问题
I'm trying to use a SCNPhysicsField.linearGravityField object to affect only specific objects in my scene. The problem is, that I can't seem to get it to affect anything. Here's a sample of my code in Swift:
let downGravityCatagory = 1 << 0
let fieldDown = SCNPhysicsField.linearGravityField()
let fieldUp = SCNPhysicsField.linearGravityField()
let fieldNode = SCNNode()
let sceneView = view as! SCNView
sceneView.scene = scene
sceneView.scene!.physicsWorld.gravity = SCNVector3(x: 0, y: 0, z: 0)
fieldDown.categoryBitMask = downGravityCatagory
fieldDown.active = true
fieldDown.strength = 3
fieldNode.physicsField = fieldDown
scene.rootNode.addChildNode(fieldNode)
var dice = SCNNode()
//I then attach geometry here
dice.physicsBody = SCNPhysicsBody(type: SCNPhysicsBodyType.Dynamic, shape: SCNPhysicsShape(geometry: dice.geometry!, options: nil))
dice.physicsBody?.categoryBitMask = downGravityCatagory
scene.rootNode.addChildNode(dice)
Even though the Physics Bodies are assigned the same catagoryBitMask as the gravity field, they just float there in zero G, only affected by the physicsworld gravity.
回答1:
Set the "downGravityCatagory" bit mask on the node:
dice.categoryBitMask = downGravityCatagory;
the physics's categoryBitMask is for physics collisions only.
回答2:
I am trying to get my ball to fall faster. Right now it falls really slowly. I tried using this answer. I think I am close, but I do not really know. The code:
import Cocoa
import SceneKit
class AppController : NSObject {
@IBOutlet weak var _sceneView: SCNView!
@IBOutlet weak var _pushButton: NSButton!
@IBOutlet weak var _resetButton: NSButton!
private let _mySphereNode = SCNNode()
private let _gravityFieldNode = SCNNode()
private let downGravityCategory = 1 << 0
private func setupScene() {
// setup ambient light source
let ambientLightNode = SCNNode()
ambientLightNode.light = SCNLight()
ambientLightNode.light!.type = SCNLightTypeAmbient
ambientLightNode.light!.color = NSColor(white: 0.35, alpha: 1.0).CGColor
// add ambient light the scene
_sceneView.scene!.rootNode.addChildNode(ambientLightNode)
// setup onmidirectional light
let omniLightNode = SCNNode()
omniLightNode.light = SCNLight()
omniLightNode.light!.type = SCNLightTypeOmni
omniLightNode.light!.color = NSColor(white: 0.56, alpha: 1.0).CGColor
omniLightNode.position = SCNVector3Make(0.0, 200.0, 0.0)
_sceneView.scene!.rootNode.addChildNode(omniLightNode)
// add plane
let myPlane = SCNPlane(width: 125.0, height: 2000.0)
myPlane.widthSegmentCount = 10
myPlane.heightSegmentCount = 10
myPlane.firstMaterial!.diffuse.contents = NSColor.orangeColor().CGColor
myPlane.firstMaterial!.specular.contents = NSColor.whiteColor().CGColor
let planeNode = SCNNode()
planeNode.geometry = myPlane
// rotote -90.0 degrees about the y-axis, then rotate -90.0 about the x-axis
var rotMat = SCNMatrix4MakeRotation(-3.14/2.0, 0.0, 1.0, 0.0)
rotMat = SCNMatrix4Rotate(rotMat, -3.14/2.0, 1.0, 0.0, 0.0)
planeNode.transform = rotMat
planeNode.position = SCNVector3Make(0.0, 0.0, 0.0)
// add physcis to plane
planeNode.physicsBody = SCNPhysicsBody.staticBody()
// add plane to scene
_sceneView.scene!.rootNode.addChildNode(planeNode)
// gravity folks...
// first, set the position for field effect
let gravityField = SCNPhysicsField.linearGravityField()
gravityField.categoryBitMask = downGravityCategory
gravityField.active = true
gravityField.strength = 3.0
gravityField.exclusive = true
_gravityFieldNode.physicsField = gravityField
_sceneView.scene!.rootNode.addChildNode(_gravityFieldNode)
// attach the sphere node to the scene's root node
_mySphereNode.categoryBitMask = downGravityCategory
_sceneView.scene!.rootNode.addChildNode(_mySphereNode)
}
private func setupBall() {
let radius = 25.0
// sphere geometry
let mySphere = SCNSphere(radius: CGFloat(radius))
mySphere.geodesic = true
mySphere.segmentCount = 50
mySphere.firstMaterial!.diffuse.contents = NSColor.purpleColor().CGColor
mySphere.firstMaterial!.specular.contents = NSColor.whiteColor().CGColor
// position sphere geometry, add it to node
_mySphereNode.position = SCNVector3(0.0, CGFloat(radius), 0.0)
_mySphereNode.geometry = mySphere
// physics body and shape
_mySphereNode.physicsBody = SCNPhysicsBody(type: .Dynamic, shape: SCNPhysicsShape(geometry: mySphere, options: nil))
_mySphereNode.physicsBody!.mass = 0.125
}
private func stopBall() {
_mySphereNode.geometry = nil
_mySphereNode.physicsBody = nil
}
override func awakeFromNib() {
// assign empty scene
_sceneView.scene = SCNScene()
setupScene()
setupBall()
}
@IBAction func moveBall(sender: AnyObject) {
let forceApplied = SCNVector3Make(35.0, 0.0, 0.0)
if _mySphereNode.physicsBody?.isResting == true {
_mySphereNode.physicsBody!.applyForce(forceApplied, impulse: true)
}
else if _mySphereNode.physicsBody?.isResting == false {
print("ball not at rest...")
}
else {
print("No physics associated with the node...")
}
}
@IBAction func resetBall(sender: AnyObject) {
// remove the ball from the sphere node
stopBall()
// reset the ball
setupBall()
}
}
Is there some trick to get "real-world" type gravity?
回答3:
Based on what @tedesignz suggested, here is the slightly modified working code:
import Cocoa
import SceneKit
class AppController : NSObject, SCNPhysicsContactDelegate {
@IBOutlet weak var _sceneView: SCNView!
@IBOutlet weak var _pushButton: NSButton!
@IBOutlet weak var _resetButton: NSButton!
private let _mySphereNode = SCNNode()
private let _myPlaneNode = SCNNode()
private let _gravityFieldNode = SCNNode()
private let BallType = 1
private let PlaneType = 2
private let GravityType = 3
private func setupScene() {
// setup ambient light source
let ambientLightNode = SCNNode()
ambientLightNode.light = SCNLight()
ambientLightNode.light!.type = SCNLightTypeAmbient
ambientLightNode.light!.color = NSColor(white: 0.35, alpha: 1.0).CGColor
// add ambient light the scene
_sceneView.scene!.rootNode.addChildNode(ambientLightNode)
// setup onmidirectional light
let omniLightNode = SCNNode()
omniLightNode.light = SCNLight()
omniLightNode.light!.type = SCNLightTypeOmni
omniLightNode.light!.color = NSColor(white: 0.56, alpha: 1.0).CGColor
omniLightNode.position = SCNVector3Make(0.0, 200.0, 0.0)
_sceneView.scene!.rootNode.addChildNode(omniLightNode)
// add plane
let myPlane = SCNPlane(width: 125.0, height: 150.0)
myPlane.widthSegmentCount = 10
myPlane.heightSegmentCount = 10
myPlane.firstMaterial!.diffuse.contents = NSColor.orangeColor().CGColor
myPlane.firstMaterial!.specular.contents = NSColor.whiteColor().CGColor
_myPlaneNode.geometry = myPlane
// rotote -90.0 degrees about the y-axis, then rotate -90.0 about the x-axis
var rotMat = SCNMatrix4MakeRotation(-3.14/2.0, 0.0, 1.0, 0.0)
rotMat = SCNMatrix4Rotate(rotMat, -3.14/2.0, 1.0, 0.0, 0.0)
_myPlaneNode.transform = rotMat
_myPlaneNode.position = SCNVector3Make(0.0, 0.0, 0.0)
// add physcis to plane
_myPlaneNode.physicsBody = SCNPhysicsBody(type: .Static, shape: SCNPhysicsShape(geometry: myPlane, options: nil))
// configure physics body
_myPlaneNode.physicsBody!.contactTestBitMask = BallType
_myPlaneNode.physicsBody!.collisionBitMask = BallType
_myPlaneNode.physicsBody!.categoryBitMask = PlaneType
// add plane to scene
_sceneView.scene!.rootNode.addChildNode(_myPlaneNode)
// add sphere node
_sceneView.scene!.rootNode.addChildNode(_mySphereNode)
// gravity folks...
// first, set the position for field effect
let gravityField = SCNPhysicsField.linearGravityField()
gravityField.categoryBitMask = GravityType
gravityField.active = true
gravityField.direction = SCNVector3(0.0, -9.81, 0.0)
print(gravityField.direction)
gravityField.strength = 10.0
gravityField.exclusive = true
_gravityFieldNode.physicsField = gravityField
_sceneView.scene!.rootNode.addChildNode(_gravityFieldNode)
// set the default gravity to zero vector
_sceneView.scene!.physicsWorld.gravity = SCNVector3(0.0, 0.0, 0.0)
}
private func setupBall() {
let radius = 25.0
// sphere geometry
let mySphere = SCNSphere(radius: CGFloat(radius))
mySphere.geodesic = true
mySphere.segmentCount = 50
mySphere.firstMaterial!.diffuse.contents = NSColor.purpleColor().CGColor
mySphere.firstMaterial!.specular.contents = NSColor.whiteColor().CGColor
// position sphere geometry, add it to node
_mySphereNode.position = SCNVector3(0.0, CGFloat(radius), 0.0)
_mySphereNode.geometry = mySphere
// physics body and shape
_mySphereNode.physicsBody = SCNPhysicsBody(type: .Dynamic, shape: SCNPhysicsShape(geometry: mySphere, options: nil))
_mySphereNode.physicsBody!.mass = 0.125
_mySphereNode.physicsBody!.contactTestBitMask = PlaneType
_mySphereNode.physicsBody!.collisionBitMask = PlaneType
_mySphereNode.physicsBody!.categoryBitMask = (BallType | GravityType)
}
private func stopBall() {
_mySphereNode.geometry = nil
_mySphereNode.physicsBody = nil
}
override func awakeFromNib() {
// assign empty scene
_sceneView.scene = SCNScene()
// contact delegate
_sceneView.scene!.physicsWorld.contactDelegate = self
setupScene()
setupBall()
}
@IBAction func moveBall(sender: AnyObject) {
let forceApplied = SCNVector3Make(5.0, 0.0, 0.0)
if _mySphereNode.physicsBody?.isResting == true {
_mySphereNode.physicsBody!.applyForce(forceApplied, impulse: true)
}
else if _mySphereNode.physicsBody?.isResting == false {
print("ball not at rest...")
}
else {
print("No physics associated with the node...")
}
}
@IBAction func resetBall(sender: AnyObject) {
// remove the ball from the sphere node
stopBall()
// reset the ball
setupBall()
}
/*** SCENEKIT DELEGATE METHODS ***/
func physicsWorld(world: SCNPhysicsWorld, didBeginContact contact: SCNPhysicsContact) {
print("we have contact...")
}
func physicsWorld(world: SCNPhysicsWorld, didEndContact contact: SCNPhysicsContact) {
print("No longer touching...")
}
}
来源：https://stackoverflow.com/questions/31577723/lineargravityfield-is-not-affecting-physics-bodies-in-the-scene-scenekit