如何获得正方形的一角

Question

Hi all I having troubles with physics in spriteKit so I decided to make my own, and I need to get the corners of a square. I've tried

    _hero.position.x-_hero.size.width/2-_hero.size.height/2

which I thought it was giving me the down left corner of a square, but when I run my game it doesn't do what I expect. I'm doing a 2D "super mario galaxy" which means that my player runs in circles in little planets, the thing is, I need to put the corners positions in an if() that will check, for example, that the top right corner of the player is greater than the bottom left corner of a square, and in that case I will set a BOOL that will tell the program the player is under the square, because didBeginContact is buggy, I had a lot of problems with it. Anyone's help would be great.

PD: I leave a sample of my game, it's still very primitive but hope you like the concept and optionally, any feedback (good or bad) is welcome.

Answer 1

The square would have an origin and a frame. See below. It may be easier to convert from the local coordinate system (square) to the parent's coordinate system if you are trying to find each corner.

However, I think your actual question would be about collision detection. In that case, make a CGRect of each object and then see if they intersecting using CGRectIntersectsRect(rect1,rect2)

Answer 2

twodayslate has some good information, but I thought I would add that there are some pretty cool CGRect APIs that I didn't know were available until recently. Consider this rect:

CGRect rect = CGRectMake(100, 100, 100, 200);

Using the following methods will return some nice convenient results:

CGRectGetWidth(rect) --> 100
CGRectGetHeight(rect) --> 200
CGRectGetMaxX(rect) --> 200
CGRectGetMaxY(rect) --> 300

This is compared to what most people use:

rect.size.width
rect.size.height
rect.origin.x + rect.size.width
rect.origin.y + rect.size.height
rect.origin.x + rect.size.width