Questions tagged [box2d]

Box2D is an open-source rigid-body 2D physics simulation library for games, written in C++, with ports in various languages

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Box2D Body cannot be serialized. How to ignore or serialize it successfully?

In my game, which implements the network functionality with Kryonet, I would like to send a class ("MyBox2DComponent") over the network which e.g. contains a field of type Body (Box2D). Of ...
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Box2D & Processing - Collision location randomly assigned to center point

I am working on a particle simulation using Box2D with Processing. The setup: I generate 4 kinds of particles that exist in equal amounts (for instance 200 in total, 50 each). They are (for now) ...
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character movment and physics on 2d game

I'm developing a client/server multiplayer game. in server side i need prevent players cross map objects like walls also i need prevent player go inside each others, instead want to slide them along ...
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Implementing a custom joint in Box2D

I would like to implement a "rail joint" in Box2D: a joint which lets a body move only along a given curve. I couldn't find anything about defining custom joints. Is it possible at all ...
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problems with displaying sfml textures

I have created a kind of framework for a game that combines box2d and sfml. All game scenes are stored in the Game class. The scenes also contain information about static and dynamic objects: ...
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How can I assign a World.createBody to a variable after initialization, `var` and `val` don't work?

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How do I correctly use userData in Box2d?

Many guides used userData. But with the source of Box2d I have, I don't see the SetUserData functions in the code as I see them in the guides. After understanding ...
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Compute normal of collision between two bodies, when multiple fixtures touch

I have a body made of multiple fixtures. Sometimes, when another body collides with it, Box2D detects contacts between more than one fixture. The figure illustrates this: the blue body is made of two ...
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Simulating a small world with Box2D

I would like to use Box2D to simulate a small world, with entity sizes around 1cm (0.01m), some smaller than that. Box2D's FAQ says twice: Your moving objects should be between 0.1 - 10 meters. You ...
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Object stuck against an obstacle still pushes other objects away

I have an object pinned against the ground by a revolute joint. A motor on the joint makes the object spin. Sometimes the object becomes stuck pushing against a static body. When it happens the object ...
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Collision filtering in Box2D: running out of bits

I have a physical simulation on the streets of a city. The simulation is 2D but in a few points it could develop on multiple "layers": for instance bridges or underground tunnels. I may have ...
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Simulating a rocket out of control in Box2D

In the void of space, a spaceship releases a rectangle shaped space-torpedo. In half a second, it starts its rocket engine and goes straight until something get in its way, and then boom! The code ...
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Avoiding jitter when snapping diagonal movement to a pixel grid

Whats the best way to be rendering the locations of objects in box2D in such a way that there no stuttering on movement beyond 8-directions. I'm looking to have object strictly snap to the pixels but ...
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What could effectively affect the falling speed of a b2Body?

I tried to set up a test demo to see if Box2D physics are working. It works, but I have one small problem: I cannot seem to get the dynamic b2Body to fall faster. I ...
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Box2D calculate distance in certain direction

I'm writing simple AI genetic learning for a 2d car. To do so I need sensors surrounding my car so I can get distance to closest obstacle in every direction. (Picture 1) Picture 1: I need every of the ...
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Way to check overlaps of a collider2d that's not set to "is trigger" in Unity

I have a system where physics2d objects are spawned and I need to know when they spawn outside of a region defined by a box collider set to "is Trigger". Using onTriggerEnter and ...
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How to create a joint, where the rotation of one object is relative to the other?

I would like to create a top down view scene, with one rectangle (top) is on top of an other (base). There is a joint, where ...
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Box2d: High screen resolution / frequency causes high friction?

I'm using Cocos Creator with (built-in) box2d for physics. Recently our game behaves weirdly on our new device Galaxy S20 Ultra 5G - which has screen size = 1440 x 3200 - frequency = 120Hz. After stop ...
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Predicting trajectory of Box2D physics body using both: linear dumping and gravity

I would like to calculate position of physics body after some time because of predicting shots trajectory in my game. I found some great answer here where Iter Ator provides equation to calculate ...
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When an object is launched off-screen, is there any way to know if it's coming back?

In this scene, the object becomes invisible and then comes back In this scene, the object becomes invisible but does not come back Is there any way I can tell if an object will come back when it ...
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3 votes
1 answer
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How to develop both a client and headless server together in Unity

I'm making a multiplayer 2d shooter platformer in unity. And after studying the different options to program an authoritarian server and with the great help that many of you have already provided me ...
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Box2d on authoritative server for Unity client

I'm creating a multiplayer platform and shooting game in unity, using unity2d's own physics system (box2d). But the truth is that I am quite lost in the creation of an authoritative server in c ++. I ...
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how to set volume of sound depending on the impulse a body receives in Libgdx / Box2d?

I am trying to set the volume of a bouncing sound of a ball depending on how hard the ball hits something. so the harder the ball hits a wall or a ground the more loud the bounce sound. I couldn't ...
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Optimizing Box2D for a couple hundred static bodies

I searched but could not find anything similar (Yet) around the web, so here I am asking my question: In my game I use around 3 to 4 hundred static bodies with like 10 dynamic bodies in the Box2D ...
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setTransform() Box2D physics not working

It's my first time posting here! I'm working on a top-down shooter game in LibGDX and Box2D (so gravity is set to (0, 0)). At the moment, to move my character, I'm ...
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Body's initial velocity is too fast when created after minimax algo

I don't know if my question is right but I cannot address the real problem. I am dropping connect 4 game chips under gravity but when I apply minimax with a depth of 3, it starts with great velocity. ...
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Box2d: crash on createBody in beginContact callback

I am getting this error on creating body in contactListener ...
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Apply impulse in direction line is pointing with force proportional to the length of line

I have a line perpetually pointed at the mouse and originating at the player, but the length is limited to a certain value. I also can create a circular object on demand in Box2D (specifically the ...
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Box2d RopeJoint bug - fix or alternative solution?

What I am trying to do is to create rope game. Below you can find a movie how it looks like now. https://youtu.be/QTULCGNF70I I am using RopeJoint and I am reducing maxLength each frame to be able ...
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Planck.js (rewritten of Box2D.js) - 8 direction box movement

I have a box in Planck.js. I want to move this box with some keys. How can I do that? My code: ...
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Box2d ContactListener function. Problem calling a function on the collided objects

I created a ContactListener class which derives from b2ContactListener. I am following the excellent tutorials found here: https://www.iforce2d.net/b2dtut/collision-callbacks Collisions are detected ...
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How do I make a hitbox for a sword in a top-down game?

Context: I'm using Box2D through LibGDX in Java. The sword and the player are in separate classes. Both extend LibGDX's Sprite class. I've got a sword attached to my character that swings when I ...
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Box2d Raycast C++. Always returning false? (trying to check if player is grounded)

I'm trying to add Box2d to my C++/SFML platformer game. I have my ground tiles with a b2staticBody. And the player character is b2_dynamicBody. My usual method to check if player is grounded is to ...
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LibGDX Box2D, how to play an animation once, then set the state back

So, I've got some animations in LibGDX that I want to get running. Currently, the walking animations work perfectly, but attacking doesn't. I want the attack animation to play once, then set the State ...
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testPoint not working - libgdx

I'm making a game like angry birds with LibGDX and box2d in which I want to drag a ball (instead of the bird) back before releasing it. I deploy with testPoint function: when I touch down the ...
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216 views

How to damp the velocity of an object only in one axis in Box2d?

I want to damp the velocity of a ball linearly on the x-axis. but when applying linear damping on the ball, the damping also applies in the y-axis which makes it look like its floating. I tried to ...
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What would be the best way to let Box2D handle collision on different (simulated) heights?

I'm working on a 2D top-down game but we are also using a Z coordinate. This is to simulate the effect of 3D/height. Now the player can walk under a bridge and also over a bridge. The next thing I did ...
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How do i draw sprite on fixture position?

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Assertion b2Assert(m_bodyCount > 0) showing an error

I have the following code for deleting a Box2D body: ...
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How to keep the value of angle between 0 and PI in box2d

In box2d, if i rotate an object multiple times in clockwise or anti clockwise direction, the value of angle ( body.getAngle() ) keeps on increasing. Like at start it is at 0 radians, then 1.57(90 deg),...
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LibGDX “EXCEPTION_ACCESS_VIOLATION” error when recreating previously disposed Box2DLights light

I just installed the Box2DLights dependency for LibGDX and I added a cave with 2 ConeLights inside. The first time I render the cave, everything works as expected. Then when I exit the cave, I make ...
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What scaling system to use in Box2d?

I'm worried about this Caution box from the Box2d manual: Box2D is tuned for MKS units. Keep the size of moving objects roughly between 0.1 and 10 meters. You'll need to use some scaling system ...
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how to apply force/impulse perpendicular to the moving direction in box2d

How can i apply or impulse to an object perpendicular to its moving direction in a top down game. Like if object is moving up, i press left or right, then force or impulse should be applied to left or ...
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3 answers
207 views

Finding an angle between two bodies

I am trying to find angle between vectors a and b. But the cosine for some reason is not within +/- 1, that means that it is not possible to find an angle between a car and a pedestrian... Any help ...
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How to limit Box2D bodies to only be affected on 1 axis

I have a side scrolling game, where I am randomly placing trees, bushes etc.. I would like these bodies to fall ( To Align with the ground ) but not to slide. What is the best way to achieve this and ...
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Rolling a circle around a square

I am stuck on a simple Box2D task. I have a box and a ball (in top-down view so no gravity), and I would like the ball to roll around the box. Here is my code. Basically now I am trying to detect ...
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Pybox2d Collision detection explanation

Hi I am working on a PyBox2D game and it became quite complex and I need to learn about collisions, so I made this very simple script in order to learn collision setting more effectively, however I am ...
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How to make a top down 2D ball rolling

I am developing a top down game similar to 8 pool billard with libgdx and box2d. How do i make a 2d ball texture look like its rolling when force is applied like this: So it feels actually 3d ? For ...
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3 votes
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Game runs at different speeds in Chrome versus Firefox

I am using Box2D for physics on the server side. Player position is updated on the server, so there is nothing the client can do except give input. But running game in Chrome only, the player moves ...
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Box2D Weird collision behavior

I'll let the gif speak first. As you can see, the small cube just kinda floats there like it has a forcefield. This weird glitch only happens with small cubes, smaller than 60 pixels for some reason. ...
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