SceneKit_中级04_约束的使用

 /* 
  * 作用: 影响因子，决定约束的强度
  * 工作原理: 如果设置为1 那么在游戏每一帧渲染的时候,系统都会调整这个约束,如果你设置为0.5 在游戏的某些帧,系统不会进行约束调整 0 完全忽略约束
  * 注意 SCNTransformConstraint  对这类约束不起作用
  */
 var influenceFactor: CGFloat,默认值为 1，这是为0 时,则

 // target 就是指向的那个目标节点 
+ (instancetype)lookAtConstraintWithTarget:(SCNNode *)target;

// 设置下面的属性为YES，就能实现上面的效果，默认为NO
var gimbalLockEnabled: Bool

 /*
  * world 设置为YES 使用世界坐标系，设置为NO 使用自身坐标系 
+ (instancetype)transformConstraintInWorldSpace:(BOOL)world  withBlock:(SCNMatrix4 (^)(SCNNode *node,  SCNMatrix4 transform))block

- (instancetype)initWithChainRootNode:(SCNNode *)chainRoot  
+ inverseKinematicsConstraintWithChainRootNode:

- (void)setMaxAllowedRotationAngle:(CGFloat)angle
                      forJoint:(SCNNode *)node

var targetPosition: SCNVector3

scnView = [[SCNView alloc]initWithFrame:self.view.bounds];
scnView.backgroundColor = [UIColor blackColor];
scnView.allowsCameraControl = true;
scnView.scene = [SCNScene scene];
scnView.scene.physicsWorld.gravity = SCNVector3Make(0, 90, 0);// 添加一个重力，我们让其方向朝上
[self.view addSubview:scnView];

 SCNNode *cameraNode = [SCNNode node];
cameraNode.camera = [SCNCamera camera];
cameraNode.camera.automaticallyAdjustsZRange = true;
cameraNode.position = SCNVector3Make(0, 0,1000);
[scnView.scene.rootNode addChildNode:cameraNode];

-(void)addArmToScene{

// 创建手掌
SCNNode *handNode = [SCNNode node];
handNode.geometry = [SCNBox boxWithWidth:20 height:20 length:20 chamferRadius:0];
handNode.geometry.firstMaterial.diffuse.contents = [UIColor purpleColor];
handNode.position = SCNVector3Make(0, -50, 0);

// 创建小手臂
SCNNode *lowerArm = [SCNNode node];
lowerArm.geometry = [SCNCylinder cylinderWithRadius:1 height:100];
lowerArm.geometry.firstMaterial.diffuse.contents = [UIColor redColor];
lowerArm.position = SCNVector3Make(0, -50, 0);
lowerArm.pivot = SCNMatrix4MakeTranslation(0, 50, 0); // 连接点
[lowerArm addChildNode:handNode];

// 创建上臂
SCNNode *upperArm = [SCNNode node];
upperArm.geometry = [SCNCylinder cylinderWithRadius:1 height:100];
upperArm.geometry.firstMaterial.diffuse.contents = [UIColor greenColor];
upperArm.pivot = SCNMatrix4MakeTranslation(0, 50, 0);
[upperArm addChildNode:lowerArm];

// 创建控制点
SCNNode *controlNode = [SCNNode node];
controlNode.geometry = [SCNSphere sphereWithRadius:10];
controlNode.geometry.firstMaterial.diffuse.contents = [UIColor blueColor];
[controlNode addChildNode:upperArm];
controlNode.position= SCNVector3Make(0, 100, 0);

// 添加到场景中去
[scnView.scene.rootNode addChildNode:controlNode];
scnView.delegate = self;

// 创建约束
 ikContrait =[SCNIKConstraint inverseKinematicsConstraintWithChainRootNode:controlNode];

// 给执行器添加约束
handNode.constraints = @[ikContrait];
}

// 添加手势
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(tapHandle)];
[scnView addGestureRecognizer:tap];
-(void)tapHandle{
[self createNodeToScene:scnView.scene andConstraint:ikContrait];
}

-(void)createNodeToScene:(SCNScene*)scene andConstraint:(SCNIKConstraint*)ikConstrait{
SCNNode *node = [SCNNode node];
node.position = SCNVector3Make(arc4random_uniform(100), arc4random_uniform(100), arc4random_uniform(100));
[scene.rootNode addChildNode:node];
node.geometry = [SCNSphere sphereWithRadius:10];
node.geometry.firstMaterial.diffuse.contents = [UIColor colorWithRed:arc4random_uniform(255.0)/255.0 green:arc4random_uniform(255.0)/255.0 blue:arc4random_uniform(255.0)/255.0 alpha:1];
// 创建动画，当手掌接触到小球时,给小球添加一个动态身体
[SCNTransaction begin];
[SCNTransaction setAnimationDuration:0.5];
ikConstrait.targetPosition = node.position;
[SCNTransaction commit];
node.physicsBody = [SCNPhysicsBody dynamicBody];  
}