Throwing ball in SpriteKit - ios

Question

Last days, I experimented some time with spriteKit and (amongst other things) tried to solve the problem to "throw" a sprite by touching it and dragging.
The same question is on Stackexchange, but they told me to first remove the bug and then let the code be reviewed.
I have tackled the major hurdles, and the code is working fine, but there consist one little problem.
(Additionally, I'd be interested if somebody has a more polished or better working solution for this. I'd also love to hear suggestions about how to perfect the feeling of realism in this interaction.)
Sometimes, the ball just gets stuck.
If you want to reproduce that, just swipe the ball really fast and short. I suspect the gestureRecognizer to make "touchesMoved" and "touchesEnded" callback asynchronous and through that some impossible state occurs in the physics simulation.
Can anybody provide a more reliable way to reproduce the issue, and what could be the solution for that?
The project is called ballThrow and BT is the class prefix.
#import "BTMyScene.h"
#import "BTBall.h"
#interface BTMyScene()
#property (strong, nonatomic) NSMutableArray *balls;
#property (nonatomic) CGFloat yPosition;
#property (nonatomic) CGFloat xCenter;
#property (nonatomic) BOOL updated;
#end
#implementation BTMyScene
const CGFloat BALLDISTANCE = 80;
-(id)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
_balls = [NSMutableArray arrayWithCapacity:5];
//define the region where the balls will spawn
_yPosition = size.height/2.0;
_xCenter = size.width/2.0;
/* Setup your scene here */
self.backgroundColor = [SKColor colorWithRed:0.15 green:0.15 blue:0.3 alpha:1.0];
}
return self;
}
-(void)didMoveToView:(SKView *)view {
//Make an invisible border
//this seems to be offset... Why the heck is this?
self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:view.frame];
[self createBalls:2];
//move balls with pan gesture
//could be improved by combining with touchesBegan for first locating the touch
[self.view addGestureRecognizer:[[UIPanGestureRecognizer alloc] initWithTarget:self action:#selector(moveBall:)]];
}
-(void)moveBall:(UIPanGestureRecognizer *)pgr {
//depending on the touch phase do different things to the ball
if (pgr.state == UIGestureRecognizerStateBegan) {
[self attachBallToTouch:pgr];
}
else if (pgr.state == UIGestureRecognizerStateChanged) {
[self moveBallToTouch:pgr];
}
else if (pgr.state == UIGestureRecognizerStateEnded) {
[self stopMovingTouch:pgr];
}
else if (pgr.state == UIGestureRecognizerStateCancelled) {
[self stopMovingTouch:pgr];
}
}
-(void)attachBallToTouch:(UIPanGestureRecognizer *)touch {
//determine the ball to move
for (BTBall *ball in self.balls) {
if ([self isMovingBall:ball forGestureRecognizer:touch])
{
//stop ball movement
[ball.physicsBody setAffectedByGravity:NO];
[ball.physicsBody setVelocity:CGVectorMake(0, 0)];
//the ball might not be touched right in its center, so save the relative location
ball.touchLocation = [self convertPoint:[self convertPointFromView:[touch locationInView:self.view]] toNode:ball];
//update location once, just in case...
[self setBallPosition:ball toTouch:touch];
if (_updated) {
_updated = NO;
[touch setTranslation:CGPointZero inView:self.view];
}
}
}
}
-(void)moveBallToTouch:(UIPanGestureRecognizer *)touch {
for (BTBall *ball in self.balls) {
if ([self isMovingBall:ball forGestureRecognizer:touch])
{
//update the position of the ball and reset translation
[self setBallPosition:ball toTouch:touch];
if (_updated) {
_updated = NO;
[touch setTranslation:CGPointZero inView:self.view];
}
break;
}
}
}
-(void)setBallPosition:(BTBall *)ball toTouch:(UIPanGestureRecognizer *)touch {
//gesture recognizers only deliver locations in views, thus convert to node
CGPoint touchPosition = [self convertPointFromView:[touch locationInView:self.view]];
//update the location to the touche´s location, offset by touch position in ball
[ball setNewPosition:CGPointApplyAffineTransform(touchPosition,
CGAffineTransformMakeTranslation(-ball.touchLocation.x,
-ball.touchLocation.y))];
//save the velocity between the last two touch records for later release
CGPoint velocity = [touch velocityInView:self.view];
//why the hell is the y coordinate inverted??
[ball setLastVelocity:CGVectorMake(velocity.x, -velocity.y)];
}
-(void)stopMovingTouch:(UIPanGestureRecognizer *)touch {
for (BTBall *ball in self.balls) {
if ([self isMovingBall:ball forGestureRecognizer:touch]) {
//release the ball: enable gravity impact and make it move
[ball.physicsBody setAffectedByGravity:YES];
[ball.physicsBody setVelocity:CGVectorMake(ball.lastVelocity.dx, ball.lastVelocity.dy)];
break;
}
}
}
-(BOOL)isMovingBall:(BTBall *)ball forGestureRecognizer:(UIPanGestureRecognizer *)touch {
//latest location of touch
CGPoint touchPosition = [touch locationInView:self.view];
//distance covered since the last call
CGPoint touchTranslation = [touch translationInView:self.view];
//position, where the ball must be, if it is the one
CGPoint translatedPosition = CGPointApplyAffineTransform(touchPosition,
CGAffineTransformMakeTranslation(-touchTranslation.x,
-touchTranslation.y));
CGPoint inScene = [self convertPointFromView:translatedPosition];
//determine weather the last touch location was on the ball
//if last touch location was on the ball, return true
return [[self nodesAtPoint:inScene] containsObject:ball];
}
-(void)update:(CFTimeInterval)currentTime {
//updating the ball position here improved performance dramatically
for (BTBall *ball in self.balls) {
//balls that move are not gravity affected
//easiest way to determine movement
if ([ball.physicsBody affectedByGravity] == NO) {
[ball setPosition:ball.newPosition];
}
}
//ball positions are refreshed
_updated = YES;
}
-(void)createBalls:(int)numberOfBalls {
for (int i = 0; i<numberOfBalls; i++) {
BTBall *ball;
//reuse balls (not necessary yet, but imagine balls spawning)
if(i<[self.balls count]) {
ball = self.balls[i];
}
else {
ball = [BTBall newBall];
}
[ball.physicsBody setAffectedByGravity:NO];
//calculate ballposition
CGPoint ballPosition = CGPointMake(self.xCenter-BALLSIZE/2+(i-(numberOfBalls-1)/2.0)*BALLDISTANCE, self.yPosition);
[ball setNewPosition:ballPosition];
[self.balls addObject:ball];
[self addChild:ball];
}
}
#end
The BTBall (subclass of SKShapeNode, because of the custom properties needed)
#import <SpriteKit/SpriteKit.h>
#interface BTBall : SKShapeNode
const extern CGFloat BALLSIZE;
//some properties for the throw animation
#property (nonatomic) CGPoint touchLocation;
#property (nonatomic) CGPoint newPosition;
#property (nonatomic) CGVector lastVelocity;
//create a standard ball
+(BTBall *)newBall;
#end
The BTBall.m with a class method to create new balls
#import "BTBall.h"
#implementation BTBall
const CGFloat BALLSIZE = 80;
+(BTBall *)newBall {
BTBall *ball = [BTBall node];
//look
[ball setPath:CGPathCreateWithEllipseInRect(CGRectMake(-BALLSIZE/2,-BALLSIZE/2,BALLSIZE,BALLSIZE), nil)];
[ball setFillColor:[UIColor redColor]];
[ball setStrokeColor:[UIColor clearColor]];
//physics
SKPhysicsBody *ballBody = [SKPhysicsBody bodyWithCircleOfRadius:BALLSIZE/2.0];
[ball setPhysicsBody:ballBody];
[ball.physicsBody setAllowsRotation:NO];
//ball is not moving at the beginning
ball.lastVelocity = CGVectorMake(0, 0);
return ball;
}
#end
1. A couple of problems (see comments in code) are related to the spriteKit coordinate system. I just do not get the border of the scene align with its actual frame, though I make it with the exact same code that Apple gives us in the programming guide. I have moved it from initWithSize to didMoveToView due to a suggestion here on Stackoverflow, but that did not help. It is possible to manually offset the border with hardcoded values, but that does not satisfy me.
2. Does anybody know a debugging tool, which colors the physics body of a sprite, in order to see its size and whether it is at the same position as the sprite?
Update: Problems above solved by using YMC Physics Debugger:
This lines of code are correct:
[ball setPath:CGPathCreateWithEllipseInRect(CGRectMake(-BALLSIZE/2,-BALLSIZE/2,BALLSIZE,BALLSIZE), nil)];
SKPhysicsBody *ballBody = [SKPhysicsBody bodyWithCircleOfRadius:BALLSIZE/2.0];
Because 0,0 is the center of the physics body, the origin of the path must be translated.