Collision object physics API documentation
The following properties are available when connecting a joint of JOINT_TYPE_SPRING
type:
length - The natural length between the anchor points.
frequency - The mass-spring-damper frequency in Hertz. A value of 0 disables softness.
damping - The damping ratio. 0 = no damping, 1 = critical damping.
The following properties are available when connecting a joint of JOINT_TYPE_FIXED
type:
max_length - The maximum length of the rope.
The following properties are available when connecting a joint of JOINT_TYPE_HINGE
type:
reference_angle - The bodyB angle minus bodyA angle in the reference state (radians).
lower_angle - The lower angle for the joint limit (radians).
upper_angle - The upper angle for the joint limit (radians).
max_motor_torque - The maximum motor torque used to achieve the desired motor speed. Usually in N-m.
motor_speed - The desired motor speed. Usually in radians per second.
enable_limit - A flag to enable joint limits.
enable_motor - A flag to enable the joint motor.
joint_angle - READ ONLYCurrent joint angle in radians.
(Read only field, available from physics.get_joint_properties()
)
joint_speed - READ ONLYCurrent joint angle speed in radians per second.
(Read only field, available from physics.get_joint_properties()
)
The following properties are available when connecting a joint of JOINT_TYPE_SLIDER
type:
local_axis_a - The local translation unit axis in bodyA.
reference_angle - The constrained angle between the bodies: bodyB_angle - bodyA_angle.
enable_limit - Enable/disable the joint limit.
lower_translation - The lower translation limit, usually in meters.
upper_translation - The upper translation limit, usually in meters.
enable_motor - Enable/disable the joint motor.
max_motor_force - The maximum motor torque, usually in N-m.
motor_speed - The desired motor speed in radians per second.
joint_translation - READ ONLYCurrent joint translation, usually in meters.
(Read only field, available from physics.get_joint_properties()
)
joint_speed - READ ONLYCurrent joint translation speed, usually in meters per second.
(Read only field, available from physics.get_joint_properties()
)
The following properties are available when connecting a joint of JOINT_TYPE_WELD
type:
reference_angle - READ ONLYThe bodyB angle minus bodyA angle in the reference state (radians).
frequency - The mass-spring-damper frequency in Hertz. Rotation only. Disable softness with a value of 0.
damping - The damping ratio. 0 = no damping, 1 = critical damping.
The following properties are available when connecting a joint of JOINT_TYPE_WHEEL
type:
local_axis_a - The local translation unit axis in bodyA.
max_motor_torque - The maximum motor torque used to achieve the desired motor speed. Usually in N-m.
motor_speed - The desired motor speed in radians per second.
enable_motor - Enable/disable the joint motor.
frequency - The mass-spring-damper frequency in Hertz. Rotation only. Disable softness with a value of 0.
damping - The spring damping ratio. 0 = no damping, 1 = critical damping.
joint_translation - READ ONLYCurrent joint translation, usually in meters.
(Read only field, available from physics.get_joint_properties()
)
joint_speed - READ ONLYCurrent joint translation speed, usually in meters per second.
(Read only field, available from physics.get_joint_properties()
)
READ ONLY Returns the defined physical mass of the collision object component as a number.
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)
The current linear velocity of the collision object component as a vector3. The velocity is measured in units/s (pixels/s).
How to query and modify 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")
-- decrease it by 10%
go.set(source, "linear_velocity", velocity * 0.9)
-- 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 })
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.
How to query and modify a collision object component's angular velocity:
-- get angular velocity from collision object "collisionobject" in gameobject "boulder"
local velocity = go.get("boulder#collisionobject", "angular_velocity")
-- do something interesting
if velocity.z < 0 then
-- clockwise rotation
...
else
-- counter clockwise rotation
...
end
-- decrease it by 10%
velocity.z = velocity.z * 0.9
go.set("boulder#collisionobject", "angular_velocity", velocity * 0.9)
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).
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
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).
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)
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.
from - the world position of the start of the ray
to - the world position of the end of the ray
groups - a lua table containing the hashed groups for which to test collisions against
[request_id] - a number between [0,-255]. It will be sent back in the response for identification, 0 by default
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
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
.
from - the world position of the start of the ray
to - the world position of the end of the ray
groups - a lua table containing the hashed groups for which to test collisions against
options - a lua table containing options for the raycast.
all
true
to return all ray cast hits. If false
, it will only return the closest hit.result - It returns a list. If missed it returns nil
. See ray_cast_response for details on the returned values.
How to perform a ray cast synchronously:
function init(self)
self.groups = {hash("world"), hash("enemy")}
end
function update(self, dt)
-- request ray cast
local result = physics.raycast(from, to, self.groups, {all=true})
if result ~= nil then
-- act on the hit (see 'ray_cast_response')
for _,result in ipairs(results) do
handle_result(result)
end
end
end
Create a physics joint between two collision object components. Note: Currently only supported in 2D physics.
joint_type - the joint type
collisionobject_a - first collision object
joint_id - id of the joint
position_a - local position where to attach the joint on the first collision object
collisionobject_b - second collision object
position_b - local position where to attach the joint on the second collision object
[properties] - optional joint specific properties table
See each joint type for possible properties field. The one field that is accepted for all joint types is:
- boolean collide_connected
: Set this flag to true if the attached bodies should collide.
Destroy an already physics joint. The joint has to be created before a destroy can be issued. Note: Currently only supported in 2D physics.
collisionobject - collision object where the joint exist
joint_id - id of the joint
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.
collisionobject - collision object where the joint exist
joint_id - id of the joint
properties - properties table. See the joint types for what fields are available, the only field available for all types is:
collide_connected
: Set this flag to true if the attached bodies should collide.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.
collisionobject - collision object where the joint exist
joint_id - id of the joint
properties - joint specific properties table
Note: The collide_connected
field cannot be updated/changed after a connection has been made.
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.
collisionobject - collision object where the joint exist
joint_id - id of the joint
force - reaction force for the joint
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.
collisionobject - collision object where the joint exist
joint_id - id of the joint
torque - the reaction torque on bodyB in N*m.
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.
gravity - the new gravity vector
function init(self)
-- Set "upside down" gravity for this collection.
physics.set_gravity(vmath.vector3(0, 10.0, 0))
end
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.
gravity - gravity vector of collection
function init(self)
local gravity = physics.get_gravity()
-- Inverse gravity!
gravity = -gravity
physics.set_gravity(gravity)
end
Flips the collision shapes horizontally for a collision object
url - the collision object that should flip its shapes
flip - true
if the collision object should flip its shapes, false
if not
function init(self)
self.fliph = true -- set on some condition
physics.set_hflip("#collisionobject", self.fliph)
end
Flips the collision shapes vertically for a collision object
url - the collision object that should flip its shapes
flip - true
if the collision object should flip its shapes, false
if not
function init(self)
self.flipv = true -- set on some condition
physics.set_vflip("#collisionobject", self.flipv)
end
Collision objects tend to fall asleep when inactive for a small period of time for efficiency reasons. This function wakes them up.
url - the collision object to wake.
function on_input(self, action_id, action)
if action_id == hash("test") and action.pressed then
physics.wakeup("#collisionobject")
end
end
Updates the group property of a collision object to the specified string value. The group name should exist i.e. have been used in a collision object in the editor.
url - the collision object affected.
group - the new group name to be assigned.
local function change_collision_group()
physics.set_group("#collisionobject", "enemy")
end
Returns the group name of a collision object as a hash.
url - the collision object to return the group of.
group - hash value of the group.
local function check_is_enemy()
local group = physics.get_group("#collisionobject")
return group == hash("enemy")
end
Sets or clears the masking of a group (maskbit) in a collision object.
url - the collision object to change the mask of.
group - the name of the group (maskbit) to modify in the mask.
maskbit - boolean value of the new maskbit. 'true' to enable, 'false' to disable.
local function make_invincible()
-- no longer collide with the "bullet" group
physics.set_maskbit("#collisionobject", "bullet", false)
end
Returns true if the specified group is set in the mask of a collision object, false otherwise.
url - the collision object to check the mask of.
group - the name of the group to check for.
maskbit - boolean value of the maskbit. 'true' if present, 'false' otherwise.
local function is_invincible()
-- check if the collisionobject would collide with the "bullet" group
local invincible = physics.get_maskbit("#collisionobject", "bullet")
return invincible
end
Gets collision shape data from a collision object
url - the collision object.
shape - the name of the shape to get data for.
table - A table containing meta data about the physics shape
type
physics.SHAPE_TYPE_SPHERE
physics.SHAPE_TYPE_BOX
physics.SHAPE_TYPE_CAPSULE
Only supported for 3D physicsphysics.SHAPE_TYPE_HULL
diameter
dimensions
vmath.vector3
of the box dimensionsdiameter
height
local function get_shape_meta()
local sphere = physics.get_shape("#collisionobject", "my_sphere_shape")
-- returns a table with sphere.diameter
return sphere
end
Sets collision shape data for a collision object. Please note that updating data in 3D can be quite costly for box and capsules. Because of the physics engine, the cost comes from having to recreate the shape objects when certain shapes needs to be updated.
url - the collision object.
shape - the name of the shape to get data for.
table - the shape data to update the shape with. See physics.get_shape for a detailed description of each field in the data table.
local function set_shape_data()
-- set capsule shape data
local data = {}
data.diameter = 10
data.height = 20
physics.set_shape("#collisionobject", "my_capsule_shape", data)
-- set sphere shape data
data = {}
data.diameter = 10
physics.set_shape("#collisionobject", "my_sphere_shape", data)
-- set box shape data
data = {}
data.dimensions = vmath.vector3(10, 10, 5)
physics.set_shape("#collisionobject", "my_box_shape", data)
end
sets a physics world event listener. If a function is set, physics messages will no longer be sent.
callback - A callback that receives information about all the physics interactions in this physics world.
self
event
data
local function physics_world_listener(self, event, data)
if event == hash("contact_point_event") then
pprint(data)
-- {
-- distance = 0.0714111328125,
-- applied_impulse = 310.00769042969,
-- a = {
-- position = vmath.vector3(446, 371, 0),
-- relative_velocity = vmath.vector3(1.1722083854693e-06, -20.667181015015, -0),
-- mass = 0,
-- group = hash: [default],
-- id = hash: [/flat],
-- normal = vmath.vector3(-0, -1, -0)
-- },
-- b = {
-- position = vmath.vector3(185, 657.92858886719, 0),
-- relative_velocity = vmath.vector3(-1.1722083854693e-06, 20.667181015015, 0),
-- mass = 10,
-- group = hash: [default],
-- id = hash: [/go2],
-- normal = vmath.vector3(0, 1, 0)
-- }
-- }
elseif event == hash("collision_event") then
pprint(data)
-- {
-- a = {
-- group = hash: [default],
-- position = vmath.vector3(183, 666, 0),
-- id = hash: [/go1]
-- },
-- b = {
-- group = hash: [default],
-- position = vmath.vector3(185, 704.05865478516, 0),
-- id = hash: [/go2]
-- }
-- }
elseif event == hash("trigger_event") then
pprint(data)
-- {
-- enter = true,
-- b = {
-- group = hash: [default],
-- id = hash: [/go2]
-- },
-- a = {
-- group = hash: [default],
-- id = hash: [/go1]
-- }
-- },
elseif event == hash("ray_cast_response") then
pprint(data)
--{
-- group = hash: [default],
-- request_id = 0,
-- position = vmath.vector3(249.92222595215, 249.92222595215, 0),
-- fraction = 0.68759721517563,
-- normal = vmath.vector3(0, 1, 0),
-- id = hash: [/go]
-- }
elseif event == hash("ray_cast_missed") then
pprint(data)
-- {
-- request_id = 0
--},
end
end
function init(self)
physics.set_listener(physics_world_listener)
end
The function recalculates the density of each shape based on the total area of all shapes and the specified mass, then updates the mass of the body accordingly. Note: Currently only supported in 2D physics.
collisionobject - the collision object whose mass needs to be updated.
mass - the new mass value to set for the collision object.
physics.update_mass("#collisionobject", 14)
Post this message to a collision-object-component to apply the specified force on the collision object. The collision object must be dynamic.
force - the force to be applied on the collision object, measured in Newton
position - the position where the force should be applied
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()})
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.
other_id - the id of the instance the collision object collided with
other_position - the world position of the instance the collision object collided with
other_group - the collision group of the other collision object
own_group - the collision group of the own collision object
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
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.
position - world position of the contact point
normal - normal in world space of the contact point, which points from the other object towards the current object
relative_velocity - the relative velocity of the collision object as observed from the other object
distance - the penetration distance between the objects, which is always positive
applied_impulse - the impulse the contact resulted in
life_time - life time of the contact, not currently used
mass - the mass of the current collision object in kg
other_mass - the mass of the other collision object in kg
other_id - the id of the instance the collision object is in contact with
other_position - the world position of the other collision object
other_group - the collision group of the other collision object
own_group - the collision group of the own collision object
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
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.
other_id - the id of the instance the collision object collided with
enter - if the interaction was an entry or not
other_group - the collision group of the triggering collision object
own_group - the collision group of the own collision object
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
This message is sent back to the sender of a ray_cast_request, or to the physics world listener if it is set (see physics.set_listener), if the ray hits a collision object. See physics.raycast_async for examples of how to use it.
fraction - the fraction of the hit measured along the ray, where 0 is the start of the ray and 1 is the end
position - the world position of the hit
normal - the normal of the surface of the collision object where it was hit
id - the instance id of the hit collision object
group - the collision group of the hit collision object as a hashed name
request_id - id supplied when the ray cast was requested
This message is sent back to the sender of a ray_cast_request, or to the physics world listener if it is set (see physics.set_listener), if the ray didn't hit any collision object. See physics.raycast_async for examples of how to use it.
request_id - id supplied when the ray cast was requested
See physics.set_listener. This message is sent to a function specified in physics.set_listener when a collision object has contact points with another collision object. Since multiple contact points can occur for two colliding objects, this event 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_event event instead.
applied_impulse - the impulse the contact resulted in
distance - the penetration distance between the objects, which is always positive
a - contact point information for object A
position
id
group
relative_velocity
mass
normal
b - contact point information for object B
position
id
group
relative_velocity
mass
normal
How to take action when a contact point occurs:
physics.set_listener(function(self, event, data)
if event == hash("contact_point_event") then
pprint(data)
-- {
-- applied_impulse = 310.00769042969,
-- distance = 0.0714111328125,
-- a = {
-- position = vmath.vector3(446, 371, 0),
-- relative_velocity = vmath.vector3(1.1722083854693e-06, -20.667181015015, -0),
-- mass = 0,
-- group = hash: [default],
-- id = hash: [/flat],
-- normal = vmath.vector3(-0, -1, -0)
-- },
-- b = {
-- position = vmath.vector3(185, 657.92858886719, 0),
-- relative_velocity = vmath.vector3(-1.1722083854693e-06, 20.667181015015, 0),
-- mass = 10,
-- group = hash: [default],
-- id = hash: [/go2],
-- normal = vmath.vector3(0, 1, 0)
-- },
-- }
end
end)
See physics.set_listener. This message is sent to a function specified in physics.set_listener when two collision objects collide. This message only reports that a collision has occurred and will be sent once per frame and per colliding pair. For more detailed information, check for the contact_point_event.
a - collision information for object A
position
id
group
b - collision information for object B
position
id
group
How to take action when a collision occurs:
physics.set_listener(function(self, event, data)
if event == hash("collision_event") then
pprint(data)
-- {
-- a = {
-- group = hash: [default],
-- position = vmath.vector3(183, 666, 0),
-- id = hash: [/go1]
-- },
-- b = {
-- group = hash: [default],
-- position = vmath.vector3(185, 704.05865478516, 0),
-- id = hash: [/go2]
-- }
-- }
end
end)
See physics.set_listener. This message is sent to a function specified in physics.set_listener when a collision object interacts with another collision object and one of them is a trigger. This message only reports that an interaction actually happened and will be sent once per colliding pair and frame. For more detailed information, check for the contact_point_event.
enter - if the interaction was an entry or not
a -
id
group
b - collision information for object B
id
group
How to take action when a trigger interaction occurs:
physics.set_listener(function(self, event, data)
if event == hash("trigger_event") then
if data.enter then
-- take action for entry
else
-- take action for exit
end
pprint(data)
-- {
-- enter = true,
-- b = {
-- group = hash: [default],
-- id = hash: [/go2]
-- },
-- a = {
-- group = hash: [default],
-- id = hash: [/go1]
-- }
-- },
end
end)