Using PathModifier or MoveYModifier to simulate sp

问题:

I am using this method in AndEngine to determine the scene being touched by the user.

@Override
public boolean onSceneTouchEvent(Scene pScene, TouchEvent pSceneTouchEvent) {
     if(pSceneTouchEvent.isActionDown()) {
         Log.e("Arcade", "Scene Tapped");
                   //Simulate player jumping

     }
    return false;
}

What i want to do is when the scene is tapped, i want to allow the player to jump.

Now two things for this would it be better to use PathModifier, or MoveYModifier considering it is landscape mode? If either please provide an example of such. Thanks

EDIT:

ive managed to use Physics to simulate a jump using this..

@Override
public boolean onSceneTouchEvent(Scene pScene, TouchEvent pSceneTouchEvent) {
     if(pSceneTouchEvent.isActionDown()) {
         Log.e("Arcade", "Scene Tapped");

          final Vector2 velocity = Vector2Pool.obtain(mPhysicsWorld.getGravity().x * -0.5f,mPhysicsWorld.getGravity().y * -0.5f);
          body.setLinearVelocity(velocity);
          Vector2Pool.recycle(velocity);
         return true;
     }
    return false;
}

As you said in the answer by changing the gravity. The only issue is, when the user keeps touching the screen the sprites keep going up and up and up. How can i set it where the user can only click once and cant make him jump again until the sprite hits the ground, which is a rectangle?

回答1:

Use the MoveYModifier. remember, you can register as many modifiers as you want. So if, for example, the game a platform game and the character always moves on the X axis, and he can jumpt if he wants (Like Gravity Guy or Yoo Ninja, although these games change the gravity which is something else).

You could do like:

Entity playerEntity = ..//It doesn't matter if the player is a sprite, animated sprite, or anything else. So I'll just use Entity here, but you can declare your player as you wish.

final float jumpDuration = 2;
final float startX = playerEntity.getX();
final float jumpHeight = 100;

final MoveYModifier moveUpModifier = new MoveYModifier(jumpDuration / 2, startX, startX + jumpHeight);
final MoveYModifier moveDownModifier = new MoveYModifier(jumpDuration / 2, startX + jumpHeight, startX);
final SequenceEntityModifier modifier = new SequenceEntityModifier(moveUpModifier, moveDownModifier);

playerEntity.registerEntityModifier(modifier);

EDIT:

For your second question:

1. Create a variable boolean mIsJumping in your scene; When the jump starts - set it to true. If the user taps the screen and mIsJumping == true, don't jump.
2. Now, register a ContactListener to your PhysicsWorld. Whenever there is contact between the player and the ground, set mIsJumping to false.

There are many samples of using ContactListeners in AndEngine forums, a quick search yields some. If you need an example, you can ask for one :)

EDIT 2: ContactListener sample:

1. Have 2 variables to hold IDs for the player and the ground: private static final String PLAYER_ID = "player", GROUND_ID = "ground";
2. When you create the ground body and the player body, set their IDs as the user data: playerBody.setUserData(PLAYER_ID); and groundBody.setUserData(GROUND_ID);

3. Create a ContactListener as a field in your scene:

   private ContactListener mContactListener = new ContactListener() { 
   /**
    * Called when two fixtures begin to touch.
    */
   public void beginContact (Contact contact) {
       final Body bodyA = contact.getFixtureA().getBody();
       final Body bodyB = contact.getFixtureB().getBody();
   
       if(bodyA.getUserData().equals(PLAYER_ID)) {
           if(bodyB.getUserData().equals(GROUND_ID))
               mIsJumping = false;
       }
       else if(bodyA.getUserData().equals(GROUND_ID)) {
           if(bodyB.getUserData().equals(PLAYER_ID))
               mIsJumping = false;
       }
   
   }
   
   /**
    * Called when two fixtures cease to touch.
    */
   public void endContact (Contact contact) { }
   
   /**
    * This is called after a contact is updated.
    */
   public void preSolve(Contact pContact) { }
   
   /**
    * This lets you inspect a contact after the solver is finished. 
    */
   public void postSolve(Contact pContact) { }
   };
   

4. Lastly, register that contact listener: physicsWorld.setContactListener(mContactListener);

EDIT 3:

To move your sprite over the X axis, you can apply a force using Body.applyForce method, or apply an impulse using Body.applyLinearImpulse method. Play around with the arguments and find what works the next.

The vector should consist a X part only; Try Vector2 force = Vector2Pool.obtain(50, 0);. Then apply the force this way: body.applyForce(force, body.getWorldCenter());.