I'm trying to get a bouncing ball effect which i'm not really having a problem with.
what i'm trying to figure out is how can i calculate the speed of the ball.
I know this is how its done in Box2d
b2Vec2 velocity = b->GetLinearVelocity();
float32 speed = velocity.Length();
how are these lines converted to sprite kit?
Thanks
Edit:
i'm trying this any idea if this is correct for speed
static inline CGFloat CGPointLength(const CGVector a) {
return sqrtf(a.dx * a.dx + a.dy * a.dy);
}
CGVector velocity=circle.physicsBody.velocity;
float speed=CGPointLength(velocity);
The SKNode's physicsBody has a CGVector property for velocity that you would use to calculate the speed.
Related
I've been struggling with this problem for a while, which appears to be buried deep inside the spritekit physics engine.
My first question would be: Does Spritekit process its physics updates in a different thread than the main thread?
I have a "world" node in the scene which I move around to simulate a "camera" view. As such, I can center the "camera" on my player character node. Since the player jumps up and down a lot, I want to smooth the camera. Without camera smoothing, there's no problems. But when I add camera smoothing, as such: (this code is called from didFinishUpdate)
CGPoint ptPosition = self.position;
float fSmoothY = m_fLastCameraY + (ptPosition.y - m_fLastCameraY) * 0.1;
CGPoint pointCamera = [self.scene convertPoint:CGPointMake(ptPosition.x, fSmoothY) fromNode:self.parent];
[gameScene centerOnPoint:pointCamera];
m_fLastCameraY = fSmoothY;
If I call the above code from didSimulatePhysics, it does the exact same thing. It stutters whenever it falls down (due to the Y camera smoothing).
When plotting it out, you can see that the player Y (the red line) is stuttering over the course of the frames.
How can I fix this, or work around it if it can't be truly "fixed"?
I suggest you apply an infinite impulse response (IIR) filter to smooth the camera. You can do that by...
First, declare the instance variables
CGFloat alpha;
CGFloat fSmoothY;
and then Initialize alpha and fSmoothY
// alpha should be in [0, 1], where a larger value = less smoothing
alpha = 0.5;
fSmoothY = ptPosition.y;
Lastly, apply the filter with
fSmoothY = fSmoothY * (1-alpha) + ptPosition.y * alpha;
I'm fiddling around with cocos2d v3 in combination with sprite builder.
The game is a simple catch and avoid game, objects coming down an the hero is standing in the bottom of the screen and you can move him around with the accelerometer.
I have a level file (cclayer) with some objects (ccnode) in it, the have physics enabled.
In my update function I move the layer slowly down.
If the objects have physics enabled, they just drop down. If I switch it to statics physics, they stay in place.
The only way I can find to move the object along with the layer is to turn off the physics completely. But then the collisions won't work anymore...
This kept me buys for the past 4 hours or so.
What is the best approach for this situation?
Thanks in advance guys!
this is my update function:
- (void)update:(CCTime)delta {
float maxX = winSize.width - _hero.contentSize.width/2;
float minX = _hero.contentSize.width/2;
CMAccelerometerData *accelerometerData = _motionManager.accelerometerData;
CMAcceleration acceleration = accelerometerData.acceleration;
CGFloat newXPosition = _hero.position.x + acceleration.x * 1000 * delta;
newXPosition = clampf(newXPosition, minX, maxX);
_hero.position = CGPointMake(newXPosition, _hero.position.y);
//level position
CGPoint oldLayerPosition = _levelNode.position;
float xNew = oldLayerPosition.x;
float yNew = oldLayerPosition.y -1.4f;
_levelNode.position = ccp(xNew, yNew);
}
This is a design decision made within the physics engine. Physics bodies do not move with their parents. See: https://github.com/cocos2d/cocos2d-iphone/issues/570
You need to change the design of your game so that your hero moves, and the obstacles stay in the same position. Then you implement a camera like mechanism to follow your moving hero.
We have used the same approach in our flappy bird tutorial.
I'm using a SneakyJoystick in Cocos2d, and I'm trying to get a sprite to rotate to face the same direction as the joystick is pointed (this is top down).
I can get it to rotate to face it, but it snaps into position as the rotation is updated every frame or so.
How can I make the sprite rotate smoothly towards the target angle, without jumping to it? I wasn't able to figure out how to do this with a CCRotateTo because the angle to rotate towards could change at any time.
I ended up fixing this simply by using a rotation method that I made, which rotates the node/sprite in the correct direction at the correct amount each update.
- (void)rotateNode:(CCNode*)aNode degrees:(float)targetRotation withSpeed:(float)rotationSpeed withTimeDelta:(ccTime)dt
{
rotationSpeed = rotationSpeed * dt;
// Convert the difference between the two angles to radians
float diff = (targetRotation - aNode.rotation) * (M_PI / 180);
// Find the rotation of the vector created by the sin and cos of the difference
float rotationDifference = atan2f(sinf(diff),cosf(diff));
// Rotate the clip accordingly
aNode.rotation += MAX(
MIN(
(180/M_PI) * rotationDifference,rotationSpeed), -rotationSpeed
);
}
Have you tried:
[CCRotateBy actionWithDuration:0.5f angle:CC_DEGREES_TO_RADIANS(90.0f)];
Obtain the Angle between the last Update the current Update, also if you wanted it so the character had a set time to turn around, you can scale your duration by the amount of the angle.
I am really looking to try to have gravity in my game. I know everyone says use Box2D, but in my case I can't. I need to use Cocos2D for the gravity.
I know Cocos2D does not have any gravity API built in so I need to do something manually. The thing is there is like no tutorials or examples anywhere on the web that show this.
Can anyone show me what they have done or can some explain step by step on how to apply a non-constant gravity (One that gets slightly stronger while falling).
I think this will help a lot of people that are facing the same issue that I am having!
Thanks!
Gravity is nothing but a constant velocity applied to the body for every physics step. Have a look at this exemplary update method:
-(void) update:(ccTime)delta
{
// use a gravity velocity that "feels good" for your app
const CGPoint gravity = CGPointMake(0, -0.2);
// update sprite position after applying downward gravity velocity
CGPoint pos = sprite.position;
pos.y += gravity.y;
sprite.position = pos;
}
Every frame the sprite y position will be decreased. That's the simple approach. For a more realistic effect you will want to have a velocity vector for each moving object, and apply gravity to the velocity (which is also a CGPoint).
-(void) update:(ccTime)delta
{
// use a gravity velocity that "feels good" for your app
const CGPoint gravity = CGPointMake(0, -0.2);
// update velocity with gravitational influence
velocity.y += gravity.y;
// update sprite position with velocity
CGPoint pos = sprite.position;
pos.y += velocity.y;
sprite.position = pos;
}
This has the effect that velocity, over time, increases in the downward y direction. This will have the object accelerate faster and faster downwards, the longer it is "falling".
Yet by modifying velocity you can still change the general direction of the object. For instance to make the character jump you could set velocity.y = 2.0 and it would move upwards and come back down again due to the effect of gravity applied over time.
This is still a simplified approach but very common in games that don't use a "real" physics engine.
Ok so I have a ship which moves up and down based on the axis regardless of where the ship is facing.
How do I make the ship move in the direction it's facing? i.e. if my ship is facing east, key up makes it go north rather than east.
Your question isn't very clear - I will assume you're using models and matrices (as opposed to SpriteBatch or something else). So, making a guess - I'd say that the order of your matrix operations is incorrect.
This answer to a similar question may help.
Each matrix operation happens around the origin. So if you're doing your rotation after you move your ship into position, your rotation will also effectively "rotate" the direction of movement.
The easiest way is to make an angle and velocity variable so when you click left and right you change the angle and when you click up and down you changle the speed of your ship.
KeyboardState ks;
float speed = 0;
float angle = 0;
protected override void Update(GameTime gameTime)
{
ks = Keyboard.GetState();
if(ks.IsKeyDown(Keys.Up)) speed += 10;
if (ks.IsKeyDown(Keys.Down)) speed -= 10;
if (ks.IsKeyDown(Keys.Right)) angle += 10;
if (ks.IsKeyDown(Keys.Left)) angle -= 10;
}
You need to have direction vector like this
Vector3 direction = Vector3.Transform(Vector3.Forward, Matrix.CreateFromYawPitchRoll(yaw, pitch, roll));
Next, get your velocity vector
Vector3 velocity = direction * speed;
And move your ship
float time (float) = gameTime.ElapsedTime.TotalSeconds;
position += velocity * time;
In this example yaw is angle, pitch and roll keep 0.