I'm trying to program a simple 2D platformer, and I want the player to go over some platforms. Unfortunately, my player stumbles after some platforms for no reason:
And that's clearly not what I want. The only thing I can imagine is that the boxes aren't the same height for some reason... But how to fix that? Here's some of my code:
createPlatform...
public static Body createPlatform(World world, int x, int y) {
BodyDef bodyDef = new BodyDef();
bodyDef.type = BodyDef.BodyType.StaticBody;
bodyDef.position.set(new Vector2(x, y));
PolygonShape shape = new PolygonShape();
shape.setAsBox(1, 1);
Body body = world.createBody(bodyDef);
body.createFixture(shape, Constants.GROUND_DENSITY);
body.resetMassData();
PlatformUserData userData = new PlatformUserData(1, 1, Constants.GROUND_IMAGE_PATH);
body.setUserData(userData);
shape.dispose();
return body;
}
Runner.java - act()
#Override
public void act(float delta) {
super.act(delta);
body.setLinearVelocity(new Vector2(10f,0));
}
When you have the ground made of multiple sections, the collision detection framework might detect the edge of the next block, like it was a little bit highrt than the previous. This is a computation error which happens with every sliding object sometimes. This is why they often set the player's shape to be an ellipse, and freeze the rotation of the object.
The problem is that the player fictions against the ground so velocity is greater than the friction support so the body stumbs.
You have to put:
body.setFixedRotation(true);
Or go down the value of the friction.
Related
I am working on developing a platformer, and everything's working fine, except, I seem to be unable to position the bodies for the static platforms.
// creating all the bodies
BodyDef bdef = new BodyDef();
bdef.position.set(x, y);
bdef.type = BodyType.STATIC;
Body body = world.createBody(bdef);
PolygonShape shape = new PolygonShape();
shape.setAsBox(width, height);
FixtureDef fdef = new FixtureDef();
fdef.friction = 0.3f;
fdef.shape = shape;
body.createFixture(fdef);
This is general code that's used to create every body in the map. The bodies work fine, but they don't line up with the width nor the coordinates of the map that I've set. I've noticed that I must specify the bottom left point as starting point for it to make body, but what else I am missing? Why bodies tend to be bigger and go past the starting point of X and Y?
Bodies in box2d are made from their center points. When you define it's position, you are setting it's center and when you define it's width/height, you are actually setting half the width/height (i.e. the size ends up double what you intended).
I'm doing some initial experiments for a CS course, where I'm trying to use JBox2D as a physics library and drawing using JavaFX. I have had some luck draw circles that fall from the top of the screen, but now I have issues doing the same with rectangles (or any other shape).
I'm able to both draw and simulate, but I cannot figure out how to rotate the drawn nodes in JavaFX using values from the Body objects.
Here's my code for the bodies using JBox2D:
#Override
public Body createBody() {
BodyDef bd = new BodyDef();
bd.type = BodyType.DYNAMIC;
bd.position.set(centerX, centerY);
PolygonShape ps = new PolygonShape();
ps.setAsBox(2.0f,4.0f);
FixtureDef fd = new FixtureDef();
fd.shape = ps;
fd.density = 0.9f;
fd.friction = 0.3f;
fd.restitution = 0.5f;
Body b = PhysicalScene.world.createBody(bd);
b.createFixture(fd);
return b;
}
}
This is drawn using nodes in JavaFX - as written here:
#Override
public Node create() {
Rectangle r = new Rectangle();
r.setHeight(20);
r.setWidth(40);
r.setStroke(Color.RED);
r.setLayoutX(Physics.toPixelX(centerX));
r.setLayoutY(Physics.toPixelY(centerY));
// THIS IS WHAT I'M MISSING
// r.setRotate(/* some value from Body */);
return r;
}
The code isn't pretty, but I hope you get the idea. I am able to rotate the nodes by inserting arguments in the method, but do not know how to get these values from the Body objects themselves.
I hope you can help, thanks!
I am using Box2d for a game, and although I use large constants to set angular velocity, the fastest speed I can get is 1 revolution at 3.86 seconds.
I had checked my source code in the following thread and everything is the same with what I have been suggested from both users in here and in tutorials:
setAngularVelocity rotates really slowly
However than I noticed the following unresolved thread:
http://www.reddit.com/r/libgdx/comments/1qr2m3/the_strangest_libgdxbox2d_behaviour/
and noticed that might actually be the problem. Here is my dispose method
public void dispose() {
//Get Rid of Everything!
Assets.Clear();
GameEngine.Clear();
BallMap.clear();
PlayerMap.clear();
shapeRenderer.dispose();
debugRenderer.dispose();
world.dispose();
batch.dispose();
font.dispose();
}
They are all reinitialized on the beginning as follows:
this.game = game;
this.cameraWidth = cameraWidth*pixelRatio;
this.cameraHeight = cameraHeight*pixelRatio;
batch = new SpriteBatch();
shapeRenderer = new ShapeRenderer();
stateTime = 0F;
Scores = new Integer[]{0, 0};
debugRenderer = new Box2DDebugRenderer();
world = new World(new Vector2(0, 0), true); //Create a world with no gravity
GameEngine.setContactListener(world);
I navigate through screens with the following code:
public void create () {
scene_menu = new MainMenuScreen(this, cameraWidth, cameraHeight);
setScreen(scene_menu);
}
public void swtogame(){
scene_menu.dispose();
scene_game = new MatchScreen(this, cameraWidth, cameraHeight);
setScreen(scene_game);
}
public void swtomenu(){
scene_game.dispose();
scene_menu = new MainMenuScreen(this, cameraWidth, cameraHeight);
setScreen(scene_menu);
}
the way i initialize objects:
public Object(World world, short category, short mask, float x, float y, float radius, Sprite image,
float maxSpeed, float frictionStrength, float linearDamping, float angularDamping, boolean movable,
float elasticity, float mass){
this.world = world;
this.category = category;
this.mask = mask;
// We set our body type
this.bodyDef = new BodyDef();
if(movable==true){bodyDef.type = BodyType.DynamicBody;}else{bodyDef.type = BodyType.StaticBody;}
// Set body's starting position in the world
bodyDef.position.set(x, y);
bodyDef.linearDamping = linearDamping;
bodyDef.angularDamping = angularDamping;
// Create our body in the world using our body definition
this.body = world.createBody(bodyDef);
// Create a circle shape and set its radius
CircleShape circle = new CircleShape();
circle.setRadius(radius);
// Create a fixture definition to apply our shape to
fixtureDef = new FixtureDef();
fixtureDef.shape = circle;
fixtureDef.density = (float) (mass/(Math.PI*radius*radius));
fixtureDef.friction = frictionStrength;
fixtureDef.restitution = elasticity;
fixtureDef.filter.categoryBits = category;
fixtureDef.filter.maskBits = mask;
// Create our fixture and attach it to the body
this.fixture = body.createFixture(fixtureDef);
// BodyDef and FixtureDef don't need disposing, but shapes do.
circle.dispose();
... unrelated functions after that
}
Am I disposing correctly? Is this a bug? Is there any way to get around it and use the setAngularVelocity properly?
Because you haven't shown much code, I can I'm not 100% sure that I'm right, but I think that you are hitting the built in maximum movement limit of 2.0 units per time step. This means that at a typical framerate of 60Hz a body covering 2 units per timestep is moving at 120 m/s or 432 km/h (270 mph). Unfortunately it seems that there is no direct way to change this limit in Java, because this limit seems to be defined in the native C++ librarys.
But I think that the real problem is that you have a wrong scale. Box2D uses MKS (meters, kilograms, and seconds). And you may have used pixels instead of meters. The FAQ of Box2D suggests to use
objects [that are] between 0.1 - 10 meters
otherwise you can get strange situations.
See http://www.iforce2d.net/b2dtut/gotchas#speedlimit
and https://code.google.com/p/box2d/wiki/FAQ
I just found the problem, and it was pretty simple. Im just going to post this here for future googlers:
Object was actually rotating properly, the problem was in my drawing method, I didn't use conversion between radians to degrees in my batch.draw, and it interpreted everything in radians. I know such an amateur mistake! Thanks a lot for your time.
I am trying to re-create Pong using LibGDX and Box2D. I have 2 problems, if I fix one it creates another.
My paddles are currently set to Kinematic and are controlled using the up/down keys via a controller class. This works just fine and I can happily play back and forth.
Problem being, my walls are static bodies and my paddles just travel right through them.
Now I can fix this by simple changing the paddle body to a dynamic one, this stops the paddles from going through the walls but then when my ball strikes off a paddle, it goes flying off the X axis and off the screen.
I have tried adding an update method in my controller class as follows:
public void update(float delta){
paddleBodyPosY = paddleBody.getPosition().x;
paddleBodyPosY = paddleBody.getPosition().y;
System.out.println(paddleBodyPosY);
}
The console reports the paddle position being updated every frame, from top to bottom of screen.
So I went back to my GameScreen class and tried all sorts of code in the Render() method like so:
if(playerOnePaddle.paddleBodyPosY < 0){
playerOnePaddle.paddleBody.getPosition().y = 0;
System.out.println("resetting paddle");
}
I have tried LOADS of variations, I can easily break movement by calling paddleBody.setLinearVelocity(0,0) but then it gets stuck like this and it's not movable anymore. Obviously the problem must lie with the fact that I can't set a position using a getter lol.
Any ideas? If you need more snippets ask, I didn't want to overload the question with 100 lines of code you don't need to see :S.
The paddle creation method:
public void createPaddle(World world, float x, float y){
//Define a body for the paddle
BodyDef paddleBodyDef = new BodyDef();
paddleBodyDef.type = BodyType.KinematicBody;
paddleBodyDef.position.set(x, y);
//Define a shape for the paddle
PolygonShape paddleShape = new PolygonShape();
paddleShape.setAsBox(paddleWidth, paddleHeight);
//Define a fixture for the paddle
FixtureDef paddleFixtureDef = new FixtureDef();
paddleFixtureDef.shape = paddleShape;
paddleFixtureDef.density = 0;
//Ensures ball bounces off paddle
//Consistently without losing velocity
paddleFixtureDef.restitution = 1.005f;
//Create the paddles
paddleBody = world.createBody(paddleBodyDef);
paddleFixture = paddleBody.createFixture(paddleFixtureDef);
paddleShape.dispose();
}
Heh, so what I did was.
Set my paddles to dynamic, then set there mass to a stupidly high number so that the a ball would not move them on the x axis, well not enough for the human eye to see at least.
Seems like a cheap fix, if anyone has anything better...that would be great lol
I'm using JBox2d to perform collision detection in a game project I'm working on.
I represent obstacles in the world with static bodies. Whenever a dynamic body (i.e. a game character) collides with one of these obstacles, there is a very noticeable drop in performance. Fps will drop from ~120 to ~5. This seems to happen more frequently when the corners of the static body are collided with.
When I set the body type of the world obstacles to be dynamic instead of static, with very high density(to prevent the body from moving when it is collided with), this issue disappears... This solution is not ideal for my situation however......
Any ideas as to what could be causing this huge fps drop?
Here's the code I use to create the static bodies:
BodyDef def = new BodyDef();
def.type = BodyType.STATIC; // If this line is commented and the other
//commented lines are uncommented, the issue goes away.
//def.type = BodyType.DYNAMIC;
def.position.set(worldBounds.getCenterX(), worldBounds.getCenterY());
Body staticBody = b2World.createBody(def);
PolygonShape box = new PolygonShape();
box.setAsBox(worldBounds.getWidth() * 0.5f, worldBounds.getHeight() * 0.5f);
FixtureDef fixture = new FixtureDef();
fixture.shape = box;
fixture.friction = 0.3f;
//fixture.density = 1000000000;
staticBody.createFixture(fixture);
//staticBody.setSleepingAllowed(true);
//staticBody.setFixedRotation(true);
I've tried using a CircleShape instead of a PolygonShape, but that doesn't help anything.
Thank you!
this is the code from the game im working on at the moment which works fine. hopefully if you copy and paste, change a few variable names and stuff it might sort your problem. im new to box2d so cant tell you exactly where the problem lies. hope it helps.
//bodydef
BodyDef bodyDef = new BodyDef();
bodyDef.type = BodyType.StaticBody;
bodyDef.position.set(position);
body = world.createBody(bodyDef);
//shape
PolygonShape shape = new PolygonShape();
shape.setAsBox(dimension.x / 2, dimension.y / 2);
//fixture
FixtureDef fixture = new FixtureDef();
fixture.friction = 0.3f;
fixture.shape = shape;
body.createFixture(fixture);
shape.dispose();