CODEWITHSUNDEEP
iosobjective-cipad
Charles D'Monte
Charles D'Monte

Reputation: 372

Rotating a view around a fixed point - ObjectiveC

I need to rotate a UIView around a fixed point. 

bubbleTail = [[BubbleTail alloc] initWithFrame:bubbleTailFrame];
[self addSubview:bubbleTail];
bubbleTail.layer.anchorPoint = triangle_top_left;
CGAffineTransform transform = CGAffineTransformMakeRotation(M_PI * 180 / 180.0);
bubbleTail.transform = transform;

This works only if I comment the .anchorPoint line. How do I rotate the view about a point inside the view?

Upvotes: 3

Views: 1767

Answers (2)

Steve
Steve

Reputation: 988

The below should help. The tricky part is that setting the anchorpoint after adding a view with a frame then moves the view. I've gotten around this by initiating the UIView without a frame, then setting the position, bounds and anchorpoint of its layer. I then use the rotation to rotate around the anchor point.

CABasicAnimation *rotation;
rotation = [CABasicAnimation animationWithKeyPath:@"transform.rotation"];
rotation.fromValue = [NSNumber numberWithFloat:0];
rotation.toValue = [NSNumber numberWithFloat:((360*M_PI)/180)];
rotation.duration = 60.0;
rotation.repeatCount = HUGE_VALF;

UIView *myview = [[UIView alloc] init];
[self.view addSubview:myview];
[myview setBackgroundColor:[UIColor orangeColor]]; 
[myview.layer setPosition:CGPointMake(10, 10)];
[myview.layer setBounds:CGRectMake(0, 0, 100, 100)];
[myview.layer setAnchorPoint:CGPointMake(0, 0)];
[myview.layer addAnimation:rotation forKey:@"myAnimation"];

Someone please correct me if this is not the best method or if there are mistakes - I only know what I currently know - e.g. when I should use a . or f after a float.

Upvotes: 2

MANIAK_dobrii
MANIAK_dobrii

Reputation: 6032

So it seems CGAffineTransformMakeRotation rotates it around the center of the view?

Say you have point P (px,py) in view, you want view to be rotated around that.
Let's A(ax,ay) = P - center = (px - centerx, py - centery).
And you have angle alpha.

Then you could make a translate matrix with - A, then multipy it with rotation matrix with alpha, then multipy it with translate matrix with + A.

The functions you'll need are: CGAffineTransformMakeTranslation, CGAffineTransformMakeRotation, CGAffineTransformConcat.

P.S. Not sure if this will work (also not sure how view rect is represented, maybe it first assumption about rotation around center is wrong, then you shoud assume A = P), but that's how it's done with affine transforms.

Upvotes: 0

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