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;
Related
I am using SpriteKit's built in Physics Engine to build a game for iOS. Basically it involves a bouncing ball which moves via me manually setting it's initial velocity and bounces via resetting the velocity within the contact event with the floor.
The issue is, the actual maths for this environment do not add up. Using 'SUVAT' equations it's easy to determine how far the ball's x-displacement should be when it reaches the floor after being thrown with a certain velocity, however (with gravity set to -9.81), it barely moves a couple of pixels.
I simplified the problem to just trying to shoot a ball a certain distance upwards (in the y-direction) and the same thing happened, it moves a couple of points up and then just falls to the floor, at least a 20th of how far it should move.
This is how I have set the physics environment up:
self.physicsWorld.contactDelegate = self;
self.physicsWorld.gravity = CGVectorMake(0.0, -9.81);
And then this is my function for generating this ball (shooting upwards) example. Mathematically it should reach the height of the tower:
-(void)generateTestBall {
self.ball = [SKSpriteNode spriteNodeWithImageNamed:#"ball"];
SKSpriteNode * tower = [SKSpriteNode spriteNodeWithImageNamed:#"player"];
self.ball.position = CGPointMake(self.scene.size.width/2,self.scene.size.height/2);
self.ball.size = CGSizeMake(20,20);
self.ball.color = [SKColor redColor];
self.ball.colorBlendFactor = 1;
tower.position = CGPointMake(self.scene.size.width/2 + 20,self.scene.size.height/2+100);
tower.size = CGSizeMake(20,200);
tower.color = [SKColor blueColor];
tower.colorBlendFactor = 1;
[self addChild:tower];
[self addChild:self.ball];
self.ball.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:10];
self.ball.physicsBody.affectedByGravity = YES;
self.ball.physicsBody.linearDamping = NO;
self.ball.physicsBody.dynamic = YES;
CGFloat ballVel = sqrt(2*9.81*tower.size.height);
NSLog(#"%f",ballVel);
self.ball.physicsBody.velocity = CGVectorMake(0.0f, ballVel);
}
Please can someone explain what I am doing wrong? I've double checked my maths (I'm a maths student so fingers crossed that's not the issue)!
Thanks!
Steve
So I FINALLY managed to figure it out. Just incase anyone else is experiencing the same issue I'll post the answer here:
The issue was that, although gravity is (apparently) in ms^-2 and velocity m2^-1 (to replicate earth), any distances in Objective C are measured in POINTS rather than the required form of METRES. Therefore any calculation done with x,y position / size values taken from SKSpriteNodes etc will be a certain factor out.
After running a few tests I found the factor to roughly be 157. This means that you must multiply any sizes / distances in POINTS by 157 to get the relative 'METRE' value which will work with SUVAT.
The actual numbers themselves seem a bit ridiculous as they're all very big (velocity, distance etc) but that doesn't actually pose a problem anyway as they all now work relative to each other!
Hope this helps anyone!
Steve
I have a game in swift using spritekit. If you tap the screen it will create a radial gravity field and pull all the other objects in. I create the gravity field like so
var fieldNode = SKFieldNode.radialGravityField();
fieldNode.falloff = 0.5;
fieldNode.strength = 1;
fieldNode.animationSpeed = 0.5;
It works but my problem is that I only want a sprite to be affected only when it is when it within a certain distance to the centre of the radial gravity, and i will have more than 1 sprite. The way I see it is that there are 2 ways to do it, 1. When a sprite is too far turn off the radial gravity for that sprite or 2. Make the radial gravity dissipate after a certain radius. There is also an overall gravity for the scene.
So the main question is:
How can I either turn off 1 gravity for a sprite OR make a radial gravity dissipate ?
A field node's region property determines its area of effect. The associated SKRegion object lets you define a circular region by its radius.
You can also use the fieldBitMask on a physics body and the categoryBitMask on a field to selectively control which fields affect which bodies.
Try using:
let radius: CGFloat = 1000.0
gravityField.strength = Float(pow(radius, 2)) * pow(10, -3)
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.