How to make a custom trackball / eyeball control with Cocoa?

Question

I'm writing my first Cocoa app and I would like to make a "trackball / eyeball / arcball / whatever it's called" button to rotate a 3D OpenGL scene.

There's a perfect example of this custom Cocoa control in Pages (Apple iWork suite) when you select a 3D chart. After some hacks, this control seems to be referenced as SFC3DRotateWidget. Here's a screenshot of the control in Pages.

Maybe this widget is reusable, but I didn't find how or where. So I try to recreate it.

I'm inexperienced with Cocoa so I'm not sure how to do that nor exactly where (i.e. what to do with Interface Builder, what to do with code...).

I'm not sure if I need to override the drawing function. I thought to use a textured button (Interface Builder) with a NSTrackingArea (code) to handle mouse events (move, drag, ...) but the area is necessarily rectangular. The interactive zones of the custom control used by Apple seem to follow the shape of the arrows. I've read on S.O. I can use NSBezierPath to create a more specific area (only via code?).

Does it sound good for you? Do I miss something?

Let met know if you have any tips, tricks or resources you can share!

Thanks!

Answer 1

It sounds like you want to build a custom control. You do this by subclassing NSControl, which there is a guide on how to do. You can control the circular clickable area, and the responses to the mouse events by implementing the various methods. For example you can track mouse events with mouseDown: and the related methods.

You probably do not need to use any custom drawing code, NSImageView subviews with the various arrows will probably suite your purposes fine, unless you'd rather draw them in code.