Fix for key presses not working in viewer and other visualization GUIs on Mac OS X systems

[translunar]

Adds VTK_USE_COCOA advanced flag for Apple users where VTK is linked. Enabled by default.

[taketwo]

Is it possible to use VTK without Cocoa?

[translunar]

@taketwo Good question.

http://www.vtk.org/Wiki/Cocoa_VTK: "On OS X, there are two windowing APIs: Carbon and Cocoa. Older versions of VTK defaulted to Carbon, but newer versions default to Cocoa. Carbon support is deprecated by both Apple and VTK, and should not be used for new development."

Here's a post from the VTK ML about changing the default: http://www.vtk.org/pipermail/vtk-developers/2007-October/004794.html

I suppose it's possible that people might want to use Carbon instead if they were on earlier versions of Mac OS X. However, both Homebrew recipes use Cocoa and don't provide an option. I'm not a Macports user, so I can't verify it, but I doubt they're supporting Carbon anymore either. And in the course of installing VTK, I didn't find a single person who was able to install it manually on a Mac (everyone used brew or ports).

The more practical problem is that I have no way of testing Carbon support, since my Macbook Air is 64-bit.

Now, I will say that it's possible to use VTK and PCL without this flag. But without this flag, the event handler won't be able to catch any events. Another issue is that the window won't show up in the launcher (which is a substantial UI problem).

This patch doesn't prevent people from using the current, broken way of doing things. They'd just have to change an option with ccmake. It does, however, ensure that on the vast majority of Mac OS X systems, the UI will work properly.

Sorry, lengthy answer, but I'm a scientist, so that's what you get from me. =)

[taketwo]

Thanks for the explanation. I am not a Mac user by the way :)

I just thought that maybe we do not even have to provide this option in order not to confuse users. But from your answer I think it is okay if we keep it (anyways it's marked as "advanced").

[translunar]

Okay. Anything else I need to do before this is merged?

[taketwo]

I don't think so. Just wanted to give an opportunity to comment to someone who actually runs Mac.