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diff --git a/src/sims/collision/GridDetector.scala b/src/sims/collision/GridDetector.scala
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+/*
+ * Simple Mechanics Simulator (SiMS)
+ * copyright (c) 2009 Jakob Odersky
+ * made available under the MIT License
+*/
+
+package sims.collision
+
+import sims.dynamics._
+import sims.geometry._
+import scala.collection._
+import scala.collection.mutable._
+
+/**Eine konkrete Implementierung von <code>Detector</code>. <code>GridDetector</code> ermittelt
+ * alle Kollisionen mit einem Gittersystem.*/
+class GridDetector(override val world: World) extends Detector {
+  
+  /**Array von Kollisionserkennungsmethoden fuer Formenpaare.*/
+  val detectionMethods = new ArrayBuffer[PartialFunction[(Shape, Shape), Boolean]]
+  detectionMethods += {
+    case (c1: Circle, c2: Circle) => {	//Kollision wenn Distanz <= Summe der Radien
+      val d = (c1.pos - c2.pos).length
+      val rSum = c1.radius + c2.radius
+      d - rSum <= 0
+      }
+    
+    case (p1: ConvexPolygon, p2: ConvexPolygon) => {	//SAT
+      val sides = p1.sides ++ p2.sides
+      val axes = sides map (_.n0)
+      axes.forall((a: Vector2D) => p1.project(a) overlaps p2.project(a))
+    }
+    
+    case (p: ConvexPolygon, c: Circle) => {	//Distanz von Zentrum zu Seiten oder Eckpunkten
+      val distances = for (s <- p.sides) yield (s distance c.pos)
+      distances.exists(_ - c.radius <= 0) || (p contains c.pos)
+      }
+    
+    case (c: Circle, p: ConvexPolygon) => {	//Distanz von Zentrum zu Seiten oder Eckpunkten
+      val distances = for (s <- p.sides) yield (s distance c.pos)
+      distances.exists(_ - c.radius <= 0) || (p contains c.pos)
+      }
+  }
+  
+   /**Array von Kollisionsmethoden fuer Formenpaare.*/
+  val collisionMethods = new ArrayBuffer[PartialFunction[(Shape, Shape), Collision]]
+  collisionMethods += {
+    case (c1: Circle, c2: Circle) => CircleCollision(c1, c2)
+    case (p1: ConvexPolygon, p2: ConvexPolygon) => PolyCollision(p1, p2)
+    case (p: ConvexPolygon, c: Circle) => PolyCircleCollision(p, c)
+    case (c: Circle, p: ConvexPolygon) => PolyCircleCollision(p, c)
+  }
+  
+  /**Gibt an, ob das Formenpaar <code>p</code> kollidiert.
+   * @param p Formenpaar.*/
+  def colliding(p: Pair) = {
+   if (detectionMethods.exists(_.isDefinedAt(p))) 
+     detectionMethods.find(_.isDefinedAt(p)).get.apply(p)
+    else throw new IllegalArgumentException("No collision method for colliding pair!")
+  }
+  
+  /**Gibt die Kollision des Formenpaares <code>p</code> zurueck.
+   * @param p Formenpaar.*/
+  def collision(p: Pair): Collision = {
+    if (collisionMethods.exists(_.isDefinedAt(p)))
+      collisionMethods.find(_.isDefinedAt(p)).get.apply(p)
+    else throw new IllegalArgumentException("No collision found in colliding pair!")
+  }
+  
+  /**Breite und Hoehe einer Gitterzelle.*/
+  var gridSide: Double = 2
+  
+  /**Ergibt potenzielle Kollisionspaare der Welt <code>world</code>.
+   * <p>
+   * Ein Kollisionspaar ist ein Paar aus zwei verschiedenen Formen, das folgenden Bedingungen unterliegt:
+   * <ul>
+   * <li>Die Formen muessen sich in der gleichen Gitterzelle befinden.</li>
+   * <li>Ihre AABBs muessen sich ueberlappen.</li>
+   * <li>Die Formen duerfen nicht von dem gleichen Koerper sein.</li>
+   * <li>Mindestens eine Form darf nicht Fixiert sein.</li>
+   * <li>Beide muessen {@link dynamics.Shape#collidable collidierbar} sein.</li>
+   * </ul>*/
+  def getPairs = {
+    val grid = new HashMap[(Int, Int), List[Shape]]
+    def gridCoordinates(v: Vector2D) = ((v.x / gridSide).toInt, (v.y / gridSide).toInt)
+    def addToGrid(s: Shape) = {
+      val aabb = s.AABB  
+      val minCell = gridCoordinates(aabb.minVertex)
+      val maxCell = gridCoordinates(aabb.maxVertex)
+      val coords = for(i <- (minCell._1 to maxCell._1); j <- (minCell._2 to maxCell._2)) yield (i, j)
+      for (c <- coords) {
+        if (grid.contains(c))
+          {if (grid(c).forall(_ ne s)) grid(c) = s :: grid(c)}
+        else
+            grid += (c -> List(s))
+      	}
+      }
+    for(s <- world.shapes) addToGrid(s)
+    var ps: List[Pair] = Nil
+    for(cell <- grid.values) {
+      ps = ps ::: (for (s1: Shape <- cell; s2: Shape <- cell;
+                    if (s1 ne s2);                       
+           			if (s1.body ne s2.body);
+           			if (s1.collidable && s2.collidable);
+                    if (s1.AABB overlaps s2.AABB);
+                    if (!s1.transientShapes.contains(s2) && !s2.transientShapes.contains(s1))) yield Pair(s1, s2)
+       				).removeDuplicates
+    }
+    ps.toSeq
+  }
+  
+  private var cache = (world.time, getPairs)
+  
+  /**Alle potentiellen Kollisionspaare der Welt.
+   * @see getPairs*/
+  def pairs = {if (world.time != cache._1) cache = (world.time, getPairs); cache._2}
+  
+  /**Ergibt alle kollidierenden Paare.*/
+  def collidingPairs: Seq[Pair] = for(p <- pairs; if (colliding(p))) yield p
+  
+  /**Ergibt alle Kollisionen.*/
+  def collisions: Seq[Collision] = for(p <- pairs; if (colliding(p))) yield collision(p)
+}