iphone: Core Animation: Reversing animation after hitting view boundary - ios

Question

I am trying hands at Core Animation on iphone.
Details of what I have done so far:
I am using layers and CAKeyFrameAnimation using path.
I have created a layer with Contents set to a bitmap file of a fly which I want to animate on a spiral path. The centre point of the spiral path is at CGPoint (150,150). The end point of the spiral path is a radius of 100.0f.
What I want to achieve:
I further want to increase the radius to a value so that the spiral can go beyond the bounds of the view frame, but when it reaches the bound, I desire the fly to trace back the path.
EDIT: (adding code):
-(IBAction) clickToAnimate:(id) sender
{
//create a path to animate the fly
CGFloat minRadius = 5.0f;
CGFloat maxRadius = 100.0f;
CGFloat radiusOffset = 5.0f;
float i;
int count =1;
int remainder;
curvePath = CGPathCreateMutable();
//this looping mimics the "spiral path"
for (i = minRadius; i <= maxRadius; i = i + 5.0f)
{
remainder = count % 2;
if (remainder == 0)
{
CGPathAddArc(curvePath, NULL, currentPoint.x, currentPoint.y, i, M_PI / 2, 1.5 * M_PI, NO);
}
else
{
CGPathAddArc(curvePath, NULL, currentPoint.x, currentPoint.y + radiusOffset, i, 1.5 * M_PI , M_PI / 2, NO);
}
count = count +1;
}
//add timer
timer = [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:#selector(checkCoordinatesOnTimer) userInfo:self repeats:YES];
CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:#"position"];
animation.calculationMode = kCAAnimationPaced;
animation.path = curvePath;
animation.duration = 25.0f;
animation.autoreverses = YES;
animation.fillMode = kCAFillModeFrozen;
CGPathRelease(curvePath);
[animationLayer addAnimation:animation forKey:#"position"];
}

Answer 1

Approach taken:
I set up a timer, which would check the co-ordinates of the animation layer every half second. The co-ordinates would be checked against the bounding x and y co-ordinates. If the co-ordinates are found to cross the boundary, we will disable the timer and start with the reverse animation process.
The reverse animation process would first check the angle from horizontal at which the animation is when it crosses the boundary. Using this angle and radius from center point, create a path for reverse animation. Details can be found in code below.
- (void) checkCoordinatesOnTimer
{
if (!presentLayer)
{
presentLayer =[[CALayer alloc] init];
}
presentLayer = [animationLayer presentationLayer];
CGPoint curPt;
curPt.x = presentLayer.position.x;
curPt.y = presentLayer.position.y;
currRadius = sqrt(pow(fabsf(curPt.x - centerPoint.x), 2) + pow(fabsf(curPt.y - centerPoint.y), 2));
if ((curPt.x >= CGRectGetMaxX(self.view.frame)) || (curPt.y >= CGRectGetMaxY(self.view.frame)))
{
[timer invalidate];
[self reverseAnimation:curPt];
}
}
-(void) reverseAnimation:(CGPoint)curPoint
{
CGFloat angle = (CGFloat)[self calculateAngleInRadians:curPoint];
maxRadius = currRadius;
float i;
int count =1;
int remainder;
BOOL firstLap = YES;
CGPathRelease(curvePath);
curvePath = CGPathCreateMutable();
for (i = maxRadius; i >= minRadius; i = i - 5.0f)
{
remainder = count % 2 ;
if (firstLap)
{
if ((angle >= (M_PI/2)) && (angle <= 1.5 *M_PI))
//2nd and third quard,
//angle to change from final angle to 90
{
CGPathAddArc(curvePath, NULL, centerPoint.x, centerPoint.y, i, angle, 1.5 * M_PI, FALSE);
}
else
{
CGPathAddArc(curvePath, NULL, centerPoint.x, centerPoint.y, i, angle, M_PI / 2 , FALSE);
}
firstLap = NO;
continue;
}
else
{
if (remainder == 0)
{
CGPathAddArc(curvePath, NULL, centerPoint.x, centerPoint.y, i, 1.5* M_PI, M_PI / 2, FALSE);
}
else
{
CGPathAddArc(curvePath, NULL, centerPoint.x, centerPoint.y + radiusOffset, i, M_PI / 2 ,1.5* M_PI, FALSE);
}
}
count = count +1;
}
animation = [CAKeyframeAnimation animationWithKeyPath:#"position"];
animation.calculationMode =kCAAnimationPaced; // for even pacing of animation in segments.
animation.path = curvePath;
animation.duration = 40.0f;
animation.fillMode = kCAFillModeForwards;
CGPathRelease(curvePath);
[animationLayer addAnimation:animation forKey:#"position"];
}
-(CGFloat) calculateAngleInRadians:(CGPoint) pt
{
CGFloat xLen = fabsf(centerPoint.x - pt.x);
CGFloat yLen = fabsf(centerPoint.y - pt.y);
double value = yLen/xLen;
double angle = atan(value);
double angleInDeg = ( 180 * angle/ M_PI);
double finalAngle;
if ((pt.x > centerPoint.x) || (pt.y > centerPoint.y)) {
finalAngle = angle;
}
else if ((centerPoint.x > pt.x) || (pt.y > centerPoint.y))
{
finalAngle = M_PI/2 + angle;
}
else if ((centerPoint.x > pt.x) || (centerPoint.y > pt.y))
{
finalAngle = M_PI + angle;
}
else {
finalAngle = (1.5 * M_PI) + angle;
}
return finalAngle;
}