How to add a jumping mechanic to a game?

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Dmartin42

Hello,

I have made a platformer but cannot figure out how to add a jumping mechanic. It is currently setup as follows:
The player presses 'space' and I move the entity up ten and let my GravityForce bring them back down.

private void jump(Creature player) {

	{
			Point2D jumpHeight = new Point2D.Double(player.getX(), player.getY()-10);
			player.setMoveDestination(jumpHeight);
			Game.getPhysicsEngine().move(player, player.getMoveDestination());
	}

However, I want it so that the player can ONLY jump if they have collision with an entity or a static collision box. I have tried the game.getPhysics.collide() method in many ways but still cant figure it out. If anyone has suggestions, that would be great.

CalvinMT

Dmartin42
You can try using "player.getBoundingBox().intersects()" in an "if" that'll be surrounding your jump code.
If true: jump. If not: nothing.
Might cost a bit though, especially if you need to go through all collidable objects... :/

steffen

Dmartin42

... ONLY jump if they have collision with an entity or a static collision box

Technically, that should never be the case because that would mean that the collision was not properly resolved previously and the entity would be stuck in a collision box.

I think what you might be looking for is something like: if the player is touching the ground or another entity.
Depending on how you configured your player's collision and size properties, you should be able to use the player's bounding box if it's bigger than the collision box and do as CalvinMT suggested. You can just use the PhysicsEngine for this, too:

if(Game.getPhysicsEngine().collides(player.getBoundingBox())){
  // allow jump
}

You can configure your player's collision and size properties like so:

player.setCollisionBoxHeight(collisionBoxHeight);
player.setCollisionBoxWidth(collisionBoxHeight);
player.setWidth(boundingBoxWidth);
player.setHeight(boundingBoxHeight);

Another option would be to write a custom class for your player that extends Creature and uses annotations.

@EntityInfo(width = 16, height = 16)
@CollisionInfo(collision = true, collisionBoxHeight = 4, collisionBoxWidth = 8)
public class MyPlayer extends Creature{
...
}

Also, I highly recommend enabling some debug rendering if you're playing around with collision boxes and bounding boxes.

Go to the game.properties file and set

dbg_debugEnabled=true
dbg_renderBoundingBoxes=true
dbg_renderCollisionBoxes=true

nightm4re

Dmartin42 In case you haven't already seen it: there's a Jump implemented in our new sample platformer project Gurk Nukem.

Dmartin42

steffen
Thank you. I did this and it still doesn't work. Here is my code:

if( (Game.getPhysicsEngine().collides(player.getBoundingBox(),CollisionType.STATIC)) ||
(Game.getPhysicsEngine().collides(player.getBoundingBox(),CollisionType.ENTITY)) ){
Point2D jumpHeight = new Point2D.Double(player.getX(), player.getY()-10);
player.setMoveDestination(jumpHeight);
Game.getPhysicsEngine().move(player, player.getMoveDestination());
}

I am still able to jump mid-air because it thinks the moving player is colliding with itself. Is there a way around this?

steffen

Dmartin42 you could just use the method overload

if(Game.getPhysicsEngine().collides(player.getBoundingBox(), player)){
  Point2D jumpHeight = new Point2D.Double(player.getX(), player.getY()-10);
  player.setMoveDestination(jumpHeight);
  Game.getPhysicsEngine().move(player, player.getMoveDestination());
}

This will explicitly exclude the specified entity from the collision detection.
I think we could improve the PhysicsEninge API a bit for such scenarios.

Dmartin42

steffen
Steffen,
The use of overloading does not work because .getBoundingBox returns a rectangle and not a point. Is there any way around these things?

steffen

Dmartin42 Damn, you're right... such a method is not available in 0.4.14
It will be in the next version.

Another workaround would be to check entity collision manually.

if(Game.getPhysicsEngine().collides(player.getBoundingBox(), CollisionType.STATIC)
|| Game.getPhysicsEngine().getCollisionEntities().stream().anyMatch(e -> !e.equals(player) && e.getCollisionBox().intersects(player.getBoundingBox))){
  Point2D jumpHeight = new Point2D.Double(player.getX(), player.getY()-10);
  player.setMoveDestination(jumpHeight);
  Game.getPhysicsEngine().move(player, player.getMoveDestination());
}

From LITIengine 0.4.15 onward, the syntax for this will be as described in my previous post.