4. Joystick driver fuckery

Of course, joystick drivers have many quirks that greatly complicate things. So much so that they deserve their own chapter. Here's a list of some of the quirks I've encountered:

Combined triggers

DirectInput combines left and right triggers into a single axis. They are combined using the strategy in Chapter 4: Dimension Reduction.

Kodi solves this by splitting the axis into two semiaxes, as explained in Chapter 2: Joystick drivers. Each semiaxis is mapped to its own trigger.

Anomalous triggers

Not all triggers start at 0.0 and travel to 1.0 (or -1.0 in DirectInput). Some triggers start at 1.0 or -1.0, and travel to 0.0 or to the opposite unit. These are called anomalous triggers. These triggers have two properties: Center - The theory here is that initial perturbations are minimal. This means that the center is determined by rounding the first value to the closest int. Range - The range can be half range (assumed) or full range (detected when a value has the opposite sign)

Discrete D-pads

Instead of four buttons or a hat enum, D-pads can sometimes be reported as floats that use the discrete values -1.0, 0.0 and 1.0. Fortunately, because analog sticks can emulate D-pads, we can simply treat the discrete D-pad as an analog stick.

Repeated input

Some buttons generate two input events. For example, some hats operate as four digital buttons AND as a discrete D-pad. This is solved via a "cooldown" while mapping, which ignores any input for around 50ms after a button is mapped.

Hat enums

I consider hat enums a quirk because it just makes so much more sense to represent them using four buttons. It doesn't even guarantee mutual exclusion between opposite directions, as this can be violated by a flag with the improper bits set.

Pressure-sensitive buttons

Pressure-sensitive buttons can be reported as an analog axis instead of a digital value.

Incomplete information

Pertinent info (name, USB VID and PID, etc) might be missing, making it hard to identify the correct button map.