How to correctly position a rectangle? - ios

Question

I'm completely new to developing apps with XCode and Objective-C. I'm trying to create a simple iOS application that creates a rectangle at the position of your finger when you tap the screen. I'm having an issue where the rectangle (the class is called Ball) isn't correctly positioned. On tap, it is positioned off the left of the screen and slightly above your finger. I'm not sure how to fix this, but I feel like it is a problem with my init function. Can anyone help?
Thanks.
GameScene.m
#import "GameScene.h"
#import "Ball.h"
#implementation GameScene
double SCREEN_WIDTH, SCREEN_HEIGHT;
NSMutableArray *screenObjects;
SKView *mainView;
- (void) didMoveToView:(SKView*)view {
mainView = view;
SCREEN_WIDTH = self.view.frame.size.width;
SCREEN_HEIGHT = self.view.frame.size.height;
screenObjects = [[NSMutableArray alloc] init];
[Ball setDefaultView: self];
[Ball setRightBounds: SCREEN_WIDTH];
[Ball setLeftBounds: 0];
[Ball setBottomBounds: SCREEN_HEIGHT];
[Ball setTopBounds: 0];
}
- (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
for (UITouch *touch in touches) {
double x = [touch locationInView: mainView].x;
double y = [touch locationInView: mainView].y;
Ball *object = [[Ball alloc] init];
[object setPosition: CGPointMake(x, y)];
[screenObjects addObject: object];
NSLog(#"%f %f", x, y);
}
}
- (void) update:(CFTimeInterval)currentTime {
for (int i = 0; i < screenObjects.count; i++) {
[screenObjects[i] applyVelocity];
[screenObjects[i] dealWithWallCollisions];
}
}
#end
Ball.h
#ifndef IndependentStudyPrototype_Ball_h
#define IndependentStudyPrototype_Ball_h
#import "GameScene.h"
#interface Ball : NSObject
#property double width;
#property double height;
#property double x;
#property double y;
#property double velocity;
+ (void) setDefaultView:(GameScene*)view;
+ (void) setTopBounds:(double)bounds;
+ (void) setBottomBounds:(double)bounds;
+ (void) setLeftBounds:(double)bounds;
+ (void) setRightBounds:(double)bounds;
- (void) setPosition:(CGPoint)point;
- (void) updatePosition;
- (void) dealWithWallCollisions;
- (void) applyVelocity;
#end
#endif
Ball.m
#import <Foundation/Foundation.h>
#import "Ball.h"
#import "GameScene.h"
static GameScene *defaultView;
static double leftBound, rightBound, topBound, bottomBound;
#implementation Ball {
SKSpriteNode *rectangle;
double stepX, stepY;
}
+ (void) setDefaultView:(GameScene*)view {
defaultView = view;
}
+ (void) setBottomBounds:(double)bounds {
bottomBound = bounds;
}
+ (void) setTopBounds:(double)bounds {
topBound = bounds;
}
+ (void) setLeftBounds:(double)bounds {
leftBound = bounds;
}
+ (void) setRightBounds:(double)bounds {
rightBound = bounds;
}
- (void) updatePosition {
self->rectangle.position = CGPointMake(self.x, self.y);
}
- (void) setPosition:(CGPoint)point {
self.x = point.x;
self.y = point.y;
[self updatePosition];
}
- (void) applyVelocity {
self.x += self->stepX;
self.y += self->stepY;
[self updatePosition];
}
- (void) dealWithWallCollisions {
if (self.x > leftBound) {
self->stepX = -self.velocity;
} else if (self.x < rightBound) {
self->stepX = self.velocity;
}
if (self.y > bottomBound) {
self->stepY = -self.velocity;
} else if (self.y < topBound) {
self->stepY = self.velocity;
}
}
- (id)init {
self = [super init];
self->rectangle = [[SKSpriteNode alloc] initWithColor: [UIColor blueColor] size: CGSizeMake(50, 50)];
self.velocity = 1;
self->stepX = self.velocity;
self->stepY = self.velocity;
[defaultView addChild: self->rectangle];
return self;
}
#end

Answer 1

If you are just looking to fine tune the position, you can do something like this:
[object setPosition: CGPointMake(x+20, y-10)];

Answer 2

Inside touchesBegan use locationInNode instead of locationInView to get your touch point.
The touch location in an SKScene should be calculated using locationInNode not locationInView. This is because the origin of SKScene is at the bottom left corner and origin of UIView is at the top left corner.
- (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
for (UITouch *touch in touches) {
CGPoint point = [touch locationInNode:self]; // Changed
Ball *object = [[Ball alloc] init];
[object setPosition: CGPointMake(point.x, point.y)]; // Changed
[screenObjects addObject: object];
}
}