-- SPDX-License-Identifier: ISC
-- Copyright (c) 2021 Camden Dixie O'Brien

module Main where

import Graphics.Gloss
import Graphics.Gloss.Geometry.Angle

data State = State { theta :: Float
                   , pTheta :: Float
                   , phi :: Float
                   , pPhi :: Float
                   }

-- Simulation parameters
particleMass = 1
rodLength = 200
initialState = State (pi / 4) 0 (pi / 6) 0
g = 0.1

-- Rendering parameters
particleRadius = 5
particleColor = black
rodColor = greyN 0.5
framesPerSecond = 100

render state = doublePendulum (theta state) (phi state)
doublePendulum theta phi = (translatePolar rodLength theta $ pendulum phi) <> pendulum theta
translatePolar radius angle = translate (radius * sin angle) (negate $ radius * cos angle)
pendulum angle = rotateRadians angle $ rod <> (translate 0 (negate rodLength) $ particle)
rod = color rodColor $ line [ (0, 0), (0, negate rodLength) ]
particle = color particleColor $ circleSolid particleRadius
rotateRadians = rotate . radToDeg  . negate

window = InWindow "Double Pendulum" (800, 800) (100, 100)
main = display window white (render initialState)