Making a ball/circle move in cocoa using nsbezierpath(objective -c))?

Question

I am trying to Create a point on an image when the application runs and then try to move the point slowly to a different location. here is my code.This code works but there are two problems.

First, The processing has already happened before the window loads so I see only the finished result.(I want to show one point moving to another point in the image)

Second,The previous point is not removed when I create a new point.So it doesn't look like the point is moving rather it looks like it is being duplicated.How do I remove a point.

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    // Insert code here to initialize your application
    NSGraphicsContext* gc = [NSGraphicsContext currentContext];

    // Save the current graphics context settings
    [gc saveGraphicsState];

    // Set the color in the current graphics context for future draw operations
    [[NSColor blackColor] setStroke];
    [[NSColor redColor] setFill];


    for(int i=1;i<100;i++){

        NSRect rect = NSMakeRect(130+i, 130, 10, 10);
        NSBezierPath* circlePath = [NSBezierPath bezierPath];
        [circlePath appendBezierPathWithOvalInRect: rect];

        // Outline and fill the path
        [circlePath stroke];
        [circlePath fill];


        //    // Restore the context to what it was before we messed with it
        //    [gc restoreGraphicsState];
    }
}

Answer 1

EDIT:

Here's a working implementation:

@interface AppDelegate ()
@property ( nonatomic, readonly ) CALayer * ballLayer ;
@end

@implementation AppDelegate
@synthesize ballLayer = _ballLayer ;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    [ ((NSView*)self.window.contentView) setWantsLayer:YES ] ;
    [ self performSelectorOnMainThread:@selector( doAnimation ) withObject:nil waitUntilDone:NO ] ;
}

-(void)doAnimation
{
    [ self.ballLayer addAnimation:[ self createBallLayerAnimation ] forKey:nil ] ;
}

-(CALayer*)ballLayer
{
    if ( !_ballLayer )
    {
        CALayer * layer = [ CALayer layer ] ;
        NSImage * image = [[ NSImage alloc ] initWithContentsOfURL:[ NSURL URLWithString:@"http://etc-mysitemyway.s3.amazonaws.com/icons/legacy-previews/icons/glossy-black-icons-sports-hobbies/044450-glossy-black-icon-sports-hobbies-ball-beach.png" ] ] ;
        layer.contents = image ;
        layer.bounds = (CGRect){ .size = { 100, 100 } } ;

        [((NSView*)self.window.contentView).layer addSublayer:layer ] ;

        _ballLayer = layer ;
    }

    return _ballLayer ;
}

-(CAAnimation*)createBallLayerAnimation
{
    CAKeyframeAnimation * anim = [ CAKeyframeAnimation animationWithKeyPath:@"position" ] ;
    {
        CGPathRef p = [ self createBallAnimationPath ] ;
        anim.path = p ;
        CGPathRelease( p ) ;
    }
    anim.duration = 3.0 ;
    anim.repeatCount = FLT_MAX ;

    return anim ;
}

-(CGPathRef)createBallAnimationPath
{
    CGRect bounds = ((NSView*)self.window.contentView).bounds ;
    CGPathRef p = CGPathCreateWithEllipseInRect( CGRectInset( bounds, bounds.size.width * 0.25, bounds.size.width * 0.25 ), NULL ) ;
    return p ;
}
@end

---

You'll want to read up on CGPath and CALayer...

As others have said, don't do this in your applicationDidFinishLaunching method--you should do it after your window/view appears. If you have your own NSView subclass loaded from a nib, one option might be to override -awakeFromNib:

-(void)awakeFromNib
{
    [ super awakeFromNib ] ;
    [ self performSelectorOnMainThread:@selector( doAnimation ) withObject:nil waitUntilDone:NO ] ; // when the main thread runs again, call `-doAnimation`
}

Then in your view subclass also have a -doAnimation method (called from -awakeFromNib, above)

-(void)doAnimation:
{
    CAAnimation * animation = [ CAKeyframeAnimation animationForKeyPath:@"position" ] ;
    CGPathRef path = [ self createBallAnimationPath ] ; // method -createBallAnimationPath is defined below...
    animation.path = path ;
    CGPathRelease( path ) ;
    [ self.ballLayer addAnimation:animation forKey:nil ] ; // ballLayer is the property that contains a reference to layer that contains the image you want to animate along the path
}

Have a method to create your path:

-(CGPathRef)createBallAnimationPath
{
    CGMutablePathRef result = CGPathCreateMutable() ;
    CGPathMoveToPoint( result, 100, 100 ) ;
    CGPathAddLineToPoint( result, 1000, 1000 ) ;
    return result ;
}