Handle Spine IK constraints
Description
This example demonstrates how to control Spine Inverse Kinematics (IK) constraints in Defold by assigning a game object as the IK target.
Move the mouse or touch in the active area (white rectangle in the background) to move the robot’s arm with IK constraints.
Project Structure
- root
- active_area.go
- collisionobject
- area.script
- sprite
- cursor.go
- collisionobject
- cursor.script
- manipulator.script
- spinemodel
How It Works
The cursor.go game object is controlled by the user and has a collision object configured as a trigger.
When the cursor overlaps with the trigger in active_area.go, it sends a message to manipulator.script.
The script uses the Defold Spine API to assign cursor.go as the target of an IK constraint with spine.set_ik_target().
When the target is no longer needed, spine.reset_ik_target() resets the constraint to its original target position.
Scripts
area.script
local NORMAL_ALPHA = 0.8
local ALPHA_PROPERTY = hash("tint.w")
function init(self)
go.set("#sprite", ALPHA_PROPERTY, NORMAL_ALPHA)
endcursor.script
local MSG_TRIGGER = hash("trigger_response")
local MSG_PARENT = hash("parent")
function init(self)
msg.post(".", "acquire_input_focus")
end
function final(self)
msg.post(".", "release_input_focus")
end
function on_input(self, action_id, action)
if action.x and action.y then
go.set_position(vmath.vector3(action.x, action.y, 1))
end
end
function on_message(self, message_id, message, sender)
if message_id == MSG_TRIGGER then
msg.post("/root#manipulator", MSG_PARENT, { parent = message.enter })
end
endmanipulator.script
local IK_BONE = hash("RED_IK")
local SPINE_COMPONENT = "#spinemodel"
local MSG_PARENT = hash("parent")
function init(self)
self.target = go.get_id("cursor")
end
function on_message(self, message_id, message, sender)
if message_id == MSG_PARENT then
if message.parent then
spine.set_ik_target(SPINE_COMPONENT, IK_BONE, self.target)
else
spine.reset_ik_target(SPINE_COMPONENT, IK_BONE)
end
end
end