71 lines
1.7 KiB
Lua
71 lines
1.7 KiB
Lua
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-- A Spring class. This is extremely useful for juicing things up.
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-- See this article https://github.com/a327ex/blog/issues/60 for more details.
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-- The argument passed in are: the initial value of the spring, its stiffness and damping.
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Spring = Object:extend()
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function Spring:init(x, k, d)
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self.x = x or 0
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self.k = k or 100
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self.d = d or 10
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self.target_x = self.x
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self.v = 0
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end
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function Spring:update(dt)
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local a = -self.k*(self.x - self.target_x) - self.d*self.v
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self.v = self.v + a*dt
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self.x = self.x + self.v*dt
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end
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-- Pull the spring with a certain amount of force. This force should be related to the initial value you set to the spring.
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function Spring:pull(f, k, d)
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if k then self.k = k end
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if d then self.d = d end
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self.x = self.x + f
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end
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-- Animates the spring such that it reaches the target value in a smoothy springy motion.
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-- Unlike pull, which tugs on the spring so that it bounces around the anchor, this changes that anchor itself.
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function Spring:animate(x, k, d)
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if k then self.k = k end
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if d then self.d = d end
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self.target_x = x
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end
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--[[
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NSpring = Object:extend()
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function NSpring:new(x, z, o)
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self.x = x or 0
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self.z = z or 0.5
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self.o = o or 2*math.pi
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self.target_x = self.x
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self.v = 0
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end
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function NSpring:update(dt)
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local f = 1 + 2*dt*self.z*self.o
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local oo = self.o*self.o
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local hoo = dt*oo
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local hhoo = dt*hoo
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local det_inv = 1/(f+hhoo)
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local det_x = f*self.x + dt*self.v + hhoo*self.target_x
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local det_v = self.v + hoo*(self.target_x - self.x)
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self.x = det_x*det_inv
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self.v = det_v*det_inv
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end
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function NSpring:animate(target_x, pd, td)
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self.z = math.log(pd)/(self.o*td)
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self.target_x = target_x
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end
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]]--
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