iOS7 SKScene如何让精灵从屏幕边缘反弹？

我正在开发一款球在 iPad 屏幕内弹跳的游戏。类似于乒乓球游戏。我看到 SKScene 的 SKPhysicsWorld 具有重力属性，并且还控制对象如何相互碰撞。

有什么方法可以自动检测精灵的边缘是否与屏幕边缘发生碰撞，以便它可以反弹？或者我需要编写自己的碰撞代码吗？

您无需编写太多代码即可使球从屏幕边缘弹起。物理环境可以处理以上所有内容，您只需要以正确的方式实例化精灵即可。

首先，您必须将场景的物理主体设置如下：

self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:self.frame];

在场景的 .h 文件中创建两个位掩码类别：

static const uint8_t ballCategory = 1;
static const uint8_t wallCategory = 2;

并给场景的物理体一个类别：

self.physicsBody.categoryBitMask = wallCategory;

然后创建你的精灵：

SKSpriteNode *spriteNode = [SKSpriteNode spriteNodeWithImageNamed:@"ball.png"]; 

spriteNode.name = @"ball";

spriteNode.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:25];
spriteNode.position = CGPointMake(10.0,10.0); //or anything you want
spriteNode.physicsBody.dynamic = YES;
spriteNode.physicsBody.affectedByGravity = NO;

spriteNode.physicsBody.categoryBitMask = ballCategory;
spriteNode.physicsBody.collisionBitMask = wallCategory;

spriteNode.physicsBody.restitution = 1.0;
spriteNode.physicsBody.friction = 0.0;
spriteNode.physicsBody.linearDamping = 0.0;
spriteNode.physicsBody.angularDamping = 0.0;

[self addChild:spriteNode];

而不是给 spriteNode[SKAction moveTo: duration:]，对其物理体施加脉冲。

CGVector impulse = CGVectorMake(1.0,1.0);
[spriteNode.physicsBody applyImpulse:impulse];

瞧！球将从墙上弹起，没有任何东西可以阻止它。

.h 文件应如下所示：

#import <SpriteKit/SpriteKit.h>

static const uint8_t ballCategory = 1;
static const uint8_t wallCategory = 2;

@interface BallBounce : SKScene

@end

.m 文件应如下所示：

#import "BallBounce.h"

@implementation BallBounce

-(instancetype)initWithSize:(CGSize)size
{
    if (self = [super initWithSize:size])
    {
        self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:self.frame];
        self.physicsBody.categoryBitMask = wallCategory;

        SKSpriteNode *spriteNode = [SKSpriteNode spriteNodeWithColor:[UIColor greenColor] size:CGSizeMake(50, 50)];

        spriteNode.name = @"ball";

        spriteNode.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:25];
        spriteNode.position = CGPointMake(10.0,10.0); //or anything you want
        spriteNode.physicsBody.dynamic = YES;
        spriteNode.physicsBody.affectedByGravity = NO;

        spriteNode.physicsBody.categoryBitMask = ballCategory;
        spriteNode.physicsBody.collisionBitMask = wallCategory;

        spriteNode.physicsBody.restitution = 1.0;
        spriteNode.physicsBody.friction = 0.0;
        spriteNode.physicsBody.linearDamping = 0.0;
        spriteNode.physicsBody.angularDamping = 0.0;

        [self addChild:spriteNode];

        CGVector impulse = CGVectorMake(100.0,100.0);
        [spriteNode.physicsBody applyImpulse:impulse];

    }

    return self;
}

@end