Easing function improvements

[sarmong]

1. Allow passing custom function to both global and local settings.
2. Make it more clear in the readme what kind of function these are - EaseIn, EaseOut or EaseInOut (perhaps using standardized names like easings.net does?)
3. When I press and hold <C-d>, everything slows down as if I am holding j. (same for upwards movement)
4. I am trying to use easeOutCirc, however it is still slow on the start, quick at the end. But this function should be reverse. I am return this math.sqrt(1 - math.pow(x - 1, 2)). What am I doing wrong?

[baptisteArno]

Definitely need more info, is it in, out or in and out ?

[karb94]

• All the animations are easing-out. I don't really think anyone would want easing-in for a scrolling motion.
• The functions are defined in scroll.lua (easing_function table) but it is not exposed as part of the module at this time. I can expose it if you really want to define your own functions.
• Easing functions are generally defined as $x(t)$ because you want to know what will be the position at time $t$. However, Neoscroll already knows the next immediate position (next line) and what needs to know instead is how much time it should wait until it moves to the next line. Therefore, Neoscroll wants $t(x)$ instead of $x(t)$. So once you have a function that you like you need to invert it before passing it to Neoscroll.
  Example: easeOutQuad function is

local function t(x)
  return 1 - math.pow(1 - x, 2)
end

but Neoscroll uses its inverse:

local function x(t)
  return 1 - math.pow(1 - x, 1 / 2)
end

Likewise, for easeOutCirc you would need:

local function x(t)
  return 1 - math.pow(1 - x * x, 1 / 2)
end

Note that these two examples are already implemented as the quadratic and circular easing functions in Neoscroll.