I quickly put together a partial recreation of Godot’s tweening system for the Playdate SDK in Lua! It definitely has room for improvement, but it served my purposes, and it might for you as well.
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MIT License
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import "CoreLibs/object"
local tweens = {}
Tween = {}
class("Tween").extends()
local dt = 0
local previousTime = nil
function Tween:init()
self.tweeners = {}
self.tweenersProcessed = 0
table.insert(tweens, self)
end
---Creates and appends a PropertyTweener. This method tweens a property of an object between an initial value and finalValue in a span of time equal to duration, in seconds. The initial value by default is the property's value at the time the tweening of the PropertyTweener starts.
---@param object any
---@param propertyName any
---@param finalValue any
---@param duration any
---@return PropertyTweener
function Tween:tweenProperty(object, propertyName, finalValue, duration)
local tweener = PropertyTweener(object, propertyName, finalValue, duration)
if self.parallel then
tweener:setParallel()
end
table.insert(self.tweeners, tweener)
return tweener
end
function Tween:tweenSprite(object, finalXValue, finalYValue, duration)
local tweener = SpriteTweener(object, finalXValue, finalYValue, duration)
if self.parallel then
tweener:setParallel()
end
table.insert(self.tweeners, tweener)
return tweener
end
function Tween:tweenCallback(callback)
local tweener = CallbackTweener(callback)
if self.parallel then
tweener:setParallel()
end
table.insert(self.tweeners, tweener)
return tweener
end
function Tween:setParallel(value)
if value == nil then
value = true
end
self.parallel = value
if #self.tweeners > 0 and value == true then
self.tweeners[#self.tweeners]:setParallel(value) -- sets the most recently added tweener to parallel, matching Godot's implementation
end
return self
end
function Tween:finished()
return self.tweenersProcessed >= #self.tweeners
end
function Tween:update()
for i=self.tweenersProcessed, #self.tweeners - 1 do
local currentTweener = self.tweeners[i + 1]
if not currentTweener.began then
currentTweener:beginProcessing()
end
if not currentTweener.finished then
currentTweener:update()
else
self.tweenersProcessed += 1
end
if not self:finished() and not self.tweeners[self.tweenersProcessed + 1].parallel then
break
end
end
if not self:finished() then return end
for i, tween in ipairs(tweens) do
if tween == self then
table.remove(tweens, i)
break
end
end
end
function Tween.updateAllTweens()
dt = 0
local currentTime <const> = playdate.getCurrentTimeMilliseconds() / 1000
if previousTime ~= nil then
dt = currentTime - previousTime
end
previousTime = currentTime
for _, tween in pairs(tweens) do
tween:update()
end
end
Tweener = {}
class('Tweener').extends()
function Tweener:init()
self.finished = false
self.began = false
self.parallel = false
end
function Tweener:beginProcessing()
self.began = true
end
function Tweener:setParallel(value)
if value == nil then
value = true
end
self.parallel = value
return self
end
function Tweener:update()
end
---Interpolates an Object's property over time.
PropertyTweener = {}
class('PropertyTweener').extends(Tweener)
function PropertyTweener:init(object, propertyName, finalValue, duration)
self.object = object
self.propertyName = propertyName
self.finalValue = finalValue
self.age = 0.0
self.duration = duration
self:setEasing(playdate.easingFunctions.linear)
end
function PropertyTweener:from(initialValue)
self.initialValue = initialValue
end
function PropertyTweener:beginProcessing()
PropertyTweener.super.beginProcessing(self)
if not self.initialValue then
self.initialValue = self.object[self.propertyName]
end
end
---@param easingFunction function
function PropertyTweener:setEasing(easingFunction)
self.easingFunction = easingFunction
return self
end
function PropertyTweener:update()
if self.finished then return end
self.age += dt
local newValue =
self.easingFunction(
self.age,
self.initialValue,
self.finalValue - self.initialValue,
self.duration
)
self.object[self.propertyName] = newValue
if self.age >= self.duration then
self.finished = true
end
end
SpriteTweener = {}
class('SpriteTweener').extends(Tweener)
function SpriteTweener:init(sprite, finalXValue, finalYValue, duration)
self.object = sprite
self.finalXValue = finalXValue
self.finalYValue = finalYValue
self.age = 0.0
self.duration = duration
self:setEasing(playdate.easingFunctions.linear)
end
function SpriteTweener:from(initialXValue, initialYValue)
self.initialXValue = initialXValue
self.initialYValue = initialYValue
end
function SpriteTweener:beginProcessing()
PropertyTweener.super.beginProcessing(self)
if not self.initialValue then
self.initialXValue = self.object.x
self.initialYValue = self.object.y
end
end
function SpriteTweener:update()
if self.finished then return end
self.age += dt
local newX, newY =
self.easingFunction(
self.age,
self.initialXValue,
self.finalXValue - self.initialXValue,
self.duration
),
self.easingFunction(
self.age,
self.initialYValue,
self.finalYValue - self.initialYValue,
self.duration
)
self.object:moveTo(newX, newY)
if self.age >= self.duration then
self.finished = true
end
end
---@param easingFunction function
function SpriteTweener:setEasing(easingFunction)
self.easingFunction = easingFunction
return self
end
CallbackTweener = {}
class('CallbackTweener').extends(Tweener)
function CallbackTweener:init(callback)
CallbackTweener.super.init(self)
self.callback = callback
end
function CallbackTweener:update()
self.callback()
self.finished = true
end