gloss-examples-1.2.0.0: Styrene/Advance.hs

{-# LANGUAGE PatternGuards #-}

-- | Advance the world to the next time step.
module Advance where
import World
import Contact
import QuadTree
import Collide
import Actor
import Config

import Graphics.Gloss.Geometry
import Graphics.Gloss.Interface.Simulate
import Graphics.Gloss.Data.Point
import Graphics.Gloss.Data.Vector

import Data.List
import qualified Data.Map	as Map
import qualified Data.Set	as Set
import Data.Set			(Set)
import Data.Map			(Map)


-- Advance -------------------------------------------------------------------------------------------

-- | Advance all the actors in this world by a certain time.
advanceWorld 
	:: ViewPort 		-- ^ current viewport
	-> Time 		-- ^ time to advance them for.
	-> World 		-- ^ the world to advance.
	-> World 		-- ^ the new world.

advanceWorld viewport time (World actors tree)
 = let	
 	rot		= viewPortRotate viewport
	force		= rotateV (degToRad $ negate rot) (0, negate gravityCoeff)

	-- move all the actors 
	actors_moved	= Map.map (moveActor_free time force) actors
      
      	-- find contacts in the world
	(contacts, tree')	
		= findContacts (World actors_moved tree)

	-- apply contacts to each pair of actors
	actors_bounced	
		= Set.fold 
			(applyContact time force) 
			actors_moved
			contacts

   in	World actors_bounced tree'


-- Move two actors which are known to be in contact.
applyContact 
	:: Time 		-- ^ time step
	-> Force 		-- ^ ambient force on the actors
	-> (Index, Index) 	-- ^ indicies of the the two actors in contact
	-> Map Index Actor 	-- ^ the old world
	-> Map Index Actor	-- ^ the new world

applyContact time force (ix1, ix2) actors
 = let	-- use the indicies to lookup the data for each actor from the map
	Just a1	= Map.lookup ix1 actors
 	Just a2	= Map.lookup ix2 actors
	
	resultActors
		-- handle a collision between bead and a wall
		| Bead _ _ r1 p1 v1	<- a1
		, Wall{}		<- a2
		= let	a1'		= collideBeadWall a1 a2
		  in	Map.insert ix1 a1' actors
		
		-- handle a collision between two beads
		| Bead ix1 m1 r1 p1 v1	<- a1
		, Bead ix2 m2 r2 p2 v2	<- a2
		= let	
			(a1', a2')
				-- if one of the beads is stuck then do a safer, static collision.
				--	with this method the beads don't transfer energy into each other
				--	so there is less of a chance of lots of beads being crushed together
				--	if there are many in the same place.
				| m1 >= beadStuckCount || m2 >= beadStuckCount
				= let 	a1'	= collideBeadBead_static a1 a2
			  		a2'	= collideBeadBead_static a2 a1
			  	  in	(a1', a2')

				-- otherwise do the real elastic collision
				--	this is much more realistic.
				| otherwise
				= collideBeadBead_elastic a1 a2

			-- write the new data for the actors back into the map
		  in	Map.insert ix1 a1'
		   $ 	Map.insert ix2 a2' actors
	  
   in	resultActors		
	

-- | Move a bead which isn't in contact with anything else.
moveActor_free 
	:: Time 		-- ^ time to move it for
	-> Force 		-- ^ ambient force on the actor during this time
	-> Actor 		-- ^ the bead to move
	-> Actor		-- ^ the new bead

moveActor_free time force actor
	-- move a bead
	| Bead ix stuck radius pos vel	<- actor
	= let 	-- assume all beads have the same mass.
		beadMass	= 1
		
		-- calculate the new position and velocity of the bead.
		pos'		= (pos + time  `mulSV` vel)
		vel'		= (vel + (time / beadMass) `mulSV` force)

		-- if the bead is travelling slowly then set it as being stuck.
		stuck'		
		 | magV vel' < 20
		 = min beadStuckCount (stuck + 1)

		 | otherwise				
		 = max 0 (stuck - 2)

	  in  Bead ix stuck' radius pos' vel'

	-- walls don't move
	| Wall{}			<- actor
	= actor