Box2D world size

Question

I have created a box2d world, and I wanted to limit the height of the world. I did search google and apparently there was an option in the previous version of box2d where you would have to define the size of your world, but I am not sure if you were able set the height of the world but in the current version they have taken that option completely off.

So I am just looking for a way to limit the height, as my player is a ball that jumps up and down and I want to limit how high it can jump (the jumps are done by physics and gravity and the speed of the ball so after a few good jumps, the ball jumps really high as its speed increases and I dont want to limit the speed) and put border on let say y=900.

score 6 · Accepted Answer · answered Nov 05 '11 at 12:40

The Box2D world has an infinite size. You can't limit the world, but you can create a shape that encloses a certain area in the Box2D world.

Here's how to create a body and shape that puts a shape just around the screen, so that objects don't leave the screen. It is easy to adapt this code by changing the corner coordinates to fit whatever you need:

        // for the screenBorder body we'll need these values
        CGSize screenSize = [CCDirector sharedDirector].winSize;
        float widthInMeters = screenSize.width / PTM_RATIO;
        float heightInMeters = screenSize.height / PTM_RATIO;
        b2Vec2 lowerLeftCorner = b2Vec2(0, 0);
        b2Vec2 lowerRightCorner = b2Vec2(widthInMeters, 0);
        b2Vec2 upperLeftCorner = b2Vec2(0, heightInMeters);
        b2Vec2 upperRightCorner = b2Vec2(widthInMeters, heightInMeters);

        // static container body, with the collisions at screen borders
        b2BodyDef screenBorderDef;
        screenBorderDef.position.Set(0, 0);
        b2Body* screenBorderBody = world->CreateBody(&screenBorderDef);
        b2EdgeShape screenBorderShape;

        // Create fixtures for the four borders (the border shape is re-used)
        screenBorderShape.Set(lowerLeftCorner, lowerRightCorner);
        screenBorderBody->CreateFixture(&screenBorderShape, 0);
        screenBorderShape.Set(lowerRightCorner, upperRightCorner);
        screenBorderBody->CreateFixture(&screenBorderShape, 0);
        screenBorderShape.Set(upperRightCorner, upperLeftCorner);
        screenBorderBody->CreateFixture(&screenBorderShape, 0);
        screenBorderShape.Set(upperLeftCorner, lowerLeftCorner);
        screenBorderBody->CreateFixture(&screenBorderShape, 0);

Note: this code is for Box2D v2.2.1. I assume that's what you're using because you said "previous version" which required this code to be written differently (with the SetAsEdge method).

thanks, works great :) ... just one question, why do people get the width in meters? I have seen a few people do this... — Ahoura Ghotbi, Nov 05 '11 at 12:54
Box2D standard length units are in meters, although how "long" a meter is in your app is for anyone to define. Hence the PTM (pixels to meter) ratio. — CodeSmile, Nov 05 '11 at 19:58
I liked your answer but I suggest removing that first sentence about infinite size. While the Box2D world doesn't explicitly have size limits, it's not infinite in any usable sense. The simulation degrades the farther bodies are from the origin (0, 0) and has hard limits imposed by the [floating point](https://en.wikipedia.org/wiki/Floating_point) representation of numbers. The Box2D manual mentions limitations as well in chapters 1.7 and 13. — Louis Langholtz, Jan 24 '17 at 21:58

Box2D world size

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