start rewriting physics to force based model

src/Physics/Classes/Mass.hs

@@ -9,11 +9,11 @@ class Mass m where
   -- | The mass of the mass object.
   mass :: m -> Double
 
-  -- | Retrieve the acceleration of the mass object.
-  acceleration :: m -> V2 Double
+  -- | Retrieve the position of the mass object.
+  position :: m -> V2 Double
 
-  -- | Overwrite the acceleration of the mass object.
-  accelerationUpdater :: m -> (V2 Double -> m)
+  -- | Overwrite the position of the mass object.
+  positionUpdater :: m -> (V2 Double -> m)
 
   -- | retrieve the velocity of the mass object.
   velocity :: m -> V2 Double
@@ -21,42 +21,35 @@ class Mass m where
   -- | Overwrite the velocity of the mass object.
   velocityUpdater :: m -> (V2 Double -> m)
 
-  -- | Retrieve the position of the mass object.
-  position :: m -> V2 Double
+  -- | Total force acting on a particle in one simulation step
+  forces :: m -> V2 Double
 
-  -- | Overwrite the position of the mass object.
-  positionUpdater :: m -> (V2 Double -> m)
+  -- | Overwrite the forces acting on a particle
+  forcesUpdater :: m -> (V2 Double -> m)
 
-  -- | The update function to let a mass react to gravitational pull.
-  -- Apply all accelerations before calling the default implementation of
-  -- this function, since it will add the gravitational pull to already
-  -- existing accelerations.
-  gravitate
-    :: V2 Double -- ^ Vector of gravitational acceleration
-    -> m         -- ^ Original mass object
-    -> m         -- ^ Updated mass object
-  gravitate g m =
-    let acc = acceleration m + g
+  -- | Reset forces vector for the begining of a new simulation step
+  resetForces :: m -> m
+  resetForces m = forcesUpdater m (V2 0 0)
+
+  -- | Calculate the loads or forces acting on the mass object except for
+  -- collision forces.
+  addLoads
+    :: m         -- ^ The mass object
+    -> V2 Double -- ^ force to be aggregated acting on the particle (e.g.: gravity)
+    -> m         -- ^ Resulting mass object
+  addLoads m vec =
+    forcesUpdater m (forces m + vec)
+
+  -- | Euler integration updates
+  updateByEuler
+    :: m      -- ^ The mass object
+    -> Double -- ^ Time step in fraction of a second
+    -> m      -- ^ Resulting mass object
+  updateByEuler m dt =
+    let acc = (/ mass m) <$> forces m
+        dvel = (* dt) <$> acc
+        nvel = velocity m + dvel
+        dpos = (* dt) <$> nvel
+        npos = position m + dpos
     in
-      accelerationUpdater m acc
-
-  -- | Apply acceleration to mass object und thus change its velocity
-  accelerate
-    :: Double -- ^ Time step duration
-    -> m      -- ^ Original mass object
-    -> m      -- ^ Updated mass object
-  accelerate dt m =
-    let vel = velocity m + ((dt *) <$> acceleration m)
-    in
-      velocityUpdater m vel
-
-  -- | Apply velocity to mass object and thus change its position
-  -- Changes in position smaller than around half a pixel per second are ignored.
-  move
-    :: Double -- ^ Time step duration
-    -> m      -- ^ Original mass object
-    -> m      -- ^ Updated mass object
-  move dt m =
-    let dpos = (dt *) <$> velocity m
-    in
-      positionUpdater m (position m + dpos)
+      positionUpdater (velocityUpdater m nvel) npos