模拟水/制作雪碧＆＃34;漂浮＆＃34;在spritekit中的水

Question

我正在尝试为我的游戏加水。除了不同的背景颜色，它没有多少。 但是，我希望player-sprite能够漂浮在它上面（或者在它的中间）。如果玩家只是从下面走进水里，我希望他漂浮到顶端。如果他摔倒了，我希望他慢慢改变方向并漂浮起来。

当他在水中时，我尝试使重力为负，但这给了我一些稍微不想要的效果。例如，当他（玩家）浮出水面时，正常的重力会将他推倒，水将推动他，等等。最终，玩家将在水中“弹跳”，从一端推到另一端。当他浮出水面时，我希望他能够平静地留在水面上。我怎样才能做到这一点？

以下是我update-loop中的代码：

SKNode *backgroundNodeAtPoint = [_bgLayer nodeAtPoint:_ball.position];
  if ([backgroundNodeAtPoint.name isEqualToString:@"WATER"]) {
    self.physicsWorld.gravity = CGVectorMake(self.physicsWorld.gravity.dx, 2);
  } else {
    if (self.physicsWorld.gravity.dy != -4) {
        self.physicsWorld.gravity = CGVectorMake(self.physicsWorld.gravity.dx, -4);
    }
}

基本上，当玩家在水中时，这会将我的重力变为2，否则会将其更改为-4，除非它已经-4。

谢谢！

Answer 1

我相信您在模拟水方面有三种可能的选择。

1）如评论中所述，您可以尝试使用SKFieldNode（iOS 8+）。但是从个人经验来看，现场节点对我来说并没有真正做到这一点，因为除非你对其进行大量定制，否则你无法用它来控制你的模拟，在这种情况下你也可以从头开始自己进行计算并减少复杂性。

2）你可以在水中调整精灵的线性和旋转阻尼。事实上，甚至苹果在他们的文档引用中也提到了这一点。然而，这不会给你带来浮力。

  

linearDamping和angularDamping属性用于计算   在身体穿过世界时身体上的摩擦力。例如，这个   可能用于模拟空气或水的摩擦。

3）自己进行计算。在更新方法中，检查身体何时进入“水”，何时进入，您可以计算粘度和/或浮力，并相应地调整节点的速度。在我看来，这是最好的选择，但也更难。

编辑：我刚刚在Swift中写了一个选项3的快速示例。我想这就是你要找的东西。我在顶部添加了因子常数，因此您可以调整它以获得您想要的结果。动态应用动作，因此它不会干扰您当前的速度（即您可以在水中控制角色）。下面是场景的代码和gif。请记住，增量时间假设为每秒60帧（1/60）并且没有速度钳制。根据您的游戏，这些是您可能想要或不想要的功能。

<强>夫特

class GameScene: SKScene {
    //MARK: Factors
    let VISCOSITY: CGFloat = 6 //Increase to make the water "thicker/stickier," creating more friction.
    let BUOYANCY: CGFloat = 0.4 //Slightly increase to make the object "float up faster," more buoyant.
    let OFFSET: CGFloat = 70 //Increase to make the object float to the surface higher.
    //MARK: -
    var object: SKSpriteNode!
    var water: SKSpriteNode!
    override func didMoveToView(view: SKView) {
        object = SKSpriteNode(color: UIColor.whiteColor(), size: CGSize(width: 25, height: 50))
        object.physicsBody = SKPhysicsBody(rectangleOfSize: object.size)
        object.position = CGPoint(x: self.size.width/2.0, y: self.size.height-50)
        self.addChild(object)
        water = SKSpriteNode(color: UIColor.cyanColor(), size: CGSize(width: self.size.width, height: 300))
        water.position = CGPoint(x: self.size.width/2.0, y: water.size.height/2.0)
        water.alpha = 0.5
        self.addChild(water)
        self.physicsBody = SKPhysicsBody(edgeLoopFromRect: self.frame)
    }
    override func update(currentTime: CFTimeInterval) {
        if water.frame.contains(CGPoint(x:object.position.x, y:object.position.y-object.size.height/2.0)) {
            let rate: CGFloat = 0.01; //Controls rate of applied motion. You shouldn't really need to touch this.
            let disp = (((water.position.y+OFFSET)+water.size.height/2.0)-((object.position.y)-object.size.height/2.0)) * BUOYANCY
            let targetPos = CGPoint(x: object.position.x, y: object.position.y+disp)
            let targetVel = CGPoint(x: (targetPos.x-object.position.x)/(1.0/60.0), y: (targetPos.y-object.position.y)/(1.0/60.0))
            let relVel: CGVector = CGVector(dx:targetVel.x-object.physicsBody.velocity.dx*VISCOSITY, dy:targetVel.y-object.physicsBody.velocity.dy*VISCOSITY);
            object.physicsBody.velocity=CGVector(dx:object.physicsBody.velocity.dx+relVel.dx*rate, dy:object.physicsBody.velocity.dy+relVel.dy*rate);
        }
    }
    override func touchesEnded(touches: NSSet!, withEvent event: UIEvent!) {object.position = (touches.anyObject() as UITouch).locationInNode(self);object.physicsBody.velocity = CGVectorMake(0, 0)}
}

<强>目标C

#import "GameScene.h"
#define VISCOSITY 6.0 //Increase to make the water "thicker/stickier," creating more friction.
#define BUOYANCY 0.4 //Slightly increase to make the object "float up faster," more buoyant.
#define OFFSET 70.0 //Increase to make the object float to the surface higher.

@interface GameScene ()
@property (nonatomic, strong) SKSpriteNode* object;
@property (nonatomic, strong) SKSpriteNode* water;
@end

@implementation GameScene
-(void)didMoveToView:(SKView *)view {
    _object = [[SKSpriteNode alloc] initWithColor:[UIColor whiteColor] size:CGSizeMake(25, 50)];
    self.object.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:self.object.size];
    self.object.position = CGPointMake(self.size.width/2.0, self.size.height-50);
    [self addChild:self.object];
    _water = [[SKSpriteNode alloc] initWithColor:[UIColor cyanColor] size:CGSizeMake(self.size.width, 300)];
    self.water.position = CGPointMake(self.size.width/2.0, self.water.size.height/2.0);
    self.water.alpha = 0.5;
    [self addChild:self.water];
    self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:self.frame];
}
-(void)update:(NSTimeInterval)currentTime {
    if (CGRectContainsPoint(self.water.frame, CGPointMake(self.object.position.x,self.object.position.y-self.object.size.height/2.0))) {
        const CGFloat rate = 0.01; //Controls rate of applied motion. You shouldn't really need to touch this.
        const CGFloat disp = (((self.water.position.y+OFFSET)+self.water.size.height/2.0)-((self.object.position.y)-self.object.size.height/2.0)) * BUOYANCY;
        const CGPoint targetPos = CGPointMake(self.object.position.x, self.object.position.y+disp);
        const CGPoint targetVel = CGPointMake((targetPos.x-self.object.position.x)/(1.0/60.0), (targetPos.y-self.object.position.y)/(1.0/60.0));
        const CGVector relVel = CGVectorMake(targetVel.x-self.object.physicsBody.velocity.dx*VISCOSITY, targetVel.y-self.object.physicsBody.velocity.dy*VISCOSITY);
        self.object.physicsBody.velocity=CGVectorMake(self.object.physicsBody.velocity.dx+relVel.dx*rate, self.object.physicsBody.velocity.dy+relVel.dy*rate);
    }
}
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    self.object.position = [(UITouch*)[touches anyObject] locationInNode:self];
    self.object.physicsBody.velocity = CGVectorMake(0, 0);
}
@end

Answer 2

当你的球员与水接触时，将他推开，直到他不再接触到水。此时，修改玩家的接触位掩码以与水碰撞，从而“让他在水上行走”。

或者，您可以通过策略性放置的隐形节点触发水接触位掩码修改，而不是等待水接触发生。

要将玩家的接触位掩码恢复正常，请使用玩家将使用的其他预定接触（例如陆地或不可见节点）作为触发器。