From Garry's Mod
Performs a linear interpolation from the start number to the end number.
This function provides a very efficient and easy way to smooth out movements.
The fraction for finding the result. This number is clamped between 0 and 1.
The starting number. The result will be equal to this if delta is 0.
The ending number. The result will be equal to this if delta is 1.
The result of the linear interpolation, (1 - t) * from + t * to.