better rotation mechanics

src/main/java/core/ExMath.java

@@ -0,0 +1,28 @@
+package core;
+
+/**
+ * Extended Math functions for the game engine
+ */
+public class ExMath {
+
+    private ExMath(){
+    }
+
+    /**
+     * Lerp an angle in radians
+     *
+     * @param from The start angle
+     * @param to The target angle
+     * @param t The value
+     * @return The new angle
+     *
+     * @see <a href="https://gist.github.com/shaunlebron/8832585"angleLerp</a>
+     */
+    public static double angleLerp(double from, double to, double t) {
+        double max = Math.PI * 2;
+        double da = (to - from) % max;
+        double shortAngleDist = 2 * da % max - da;
+
+        return from + shortAngleDist * t;
+    }
+}

src/main/java/core/Vector2D.java

@@ -133,6 +133,30 @@ public class Vector2D {
         return new Vector2D(rotatedX + center.x, rotatedY + center.y);
     }
 
+    /**
+     * Rotate a point around another point
+     *
+     * This method can now be trusted
+     *
+     * @param center The center of the rotation
+     * @param value The point to be rotated, absolut to the center
+     * @param rotation The rotation angle in radians
+     * @return The rotated point
+     */
+    public static Vector2D rotateAround(Vector2D center, Vector2D value, double rotation){
+        return rotateAround(center, value, rotation, COUNTERCLOCKWISE);
+    }
+
+
+    /**
+     * Get a unit vector with magnitude 1 and the direction
+     * @param direction The direction of the vector
+     * @return The unit vector
+     */
+    public static Vector2D getUnitVector(double direction){
+        return rotateAround(new Vector2D(), new Vector2D(0, 1), direction);
+    }
+
     /**
      * Copy this object
      * @return A copy of this object
@@ -165,4 +189,8 @@ public class Vector2D {
         if (Double.compare(vector2D.x, x) != 0) return false;
         return Double.compare(vector2D.y, y) == 0;
     }
+
+    public double getRotation() {
+        return Math.atan2(y, x);
+    }
 }

src/main/java/objects/ships/BattleShip.java

@@ -18,8 +18,8 @@ public class BattleShip extends GameObject {
         super(20, 20, 5, 40);
         turrets = new ArrayList<>();
         turrets.add(new Turret(this, 25, 25, 50, 3));
-        turrets.add(new Turret(this, 25, 10, 50, 2));
-        turrets.add(new Turret(this, 25, 70, 50, 2));
+        //turrets.add(new Turret(this, 25, 10, 50, 2));
+        //turrets.add(new Turret(this, 25, 70, 50, 2));
         this.mainColor = mainColor;
     }
 

src/main/java/objects/ships/Submarine.java

@@ -0,0 +1,18 @@
+package objects.ships;
+
+import core.Master;
+import objects.GameObject;
+
+import java.awt.*;
+
+public class Submarine extends GameObject {
+    @Override
+    public void draw(Graphics2D g2d, int w, Master master) {
+
+    }
+
+    @Override
+    public void update(Master master) {
+
+    }
+}

src/main/java/objects/ships/Turret.java

@@ -1,5 +1,6 @@
 package objects.ships;
 
+import core.ExMath;
 import core.Master;
 import core.Vector2D;
 import objects.GameObject;
@@ -11,18 +12,21 @@ import java.awt.*;
  */
 public class Turret extends GameObject {
 
-    private static final double ROTATION_SPEED = 2;
+    private static final double ROTATION_SPEED = 0.05;
+    private static final int SHOT_EFFECT_TIME = 300;
+    private static final int SHELL_SPEED = 10;
 
     BattleShip battleShip;
 
     private int barrelAmount = 3;
 
+    private double rotation;
+
     private Color mainColor;
 
     private long lastShot = 0;
-    private static int SHOT_EFFECT_TIME = 300;
-    private static int SHELL_SPEED = 10;
-    private double rotation;
+
+    //private double rotation;
 
     public Turret(BattleShip battleShip, double x, double y, double size, int barrelAmount) {
         super(x, y, size, size);
@@ -58,6 +62,7 @@ public class Turret extends GameObject {
         g2d.setPaint(Color.BLACK);
         int barrelSpacing = sizeAbs / (barrelAmount + 1);
         g2d.rotate(rotation, xCenterAbs, yCenterAbs);
+
         for (int i = 0; i < barrelAmount; i++) {
             int barrelX = xAbs + (i + 1) * barrelSpacing;
             int frontPosY = yAbs - sizeAbs / 2;
@@ -82,7 +87,10 @@ public class Turret extends GameObject {
         int yCenterAbs = yAbs + sizeAbs / 2;
 
         Point msLoc = master.getMouseLocation();
-        rotation = -Math.atan2(xCenterAbs - msLoc.x, yCenterAbs - msLoc.y);
+        double targetRotation = -Math.atan2(xCenterAbs - msLoc.x, yCenterAbs - msLoc.y);
+
+
+        rotation = ExMath.angleLerp(rotation, targetRotation, ROTATION_SPEED);
 
         int barrelSpacing = sizeAbs / (barrelAmount + 1);
 
@@ -93,7 +101,7 @@ public class Turret extends GameObject {
             if (master.isMousePressed()) {
                 lastShot = System.currentTimeMillis();
 
-                Vector2D shellVel = new Vector2D(xCenterAbs - msLoc.x, yCenterAbs - msLoc.y).normalized().negative().multiply(SHELL_SPEED);
+                Vector2D shellVel = Vector2D.getUnitVector(rotation).negative().multiply(SHELL_SPEED);
                 Vector2D pos = Vector2D.rotateAround(new Vector2D(xCenterAbs, yCenterAbs), new Vector2D(barrelX, frontPosY), rotation, Vector2D.COUNTERCLOCKWISE);
 
                 master.create(new Shell(pos, new Vector2D(10, 10), shellVel));

src/test/java/core/Vector2DTest.java

@@ -67,7 +67,15 @@ class Vector2DTest {
         assertEquals(round(expected), round(rotated));
     }
 
+
     public static Vector2D round(Vector2D a){
         return new Vector2D(Math.round(a.x*10000d)/10000d, Math.round(a.y*10000d)/10000d);
     }
+
+    @Test
+    void getUnitVectorSimple() {
+        double dir = Math.PI;
+        Vector2D expected = new Vector2D(0, -1);
+        assertEquals(round(expected), round(Vector2D.getUnitVector(dir)));
+    }
 }