First try integrating a Arc. Status: Still alot to do

src/awlex/ospu/polymover/Arc.java

@@ -30,16 +30,16 @@ public class Arc extends PolyMover {
 	
 	private void init() {
 		Matrix m = prepareMatrix(p1, middle, p2);
-		xm = m.get(2, 1);
-		ym = m.get(3, 1);
-		r = pow(xm, 2) + pow(ym, 2) - m.get(1, 1);
+		xm = m.get(1, 0) * 0.5;
+		ym = m.get(2, 0) * 0.5;
+		r = sqrt(pow(xm, 2) + pow(ym, 2) - m.get(0, 0));
 		alpha = atan2(p1.end.y - ym, p1.end.x - xm);
 		beta = atan2(middle.end.y - ym, middle.end.x - xm);
 		gamma = atan2(p2.start.y - ym, p2.start.x - xm);
 	}
 	
 	@Override
-	public double[] getPoint(int time) {
+	public double[] getPointAt(int time) {
 		double percent;
 		double angle;
 		if (time < middle.getTime()) {

src/awlex/ospu/polymover/PolyMover.java

@@ -6,7 +6,7 @@ import itdelatrisu.opsu.objects.GameObject;
  * Created by Awlex on 18.11.2016.
  */
 public abstract class PolyMover {
-	public abstract double[] getPoint(int time);
+	public abstract double[] getPointAt(int time);
 	
 	public abstract GameObject[] getItems();
 }

src/awlex/ospu/polymover/factory/ArcFactory.java

@@ -7,19 +7,18 @@ import itdelatrisu.opsu.objects.GameObject;
 /**
  * Created by Awlex on 18.11.2016.
  */
-public class ArcFactory implements MultiMoverFactory {
+public class ArcFactory implements PolyMoverFactory {
 	
 	private static final int PREFFERED_BUFFER_SIZE = 3;
 	private PolyMover arc1, arc2;
 	
-	@Override
-	public double[] getPoint(int time) {
+	public double[] getPointAt(int time) {
 		if (arc2 == null) {
-			return arc1.getPoint(time);
+			return arc1.getPointAt(time);
 		}
 		
-		double[] point1 = arc1.getPoint(time);
-		double[] point2 = arc2.getPoint(time);
+		double[] point1 = arc1.getPointAt(time);
+		double[] point2 = arc2.getPointAt(time);
 		
 		return new double[]{
 			(point1[0] + point2[0]) * 0.5,
@@ -31,15 +30,18 @@ public class ArcFactory implements MultiMoverFactory {
 	public void init(GameObject[] objects, int startIndex) {
 		if (objects == null)
 			throw new NullPointerException("Objects musn't be null");
-		if (objects.length < startIndex + 2)
 		arc1 = new Arc(objects[startIndex], objects[startIndex + 1], objects[startIndex + 2]);
 		arc2 = null;
 	}
 	
 	public void update(GameObject p) {
-		if (arc2 != null)
-			arc1 = arc2;
-		arc2 = new Arc(arc1, p);
+		GameObject[] items = (arc2 == null ? arc1 : arc2).getItems();
+		GameObject last = items[items.length - 1];
+		if (last != p) {
+			if (arc2 == null)
+				arc2 = arc1;
+			arc1 = new Arc(arc2, p);
+		}
 	}
 	
 	@Override
@@ -51,4 +53,9 @@ public class ArcFactory implements MultiMoverFactory {
 	public String toString() {
 		return "Arcs";
 	}
+	
+	@Override
+	public boolean isInitialized() {
+		return arc1 != null;
+	}
 }

src/awlex/ospu/polymover/factory/PolyMoverFactory.java

@@ -5,14 +5,13 @@ import itdelatrisu.opsu.objects.GameObject;
 /**
  * Created by Awlex on 18.11.2016.
  */
-public interface MultiMoverFactory {
-	
+public interface PolyMoverFactory {
 	
 	/**
 	 * @param time point in time whose cursor position has to be calculated
 	 * @return [x, y]
 	 */
-	double[] getPoint(int time);
+	double[] getPointAt(int time);
 	
 	void init(GameObject[] objects, int startIndex);
 	
@@ -24,4 +23,6 @@ public interface MultiMoverFactory {
 	 * @return
 	 */
 	int getPrefferedBufferSize();
+	
+	boolean isInitialized();
 }