# Parallax

In this sample, we demonstrate how to use a parallax effect to simulate depth in the game world. There are two layers of clouds, where one of the layers has the appearance of being further back than the other. There is also an animated saucer for flavor.

The cloud layers are built as two separate game objects, containing a Tile Map and Script each. The layers are moved at different speeds, to give the parallax effect. This is done in update() of background1.script and background2.script below.

-- file: background1.script

function init(self)
msg.post("@render:", "clear_color", { color = vmath.vector4(0.52, 0.80, 1, 0) } )
end

-- the background is a tilemap in a gameobject
-- we move the gameobject for the parallax effect

function update(self, dt)
-- decrease x-position by 1 units per frame for parallax effect
local p = go.get_position()
p.x = p.x + 1
go.set_position(p)
end

-- file: background2.script

-- the background is a tilemap in a gameobject
-- we move the gameobject for the parallax effect

function update(self, dt)
-- decrease x-position by 0.5 units per frame for parallax effect
local p = go.get_position()
p.x = p.x + 0.5
go.set_position(p)
end


The saucer is a separate game object, containing a Sprite and a Script. It is moved to the left at a constant speed. The up-down-motion is obtained by animating its y-component around a fixed value using the Lua sine function (math.sin()). This is done in update() of spaceship.script.

-- file: spaceship.script

function init(self)
-- remeber initial y position such that we
-- can move the spaceship without changing the script
self.start_y = go.get_position().y
-- set counter to zero. use for sin-movement below
self.counter = 0
end

function update(self, dt)
-- decrease x-position by 2 units per frame
local p = go.get_position()
p.x = p.x - 2

-- move the y position around initial y
p.y = self.start_y + 8 * math.sin(self.counter * 0.08)

-- update position
go.set_position(p)

-- remove shaceship when outside of screen
if p.x < - 32 then
go.delete()
end

-- increase the counter
self.counter = self.counter + 1
end

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