HaxeFlixel has advanced tweening built in for interpolation over time.

Tweens are a useful part of any framework and its applications are many. It can be game object movements, color changes and even tweening variables over time. The current tween types include:

VarTween
MultiVarTween
AngleTween
ColorTween
NumTween
LinearMotion
LinearPath
CircularMotion
CubicMotion
QuadMotion
QuadPath
There is also an impressive choice of Ease types for every Tween type to choose from:

quadIn
quadOut
cubeIn
cubeOut
cubeInOut
quartIn
quartOut
quartInOut
quintIn
quintOut
quintInOut
sineIn
sineOut
sineInOut
bounceIn
bounceOut
bounceInOut
circIn
circOut
circInOut
expoIn
expoOut
expoInOut
backIn
backOut
backInOut
elasticIn
elasticOut
elasticInOut