Can someone suggest how I can vary the UIPushBehavior magnitude force by distance from source. To mirror the affect of the force of wind from a fan on another object. So the closer the object is to the fan the stronger the force.
if String(describing: identifier) == "fan1" {
self.push = UIPushBehavior(items: [self.object], mode: .instantaneous)
self.push.setAngle(.pi/4, magnitude: 1)
self.animator.addBehavior(self.push)
self.push.addItem(self.object)
}
Use a UIFieldBehaviour to create a linear gravitational field in the direction of the fan. Then you can specify a falloff:
var forceField: UIFieldBehaviour!
// ...
forceField = UIFieldBehavior.linearGravityField(direction: CGVector(dx: 1, dy: -5))
// example values for a "fan" on the bottom left blowing mostly upwards:
forceField.position = CGPoint(x: view.bounds.minX, y: view.bounds.maxY)
forceField.region = UIRegion(radius: 3000)
forceField.minimumRadius = 100
forceField.falloff = 5
forceField.strength = 10
forceField.addItem(view1)
forceField.addItem(view2)
animator.addBehavior(forceField)
Have fun playing around with these values!
Adding collision, another gravity behaviour, and a dynamic item behaviour to two views, we get the following effect:
That feels like a fan on the bottom left to me!
You can also choose a radial gravitational field positioned at where the fan is, if your fan is in a corner and blows "radially", but note that you should use a negative value for strength in that case to say that the field repels rather than attracts.
Related
I've been trying to implement an infinite background animation, which should change between 4 images of equal height and then repeat the sequence. However, it does not seem to work properly.
Note anchorPoint = CGPoint(x: 0.5, y: 0)
func updateBackground(currentTime: TimeInterval){
var delta: CGFloat = 0.0
if lastUpdate != nil {
delta = CGFloat(currentTime - lastUpdate)
}
//First increment position
activeBackground1.position.y += delta*backgroundVelocity
activeBackground2.position.y += delta*backgroundVelocity
//Detect bounds surpass
if activeBackground1.position.y > activeBackground1.size.height + screen.height/2 {
lastSky = (lastSky + 1)%4
sky1 = SKTexture(imageNamed: "sky" + String(lastSky))
activeBackground1.texture = sky1
//Reposition: background1 new position is equal to minus the entire height of
//background2 + its y size.
activeBackground1.position.y = -abs(activeBackground2.size.height-activeBackground2.position.y)
}
if activeBackground2.position.y > activeBackground2.size.height + screen.height/2 {
lastSky = (lastSky + 1)%4
sky1 = SKTexture(imageNamed: "sky" + String(lastSky))
activeBackground2.texture = sky1
activeBackground2.position.y = -abs(activeBackground1.size.height-activeBackground1.position.y)
}
}
The update algorithm works fine, but when it is needed to reposition one of the two background, it seems there is an offset of about 10.0 CGFloat from one background to another. What am I doing wrong?
EDIT: It turned out that the error was located in my image, which presented some blank rows and therefore generated visualisation glitches. So my code works perfectly.
I do the test and most likely you should use something like:
activeBackground2.position.y = activeBackground1.size.height + activeBackground1.position.y
instead of
activeBackground2.position.y = -abs(activeBackground1.size.height-activeBackground1.position.y)
I did this example and it works correctly: https://github.com/Maetschl/SpriteKitExamples/tree/master/InfiniteBackground/InfiniteBackground
Feel free to see and use.
Your problem is floating point math causing rounding errors. I am on a phone right now so I can’t wrote code, but what you want to do is have 1 parent SKNode to handle your entire background.
Add your background slivers to the parent node.
You then place the moving action on the parent only.
As each sliver leaves the screen, you take the sliver, and move it to the end of the other slivers.
This jumping should always be done with integer math, leaving no holes.
Basically:
The floating point moving math is done on the parent node.
The integer based tile jumping is done on each of the slivers.
Hello I'm trying to spawn bullets at the bottom of my screen to travel upwards but the current code that I have spawns the bullets at the top of the screen. I've tried making the height negative and nothing happened. Here's the code I'm working with, thanks.
let randomBulletPosition = GKRandomDistribution(lowestValue: -300, highestValue: 300)
let position = CGFloat(randomBulletPosition.nextInt())
bullet.position = CGPoint(x: position, y: self.frame.size.height + bullet.size.height)
Some nice conversions will help you.
Now, do not do this all the time, this should be a one and done type deal, like in a lazy property.
First, we want to get the bottom of our view
let viewBottom = CGPoint(x:scene!.view!.midX,y:scene!.view!.frame.maxY) //In a UIView, 0,0 is the top left corner, so we look to bottom middle
Second, we want to convert the position to the scene
let sceneBottom = scene!.view!.convert(viewBottom, to:scene!)
Finally we want to convert to whatever node you need it to be a part of. (This is optional if you want to place it on the scene)
let nodeBottom = scene!.convert(sceneBottom,to:node)
Code should look like this:
let viewBottom = CGPoint(x:scene!.view!.midX,y:scene!.view!.frame.maxY)
let sceneBottom = scene!.view!.convert(viewBottom!, to:scene!)
let nodeBottom = scene!.convert(sceneBottom,to:node)
Of course, this is a little ugly.
Thankfully we have convertPoint and convert(_from:) to clean things up a little bit
let sceneBottom = scene.convertPoint(from:viewBottom)
Which means we can clean up the code to look like this:
let sceneBottom = scene.convertPoint(from:CGPoint(x:scene!.view!.midX,y:scene!.view!.frame.maxY))
let nodeBottom = node.convert(sceneBottom,from:scene!)
Then we can make it 1 line as:
let nodeBottom = node.convert(scene.convertPoint(from:CGPoint(x:scene!.view!.midX,y:scene!.view!.frame.maxY),from:scene!)
As long as the node is available to the class, we can make it lazy:
lazy var nodeBottom = self.node.convert(self.scene!.convertPoint(CGPoint(x:self.scene!.view!.midX,y:self.scene!.view!.frame.maxY),from:self.scene!)
This means the first time you call nodeBottom, it will do these calculations for you and store it into memory. Everytime after that, the number is preserved.
Now that you know where the bottom of the screen is in the coordinate system you want to use, you can assign the x value to whatever your random is producing, and you can subtract the (node.height * (1 - node.anchorPoint.y)) to fully hide your node from the scene.
Now keep in mind, if your node moves between various parents, this lazy will not update.
Also note, I unwrapped all optionals with !, you may want to be using ? and checking if it exists first.
I have a game with a character who is affected by normal gravity as he jumps across platforms. He collects coins and power ups. I'm making a power up that makes coins gravitate to the characterSpriteNode.
In the case that magneticPowerUp = true I want it to appear that a gravitational field has activated about the character that makes only the coins attract to the character, like a magnetic field.
I've been fideling with Epic Bytes SO answer here but i'm not having much luck as i don't have much experience with vectors and haven't got too deep into physicsBody.
So I just can't work out the part that will make the coins move once it has decided the coin is close enough to move to the char.
My thoughts are something like this:
override func update(currentTime: NSTimeInterval) {
if magneticPowerUp {
for coin in scoreNode.children {
let disp = CGVector(dx: coin.position.x-character.position.x, dy: coin.position.y-character.position.y)
let radius = sqrt(disp.dx*disp.dx+disp.dy*disp.dy) // Distance between character and coin
if radius < character.frame.height * 3 {
// Use physics methods here to push the coin to the character
let dt: CGFloat = 1.0/60.0
let strength: CGFloat = 10000
let m1 = character.physicsBody!.mass*strength
let m2 = coin.physicsBody!.mass*strength
let force = (m1*m2)/(radius*radius);
let normal = CGVector(dx: disp.dx/radius, dy: disp.dy/radius)
let impulse = CGVector(dx: normal.dx*force*dt, dy: normal.dy*force*dt)
// Something wrong with this?
coin.physicsBody!.velocity = CGVector(dx: coin.physicsBody!.velocity.dx + impulse.dx, dy: coin.physicsBody!.velocity.dy + impulse.dy)
}
}
}
}
SpriteKit has SKFieldNode for creating gravity and magnets that apply to bodies. Normally it deflects charged bodies instead of attracting them like ferromagnetism in the real world.
If you want a field that attracts things you'll need a radialGravityField() method around your hero. To attract specific things like your coins you would use categoryBitMask on the hero field and fieldBitMask on the coin sprites you want to attract.
With the electricField() method you could also have your hero attract different bodies with stronger or weaker forces. Or even attract and repel different bodies at the same time. You can use the charge property of physics bodies.
Code examples:
var field:SKFieldNode?
switch( name )
{
case .Electric:
var electric = SKFieldNode.electricField()
electric.strength = 100.0
bestBodyMass = 0.5
impulseMultiplier = 400
field = electric
case .Magnetic:
var magnetic = SKFieldNode.magneticField()
magnetic.strength = 1.0
bestBodyMass = 0.5
impulseMultiplier = 400
field = magnetic
}
The Apple documentation for SKFieldNode is awesome.
https://developer.apple.com/reference/spritekit/skfieldnode
Here's are two cool YT videos showing the effect.
https://www.youtube.com/watch?v=-mjRPgP0oAE
https://www.youtube.com/watch?v=JGk3agy-c50
I currently have two SKSpriteNodes on top of each other like so (The white part is one and the brown round circle part is the other one):
The white part is positioned 1/3 the way down on top of the round brown sprite node. In the picture, the brown round part has a SKPhysicsBody applied to it already as seen by the light blue outline around it. When I add a SKPhysicsBody around the top ovalish white part it pushes it up and not in the position I wanted it.
How can I have a SKPhysics body coving both bodies of sprites but not have the physics bodies push on one another which makes the white part move upwards? I would like the white part to stay in the position it was in the first image.
Thanks for anyone help!
Here's the code I used for the SKPhysicsBody's:
// create, position, scale & add the round body
roundBody = SKSpriteNode( imageNamed: "roundBody" )
roundBody.position = CGPoint( x: 207, y: 70 )
roundBody.zPosition = 1
roundBody.xScale = 0.3
roundBody.yScale = 0.3
// add sprite node to view
self.addChild( roundBody )
// create, position, scale & add the head
theHead!.position = CGPoint( x: 207, y: roundBody.frame.maxY / 1.15 )
theHead!.zPosition = 2
theHead!.xScale = 0.3
theHead!.yScale = 0.3
// setting up a SKPhysicsBody for the round body
roundBody.physicsBody = SKPhysicsBody( circleOfRadius: roundBody.size.width / 4 )
roundBody.physicsBody!.dynamic = true
roundBody.physicsBody!.affectedByGravity = true
roundBody.physicsBody!.allowsRotation = false
roundBody.physicsBody!.pinned = false
// setting up a SKPhysicsBody for the head
theHead!.physicsBody = SKPhysicsBody(circleOfRadius: theHead!.size.width / 2 )
theHead!.physicsBody!.dynamic = true
theHead!.physicsBody!.affectedByGravity = false
theHead!.physicsBody!.allowsRotation = false
theHead!.physicsBody!.pinned = false
I was able to figure out that if you use SKPhysicsJointPin it does the exact thing I needed! (Which was to basically pin a sprite head on it's body and share a physics body)
let joinTogether = SKPhysicsJointPin.jointWithBodyA(
roundBody.physicsBody!,
bodyB:theHead!.physicsBody!,
anchor: GPointMake(CGRectGetMidX(roundBody.frame),
CGRectGetMinY(theHead!.frame)))
scene!.physicsWorld.addJoint(joint)
Hope this helps someone in the future!
If you never want it to move, set it's .dynamic property to false. Then other objects may or may not bounce/collide with it (depending upon their collisionBitMask) but it won't move in response to those collisions.
Your own answer is correct and a better solution but just to explain further.
The reason of the bodies colliding is that by default a physics body's collision bit mask is set to all categories which means it will collide with everything. In your code you are not calling
roundBody.physicsBody?.collisionBitMask = ...
which is why its using the default values.
To change that you could give your body and head a different collisionBitMask.
Im sure you will deal with this sooner or later when you handle collisions
Also as a tip it's a better idea to not force unwrap the physics bodies unless you have too, even though you know they exist. So you should replace your ! with ? whenever possible.
I'm trying to implement mouse selection for my game. When I QueryAABB it looks like it's treating objects much larger than they really are.
Here's what's going on in the image
The blue box is an actor containing a body that I'd like to select
The outline on the blue box is drawn by Box2DDebugRenderer
The mouse selects a region on the screen (white box), this is entirely graphical
The AABB is converted to meters and passed to QueryAABB
The callback was called for the blue box and turned it red
The green outline left behind is a separate body to check if my conversions were correct, this is not used for the actual selection process
It seems to be connected to my meter size, the larger it is, the more inaccurate the result is. At 1 meter = 1 pixel it works perfectly.
Meter conversions
val MetersToPixels = 160f
val PixelsToMeters = 1/MetersToPixels
def toMeters(n: Float) = n * PixelsToMeters
def toPixels(n: Float) = n * MetersToPixels
In the image I'm using MetersToPixels = 160f so the inaccuracy is more visible, but I really want MetersToPixels = 16f.
Relevant selection code
val x1 = selectPos.x
val y1 = selectPos.y
val x2 = getX
val y2 = getY + getHeight
val (l,r) =
if (x2 < x1)
(x2,x1)
else
(x1,x2)
val (b,t) =
if (y2 < y1)
(y2,y1)
else
(y1,y2)
world.QueryAABB(selectCallback, toMeters(l),toMeters(b), toMeters(r),toMeters(t))
This code is inside the act method of my CursorActor class. And selectPos represents the initial point where the use pressed down the left mouse button and getX and getY are Actor methods giving the current position. The next bit sorts them because they might be out of order. Then they are converted to meters because they are all in pixel units.
selectCallback: QueryCallback
override def reportFixture(fixture: Fixture): Boolean = {
fixture.getBody.getUserData match {
case selectable: Selectable =>
selected += selectable
true
case _ => true
}
}
Selectable is a trait that sets a boolean flag internally after the query which helps determines the color of the blue box. And selected is a mutable.HashSet[Selectable] defined inside of CursorActor.
Other things possibly worth noting
I'm new to libgdx and box2d.
The camera is scaled x2
My Box2DDebugRenderer uses the camera's combined matrix multiplied by MetersToPixels
From what I was able to gather, QueryAABB is naturally inaccurate for optimization. However, I've hit a roadblock with libgdx because it doesn't have any publicly visible function like b2testOverlap and from what I understand, there's no plan for there to be one any time soon.
I think my best solution would probably be to use jbox2d and pretend that libgdx's physics implementation doesn't exist.
Or as noone suggested I could add it to libgdx myself.
UPDATE
I decided to go with a simple solution of gathering the vertices from the fixture's shape and using com.badlogic.gdx.math.Intersector against the vertices of the selection. It works I guess. I may stop using QueryAABB all together if I decide to switch to using a sensor for the select box.