While working on my current project I noticed a problem with the OS X implementation of joystick support.

I have a Mayflash Wii U Pro Controller adapter connected to my Mac. This device supports connecting up to 4 Wii U Pro Controllers. All of the inputs are are reported through the same HID device which means there are lots of buttons and sticks to keep track of.

This brings me to the first problem. Allegro has a hard-coded limit of 32 buttons. This is not enough to handle the maximum number of buttons that can be reported by the adapter (48).

The second problem is in the way the OS X implementation enumerates the buttons. Allegro uses IOHIDElementGetUsage() to determine button indices, but this is not enough to differentiate between the buttons of separate controllers connected to the adapter. Each controller reports usage values of 1-12 so Allegro will only count the buttons on the first controller. Buttons on all other controllers are ignored.

I have attached a patch that fixes these issues. I have raised the hard-coded limit to 64 and changed how the buttons are enumerated.

Append: I'm going to look into this further. I think the device may break each controller's inputs up into separate collections. If that's the case, I should be able to separate the data for each controller.

Append 2: I've attached a new patch which breaks up the inputs for each controller based on the collections specified by the device. The imeplementation now creates four ALLEGRO_JOYSTICKs for the device, as it should.

Append 3: New patch (osx_joystick_patch_r3.diff) described below.

I can have a look at this but I don't have any hardware to test it with, unfortunately.
Pete