Interact with complex figure in iOS

Question

I need to be able to interact with a representation of a cilinder that has many different parts in it. When the users taps over on of the small rectangles, I need to display a popover related to the specific piece (form).

The next image demonstrates a realistic 3d approach. But, I repeat, I need to solve the problem, the 3d is NOT required (would be really cool though). A representation that complies the functional needs will suffice.

The info about the parts to make the drawing comes from an API (size, position, etc)

I dont need it to be realistic really. The simplest aproximation would be to show a cilinder in a 2d representation, like a rectangle made out of interactable small rectangles.

So, as I mentioned, I think there are (as I see it) two opposite approaches: Realistic or Simplified

Is there a way to achieve a nice solution in the middle? What libraries, components, frameworks that I should look into?

My research has led me to SceneKit, but I still dont know if I will be able to interact with it. Interaction is a very important part as I need to display a popover when the user taps on any small rectangle over the cylinder.

Thanks

Answer 1

You don't need any special frameworks to achieve an interaction like this. This effect can be achieved with standard UIKit and UIView and a little trigonometry. You can actually draw exactly your example image using 2D math and drawing. My answer is not an exact formula but involves thinking about how the shapes are defined and break the problem down into manageable steps.

A cylinder can be defined by two offset circles representing the end pieces, connected at their radii. I will use an orthographic projection meaning the cylinder doesn't appear smaller as the depth extends into the background (but you could adapt to perspective if needed). You could draw this with CoreGraphics in a UIView drawRect.

A square slice represents an angle piece of the circle, offset by an amount smaller than the length of the cylinder, but in the same direction, as in the following diagram (sorry for imprecise drawing).

This square slice you are interested in is the area outlined in solid red, outside the radius of the first circle, and inside the radius of the imaginary second circle (which is just offset from the first circle by whatever length you want the slice).

To draw this area you simply need to draw a path of the outline of each arc and connect the endpoints.

To check if a touch is inside one of these square slices:

1. Check if the touch point is between angle a from the origin at a.
2. Check if the touch point is outside the radius of the inside circle.
3. Check if the touch point is inside the radius of the outside circle. (Note what this means if the circles are more than a radius apart.)

To find a point to display the popover you could average the end points on the slice or find the middle angle between the two edges and offset by half the distance.

Answer 2

Theoretically, doing this in Scene Kit with either SpriteKit or UIKit Popovers is ideal.

However Scene Kit (and Sprite Kit) seem to be in a state of flux wherein nobody from Apple is communicating with users about the raft of issues folks are currently having with both. From relatively stable and performant Sprite Kit in iOS 8.4 to a lot of lost performance in iOS 9 seems common. Scene Kit simply doesn't seem finished, and the documentation and community are both nearly non-existent as a result.

That being said... the theory is this:

Material IDs are what's used in traditional 3D apps to define areas of an object that have different materials. Somehow these Material IDs are called "elements" in SceneKit. I haven't been able to find much more about this.

It should be possible to detect the "element" that's underneath a touch on an object, and respond accordingly. You should even be able to change the state/nature of the material on that element to indicate it's the currently selected.

When wanting a smooth, well rounded cylinder as per your example, start with a cylinder that's made of only enough segments to describe/define the material IDs you need for your "rectangular" sections to be touched.

Later you can add a smoothing operation to the cylinder to make it round, and all the extra smoothing geometry in each quadrant of unique material ID should be responsive, regardless of how you add this extra detail to smooth the presentation of the cylinder.

Answer 3

Idea for the "Simplified" version:

if this representation is okey, you can use a UICollectionView. Each cell can have a defined size thanks to

collectionView:layout:sizeForItemAtIndexPath:

Then each cell of the collection could be a small rectangle representing a touchable part of the cylinder.

and using

collectionView:(UICollectionView *)collectionView 
   didSelectItemAtIndexPath:(NSIndexPath *)indexPath

To get the touch.

This will help you to display the popover at the right place:

CGRect rect = [collectionView layoutAttributesForItemAtIndexPath:indexPath].frame;

Finally, you can choose the appropriate popover (if the app has to work on iPhone) here: https://www.cocoacontrols.com/search?q=popover

Not perfect, but i think this is efficient!