How to generate CGPoint-Array out of UIBezierPath (to touch-slide object along given path)

Question

I have a UIBezierPath (curved like an '8', with only 4 points in it) and I need to make some kind of CGPoint-Array out of it. Any ideas? thanx!

edit:

I have my bezier initlialized like that

-(void) initBezier
{
    theBezierPath = [UIBezierPath bezierPath];    
    [theBezierPath moveToPoint:P(211.00, 31.00)];
    [theBezierPath addCurveToPoint:P(870.00, 191.00) controlPoint1:P(432.00, -11.00) controlPoint2:P(593.00, 209.00)];
    [theBezierPath addCurveToPoint:P(731.00, 28.00) controlPoint1:P(1061.95, 178.53) controlPoint2:P(944.69, 5.78)];
    [theBezierPath addCurveToPoint:P(189.00, 190.00) controlPoint1:P(529.00, 49.00) controlPoint2:P(450.00, 189.00)];
    [theBezierPath addCurveToPoint:P(211.00, 31.00) controlPoint1:P(-33.01, 190.85) controlPoint2:P(71.00, 37.00)];
}

and I animate an object on it with

anim = [CAKeyframeAnimation animationWithKeyPath:@"emitterPosition"];
anim.path = theBezierPath.CGPath;
anim.calculationMode = kCAAnimationCubicPaced;
anim.repeatCount = HUGE_VALF;
anim.duration = tme;

I want to animate the object on the path pixel by pixel (via touch-position). I want the object to "snap" a given coordinate of a touch to the nearest point on the curve so it touch-slides the object along the path.

So you're looking for the point on bezier path that is closest to the point being touched? [Here](http://stackoverflow.com/questions/4854035/how-do-i-detect-a-touch-on-a-uibezierpath-and-move-a-ball-along-that) you can find some discussion on this topic. Don't miss that link that Cory gave. You should first find the point (from original points) closest to touch - then use the left and right original point to get that part of the curve and you'll soon be on your way. — Rok Jarc, Jun 10 '12 at 20:26

score 7 · Answer 1 · answered Jun 10 '12 at 16:45

7

Use the CGPathApply() function to iterate over all elements in a path. As one of the arguments, you have to specify a pointer to a function that will then be called for each path element. The path element data structure (of type CGPathElement) then contains the point(s) that describe it.

Use NSValue as a wrapper to add the points to an NSMutableArray.

answered Jun 10 '12 at 16:45

Ole Begemann

135,006
31
278
256

CGPathApply() will just return the points that I used to create the path. this won't help me... :-( – headkit Jun 10 '12 at 17:14
What do you need then if not the points you used to create the path? – Ole Begemann Jun 10 '12 at 17:59
I edited my question, tried to be more precise... – headkit Jun 10 '12 at 18:58

score 4 · Answer 2 · answered Jun 10 '12 at 19:38

4

Neither UIBezierPath nor CGPath provide a way to evaluate the points along an arbitrary Bezier path, or a way to find the nearest point on the path. You'll have to write that code yourself.

Fortunately, this is a very well-studied topic. This tutorial has a lot of useful information, to get you started. You're interested in "cubic" or "third-order" Bezier curves.

answered Jun 10 '12 at 19:38

Kurt Revis

27,695
5
68
74

ai caramba! looks nice but I know I will never make it through that mathematical mountain to some usable code. but thank you for the hint! – headkit Jun 10 '12 at 20:00
If you search a bit, you should be able to find some code to try. It's not as complicated as it looks. [Here's one example](http://cubic.org/docs/bezier.htm). – Kurt Revis Jun 10 '12 at 20:08
I will have a try - thank you! – headkit Jun 10 '12 at 20:31

How to generate CGPoint-Array out of UIBezierPath (to touch-slide object along given path)

2 Answers2

Linked

Related