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June 9, 2022 17:45
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A pid controller (proportional–integral–derivative controller) in lua
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| -- Public domain/CC0 | |
| -- A pid controller (proportional–integral–derivative controller). | |
| -- Useful to track an entity without overshooting (like a docking spaceship). | |
| -- Could be expanded to control orientation, speed, or other values. | |
| -- Requires tuning values: | |
| -- tuning = { | |
| -- gain = { | |
| -- -- all in [0,1] | |
| -- proportional = 0.1, | |
| -- derivative = 0.9, | |
| -- integral = 0.1, | |
| -- }, | |
| -- -- in output distance units | |
| -- max_accumulated_error = 50, | |
| -- } | |
| local Vec2 = require "cpml.modules.vec2" | |
| local class = require "gabe.class" | |
| local mathx = require "batteries.mathx" | |
| local Pid = class('pid') | |
| -- min/max are numbers | |
| local function clamp_vec(v, min, max) | |
| local n, len = v:normalize() | |
| len = mathx.clamp(len, min, max) | |
| return n * len | |
| end | |
| function Pid:init(tuning) | |
| self.tuning = tuning | |
| self.value_fns = {} | |
| end | |
| function Pid:getCurrent() | |
| return self.current | |
| end | |
| function Pid:trackEntityPosition(target) | |
| self.target = target | |
| self.current = target.transform.pos:clone() | |
| self:resetState() | |
| end | |
| function Pid:resetState() | |
| self.accumulated_error = Vec2.zero | |
| self.prev_error = Vec2.zero | |
| -- Start with a state of zero error to prevent derivative kick. | |
| self.prev_error = self:_calcError() | |
| end | |
| function Pid:_calcError() | |
| return self.target.transform.pos - self.current | |
| end | |
| function Pid:update(dt) | |
| if not self.target then | |
| return | |
| end | |
| local error_delta = self:_calcError() | |
| local error_velocity = error_delta - self.prev_error | |
| self.prev_error = error_delta | |
| local limit = self.tuning.max_accumulated_error | |
| self.accumulated_error = self.accumulated_error + (error_delta * dt) | |
| self.accumulated_error = clamp_vec(self.accumulated_error, -limit, limit) | |
| local gain = self.tuning.gain | |
| local proportional = error_delta * gain.proportional | |
| local derivative = error_velocity * gain.derivative | |
| local integral = self.accumulated_error * gain.integral | |
| local pid = proportional + derivative + integral | |
| self.current = self.current + pid | |
| local limits = self.tuning.output_limit | |
| if limits then | |
| self.current = clamp_vec(self.current, limits.min, limits.max) | |
| end | |
| if self.tuning.max_total_error then | |
| error_delta = self:_calcError() | |
| error_delta = clamp_vec(error_delta, 0, self.tuning.max_total_error) | |
| self.current = self.target.transform.pos + error_delta | |
| end | |
| end | |
| return Pid |
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