I am developing a game recently (it's should be a space ship game like reassembly).
So my situation:
- i got 2 bodies with 0 restitution and 0 friction
- when they are colliding they slide and lose velocity because of my lineardumping
- but when 1 of them both is rotating (with setangularvelocity), they bounce off with a very high velocity and i can't figure out why they even bounce this hard.
( and i read that there should just be a little bouncing even if there is no restitution, but i am not expecting something like this)
here's some code:
b2PolygonShape shape;
b2BodyDef def;
def.type = b2_dynamicBody;
b2FixtureDef fix;
fix.density = 1.f;
fix.restitution = .0f;
fix.friction = 0.f;
bbody = world->CreateBody(&def);
bbody2 = world->CreateBody(&def);
bbody->SetLinearDamping(2.0f);
bbody2->SetLinearDamping(2.0f);
// PIXELPERMETER is the scaling from pixels to meter. (30)
shape.SetAsBox(32 / PIXELPERMETER/*=30*/, 32 / PIXELPERMETER);
fix.shape = &shape;
bbody->CreateFixture(&fix);
bbody2->CreateFixture(&fix);
bbody2->SetTransform(b2Vec2(-100 / PIXELPERMETER, 0), 0);
Maybe you should try to tweak the mass data of your bodies ?
b2MassData massData;
massData.mass = 50; //Just tweak me
massData.I = 1; //Just never set me to 0 if you don't want to have nAn propagating
massData.center = b2Vec2_zero;
bbody->SetMassData(&massData);
Related
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.
As I am newbie to cocoa2d I am struggling alot to rotate the physics or dynamic body along an arc path.
The way I tried is as follows:
#define COS_ANIMATOR(position, timeCount, speed, waveMagnitude) ((cosf(timeCount * speed) * waveMagnitude) + position)
#define SIN_ANIMATOR(position, timeCount, speed, waveMagnitude) ((sinf(timeCount * speed) * waveMagnitude) + position)
CCSpriteBatchNode *pipe_parent = [CCSpriteBatchNode batchNodeWithFile:#"pipe.png" capacity:100];
CCTexture2D *pipeSpriteTexture_ = [pipe_parent texture];
PhysicsSprite *pipeSprite = [PhysicsSprite spriteWithTexture:pipeSpriteTexture_ rect:CGRectMake(0 ,0 ,55,122)];
//pipe = [CCSprite spriteWithFile:#"pipe.png"
// rect:CGRectMake(0, 0, 55, 122)];
[self addChild:pipeSprite];
// pipe.position = ccp(s.width/2 , 420.0);
b2BodyDef myBodyDef;
myBodyDef.type = b2_staticBody; //this will be a dynamic body
myBodyDef.position.Set(((s.width/2) - 90)/PTM_RATIO, 420.0/PTM_RATIO); //set the starting position
myBodyDef.angle = 0; //set the starting angle
b2Body* staticBody = world->CreateBody(&myBodyDef);
b2PolygonShape boxShape;
boxShape.SetAsBox(1,1);
b2FixtureDef boxFixtureDef;
boxFixtureDef.shape = &boxShape;
boxFixtureDef.density = 1;
boxFixtureDef.userData = pipeSprite;
boxFixtureDef.filter.groupIndex = -1;
staticBody->CreateFixture(&boxFixtureDef);
[pipeSprite setPhysicsBody:staticBody];
-(void) draw
{
//
// IMPORTANT:
// This is only for debug purposes
// It is recommend to disable it
//
[super draw];
const CGPoint newSpritePosition = ccp(COS_ANIMATOR(150, mTimeCounter, 0.05,50), SIN_ANIMATOR(400, mTimeCounter, -0.05, 50));
pipeSprite.position = newSpritePosition;
ccGLEnableVertexAttribs( kCCVertexAttribFlag_Position );
kmGLPushMatrix();
world->DrawDebugData();
kmGLPopMatrix();
}
on following this approach my sprite rotating in circular motion instead of rotating in an arc path.
Please give your ideas or suggestions.
Thanks all
I'm not entirely sure what it is you are looking to accomplish when you talk about rotating in an arc path. I only see you setting a position, not a rotation, so are you just wanting to set a position, or a rotation, or both? Your position code looks like you are trying to achieve a circular (or elliptical) path because you are using the sine and cosine in the x,y position.
If you're looking to move a sprite along a sine curve, I did that today and it took a bit of trial and error. I had some variables for the amplitude and period, and from there I traced out a nice sine curve movement in the sprite's update: method.
CGPoint initialPosition; // set this to the sprite's initial position
float amplitude; // in points
float period; // in points
float y, x = initialPosition.x;
-(void) update:(ccTime)dt
{
x += dt * 100; // speed of movement across the screen. Picked by trial and error.
y = initalPosition.y + amplitude * sinf((x - initialPosition.x)/period);
sprite.position = ccp(x,y);
sprite.rotation = cosf((x - initialPosition.x)/period); // optional if you want to rotate along the path as well
}
Don't know if this is anything you are looking for but it might give you some ideas.
Using Box2d, how to create a rubber thread (rubber band / elastic rope) like Parachute Ninja (ZeptoLab)?
-(void) CreateElasticRope {
//=======Params
// Position and size
b2Vec2 lastPos = b2Vec2(4,4); //set position first body
float widthBody = 0.35;
float heightBody = 0.1;
// Body params
float density = 0.05;
float restitution = 0.5;
float friction = 0.5;
// Distance joint
float dampingRatio = 0.85;
float frequencyHz = 10;
// Rope joint
float kMaxWidth = 1.1;
// Bodies
int countBodyInChain = 10;
b2Body* prevBody;
//========Create bodies and joints
for (int k = 0; k < countBodyInChain; k++) {
b2BodyDef bodyDef;
if(k==0 || k==countBodyInChain-1) bodyDef.type = b2_staticBody; //first and last bodies are static
else bodyDef.type = b2_dynamicBody;
bodyDef.position = lastPos;
lastPos += b2Vec2(2*widthBody, 0); //modify b2Vect for next body
bodyDef.fixedRotation = YES;
b2Body* body = world->CreateBody(&bodyDef);
b2PolygonShape distBodyBox;
distBodyBox.SetAsBox(widthBody, heightBody);
b2FixtureDef fixDef;
fixDef.density = density;
fixDef.restitution = restitution;
fixDef.friction = friction;
fixDef.shape = &distBodyBox;
body->CreateFixture(&fixDef);
if(k>0) {
//Create distance joint
b2DistanceJointDef distJDef;
b2Vec2 anchor1 = prevBody->GetWorldCenter();
b2Vec2 anchor2 = body->GetWorldCenter();
distJDef.Initialize(prevBody, body, anchor1, anchor2);
distJDef.collideConnected = false;
distJDef.dampingRatio = dampingRatio;
distJDef.frequencyHz = frequencyHz;
world->CreateJoint(&distJDef);
//Create rope joint
b2RopeJointDef rDef;
rDef.maxLength = (body->GetPosition() - prevBody->GetPosition()).Length() * kMaxWidth;
rDef.localAnchorA = rDef.localAnchorB = b2Vec2_zero;
rDef.bodyA = prevBody;
rDef.bodyB = body;
world->CreateJoint(&rDef);
} //if k>0
prevBody = body;
} //for -loop
}
I use distance and rope Joints, set different values of parameters dampingRatio and frequencyHz, but the effect is far from being an example (my thread for a long time coming to original state, and not so elastic.).
You can simulate springs by applying forces. At each timestep update the forces on the connected bodies (wake the bodies up if necessary too). If one of the bodies is the ground (or a static body) then you don't need to apply any force to the ground just the dynamic body.
A regular spring would apply both tension and compression forces (pull and push) depending on the deflection. In your case you have a bungee so there would be no compression force just tension (pull).
This is the formula you need:
F = K * x
Where F is the force, K is the spring stiffness (force/deflection), and x is the deflection. Deflection is computed as the difference between the initial length and the current length (the distance between connection points). The sign of the F determines if it is pulling or pushing. Once you compute F then you need to apply it along the line connecting two spring connection points. To satisfy force balance you need to apply this force in opposing directions (one of the bodies gets positive the other one gets negative force). This is because Sir Newton says so.
Here is an example (works with pyBox2D but you can easily convert this to C++)
You need spring objects with some properties. Your spring objects need to know their initial lengths, stiffness, body1, body2, connection coordinates (b1x, b1y, b2x, b2y (in local coordinates))
In your case you need to check if length < spr.initialLength, if this is True then you don't apply any force.
body1 = spr.box2DBody1
body2 = spr.box2DBody2
pA = body1.GetWorldPoint(b2Vec2(spr.box2Db1x, spr.box2Db1y))
pB = body2.GetWorldPoint(b2Vec2(spr.box2Db2x, spr.box2Db2y))
lenVector = pB - pA
length = lenVector.Length()
deltaL = length - spr.initialLength
force = spr.K * deltaL
#normalize the lenVector
if length == 0:
lenVector = b2Vec2(0.70710678118654757, 0.70710678118654757)
else:
lenVector = b2Vec2(lenVector.x / length, lenVector.y / length)
sprForce = b2Vec2(lenVector.x * force, lenVector.y * force)
body1.ApplyForce(sprForce, pA)
body2.ApplyForce(-sprForce, pB)
I very much doubt they are using any joints there. They are probably just taking the distance between the current position of the ninja guy, and the middle of the two posts, to calculate a direction and starting impulse... and just drawing two lines between the posts and the ninja guy.
The best physics implementation added to games I have seen was done by a guy with an engineering degree. He used the calculations you would do in physics / engineering translated into C++. Everything from simple gravity, recoil, thrust, to rotational velocities caused by incidental explosions. All the math was separated into a module that was distinct from the animation.
I would suggest looking up formulas for properties of elastics, and also consider that you have three situations for the elastic band:
1) A shaped force is being applied to stretch it back
2) The shape is now driven by the elastic properties of the band
3) The shape is no longer touching the band, and the band is loosely oscillating by its own weight and inertia
The closer you get to using the true physics calculations, the more realistic it will appear. I'm sure you can fudge it to make it easier on yourself, but humans are inherently good at seeing fakeness.
In my game every 2 seconds I create a new body and then I apply an impulse to this Box2d body.
My problem is that impulse is still the same, but the body behaves in two ways:
It slowly goes upwards , or another time it quickly falls down
I want the body to behave in the same way after impulse, is it possible?
Code:
- (void)newBullet
{
CGPoint touchedAt;
touchedAt.x = 184;
touchedAt.y = 1200;
bullet = [CCSprite spriteWithSpriteSheet:spriteSheet rect:CGRectMake(586, 719, 32, 32)];
[spriteSheet addChild: bullet z: 10 tag: 8];
bullet.position = ccp( touchedAt.x , touchedAt.y);
bullet.rotation = 90;
bulletBodyDef.type = b2_dynamicBody;
bulletBodyDef.position.Set(touchedAt.x / PTM_RATIO, touchedAt.y / PTM_RATIO);
bulletBodyDef.userData = bullet;
bulletBodyDef.angle = CC_DEGREES_TO_RADIANS( 90 );
bulletBody = _world->CreateBody(&bulletBodyDef);
b2CircleShape bulletShape;
bulletShape.m_radius = bullet.contentSize.width/PTM_RATIO/2;
b2FixtureDef bulletShapeDef;
bulletShapeDef.shape = &bulletShape;
bulletShapeDef.density = 0.0f;
bulletShapeDef.friction = 0.9f;
bulletShapeDef.restitution = 0.0f;
bulletShapeDef.isSensor = false;
bulletFixture = bulletBody->CreateFixture(&bulletShapeDef);
b2Vec2 force = b2Vec2(6.0f, 4.0f );
bulletBody->ApplyImpulse(force, bulletBody->GetPosition());
}
Video(Sorry for poor quality, but you can see what I mean)
http://vimeo.com/34215327
I don't know how you are calling this method, but I suggest that you have more control over where you call the method and where you do the box2d time step, it might not be related to that, but its worth checking out. What might be happening is that the impulse is not being applied because the solver which determines the speed of the body isn't called until you reset forces (which I assume you are doing), and so the effect is lost.
Hi I have finally made a working joystick in cocos2d. I am able to rotate a sprite to the exact angle that the joystick thumb, or cap, is 'pointing'. However, I am unable to move the sprite in that same direction. Is there an easy way to move the sprite with the way I have the rotating code set up? Also is there a way to keep it moving if your thumb is still pressed, but not moving the joystick?. PS this code is all within the TouchesMoved method. PPS. the cap is the thumb, the pad is the joystick background, and the Sprite2 is the sprite that I want to move. (95, 95) is the center of the pad sprite.
if(capSprite.position.x>=padSprite.position.x){
id a3 = [CCFlipX actionWithFlipX:NO];
[sprite2 runAction:a3];
}
if(capSprite.position.x<=padSprite.position.x){
id a4 = [CCFlipX actionWithFlipX:YES];
[sprite2 runAction:a4];
}
CGPoint pos1 = ccp(95, 95);
CGPoint pos2 = ccp(capSprite.position.x, capSprite.position.y);
int offX = pos2.x-pos1.x;
int offY = pos2.y-pos1.y;
float angleRadians = atanf((float)offY/(float)offX);
float angleDegrees = CC_RADIANS_TO_DEGREES(angleRadians);
float theAngle = -1 * angleDegrees;
sprite2.rotation = theAngle;
I'm not familiar with cocos2d but I had a quick look at the documentation and this sample might be of use to you:
if keys[key.UP]:
self.target.acceleration = (200 * rotation_x, 200 * rotation_y)
I had written a long explanation answering your second question but I believe this "self.target.acceleration" solves that too. You can read more at the cocos2d API documentation.
What I generally do is get the angle, convert it to a CGPoint with ccpForAngle(float) and then multiply the CGPoint by a value:
float angle = whatever;
CGPoint anglePoint = ccpForAngle(angle);
// You will need to play with the mult value
angle = ccpMult(angle, 2.5);
// This also works with box2D or probably Chipmunk.
sprite.position = angle;