Need help setting up BOX2D - GameCreators Forum

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Joined: 17th May 2006

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Posted: 14th Jun 2009 06:15

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Hi, i was wondering if someone could give me a hand setting up BOX2.
This is what ive tried to do:

#include "DarkGDK.h"
#include "Box2D.h"

#define CUBE 1
#define CUBE2 2
#define IMAGE_CUBE 1
#define SCREEN_TO_WORLD(n) ((n) / 30)
#define WORLD_TO_SCREEN(n) ((n) * 30)

void DarkGDK ( void )
{
	// turn on sync rate and set maximum rate to 60 fps
	dbSyncOn   ( );
	dbSyncRate ( 60 );
	dbSetDisplayMode(800,600,32);
//Set up BOX2D
	b2AABB worldAABB;
	worldAABB.minVertex.Set(0, 0);
	worldAABB.maxVertex.Set(SCREEN_TO_WORLD(800), SCREEN_TO_WORLD(600));
	b2Vec2 gravity(0.0f,10.0f);
	bool doSleep = true;
	b2World world(worldAABB, gravity, doSleep);

//Make sprites from Cube.png
	dbLoadImage("Cube.png",IMAGE_CUBE); //Cube.png size is 100x100
	dbSprite(CUBE,0,0,IMAGE_CUBE);
	dbSprite(CUBE2,0,0,IMAGE_CUBE);
	dbHideSprite(CUBE);
	dbHideSprite(CUBE2);

// Define the ground box shape.
	b2BoxDef groundBoxDef;
// The extents are the half-widths of the box.
	groundBoxDef.extents.Set(50.0f, 5.0f);
// Set the density of the ground box to zero. This will
// make the ground body static (fixed).
	groundBoxDef.density = 0.0f;
// Define the ground body.
	b2BodyDef groundBodyDef;
	groundBodyDef.position.Set(0.0f, SCREEN_TO_WORLD(600));
// Part of a body's def is its list of shapes.
	groundBodyDef.AddShape(&groundBoxDef);
// 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.
	world.CreateBody(&groundBodyDef);
// Define another box shape for our dynamic body.
	b2BoxDef boxDef;
	boxDef.extents.Set(0.5f, 0.5f);
// Set the box density to be non-zero, so it will be dynamic.
	boxDef.density = 5.0f;
// Override the default friction.
	boxDef.friction = 0.3f;
// Define the dynamic body. We set its position,
// add the box shape, and call the body factory.
	b2BodyDef bodyDef;
	bodyDef.position.Set(SCREEN_TO_WORLD(80), 0);
	bodyDef.AddShape(&boxDef);
	b2Body* body = world.CreateBody(&bodyDef);

// Define the dynamic body. We set its position,
// add the box shape, and call the body factory.
	b2BodyDef bodyDef2;
	bodyDef2.position.Set(SCREEN_TO_WORLD(100), SCREEN_TO_WORLD(200));
	bodyDef2.AddShape(&boxDef);
	b2Body* body2 = world.CreateBody(&bodyDef2);

// 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 iterations = 10;

// our main loop
	while ( LoopGDK ( ) )
	{
		world.Step(timeStep, iterations);
		dbPasteSprite(CUBE,WORLD_TO_SCREEN(body->GetCenterPosition().x),WORLD_TO_SCREEN(body->GetCenterPosition().y));
		dbRotateSprite(CUBE,body->GetRotation()*(180.0 / 3.141592653589793238));
		dbPasteSprite(CUBE2,WORLD_TO_SCREEN(body2->GetCenterPosition().x),WORLD_TO_SCREEN(body2->GetCenterPosition().y));
	// update the screen
		dbSync ( );
	}

// return back to windows
	return;
}

+ Code Snippet

#include "DarkGDK.h"
#include "Box2D.h"

#define CUBE 1
#define CUBE2 2
#define IMAGE_CUBE 1
#define SCREEN_TO_WORLD(n) ((n) / 30)
#define WORLD_TO_SCREEN(n) ((n) * 30)

void DarkGDK ( void )
{
	// turn on sync rate and set maximum rate to 60 fps
	dbSyncOn   ( );
	dbSyncRate ( 60 );
	dbSetDisplayMode(800,600,32);
//Set up BOX2D
	b2AABB worldAABB;
	worldAABB.minVertex.Set(0, 0);
	worldAABB.maxVertex.Set(SCREEN_TO_WORLD(800), SCREEN_TO_WORLD(600));
	b2Vec2 gravity(0.0f,10.0f);
	bool doSleep = true;
	b2World world(worldAABB, gravity, doSleep);

//Make sprites from Cube.png
	dbLoadImage("Cube.png",IMAGE_CUBE); //Cube.png size is 100x100
	dbSprite(CUBE,0,0,IMAGE_CUBE);
	dbSprite(CUBE2,0,0,IMAGE_CUBE);
	dbHideSprite(CUBE);
	dbHideSprite(CUBE2);

// Define the ground box shape.
	b2BoxDef groundBoxDef;
// The extents are the half-widths of the box.
	groundBoxDef.extents.Set(50.0f, 5.0f);
// Set the density of the ground box to zero. This will
// make the ground body static (fixed).
	groundBoxDef.density = 0.0f;
// Define the ground body.
	b2BodyDef groundBodyDef;
	groundBodyDef.position.Set(0.0f, SCREEN_TO_WORLD(600));
// Part of a body's def is its list of shapes.
	groundBodyDef.AddShape(&groundBoxDef);
// 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.
	world.CreateBody(&groundBodyDef);
// Define another box shape for our dynamic body.
	b2BoxDef boxDef;
	boxDef.extents.Set(0.5f, 0.5f);
// Set the box density to be non-zero, so it will be dynamic.
	boxDef.density = 5.0f;
// Override the default friction.
	boxDef.friction = 0.3f;
// Define the dynamic body. We set its position,
// add the box shape, and call the body factory.
	b2BodyDef bodyDef;
	bodyDef.position.Set(SCREEN_TO_WORLD(80), 0);
	bodyDef.AddShape(&boxDef);
	b2Body* body = world.CreateBody(&bodyDef);

// Define the dynamic body. We set its position,
// add the box shape, and call the body factory.
	b2BodyDef bodyDef2;
	bodyDef2.position.Set(SCREEN_TO_WORLD(100), SCREEN_TO_WORLD(200));
	bodyDef2.AddShape(&boxDef);
	b2Body* body2 = world.CreateBody(&bodyDef2);

// 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 iterations = 10;

// our main loop
	while ( LoopGDK ( ) )
	{
		world.Step(timeStep, iterations);
		dbPasteSprite(CUBE,WORLD_TO_SCREEN(body->GetCenterPosition().x),WORLD_TO_SCREEN(body->GetCenterPosition().y));
		dbRotateSprite(CUBE,body->GetRotation()*(180.0 / 3.141592653589793238));
		dbPasteSprite(CUBE2,WORLD_TO_SCREEN(body2->GetCenterPosition().x),WORLD_TO_SCREEN(body2->GetCenterPosition().y));
	// update the screen
		dbSync ( );
	}

	// return back to windows
	return;
}

I create the floor and 2 boxes with a size of 100x100 px.
But they dont collide correctly (And the rotation is messed up)
To run the code you need a cube.png image of 100x100px
Thanks.

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Diggsey

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Joined: 24th Apr 2006

Location: On this web page.

Posted: 14th Jun 2009 21:38

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For a start, change these lines:

+ Code Snippet

#define SCREEN_TO_WORLD(n) ((n) / 30)
#define WORLD_TO_SCREEN(n) ((n) * 30)

To this:

+ Code Snippet

#define SCREEN_TO_WORLD(n) ((n) / 30.0f)
#define WORLD_TO_SCREEN(n) ((n) * 30.0f)

Secondly, the rotation may be messed up because clockwise/anticlockwise depend on the up direction, and so are application dependent. Try negating the angles you use for dbRotateSprite().

Thirdly, update to the latest version of Box2D, (which means that you will then add shapes to the body rather than the body def

)

Fourthly, once you have updated, there will be a command called 'SetMassFromShapes' which you must call after adding shapes to a body.

New DBPro IDE + integrated debugger!

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FERSIS

18

Years of Service

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Joined: 17th May 2006

Location:

Posted: 14th Jun 2009 22:18 Edited at: 14th Jun 2009 22:26

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Thanks Diggsey my #macros were bad. (Bad macro,bad!)
The rotation was messed up because i didnt know about the dbOffsetSprite command...
Again , thanks... have you tought on making a wrapper of BOX2D ?
You know for physics noobs like me

Code fixed:

#include "DarkGDK.h"
#include "Box2D.h"

#define CUBE 1
#define CUBE2 2
#define CUBE3 3
#define IMAGE_CUBE 1
#define SCREEN_TO_WORLD(n) ((n) / 30.0f)
#define WORLD_TO_SCREEN(n) ((n) * 30.0f)
float fAngle = 0;
void DarkGDK ( void )
{
	// turn on sync rate and set maximum rate to 60 fps
	dbSyncOn   ( );
	dbSyncRate ( 60 );
	dbSetDisplayMode(800,600,32);
//Make sprites from Cube.png
	dbLoadImage("Cube.png",IMAGE_CUBE); //Cube.png size is 100x100
	dbSprite(CUBE,0,0,IMAGE_CUBE);
	dbSprite(CUBE2,0,0,IMAGE_CUBE);
	dbSprite(CUBE3,0,0,IMAGE_CUBE);
	dbOffsetSprite(CUBE,dbSpriteWidth(CUBE)/2,dbSpriteHeight(CUBE)/2);
	dbOffsetSprite(CUBE2,dbSpriteWidth(CUBE2)/2,dbSpriteHeight(CUBE2)/2);
	dbOffsetSprite(CUBE3,dbSpriteWidth(CUBE3)/2,dbSpriteHeight(CUBE3)/2);
	dbHideSprite(CUBE);
	dbHideSprite(CUBE2);
	dbHideSprite(CUBE3);
// Define the size of the world. Simulation will still work
	// if bodies reach the end of the world, but it will be slower.
	b2AABB worldAABB;
	worldAABB.lowerBound.Set(0,0);
	worldAABB.upperBound.Set(SCREEN_TO_WORLD(800), SCREEN_TO_WORLD(600));

// 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(worldAABB, gravity, doSleep);

// Define the ground body.
	b2BodyDef groundBodyDef;
	groundBodyDef.position.Set(0.0f, SCREEN_TO_WORLD(600));

// 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.
	b2PolygonDef groundShapeDef;

// The extents are the half-widths of the box.
	groundShapeDef.SetAsBox(50.0f, 5.0f);

// Add the ground shape to the ground body.
	groundBody->CreateShape(&groundShapeDef);

// Define the dynamic body. We set its position and call the body factory.
	b2BodyDef bodyDef;
	bodyDef.position.Set(SCREEN_TO_WORLD(400), SCREEN_TO_WORLD(100));
	b2Body* body = world.CreateBody(&bodyDef);
	bodyDef.position.Set(SCREEN_TO_WORLD(450), SCREEN_TO_WORLD(-20));
	b2Body* body2 = world.CreateBody(&bodyDef);
	bodyDef.position.Set(SCREEN_TO_WORLD(360), SCREEN_TO_WORLD(250));
	b2Body* body3 = world.CreateBody(&bodyDef);
	// Define another box shape for our dynamic body.
	b2PolygonDef shapeDef;
	shapeDef.SetAsBox(1.0f, 1.0f);

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

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

// Add the shape to the body.
	body->CreateShape(&shapeDef);
	body2->CreateShape(&shapeDef);
	body3->CreateShape(&shapeDef);
	// Now tell the dynamic body to compute it's mass properties base
	// on its shape.
	body->SetMassFromShapes();
	body2->SetMassFromShapes();
	body3->SetMassFromShapes();
// 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 iterations = 10;

// our main loop
	while ( LoopGDK ( ) )
	{
		world.Step(timeStep, iterations);
	// update the screen
		dbRotateSprite(CUBE,body->GetAngle()*(180.0 / 3.141592653589793238));
		dbRotateSprite(CUBE2,body2->GetAngle()*(180.0 / 3.141592653589793238));
		dbRotateSprite(CUBE3,body3->GetAngle()*(180.0 / 3.141592653589793238));
		dbPasteSprite(CUBE,WORLD_TO_SCREEN(body->GetPosition().x),WORLD_TO_SCREEN(body->GetPosition().y));
		dbPasteSprite(CUBE2,WORLD_TO_SCREEN(body2->GetPosition().x),WORLD_TO_SCREEN(body2->GetPosition().y));
		dbPasteSprite(CUBE3,WORLD_TO_SCREEN(body3->GetPosition().x),WORLD_TO_SCREEN(body3->GetPosition().y));
		dbSync ( );
	}

// return back to windows
	return;
}

+ Code Snippet

#include "DarkGDK.h"
#include "Box2D.h"

#define CUBE 1
#define CUBE2 2
#define CUBE3 3
#define IMAGE_CUBE 1
#define SCREEN_TO_WORLD(n) ((n) / 30.0f)
#define WORLD_TO_SCREEN(n) ((n) * 30.0f)
float fAngle = 0;
void DarkGDK ( void )
{
	// turn on sync rate and set maximum rate to 60 fps
	dbSyncOn   ( );
	dbSyncRate ( 60 );
	dbSetDisplayMode(800,600,32);
//Make sprites from Cube.png
	dbLoadImage("Cube.png",IMAGE_CUBE); //Cube.png size is 100x100
	dbSprite(CUBE,0,0,IMAGE_CUBE);
	dbSprite(CUBE2,0,0,IMAGE_CUBE);
	dbSprite(CUBE3,0,0,IMAGE_CUBE);
	dbOffsetSprite(CUBE,dbSpriteWidth(CUBE)/2,dbSpriteHeight(CUBE)/2);
	dbOffsetSprite(CUBE2,dbSpriteWidth(CUBE2)/2,dbSpriteHeight(CUBE2)/2);
	dbOffsetSprite(CUBE3,dbSpriteWidth(CUBE3)/2,dbSpriteHeight(CUBE3)/2);
	dbHideSprite(CUBE);
	dbHideSprite(CUBE2);
	dbHideSprite(CUBE3);
// Define the size of the world. Simulation will still work
	// if bodies reach the end of the world, but it will be slower.
	b2AABB worldAABB;
	worldAABB.lowerBound.Set(0,0);
	worldAABB.upperBound.Set(SCREEN_TO_WORLD(800), SCREEN_TO_WORLD(600));

	// 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(worldAABB, gravity, doSleep);

	// Define the ground body.
	b2BodyDef groundBodyDef;
	groundBodyDef.position.Set(0.0f, SCREEN_TO_WORLD(600));

	// 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.
	b2PolygonDef groundShapeDef;

	// The extents are the half-widths of the box.
	groundShapeDef.SetAsBox(50.0f, 5.0f);

	// Add the ground shape to the ground body.
	groundBody->CreateShape(&groundShapeDef);

	// Define the dynamic body. We set its position and call the body factory.
	b2BodyDef bodyDef;
	bodyDef.position.Set(SCREEN_TO_WORLD(400), SCREEN_TO_WORLD(100));
	b2Body* body = world.CreateBody(&bodyDef);
	bodyDef.position.Set(SCREEN_TO_WORLD(450), SCREEN_TO_WORLD(-20));
	b2Body* body2 = world.CreateBody(&bodyDef);
	bodyDef.position.Set(SCREEN_TO_WORLD(360), SCREEN_TO_WORLD(250));
	b2Body* body3 = world.CreateBody(&bodyDef);
	// Define another box shape for our dynamic body.
	b2PolygonDef shapeDef;
	shapeDef.SetAsBox(1.0f, 1.0f);

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

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

	// Add the shape to the body.
	body->CreateShape(&shapeDef);
	body2->CreateShape(&shapeDef);
	body3->CreateShape(&shapeDef);
	// Now tell the dynamic body to compute it's mass properties base
	// on its shape.
	body->SetMassFromShapes();
	body2->SetMassFromShapes();
	body3->SetMassFromShapes();
// 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 iterations = 10;

// our main loop
	while ( LoopGDK ( ) )
	{
		world.Step(timeStep, iterations);
	// update the screen
		dbRotateSprite(CUBE,body->GetAngle()*(180.0 / 3.141592653589793238));
		dbRotateSprite(CUBE2,body2->GetAngle()*(180.0 / 3.141592653589793238));
		dbRotateSprite(CUBE3,body3->GetAngle()*(180.0 / 3.141592653589793238));
		dbPasteSprite(CUBE,WORLD_TO_SCREEN(body->GetPosition().x),WORLD_TO_SCREEN(body->GetPosition().y));
		dbPasteSprite(CUBE2,WORLD_TO_SCREEN(body2->GetPosition().x),WORLD_TO_SCREEN(body2->GetPosition().y));
		dbPasteSprite(CUBE3,WORLD_TO_SCREEN(body3->GetPosition().x),WORLD_TO_SCREEN(body3->GetPosition().y));
		dbSync ( );
	}

	// return back to windows
	return;
}

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Dark GDK / Need help setting up BOX2D