Implement rendering

Main.hs

@@ -3,6 +3,9 @@
 
 module Main where
 
+import Graphics.Gloss
+import Graphics.Gloss.Geometry.Angle
+
 data State = State { theta :: Float
                    , pTheta :: Float
                    , phi :: Float
@@ -21,5 +24,13 @@ particleColor = black
 rodColor = greyN 0.5
 framesPerSecond = 100
 
-main :: IO ()
+render state = doublePendulum (theta state) (phi state)
-main = putStrLn "Hello, Haskell!"
+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)