XInput and HID - architecture

[Roderick Colenbrander]

On Tue, Mar 22, 2016 at 12:18 PM, Juan Jose Gonzalez <juanj.gh at gmail.com> wrote:
> On 03/22/2016 01:27 AM, Roderick Colenbrander wrote:
>>
>>>> As you have seen the xbox controller lacks proper HID descriptors and
>>>> on Windows the drivers fake descriptors to allow DirectInput to work
>>>> as well. We would be doing something not to different. For the
>>>> DirectInput I would report the real device name and the real ranges,
>>>> similar if games use raw input (not sure if there are games which do
>>>> this).
>>> On Wine, this would work the other way around. We would have raw (HID)
>>> devices as a base, and create DInput and XInput devices from those.
>> I understand that part. What I meant is that Windows reports 2
>> different devices one with HID and one without. I was suggesting this
>> as a way to potentially handle non-native xinput devices, e.g. the
>> non-native device is made to appear like the xbox one on windows with
>> the missing descriptors etcetera.
> I'm not sure I understand what you mean.
 The currently planned wine
> architecture uses the HID subsystem as a common base, allowing us to
> create a single minidriver per backend (evdev, hidraw, etc.), and then
> lets DInput and XInput access that. Are you suggesting putting all the
> XInput code (gamepad matching, control mapping) into the HID subsystem?

I suggested maybe following the Windows 2 device approach for maybe
dealing with xinput for non-native devices (the mapping is pretty much
the same for steam / ds3 / ds4 / wii u gamepad, just slightly
different ranges and button names). For such devices it could make
sense to map them to a fixed mapping to simplify handling for xinput.
Also I'm not sure how important remapping is normally for users since
many games have configurable input.

>> Though this still wouldn't handle
>> the enumeration situation for apps using wmi.
> Sorry, as you may have noticed, I'm not too savvy about Windows APIs.
> What is wmi?

WMI is a subsystem let's say a bit comparable to /proc & /sys on Linux
providing all sorts of information about the system. Through WMI you
can provide information on e.g. CPU, USB devices, PCIe devices,
network information etcetera. As a developer you provide an SQL-like
query to request certain type of information.

For xinput, Microsoft directly provided the xbox API without really
considering enumeration well (except for naive polling). One mechanism
Microsoft recommended as a bit of an oversight in my opinion was to
use WMI to enumerate input devices.

Also before I forget one other important thing for xinput are window
messages. I forgot the exact message name but something like
WM_DEVICECHANGED or something is important. Various applications
listen for the message to detect hotplugging of input devices and then
triggering a new device enumeration. For Linux this would require us
to tap into udev (SDL2 does this too, the code can give some
inspiration).

>
> - Juan