXAMPLES

How to query a collision object component's mass:

-- get mass from collision object component "boulder"
local mass = go.get("#boulder", "mass")
-- do something useful
assert(mass > 1)