I have a simple scene there is a floor, block, camera and light.
The floor is static
SCNNode* floor = [SCNNode node];
SCNPhysicsBody *staticBody = [SCNPhysicsBody staticBody];
floor.physicsBody = staticBody;
[[scene rootNode] addChildNode:floor];
The block is dynamic
SCNNode *block = [SCNNode node];
block.position = SCNVector3Make(-10, 45, -20)
block.geometry = [SCNBox boxWithWidth:5 height:5 length:5 chamferRadius:0];
block.physicsBody = [SCNPhysicsBody dynamicBody];
The block's starting position is above the floor, so when the app runs, the block falls to the floor as expected.
I have added motion manager that will move the floor down, simulating the floor being pulled out from under the block by translating negative changes in Y to the block and this is where the trouble begins.
if(userAcceleration.y < 0)
{
SCNVector3 vector = floor.position;
vector.y += userAcceleration.y*10.0;
floor.position = vector;
}
If the motion occurs before the block has come to rest, I can shake the device and can keep the block moving around as expected.
However, if the motion occurs after the block has come to a rest for a few seconds, the block will only rise (higher and higher with each motion) above the floor never to fall again.
Why does the gravity affect appear to stop?
Is there something that turns off gravity that I need to checking during the motion check? or is there something else I am missing?
It might sound silly, but have you set the playing property of your renderer to true?
If that doesn't work, my hack is to add an empty SCNNode and make it rotate forever with a SCNAction. It keeps the scene rendering/calculations going even if nothing is moving.
EDIT: I forgot about the allowResting property. It's probably what is causing your problem. Just turn it off for your object!
You can read more about it here: https://developer.apple.com/library/prerelease/ios/documentation/SceneKit/Reference/SCNPhysicsBody_Class/index.html#//apple_ref/occ/instp/SCNPhysicsBody/allowsResting
Related
I am making a game with sprites that move and obstacles to learn SpriteKit. I want the sprites that move to collide with the obstacles and bounce off of them but I want the obstacles to stay fixed. How do I do this? I have tried the following with no success:
Setting obstacle.physicsBody?.isDynamic = true. This made the sprites go through the obstacle.
Fixing the movement and rotation of the object with SKConstraint. When I do this they just go through each other.
Setting the mass of the body to be really high as follows obstacle.physicsBody?.mass = CGPoint.maxFiniteMagnitude but this freezes the game. When I set it really high it doesn't seem to do anything.
Setting obstacle?.physicsBody.velocity = CGVector(dx: 0, dy: 0) when the objects collide. I know that the contact.bodyA and contact.bodyB are passed by value and not reference so I loop through an array with the obstacles and set the velocity this way. The obstacles are still pushed by the other sprites.
Update:
- Setting obstacle.physicsBody?.collisionBitMask = PhysicsCategory.none so the sprite collides with the obstacle but not the other way around.
The object is setup as follows, with fish being the other sprite:
obstacle.position = location
obstacle.physicsBody = SKPhysicsBody(rectangleOf: obstacle.size)
obstacle.physicsBody?.isDynamic = true
obstacle.physicsBody?.categoryBitMask = PhysicsCategory.obstacle
obstacle.physicsBody?.contactTestBitMask = PhysicsCategory.fish
obstacle.physicsBody?.collisionBitMask = PhysicsCategory.fish
obstacle.physicsBody?.usesPreciseCollisionDetection = true
self.obstacles.append(obstacle)
super.addChild(obstacle)
Please let me know if there is something I am doing wrong / misunderstanding. Thanks.
Found the answer here. One of the objects needs to have .physicsBody?.isDynamic = true. In this case I set the obstacle to false so it is stationary.
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 need to fire a "shot" from a static SKSpriteNode towards another dynamic node. I've created a shot as a sprite node as the shot and moved it to by SKAction to the main sprite node, like so:
let node = info["node"] as SKSpriteNode // The static node
let shot = SKSpriteNode(color: UIColor.blueColor(), size: CGSize(width:node.frame.width / 3, height: node.frame.height / 1.2))
shot.physicsBody = SKPhysicsBody(edgeLoopFromRect: shot.frame)
shot.position = node.position
shot.physicsBody?.categoryBitMask = shotMask
shot.physicsBody?.contactTestBitMask = spriteMask
shot.physicsBody?.collisionBitMask = 0
shot.physicsBody?.usesPreciseCollisionDetection = true
self.addChild(shot)
shot.runAction(SKAction.moveTo(sprite.position, duration: 1.0))
My problem is that the shot stops after it reaches the point. Is there a way to make the shot continue moving in it's direction, or is there another way of doing what I need? Thanks!
Don't use a SKAction to move the shot. Instead change the shot's position by directly modifying it's position.
shot.position = CGPointMake(shot.position.x+1, shot.position.y);
Run the above in your update method. To speed up the shot, change the +1 to whatever value you need. Obviously you will need to remove the shot node from parent once it leaves the screen, hits the target, etc...
You'll need to calculate the vector from the shot's origin to it's destination. Then extend the vector until the shot will be off screen, possibly by finding the unit vector (a vector of length 1) and multiplying it by 3000 or so. As you have a definite endpoint now, you could still use an SKAction.
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 am using the following code to put a floor in my SpriteKit based game:
var floorNode = SKSpriteNode()
var floorBody = SKPhysicsBody(edgeFromPoint: CGPointMake(self.frame.minX, self.frame.minY), toPoint: CGPointMake(self.frame.maxX, self.frame.minY))
floorNode.physicsBody = floorBody
addChild(floorNode)
This places a floor at the bottom of the screen as expected. However as I add more things to the scene, one end of the floor eventually sinks down and everything in the scene that is resting on it slides off into the abyss.
I am at a complete loss here since Apple's documentation says that "an edge-based body does not have mass or volume, and is unaffected by forces or impulses in the system. Edge-based bodies are used to represent volume-less boundaries or hollow spaces in your physics simulation."
Anyone else seen this kind of behavior?
The easiest way to define floor for your scene, without adding any nodes to it:
self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:self.frame];
where self is your SKScene.
If you don't want ceiling on the scene, define physicsBody as this:
[SKPhysicsBody bodyWithEdgeLoopFromRect:CGRectMake(self.frame.origin.x,
self.frame.origin.y,
self.frame.size.width,
self.frame.size.height*5)];