如何使背景向左滚动

Question

我正在制作一个用 Objective-C 和 SpriteKit 编写的游戏，其中玩家可以从右向左或从左向右滚动背景。

目前我已经想出如何编写代码使用户滑动时背景向右滚动，但不知道如何使其向左滚动。

所以，我的问题是如何让它向左滚动？这是代码：

Sprites:

  bg1 = [SKSpriteNode spriteNodeWithImageNamed:@"bg1"];
  bg1.anchorPoint = CGPointZero;
  bg1.position = CGPointMake(0, 0);
  [self addChild:bg1];

  bg2 = [SKSpriteNode spriteNodeWithImageNamed:@"bg2"];
  bg2.anchorPoint = CGPointZero;
  bg2.position = CGPointMake(bg1.size.width-1, 0);
  [self addChild:bg2];

//Update Method:

bg1.position = CGPointMake(bg1.position.x-4, bg1.position.y);
bg2.position = CGPointMake(bg2.position.x-4, bg2.position.y);

if (bg1.position.x < -bg1.size.width){
    bg1.position = CGPointMake(bg2.position.x + bg2.size.width,  bg1.position.y);
}

if (bg2.position.x < -bg2.size.width) {
    bg2.position = CGPointMake(bg1.position.x + bg1.size.width, bg2.position.y);
}

Answer 1

尝试

 bg1.position = CGPointMake(bg1.position.x+4, bg1.position.y);
    bg2.position = CGPointMake(bg2.position.x+4, bg2.position.y);

if (bg1.position.x > bg1.size.width){
    bg1.position = CGPointMake(bg2.position.x - bg2.size.width,  bg1.position.y);
}

if (bg2.position.x > bg2.size.width) {
    bg2.position = CGPointMake(bg1.position.x - bg1.size.width, bg2.position.y);
}

如何使背景向左滚动

How to make a background scroll left

objective-c

sprite