CODEWITHSUNDEEP
iphoneioscocoa-touchmathuiview
Ser Pounce
Ser Pounce

Reputation: 14527

Rotating a rectangle using a UIPanGestureRecognizer

I have the following view where I'm using a pan gesture in the upwards or downwards direction to rotate it positively or negatively:

enter image description here

I'm wondering, is there a mathematical equation to precisely covert the amount panned to the amount it should be rotated so the timing is correct to keep the users finger on the view while it is rotating? For instance, if the pan translation comes back as 1, what would the proper amount be to rotate it?.

Upvotes: 0

Views: 172

Answers (2)

Ser Pounce
Ser Pounce

Reputation: 14527

The answer is the angle would be panAmount.y / rectangleWidth.

Here is proof: https://math.stackexchange.com/questions/322694/angle-of-rotated-line-segment

Upvotes: 0

Tony
Tony

Reputation: 3478

There are a few details you need to provide to give a meaningful answer:

  1. Are you rotating the view about its centre (the default) or is there an anchor point?
  2. Since the view is rotating, while the touch is moving strictly vertically in the superview, what's the expected behaviour as the view rotates further away from the vertical line defining the pan?
  3. Is there a reason you're using a pan gesture instead of a rotation gesture, or even just direct touch tracking? It seems like it creates more problems than it solves.

I'm going to assume the view is rotating about its centre for the sake of simplicity, and I'll use a pan starting on the right side of the view as an example, with the rotation not exceeding ±90°. Here are two options:

  1. Movement up and down translates linearly to the angle of rotation, i.e., a pan of a given distance rotates the view the same amount, no matter where the pan starts. In that case, you need to decide what the top and bottom limits of the pan are. They might be the bounds of the superview. Regardless, you want to convert the distance travelled in the Y direction to a value between -1 and 1, where -1 represents the bottom limit and 1 represents the top limit. Something like 2 * (dy / superview.bounds.size.height - 0.5). Multiply that by π/2 (M_PI_2 in math.h) to scale from the range [-1, 1] to the range [-π/2, π/2] and you've got the angle to add/subtract from the view's rotation at the beginning of the gesture.

  2. The view tracks the touch so that its right edge is always "pointed at" the touch. In this case, pan isn't terribly useful because you only need the location of the touch in the superview, not the distance travelled. Calculate dx and dy as the difference in x and y coordinates from the view's centre to the touch location. Then calculate atan2(dy, dx) and you've got the absolute angle of rotation for the view.

I hope this puts you on the right track.

Upvotes: 1

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