I have a box2d object that is being moved down the screen via gravity
int32 velocityIterations = 6;
int32 positionIterations = 2;
self.world->Step(dt, velocityIterations, positionIterations);
self.world->ClearForces();
for(b2Body *b = self.world->GetBodyList(); b; b=b->GetNext()) {
if (b->GetUserData() != NULL) {
id object = (id)b->GetUserData();
if([object isKindOfClass:[FallingObject class]])
{
CCSprite *sprite = (CCSprite *)b->GetUserData();
sprite.position = CGPointMake(b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO);
sprite.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
}
}
}
When the user moves their finger across the screen either left or right i want to move the box2d object left or right while the object is still moving down the screen.
Can anyone suggest the best way to do this. I have tried applying linear velocity but it just seems to shoot of screen.
Any suggestions
Thanks
There some ways to do this, and you need to try the best for your case.
You can apply forces, impulse, or change the body velocity manually just for X parameter:
// x axis force
b2Vec2 xAxisForce = b2Vec2(10, 0);
// Try one of these
b->ApplyForce(xAxisForce, b->GetWorldCenter());
b->ApplyForceToCenter(xAxisForce);
b->ApplyLinearImpulse(xAxisForce, b->GetWorldCenter());
// Or change the body velocity manually
b->SetLinearVelocity(b2Vec2(10, b->GetLinearVelocity().y));
Related
setTouchEnabled(true);
ball=CCSprite::create("soccer_ball.png");
ball->setPosition(ccp(100,100));
addChild(ball,1);
//CREATE WORLD
b2Vec2 gravity(0, -9.8); //normal earth gravity, 9.8 m/s/s straight down!
bool doSleep = true;
myWorld = new b2World(gravity);
myWorld->SetAllowSleeping(doSleep);
//BODY DEFINITION
myBodyDef.type = b2_dynamicBody; //this will be a dynamic body
myBodyDef.position.Set(0, 20); //set the starting position
myBodyDef.angle = 0; //set the starting angle return true;
myBodyDef.userData=ball;
//CREATE SHAPE
b2CircleShape ballShape;
ballShape.m_p.Set(2.0f,3.0f);
ballShape.m_radius=50.0/PTM_RATIO;
//CREATE BODY
dynamicBody = myWorld->CreateBody(&myBodyDef);
//FIXTURE DEFINITION
b2FixtureDef ballFixtureDef;
ballFixtureDef.shape = &ballShape;
ballFixtureDef.density = 1;
dynamicBody->CreateFixture(&ballFixtureDef);
}
void HelloWorld::update()
{
float32 timeStep = 1/20.0; //the length of time passed to simulate (seconds)
int32 velocityIterations = 8; //how strongly to correct velocity
int32 positionIterations = 3; //how strongly to correct position
myWorld->Step( timeStep, velocityIterations, positionIterations);
}
I am learning box2d basic concepts and i have put my code here. I created a box2d circle shape. now i want to add sprite of ball in that circle shape. I have used myBodyDef.userData=ball; but it is not working .. i used gles-render code to debug draw but in that circle body is different and ball sprite is different. when i applyforce or impluse body works perfectly but dont attached to ball sprite..is any mistake in my code. I want to apply force to ball and ball should bounce according to physics but i can not attach to body plz help me.
Body and sprite looks like this
Here's my version working for V-3.6:
void GamePlayScreen::update(float dt) {
phyWorld->Step(dt, 8, 1);
// Iterate over the bodies in the physics phyWorld
for (b2Body* b = phyWorld->GetBodyList(); b; b = b->GetNext()) {
if (b->GetUserData() != NULL) {
// Synchronize the AtlasSprites position and rotation with the corresponding body
Sprite* sprActor = (Sprite*) b->GetUserData();
sprActor->setPosition(b->GetPosition().x * PTM_RATIO,
b->GetPosition().y * PTM_RATIO);
sprActor->setRotation(-1 * CC_RADIANS_TO_DEGREES(b->GetAngle()));
}
}
}
I have used soft body physics in my game to make ball.Now when ball falls down on some platforms which are also b2Bodies or on GrounBody it completely destroyed & it's shape also changed.
I have referred this link : http://www.uchidacoonga.com/2012/04/soft-body-physics-with-box2d-and-cocos2d-part-44/
but when i am trying to change some of values like radius,frequencyHz ,dampingRatio etc then it gives result as per my first image , in which my ball looks so unshaped & destructed .
- (void) createPhysicsObject:(b2World *)world {
// Center is the position of the circle that is in the center (inner circle)
b2Vec2 center = b2Vec2(240/PTM_RATIO, 160/PTM_RATIO);
b2CircleShape circleShape;
circleShape.m_radius = 0.20f;
b2FixtureDef fixtureDef;
fixtureDef.shape = &circleShape;
fixtureDef.density = 0.1;
fixtureDef.restitution = -2;
fixtureDef.friction = 1.0;
// Delta angle to step by
deltaAngle = (2.f * M_PI) / NUM_SEGMENTS;
// Radius of the wheel
float radius = 50;
// Need to store the bodies so that we can refer back
// to it when we connect the joints
bodies = [[NSMutableArray alloc] init];
for (int i = 0; i < NUM_SEGMENTS; i++) {
// Current angle
float theta = deltaAngle*i;
// Calculate x and y based on theta
float x = radius*cosf(theta);
float y = radius*sinf(theta);
// Remember to divide by PTM_RATIO to convert to Box2d coordinate
b2Vec2 circlePosition = b2Vec2(x/PTM_RATIO, y/PTM_RATIO);
b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
// Position should be relative to the center
bodyDef.position = (center + circlePosition);
// Create the body and fixture
b2Body *body;
body = world->CreateBody(&bodyDef);
body->CreateFixture(&fixtureDef);
// Add the body to the array to connect joints to it
// later. b2Body is a C++ object, so must wrap it
// in NSValue when inserting into it NSMutableArray
[bodies addObject:[NSValue valueWithPointer:body]];
}
// Circle at the center (inner circle)
b2BodyDef innerCircleBodyDef;
// Make the inner circle larger
circleShape.m_radius = 0.8f;
innerCircleBodyDef.type = b2_dynamicBody;
// Position is at the center
innerCircleBodyDef.position = center;
innerCircleBody = world->CreateBody(&innerCircleBodyDef);
innerCircleBody->CreateFixture(&fixtureDef);
// Connect the joints
b2DistanceJointDef jointDef;
for (int i = 0; i < NUM_SEGMENTS; i++) {
// The neighbor
const int neighborIndex = (i + 1) % NUM_SEGMENTS;
// Get current body and neighbor
b2Body *currentBody = (b2Body*)[[bodies objectAtIndex:i] pointerValue];
b2Body *neighborBody = (b2Body*)[[bodies objectAtIndex:neighborIndex] pointerValue];
// Connect the outer circles to each other
jointDef.Initialize(currentBody, neighborBody,
currentBody->GetWorldCenter(),
neighborBody->GetWorldCenter() );
// Specifies whether the two connected bodies should collide with each other
jointDef.collideConnected = true;
jointDef.frequencyHz = 25.0f;
jointDef.dampingRatio = 0.5f;
world->CreateJoint(&jointDef);
// Connect the center circle with other circles
jointDef.Initialize(currentBody, innerCircleBody, currentBody->GetWorldCenter(), center);
jointDef.collideConnected = true;
jointDef.frequencyHz = 25.0;
jointDef.dampingRatio = 0.5;
world->CreateJoint(&jointDef);
}
}
This code give me the result as shown here.Is there any solution to avoid this situation ???
i want output like this
for that what changes i should made ? any suggestions !! please help.
i would also like to know the reason behind this.
It looks like the triangle fan is reacting with itself. Since you use a triangle fan to create a ball the triangles shouldn't interact, they are connected only. The code on the website you provided is a little bit different. After the first jointDef.Initialize the frequency and dampingRatio are 0.
But some other informations are missing like your NUM_SEGMENTS. Provide complete working code/functions (not the whole application), so someone other could compile and check it also.
I need to have the Cocos2d camera follow a sprite (attached to a Box2D body) that the user is touching on the screen. As the user is dragging the player around, I need it to be able to go to other parts of the world. This has to be through touch, and not automatic scrolling.
I tried several approaches based on tutorials but nothing seem to address this issue. For example the solution offered here Move CCCamera with the ccTouchesMoved method? (cocos2d,iphone) by #Michael Fredrickson has the entire layer move, but when it moves, the sprites / bodies on the screen have unmatched coordinations and when I test to see if they're touched, the if(fixture->TestPoint(locationWorld)) fails.
I also looked at the tutorials here http://www.learn-cocos2d.com/2012/12/ways-scrolling-cocos2d-explained/ but this also isn't what I'm looking for.
Any help would be greatly appreciated.
EDIT:
I'm accepting Liolik's answer below because it put me on the right track. The last piece of the puzzle, though, is to make the value received from the getPoint method an instance variable, and deduce it from locationWorld which I'm doing the TestPoint against. Like this:
UITouch *myTouch = [touches anyObject];
CGPoint location = [myTouch locationInView:[myTouch view]];
location = [[CCDirector sharedDirector] convertToGL:location];
b2Vec2 locationWorld = b2Vec2(location.x/PTM_RATIO, location.y/PTM_RATIO);
b2Vec2 diff = b2Vec2(difference.x, difference.y);
for (b2Body* b = _world->GetBodyList(); b; b = b->GetNext()) {
b2Fixture* f = b->GetFixtureList();
while(f != NULL) {
if(f->TestPoint(locationWorld-diff)) {
b2MouseJointDef def;
def.bodyA = _groundBody;
def.bodyB = b;
def.target = locationWorld-diff;
def.maxForce = 9999999.0f * b->GetMass();
_mouseJoint = (b2MouseJoint*)_world->CreateJoint(&def);
b->SetAwake(true);
}
f = f->GetNext();
}
}
in update function :
CGPoint direction = [self getPoint:myBody->GetPosition()];
[self setPosition:direction];
- (CGPoint)getPoint:(b2Vec2)vec
{
CGSize screen = [[CCDirector sharedDirector] winSize];
float x = vec.x * PTM_RATIO;
float y = vec.y * PTM_RATIO;
x = MAX(x, screen.width/2);
y = MAX(y, screen.height/2);
float _x = area.width - (screen.width/2);
float _y = area.height - (screen.height/2);
x = MIN(x, _x);
y = MIN(y, _y);
CGPoint goodPoint = ccp(x,y);
CGPoint centerOfScreen = ccp(screen.width/2, screen.height/2);
CGPoint difference = ccpSub(centerOfScreen, goodPoint);
return difference;
}
So if i understand correctly, when the sprite is inside of the middle of the screen, the background is stationary and the sprite follows your finger, but when you scroll toward the edge, the camera starts to pan?
I had something roughly similar in my game Star Digger where there's a ship in the middle of the screen on its own layer that has to fly around the world, and had the same problem when the ship fired bullets into the main world layer.
heres what I did:
float thresholdMinX = winSize*1/3;
float thresholdMaxX = winSize*2/3;
if(touch.x > thresholdMaxX) //scrolling right
{
self.x += touch.x - thresholdMaxX;
}
else if(touchX < thresholdMinX)
{
self.x += thresholdMinX - touchX;
}
else
{
sprite.position = touch;
}
CGPoint spritePointInWorld = ccp(sprite.x - self.x, sprite.y - self.y);
then every time you calculate collisions, you need to recompute the sprites "actual" position in the world, which is its screen position minus the worlds offset, instead of the sprites screen position.
I have a little issue with my game. In my main game scene I create a Player object from a class, like this:
player = [Player spriteWithFile:#"Icon-Small#2x.png"];
player.position = ccp(100.0f, 180.0f);
[player createBox2dObject:world];
Below is the main chunk of my small Player class that creates the body and the fixture so I can use it in a box2d world.
b2BodyDef playerBodyDef;
playerBodyDef.type = b2_dynamicBody;
playerBodyDef.position.Set(self.position.x/PTM_RATIO, self.position.y/PTM_RATIO);
playerBodyDef.userData = self;
playerBodyDef.fixedRotation = true;
playerBodyDef.linearDamping = 4.0;
body = world->CreateBody(&playerBodyDef);
b2CircleShape circleShape;
circleShape.m_radius = 0.7;
b2FixtureDef fixtureDef;
fixtureDef.shape = &circleShape;
fixtureDef.density = 1.0f;
fixtureDef.friction = 1.0f;
fixtureDef.restitution = 1.0f;
body->CreateFixture(&fixtureDef);
The result of this code is a Box2d object with Icon-Small#2x.png over it. When I move a joystick, a Box2D impulse is applied and the player moves. Simple enough, right?
In non-retina displays, this works fine. However, when I switch to Retina in the simulator, Icon-Small#2x.png is created a little higher and farther to the right, not over the Box2D circle. Then, gravity is applied and they both fall down to the platform. Icon-Small#2x.png falls twice as fast. When I move the joystick, the Box2D circle moves, but Icon-Small#2x.png moves twice as fast and the camera follows it, soon leaving the circle off the screen. I doubt this issue has really anything to do with the code I have here, I feel like its a scaling issue hidden somewhere in my game. Does anyone have suggestions?
Edit:
I move the sprite with:
[player moveRight];
This is moveRight in the player class:
-(void) moveRight {
b2Vec2 impulse = b2Vec2(2.0f, 0.0f);
body->ApplyLinearImpulse(impulse, body->GetWorldCenter());
}
Shouldn't be any issue here, right?
Edit (again):
Here's my update: method-
- (void) update:(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) {
CCSprite *myActor = (CCSprite*)b->GetUserData();
myActor.position = CGPointMake( b->GetPosition().x *PTM_RATIO,
b->GetPosition().y * PTM_RATIO);
myActor.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
}
}
b2Vec2 pos = [player body]->GetPosition();
CGPoint newPos = ccp(-1 * pos.x * PTM_RATIO + 50, self.position.y * PTM_RATIO);
[self setPosition:newPos];
}
I have a feeling that the issue is somewhere in here. I've tried changing PTM_RATIO around, but it doesn't affect the speed. Any ideas?
Edit: see comment below, almost have this figured out
You problem probably stems from the fact you are using a #2x image... Read, http://www.cocos2d-iphone.org/wiki/doku.php/prog_guide:how_to_develop_retinadisplay_games_in_cocos2d
There it states:
WARNING: It is NOT recommend to use the ”#2x” suffix. Apple treats those images in a special way which might cause bugs in your cocos2d application.
So to solve your problem read through the information on using png files with the -hd suffix.
For the comment:
Do you have some code that looks something like...
world->Step(dt, 10, 10);
for(b2Body *b = world->GetBodyList(); b; b=b->GetNext()) {
if (b->GetUserData() != NULL) {
CCSprite *sprite = (CCSprite *)b->GetUserData();
sprite.position = ccp(b->GetPosition().x * PTM_RATIO,b->GetPosition().y * PTM_RATIO);
}
}
See how the code loops through all the box2d bodies in the word and sets the position of the sprite that is associated with the box2d body?
I am working on a hockey game and I am implementing Single Player mode. I am trying to move the "computer's" paddle in offense mode (move towards the ball). I am using CoCos2d and Box2d. I am moving the paddle using MouseJoints. The problem is the Paddle doesnt move at all!
tick is called in init method
[self schedule:#selector(tick:)];
...
- (void)tick:(ccTime) dt
{
_world->Step(dt, 10, 10);
CCSprite *computer_paddle;
CCSprite *ball;
b2Body *computer_paddle_b2Body;
float32 direction;
b2Vec2 velocity;
for(b2Body *b = _world->GetBodyList(); b; b=b->GetNext()) {
if (b->GetUserData() != NULL) {
CCSprite *sprite = (CCSprite *)b->GetUserData();
if (sprite.tag == 1) { //ball
ball = sprite;
static int maxSpeed = 10;
velocity = b->GetLinearVelocity();
float32 speed = velocity.Length();
direction = velocity.y;
if (speed > maxSpeed) {
b->SetLinearDamping(0.5);
} else if (speed < maxSpeed) {
b->SetLinearDamping(0.0);
}
}
if (sprite.tag == 3){ // paddle
computer_paddle = sprite;
computer_paddle_b2Body = b;
}
// update sprite position
sprite.position = ccp(b->GetPosition().x * PTM_RATIO,b->GetPosition().y * PTM_RATIO);
sprite.rotation = -1 * CC_RADIANS_TO_DEGREES(b->GetAngle());
}
}
// update the computer paddle in single player moving it towards the ball using MouseJoint
//move towards the ball
b2Vec2 b2Position = b2Vec2(ball.position.x/PTM_RATIO,ball.position.y/PTM_RATIO);
b2MouseJointDef md1;
md1.bodyA = _groundBody;
md1.bodyB = computer_paddle_b2Body;
md1.target = b2Position;
md1.collideConnected = true;
md1.maxForce = 9999.0 * computer_paddle_b2Body->GetMass();
_mouseJoint = (b2MouseJoint *)_world->CreateJoint(&md1);
computer_paddle_b2Body->SetAwake(true);
Check whether:
a) the body is sleeping
b) the body is a static body
If it is sleeping and you have no other bodies, disable sleeping entirely. Otherwise disable sleeping of the body: body->SetSleepingAllowed(NO)
Note: this is according to Box2D 2.2.1 API Reference which isn't the default in cocos2d 1.0 yet, so the function may be different in your Box2D version.
Also check that your body is dynamic by looking up the b2BodyDef's type member and, if necessary, set it to be dynamic (see the b2BodyType enumeration). I'm not sure what the default is, it should be dynamic but this may depend on the Box2D version.