在X轴上随机生成精灵

Question

Hi I need to spawn balloons which are my sprites along the bottom of the x axis out of the screen randomly. I used this code from Ray Wenderliches website but when i click the button that starts the spawning they don't spawn?

 @implementation MyScene2



 - (void)addMonster {

// Create sprite
SKSpriteNode * monster = [SKSpriteNode spriteNodeWithImageNamed:@"balloon11.png"];

// Determine where to spawn the monster along the X axis
int minX = monster.size.height / 2;
int maxX = self.frame.size.height - monster.size.height / 2;
int rangeX = maxX - minX;
int actualX = (arc4random() % rangeX) + minX;

// Create the monster slightly off-screen along the right edge,
// and along a random position along the X axis as calculated above
monster.position = CGPointMake(self.frame.size.width + monster.size.width/2, actualX);
[self addChild:monster];

// Determine speed of the monster
int minDuration = 2.0;
int maxDuration = 4.0;
int rangeDuration = maxDuration - minDuration;
int actualDuration = (arc4random() % rangeDuration) + minDuration;

   // Create the actions
SKAction * actionMove = [SKAction moveTo:CGPointMake(-monster.size.width/2, actualX)   
 duration:actualDuration];
SKAction * actionMoveDone = [SKAction removeFromParent];
[monster runAction:[SKAction sequence:@[actionMove, actionMoveDone]]];

}


  - (void)updateWithTimeSinceLastUpdate:(CFTimeInterval)timeSinceLast {

  self.lastSpawnTimeInterval += timeSinceLast;
  if (self.lastSpawnTimeInterval > 1) {
    self.lastSpawnTimeInterval = 0;
     [self addMonster];
   }
 }



  - (void)update:(NSTimeInterval)currentTime {
 // Handle time delta.
 // If we drop below 60fps, we still want everything to move the same distance.
 CFTimeInterval timeSinceLast = currentTime - self.lastUpdateTimeInterval;
 self.lastUpdateTimeInterval = currentTime;
 if (timeSinceLast > 1) { // more than a second since last update
    timeSinceLast = 1.0 / 60.0;
    self.lastUpdateTimeInterval = currentTime;
    }

  [self updateWithTimeSinceLastUpdate:timeSinceLast];

 }

Answer 1

Your main problem lies in this lines of code:

monster.position = CGPointMake(self.frame.size.width + monster.size.width/2 , actualX);

That method works like this: CGPointMake( x_coord , y_coord ); .

Right now, you are setting the x value to width of the frame plus the width of the sprite, so this will cause the sprite to be spawned off the screen. You are giving the y coordinate the randomized value. Instead, use

CGPointMake(actualX , self.frame.size.height);

Now there is another problem with this code. These coordinates are based on the view, but monster.position is based on the SKScene . The SKScene origin usually does not match up with the origin for the view. So you have to do it like this:

monster.position = [CGPointMake(actualX , self.frame.size.height); locationInNode: self];

Also, I noticed that you are using frame.size.width for intended Y axis coordinates and frame.size.height for intended X axis coordinates. Width is for x and height is for y, so make sure you are using those properly.