spine-runtimes/spine-lua/Interpolation.lua

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local interpolation = {}

local math_pow = math.pow

function interpolation.apply (func, start, _end, a)
	return start + (_end - start) * func(a)
end

function interpolation.pow2(a)
	if (a <= 0.5) then return math_pow(a * 2, 2) / 2 end
	return math_pow((a - 1) * 2, 2) / -2 + 1
end

function interpolation.pow2out(a)
	return math_pow(a - 1, 2) * -1 + 1
end

return interpolation