SpriteKit find point on perimeter of screen - ios

Question

I need to find a generate a random point just outside the screen to spawn an enemy. How can I do this? I looked up other topics on this but they were all confusing.

Answer 1

You could use a method like this :
+(CGPoint)randomPointInRects:(NSArray*)rects
{
// choose one of the rects in the array randomly
int randomIndex = arc4random() % rects.count;
CGRect rect = [(NSValue*)rects[randomIndex] CGRectValue];
// get a random x and y location based on the chosen rect
float randX = arc4random() % (int)rect.size.width + rect.origin.x;
float randY = arc4random() % (int)rect.size.height + rect.origin.y;
// store value in point
CGPoint randomPoint = CGPointMake(randX, randY);
return randomPoint;
}
Then to get that random point on say a 1024x768 screen you might do something like this :
NSMutableArray *rects = [NSMutableArray array];
// define spawn areas with CGRect's
//top
[rects addObject:[NSValue valueWithCGRect:CGRectMake(0, 768, 1024, 50)]];
// bottom
[rects addObject:[NSValue valueWithCGRect:CGRectMake(0, -50, 1024, 50)]];
//left
[rects addObject:[NSValue valueWithCGRect:CGRectMake(-50, 0, 50, 768)]];
//right
[rects addObject:[NSValue valueWithCGRect:CGRectMake(1024, 0, 50, 768)]];
// pass array to method to return a random point in those rects.
CGPoint randomPoint = [self randomPointInRects:rects];
You basically define the areas you want to have nodes spawned, store them in an array, pass them to the method and it will return a random point from those rects.
I added a 50 pixel buffer for each edge.
I did this quickly, so it might have a bug, but the logic of the approach should get you there if so! :)
This solution would also work for any situation where you wanted to have something spawned in multiple areas, defined by CGRects.