Virtual keyboard using UHID

I am trying to achieve what the QMK firmware does for keyboards but using software. So, I would like to turn off keys, substitute some keys for others, layers and etc. The first thing that appeared for me when searching was [this example](https://github.com/torvalds/linux/blob/master/samples/uhid/uhid-example.c) . The problem is, running the test it only works when the terminal that is executing the binary has focus, and I would like to overpass the windowing system. Also the code presents this array that I don't have any idea how to fill.

-C
static unsigned char rdesc[] = {
	0x05, 0x01,	/* USAGE_PAGE (Generic Desktop) */
	0x09, 0x02,	/* USAGE (Mouse) */
	0xa1, 0x01,	/* COLLECTION (Application) */
	0x09, 0x01,		/* USAGE (Pointer) */
	0xa1, 0x00,		/* COLLECTION (Physical) */
	0x85, 0x01,			/* REPORT_ID (1) */
	0x05, 0x09,			/* USAGE_PAGE (Button) */
	0x19, 0x01,			/* USAGE_MINIMUM (Button 1) */
	0x29, 0x03,			/* USAGE_MAXIMUM (Button 3) */
	0x15, 0x00,			/* LOGICAL_MINIMUM (0) */
	0x25, 0x01,			/* LOGICAL_MAXIMUM (1) */
	0x95, 0x03,			/* REPORT_COUNT (3) */
	0x75, 0x01,			/* REPORT_SIZE (1) */
	0x81, 0x02,			/* INPUT (Data,Var,Abs) */
	0x95, 0x01,			/* REPORT_COUNT (1) */
	0x75, 0x05,			/* REPORT_SIZE (5) */
	0x81, 0x01,			/* INPUT (Cnst,Var,Abs) */
	0x05, 0x01,			/* USAGE_PAGE (Generic Desktop) */
	0x09, 0x30,			/* USAGE (X) */
	0x09, 0x31,			/* USAGE (Y) */
	0x09, 0x38,			/* USAGE (WHEEL) */
	0x15, 0x81,			/* LOGICAL_MINIMUM (-127) */
	0x25, 0x7f,			/* LOGICAL_MAXIMUM (127) */
	0x75, 0x08,			/* REPORT_SIZE (8) */
	0x95, 0x03,			/* REPORT_COUNT (3) */
	0x81, 0x06,			/* INPUT (Data,Var,Rel) */
	0xc0,			/* END_COLLECTION */
	0xc0,		/* END_COLLECTION */
	0x05, 0x01,	/* USAGE_PAGE (Generic Desktop) */
	0x09, 0x06,	/* USAGE (Keyboard) */
	0xa1, 0x01,	/* COLLECTION (Application) */
	0x85, 0x02,		/* REPORT_ID (2) */
	0x05, 0x08,		/* USAGE_PAGE (Led) */
	0x19, 0x01,		/* USAGE_MINIMUM (1) */
	0x29, 0x03,		/* USAGE_MAXIMUM (3) */
	0x15, 0x00,		/* LOGICAL_MINIMUM (0) */
	0x25, 0x01,		/* LOGICAL_MAXIMUM (1) */
	0x95, 0x03,		/* REPORT_COUNT (3) */
	0x75, 0x01,		/* REPORT_SIZE (1) */
	0x91, 0x02,		/* Output (Data,Var,Abs) */
	0x95, 0x01,		/* REPORT_COUNT (1) */
	0x75, 0x05,		/* REPORT_SIZE (5) */
	0x91, 0x01,		/* Output (Cnst,Var,Abs) */
	0xc0,		/* END_COLLECTION */
};

I could not find any more documentation on the matter. At this time, I am not even sure if it is possible to do what I want. I have seen things like [KMonad](https://github.com/kmonad/kmonad) that I could not get to work. At the end, these are my questions: * How to fill the rdesc array to keyboards? * How to overpass the windowing system? * Where can I find documentation about UHID?