我正在努力为我的游戏加水。除了不同的背景颜色外，没有太多其他内容。 但是，我希望 player-sprite 漂浮在它上面(或中间)。如果玩家只是从下面走进水里，我希望他能浮到水面上。如果他摔倒了，我希望他慢慢改变方向，然后重新浮起来。

当他在水中时，我试着让重力为负，但这给我带来了一些不太想要的效果。例如，当他(玩家)浮出水面时，正常重力会将他推回下方，水会将他推上去，等等。最终，玩家将在水中“弹跳”，从一端被推到另一端。当他浮出水面时，我希望他能平静地留在水面上。我怎样才能做到这一点？

这是我的更新循环中的代码:

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，这会将我的重力更改为 2，否则将其更改为 -4，除非它已经是 -4。

谢谢!

最佳答案

关于模拟水，我相信您有三种可能的选择。

1) 如评论中所述，您可以尝试使用 SKFieldNode (iOS 8+)。但根据个人经验，现场节点并没有真正为我做这件事，因为除非你大量定制它，否则你无法用它来控制你的模拟，在这种情况下你还不如从头开始自己计算并减少复杂性。

2) 您可以在水中调整 Sprite 的线性和旋转阻尼。事实上，即使是苹果公司也在他们的文档中引用了这一点。然而，这不会给你带来浮力。

The linearDamping and angularDamping properties are used to calculate friction on the body as it moves through the world. For example, this might be used to simulate air or water friction.

3) 自己进行计算。在更新方法中，检查 body 何时进入您的“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。我认为这是最好的选择，但也更困难。

编辑:我刚刚用 Swift 写了一个选项 3 的简单示例。我想这就是你要找的。我在顶部添加了因子常数，因此您可以对其进行调整以获得您想要的结果。运动是动态应用的，因此它不会干扰您当前的速度(即您可以在水中控制您的角色)。下面是场景代码和 gif 动图。请记住，增量时间假定为每秒 60 帧 (1/60)，并且没有速度限制。根据您的游戏，您可能需要或不需要这些功能。

swift

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)}
}

objective-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

关于ios - 在spritekit中模拟水/在水上制作 Sprite "float"，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25344808/