How do I understand the lerp function

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  • Dear all.

    Could you explain the purpose of the lerp function ?


  • Using the search function with the words "lerp explanation" this is one one of the posts I found..

    You can try the search function yourself and find even more..

    Lerp is a very simple function

    Lerp stands for Linear intERPolation

    This function need 3 numbers parameter


    a and b are whatever number you want

    but t goes from 0 to 1 (well it can go under and over but... let's keep things simple)

    lerp(a,b,0) returns a

    learp(a,b,1) returns b

    the values in between 0 and 1 returns a number X between a and b such as X-a = (b-a)*t

    so t describe more or less where you are in between a and b

    lerp(a,b,0.5) return the middle so a+(b-a)/2

    lerp(0,10,0) = 0

    lerp(0,10,1) = 10

    lerp(0,10,0.5) = 5

    the way newt use it with

    sprite set X to lerp(self.X,destination,0.5*dt)[/code:y7rtf1sp] is a little trick
    the .X you have in the lerp is the .X you change in the expression
    and 0.5*dt is always more or less the same (depending on fps)
    so from step to step in the movement, destination-self.X will be shorter and shorter, so the lerp(self.X,destination,0.5*dt) will continue to move the sprite but slower and slower (ease out)
    In short the only issue with this technique is that the sprite will takes time to exactly get to destination. Mathematically it should never arrive but thanks to float rounding stuff it will.
    Anyway you should not rely too much on
    if sprite.X = destination
    that's all 
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  • Thank's that clear now.

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