I'm investigating supporting a touchscreen digitizer on macOS. I'd like to receive multi-touch reports from the device, and have them intercepted by my app. I also want to suppress the default absolute positioning 'mouse' behavior of the touch screen.
The device exposes three HID interface: #0 - multi-touch (PrimaryUsagePage 0xD, PrimaryUsage 4) #1 - vendor-specific #2 - single-touch (PrimaryUsagePage 1, PrimaryUsage 2)
I've only been able to achieve half of my goal using a HIDDriverKit dext - I can outmatch the OS for the single-touch HID interface and ignore its 7-byte single-touch reports.
However, although I can match to the multi-touch interface, I never see any reports at all there, as if the OS never polls the interrupt endpoint.
On Windows, the device "just works" - I've traced its behavior in Wireshark. The OS doesn't do any special setup, it sends no SET_FEATURE commands, it just reads from the multi-touch interrupt endpoint, where it receives 54-byte reports. Windows doesn't even get any 7-byte single-touch reports.
On macOS, I managed to use Wireshark on an old Intel Mac, where I can still use XHC20 for logging. Here, macOS tries to read from all the interrupt endpoints for all the HID interfaces, and the digitizer only responds on the single-touch interface.
MSDN's documentation for multi-touch support is quite unhelpful here, because it just says "use the OS driver", but doesn't detail how a digitizer switches between multi-touch and single-touch mode. If I were making a digitizer, I'd send reports on both interfaces, expecting the OS to read the single- or multi-touch interface as required. Although unlikely, it seems that this digitizer changes its behavior based on how it is accessed.
I can outmatch the USB interface for the single-touch reports, so that the OS HID driver doesn't even see it. That doesn't change the device behavior.
The HIDDriverKit APIs I use imply setting up an interrupt read. I call Open on the interface, and implement a ReportAvailable callback. This works for the single-touch interface, but I get no reports on the multi-touch interface. All the calls with return values return kIOReturnSuccess.
Does anyone know how multi-touch digitizers switch between single- and multi-touch mode (if indeed they have a mode at all), or why macOS apparently doesn't even read the multi-touch interrupt end point? Does anyone know how I can ensure that my HID driver actually reads the interrupt endpoint on the HID interface it is matched to? Does macOS deliberately prevent access to multi-touch HID interfaces?
