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Knockback


Setup

This example shows how to create a knockback effect when hit. The setup consists of three game objects; one for the player, one for the enemy and one for the bullet that is spawned using a factory (see example on how to spawn bullets).

player
The red ship at the bottom. Contains:
  • A Sprite component with the spaceship image.
  • A Factory component to spawn bullet game objects
  • A script to handle spawning of bullets.
bullet
The bullet fired by the player. Contains:
  • A Sprite component with a bullet image.
  • A Collision object component. Type is set to KINEMATIC. It has a sphere Shape matching image.
enemy
The black ship at the top. Contains:
  • A Sprite component with the spaceship image.
  • A Collision object component. Type is set to KINEMATIC. It has a sphere Shape matching image.
  • A script to handle collisions with bullets.

Scripts

enemy.script

-- move game object back and forth from the current position to a target position
local function move()
    local pos = go.get_position()
    local to = vmath.vector3(pos.x, 300, 0)
    local distance = pos.y - to.y
    local speed = 40
    local duration = distance / speed
    go.animate(".", "position", go.PLAYBACK_LOOP_PINGPONG, to, go.EASING_INOUTQUAD, duration)
end

function init(self)
    move()
end

function on_message(self, message_id, message, sender)
    if message_id == hash("contact_point_response") then
        if message.other_group == hash("bullet") then
            -- delete the bullet
            go.delete(message.other_id)

            -- get the position of the game object
            local pos = go.get_position()
            -- set a pushback direction based on the collision normal
            local to = pos + message.normal * 30
            -- knockback animation, then continue moving
            go.animate(".", "position", go.PLAYBACK_ONCE_FORWARD, to, go.EASING_OUTQUAD, 0.1, 0, move)
        end
    end
end

If you want to play with these examples, you can get the project on Github.

Do you want to see more examples? Why not write a few yourself and submit a pull request? We love contributions.

GITHUB