A really simple Box2d sample that it doesn't works... Why ?

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A really simple Box2d sample that it doesn't works... Why ?

(5 posts) (3 voices)

Started 2 years ago by jfradj
Latest reply from jfradj

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jfradj
Member

Hi all,

I'm new with physics engine (but not in cocos2d, I already helped riq to find and fix some memory leak issues) and I want to make a very simple example which will make me more comfortable for my new iPhone game.

I just want to create a world that some little boxes move perpetually bouncing on every side. Moreover I want the little boxes don't collide each others. Here is my code (in which I delete all iPhone specific code to simplify it) :

-(void) initTheWorld
{
	CGSize screenSize = [Director sharedDirector].winSize;

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

	// Do we want to let bodies sleep?
	// This will speed up the physics simulation
	bool doSleep = true;

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

	world->SetContinuousPhysics(true);

	// Define the ground body.
	b2BodyDef groundBodyDef;
	groundBodyDef.position.Set(0, 0); // bottom-left corner

	// 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;		

	// bottom
	groundBox.SetAsEdge(b2Vec2(0,0), b2Vec2(screenSize.width/PTM_RATIO,0));
	groundBody->CreateFixture(&groundBox);

	// top
	groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO));
	groundBody->CreateFixture(&groundBox);

	// left
	groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(0, 0));
	groundBody->CreateFixture(&groundBox);

	// right
	groundBox.SetAsEdge(b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,0));
	groundBody->CreateFixture(&groundBox);
}

-(void) addNewBoxWithCoords:(CGPoint)p
{
	// Define the dynamic body.
	b2BodyDef bodyDef;
	bodyDef.position.Set(p.x/PTM_RATIO, p.y/PTM_RATIO);
	b2Body *body = world->CreateBody(&bodyDef);

	// Define another box shape for our dynamic body.
	b2PolygonShape dynamicBox;
	dynamicBox.SetAsBox(0.5f, 1.0f);

	b2MassData massData;
	massData.mass = 0.01f;
	body->SetMassData(&massData);

	// Define the dynamic body fixture.
	b2FixtureDef fixtureDef;
	fixtureDef.shape = &dynamicBox;
	fixtureDef.density = 0.0f;
	fixtureDef.friction = 0.0f;
	fixtureDef.restitution = 1.0f;
	fixtureDef.filter.categoryBits = 0x0008;
	fixtureDef.filter.maskBits = 0xFFFF ^ 0x0008;
	body->CreateFixture(&fixtureDef);

	body->SetLinearVelocity(b2Vec2(10.0f, 10.0f));
}

This code crashes, with the following error, when a box collide a side of the world:

Assertion failed: (kNormal > 1.19209290e-7F), function b2ContactSolver

Moreover I want to add two other boxes (on the lower left and right corner) which they are static and on which the little boxes bounce. So to do it I just add the following code at the end of the initWorld method :

b2BodyDef leftBoxDef;
	leftBoxDef.position.Set(25.0f / PTM_RATIO, 25.0f / PTM_RATIO);
	b2Body *leftBox = world->CreateBody(&leftBoxDef);

	b2MassData leftBoxMassData;
	leftBoxMassData.mass = 0.9f;
	leftBox->SetMassData(&leftBoxMassData);

	b2PolygonShape staticLeftBox;
	staticLeftBox.SetAsBox(25.0f / PTM_RATIO, 25.0f / PTM_RATIO);

	b2FixtureDef leftBoxFixtureDef;
	leftBoxFixtureDef.shape = &staticLeftBox;
	leftBoxFixtureDef.filter.categoryBits = 0x0004;
	leftBox->CreateFixture(&leftBoxFixtureDef);

	b2BodyDef rightBoxDef;
	rightBoxDef.position.Set((screenSize.width/PTM_RATIO) - (25.0f / PTM_RATIO), 25.0f / PTM_RATIO);
	b2Body *rightBox = world->CreateBody(&rightBoxDef);

	b2MassData rightBoxMassData;
	rightBoxMassData.mass = 0.9f;
	rightBox->SetMassData(&rightBoxMassData);

	b2PolygonShape staticRightBox;
	staticRightBox.SetAsBox(25.0f / PTM_RATIO, 25.0f / PTM_RATIO);

	b2FixtureDef rightBoxFixtureDef;
	rightBoxFixtureDef.shape = &staticRightBox;
	rightBoxFixtureDef.filter.categoryBits = 0x0004;
	rightBox->CreateFixture(&rightBoxFixtureDef);

Someone can help me to understand what I'm doing wrong ?
I start from the box2d sample include in the 0.8.2 cocos2d release.

PS: This is a cross posting from box2d forums ;-) and I will synchronise the two thread.

Regards.

Posted 2 years ago #

riq
Key Master

I don't know why it is crashing, but I suggest doing the following:
* remove some parts of the code, until it doesn't crash anymore
* once you find the statement that was causing the crash, either you can:
- search in the box2d tests to see how it does it (this is what I usually do)
- or post that code here and/or the box2d forum.

Posted 2 years ago #
pabloruiz55
Member

sometimes i get that error when trying to do x/PTM_RATIO if x is less than PTM_RATIO. Try changing that everywhere to see if that's your case. If it is, i solved that by casting that to float if i remember well...

Posted 2 years ago #

jfradj
Member

@riq: I followed your suggests and it seems the crash is due to the added sprite...

Here the code without sprite :

-(id) init
{
	if((self=[super init])) {
		// enable touches
		self.isTouchEnabled = YES;

		CGSize screenSize = [Director sharedDirector].winSize;
		CCLOG(@"Screen width %0.2f screen height %0.2f",screenSize.width,screenSize.height);

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

		// Do we want to let bodies sleep?
		// This will speed up the physics simulation
		bool doSleep = true;

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

		world->SetContinuousPhysics(true);

		// Debug Draw functions
		m_debugDraw = new GLESDebugDraw( PTM_RATIO );
		world->SetDebugDraw(m_debugDraw);

		uint32 flags = 0;
		flags += b2DebugDraw::e_shapeBit;
		flags += b2DebugDraw::e_jointBit;
		flags += b2DebugDraw::e_aabbBit;
		flags += b2DebugDraw::e_pairBit;
		flags += b2DebugDraw::e_centerOfMassBit;
		m_debugDraw->SetFlags(flags);		

		// Define the ground body.
		b2BodyDef groundBodyDef;
		groundBodyDef.position.Set(0, 0); // bottom-left corner

		// 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;		

		// bottom
		groundBox.SetAsEdge(b2Vec2(0,0), b2Vec2(screenSize.width/PTM_RATIO,0));
		groundBody->CreateFixture(&groundBox);

		// top
		groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO));
		groundBody->CreateFixture(&groundBox);

		// left
		groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(0, 0));
		groundBody->CreateFixture(&groundBox);

		// right
		groundBox.SetAsEdge(b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,0));
		groundBody->CreateFixture(&groundBox);

		[self schedule: @selector(tick:)];
	}
	return self;
}

-(void) addNewSpriteWithCoords:(CGPoint)p
{
	// Define the dynamic body.
	//Set up a 1m squared box in the physics world
	b2BodyDef bodyDef;
	bodyDef.position.Set(p.x/PTM_RATIO, p.y/PTM_RATIO);
	b2Body *body = world->CreateBody(&bodyDef);

	// Define another box shape for our dynamic body.
	b2PolygonShape dynamicBox;
	dynamicBox.SetAsBox(0.5f, 1.0f);

	b2MassData massData;
	massData.mass = 0.01f;
	body->SetMassData(&massData);

	// Define the dynamic body fixture.
	b2FixtureDef fixtureDef;
	fixtureDef.shape = &dynamicBox;
	fixtureDef.density = 0.0f;
	fixtureDef.friction = 0.0f;
	fixtureDef.restitution = 1.0f;
	fixtureDef.filter.categoryBits = 0x0008;
	fixtureDef.filter.maskBits = 0xFFFF ^ 0x0008;
	body->CreateFixture(&fixtureDef);

	body->SetLinearVelocity(b2Vec2(CCRANDOM_0_1() * 10.0f, CCRANDOM_0_1() * 10.0f));
}

And there is the code with sprite management :

-(id) init
{
	if((self=[super init])) {
		// enable touches
		self.isTouchEnabled = YES;

		CGSize screenSize = [Director sharedDirector].winSize;
		CCLOG(@"Screen width %0.2f screen height %0.2f",screenSize.width,screenSize.height);

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

		// Do we want to let bodies sleep?
		// This will speed up the physics simulation
		bool doSleep = true;

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

		world->SetContinuousPhysics(true);

		// Debug Draw functions
		m_debugDraw = new GLESDebugDraw( PTM_RATIO );
		world->SetDebugDraw(m_debugDraw);

		uint32 flags = 0;
		flags += b2DebugDraw::e_shapeBit;
		flags += b2DebugDraw::e_jointBit;
		flags += b2DebugDraw::e_aabbBit;
		flags += b2DebugDraw::e_pairBit;
		flags += b2DebugDraw::e_centerOfMassBit;
		m_debugDraw->SetFlags(flags);		

		// Define the ground body.
		b2BodyDef groundBodyDef;
		groundBodyDef.position.Set(0, 0); // bottom-left corner

		// 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;		

		// bottom
		groundBox.SetAsEdge(b2Vec2(0,0), b2Vec2(screenSize.width/PTM_RATIO,0));
		groundBody->CreateFixture(&groundBox);

		// top
		groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO));
		groundBody->CreateFixture(&groundBox);

		// left
		groundBox.SetAsEdge(b2Vec2(0,screenSize.height/PTM_RATIO), b2Vec2(0, 0));
		groundBody->CreateFixture(&groundBox);

		// right
		groundBox.SetAsEdge(b2Vec2(screenSize.width/PTM_RATIO,screenSize.height/PTM_RATIO), b2Vec2(screenSize.width/PTM_RATIO,0));
		groundBody->CreateFixture(&groundBox);

		//Set up sprite
		AtlasSpriteManager *mgr = [AtlasSpriteManager spriteManagerWithFile:@"blocks.png" capacity:150];
		[self addChild:mgr z:0 tag:kTagSpriteManager];

		[self schedule: @selector(tick:)];
	}
	return self;
}

-(void) addNewSpriteWithCoords:(CGPoint)p
{
	//AtlasSpriteManager *mgr = (AtlasSpriteManager*) [self getChildByTag:kTagSpriteManager];

	int idx = (CCRANDOM_0_1() > .5 ? 0:1);
	AtlasSprite *sprite = [AtlasSprite spriteWithRect:CGRectMake(32*idx,0,32,64) spriteManager:mgr];
	[mgr addChild:sprite];

	sprite.position = ccp(p.x, p.y);

	// Define the dynamic body.
	//Set up a 1m squared box in the physics world
	b2BodyDef bodyDef;
	bodyDef.position.Set(p.x/PTM_RATIO, p.y/PTM_RATIO);
	bodyDef.userData = sprite;
	b2Body *body = world->CreateBody(&bodyDef);

	// Define another box shape for our dynamic body.
	b2PolygonShape dynamicBox;
	dynamicBox.SetAsBox(0.5f, 1.0f);

	b2MassData massData;
	massData.mass = 0.01f;
	body->SetMassData(&massData);

	// Define the dynamic body fixture.
	b2FixtureDef fixtureDef;
	fixtureDef.shape = &dynamicBox;
	fixtureDef.density = 0.0f;
	fixtureDef.friction = 0.0f;
	fixtureDef.restitution = 1.0f;
	fixtureDef.filter.categoryBits = 0x0008;
	fixtureDef.filter.maskBits = 0xFFFF ^ 0x0008;
	body->CreateFixture(&fixtureDef);

	body->SetLinearVelocity(b2Vec2(CCRANDOM_0_1() * 10.0f, CCRANDOM_0_1() * 10.0f));
}

-(void) tick: (ccTime) dt
{
	int32 velocityIterations = 8;
	int32 positionIterations = 1;

	world->Step(dt, velocityIterations, positionIterations);

	for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())
	{
		if (b->GetUserData() != NULL) {
			AtlasSprite* myActor = (AtlasSprite*)b->GetUserData();
			myActor.position = CGPointMake( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO);
			myActor.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
		}
	}
}

The code without sprite managing doesn't crash.... It's very strange because I don't really change the sprite management code from the box2d template... I'm lost :'-(

Posted 2 years ago #

jfradj
Member
Ok I can figured out !
It's very very strange but the following line make my code crash systematically :
```
sprite.position = ccp(p.x, p.y);
```
So without setting the sprite position, the code doesn't crash but the first box don't bounce on the first side which it collide to and go outside the screen. It seems this strange behavior is due to a call to :
```
CCRANDOM_0_1()
```
I don(t understand why, but when I removed these two lines, the sample works correctly !

@riq: if you want, I can provide you the complete Xcode project.

Regards,
Posted 2 years ago #

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