feat: added support for box2d prismatic joint

AlmasB · AlmasB · commit 3a1e7adb375e · 2022-01-20T19:59:38.000Z
diff --git a/fxgl-entity/src/main/java/com/almasb/fxgl/physics/PhysicsWorld.java b/fxgl-entity/src/main/java/com/almasb/fxgl/physics/PhysicsWorld.java
@@ -711,6 +711,30 @@ public RopeJoint addRopeJoint(Entity e1, Entity e2, Point2D localAnchor1, Point2
         return addJoint(e1, e2, def);
     }
 
+    /**
+     * Add a prismatic joint (a slider along a given axis) between two entities.
+     * More details: https://en.wikipedia.org/wiki/Prismatic_joint
+     *
+     * @param e1 entity1
+     * @param e2 entity2
+     * @param axis the axis along which to slide
+     * @param limit max slide distance in pixels
+     * @return joint
+     */
+    public PrismaticJoint addPrismaticJoint(Entity e1, Entity e2, Point2D axis, double limit) {
+        checkJointRequirements(e1, e2);
+
+        var p1 = e1.getComponent(PhysicsComponent.class);
+        var p2 = e2.getComponent(PhysicsComponent.class);
+
+        var def = new PrismaticJointDef();
+        def.initialize(p1.getBody(), p2.getBody(), p2.getBody().getWorldCenter(), toVector(axis));
+        def.enableLimit = true;
+        def.upperTranslation = toMetersF(limit);
+
+        return addJoint(e1, e2, def);
+    }
+
     /**
      * Add a joint constraining two entities with PhysicsComponent.
      * The entities must already be in the game world.
diff --git a/fxgl-entity/src/main/java/com/almasb/fxgl/physics/box2d/dynamics/joints/PrismaticJointDef.java b/fxgl-entity/src/main/java/com/almasb/fxgl/physics/box2d/dynamics/joints/PrismaticJointDef.java
@@ -16,76 +16,61 @@
  * coincide in world space. Using local anchors and a local axis helps when saving and loading a
  * game.
  *
- * @warning at least one body should by dynamic with a non-fixed rotation.
- * @author Daniel
+ * Note: at least one body should by dynamic with a non-fixed rotation.
  *
+ * @author Daniel
  */
 public class PrismaticJointDef extends JointDef<PrismaticJoint> {
 
-
     /**
      * The local anchor point relative to body1's origin.
      */
-    public final Vec2 localAnchorA;
+    public final Vec2 localAnchorA = new Vec2();
 
     /**
      * The local anchor point relative to body2's origin.
      */
-    public final Vec2 localAnchorB;
+    public final Vec2 localAnchorB = new Vec2();
 
     /**
      * The local translation axis in body1.
      */
-    public final Vec2 localAxisA;
+    public final Vec2 localAxisA = new Vec2(1.0f, 0.0f);
 
     /**
      * The constrained angle between the bodies: body2_angle - body1_angle.
      */
-    public float referenceAngle;
+    public float referenceAngle = 0.0f;
 
     /**
      * Enable/disable the joint limit.
      */
-    public boolean enableLimit;
+    public boolean enableLimit = false;
 
     /**
      * The lower translation limit, usually in meters.
      */
-    public float lowerTranslation;
+    public float lowerTranslation = 0.0f;
 
     /**
      * The upper translation limit, usually in meters.
      */
-    public float upperTranslation;
+    public float upperTranslation = 0.0f;
 
     /**
      * Enable/disable the joint motor.
      */
-    public boolean enableMotor;
+    public boolean enableMotor = false;
 
     /**
      * The maximum motor torque, usually in N-m.
      */
-    public float maxMotorForce;
+    public float maxMotorForce = 0.0f;
 
     /**
      * The desired motor speed in radians per second.
      */
-    public float motorSpeed;
-
-    public PrismaticJointDef() {
-        localAnchorA = new Vec2();
-        localAnchorB = new Vec2();
-        localAxisA = new Vec2(1.0f, 0.0f);
-        referenceAngle = 0.0f;
-        enableLimit = false;
-        lowerTranslation = 0.0f;
-        upperTranslation = 0.0f;
-        enableMotor = false;
-        maxMotorForce = 0.0f;
-        motorSpeed = 0.0f;
-    }
-
+    public float motorSpeed = 0.0f;
 
     /**
      * Initialize the bodies, anchors, axis, and reference angle using the world anchor and world
