Getting Box2D Physics Working in Xcode

Here is an easy way to get up and running with Box2D in Xcode 3.2. I recently had to install Box2D and thought I might share my method for installing and creating an example Xcode project.

First, If you haven’t already got it, download MacPorts from this website as this makes installing libraries a breeze – http://www.macports.org/

Next, open up a terminal and type “sudo port install box2d”
This command downloads and starts to install the box2d libraries. The default installation places the library files in /opt/local/lib and the header files in /opt/local/include.

Once the install has finished, open up a new Xcode project and choose Application > Command Line Tool > c++ stdc++

Next, we are going to add the include and header search paths. In the top menu click Project -> Edit Active Target -> Build and under the search paths heading change the header search path to /opt/local/include and the library search path to /opt/local/lib. Note: DON’T set the recursive checkbox to true. I had problems with this, so it’s probably best to avoid it.

In the same window, click on the General tab and add a file to the “Linked Libraries” Click “add other” and navigate to /opt/local/lib/libBox2D.a

Finally, add the hello world source (this is from the original distribution)



/*
* Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

#include <Box2D/Box2D.h>
#include <cstdio>

// This is a simple example of building and running a simulation
// using Box2D. Here we create a large ground box and a small dynamic
// box.
// There are no graphics for this example. Box2D is meant to be used
// with your rendering engine in your game engine.

int main(int argc, char** argv)
{
B2_NOT_USED(argc);
B2_NOT_USED(argv);

// Define the gravity vector.
b2Vec2 gravity(0.0f, -10.0f);

// Do we want to let bodies sleep?
bool doSleep = true;

// Construct a world object, which will hold and simulate the rigid bodies.
b2World world(gravity, doSleep);

// Define the ground body.
b2BodyDef groundBodyDef;
groundBodyDef.position.Set(0.0f, -10.0f);

// Call the body factory which allocates memory for the ground body
// from a pool and creates the ground box shape (also from a pool).
// The body is also added to the world.
b2Body* groundBody = world.CreateBody(&groundBodyDef);

// Define the ground box shape.
b2PolygonShape groundBox;

// The extents are the half-widths of the box.
groundBox.SetAsBox(50.0f, 10.0f);

// Add the ground fixture to the ground body.
groundBody->CreateFixture(&groundBox, 0.0f);

// Define the dynamic body. We set its position and call the body factory.
b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
bodyDef.position.Set(0.0f, 4.0f);
b2Body* body = world.CreateBody(&bodyDef);

// Define another box shape for our dynamic body.
b2PolygonShape dynamicBox;
dynamicBox.SetAsBox(1.0f, 1.0f);

// Define the dynamic body fixture.
b2FixtureDef fixtureDef;
fixtureDef.shape = &dynamicBox;

// Set the box density to be non-zero, so it will be dynamic.
fixtureDef.density = 1.0f;

// Override the default friction.
fixtureDef.friction = 0.3f;

// Add the shape to the body.
body->CreateFixture(&fixtureDef);

// Prepare for simulation. Typically we use a time step of 1/60 of a
// second (60Hz) and 10 iterations. This provides a high quality simulation
// in most game scenarios.
float32 timeStep = 1.0f / 60.0f;
int32 velocityIterations = 6;
int32 positionIterations = 2;

// This is our little game loop.
for (int32 i = 0; i GetPosition();
float32 angle = body->GetAngle();

printf("%4.2f %4.2f %4.2f\n", position.x, position.y, angle);
}

// When the world destructor is called, all bodies and joints are freed. This can
// create orphaned pointers, so be careful about your world management.

return 0;
}

That’s it! Compile and have fun! Check out the box2d project on google code for other examples and documentation – http://code.google.com/p/box2d/

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