XPPen__ArtistPro16Gen2.bpf.c

// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2023 Benjamin Tissoires
 */

#include "vmlinux.h"
#include "hid_bpf.h"
#include "hid_bpf_helpers.h"
#include <bpf/bpf_tracing.h>

#define VID_UGEE 0x28BD /* VID is shared with SinoWealth and Glorious and prob others */
#define PID_ARTIST_PRO14_GEN2 0x095A
#define PID_ARTIST_PRO16_GEN2 0x095B
#define PID_ARTIST_PRO19_GEN2 0x096A

HID_BPF_CONFIG(
	HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_PRO14_GEN2),
	HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_PRO16_GEN2),
	HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_PRO19_GEN2)
);

/*
 * We need to amend the report descriptor for the following:
 * - the device reports Eraser instead of using Secondary Barrel Switch
 * - when the eraser button is pressed and the stylus is touching the tablet,
 *   the device sends Tip Switch instead of sending Eraser
 *
 * This descriptor uses the physical dimensions of the 16" device.
 */
static const __u8 fixed_rdesc[] = {
	0x05, 0x0d,                    // Usage Page (Digitizers)             0
	0x09, 0x02,                    // Usage (Pen)                         2
	0xa1, 0x01,                    // Collection (Application)            4
	0x85, 0x07,                    //  Report ID (7)                      6
	0x09, 0x20,                    //  Usage (Stylus)                     8
	0xa1, 0x00,                    //  Collection (Physical)              10
	0x09, 0x42,                    //   Usage (Tip Switch)                12
	0x09, 0x44,                    //   Usage (Barrel Switch)             14
	0x09, 0x5a,                    //   Usage (Secondary Barrel Switch)   16  /* changed from 0x45 (Eraser) to 0x5a (Secondary Barrel Switch) */
	0x09, 0x3c,                    //   Usage (Invert)                    18
	0x09, 0x45,                    //   Usage (Eraser)                    16  /* created over a padding bit at offset 29-33 */
	0x15, 0x00,                    //   Logical Minimum (0)               20
	0x25, 0x01,                    //   Logical Maximum (1)               22
	0x75, 0x01,                    //   Report Size (1)                   24
	0x95, 0x05,                    //   Report Count (5)                  26  /* changed from 4 to 5 */
	0x81, 0x02,                    //   Input (Data,Var,Abs)              28
	0x09, 0x32,                    //   Usage (In Range)                  34
	0x15, 0x00,                    //   Logical Minimum (0)               36
	0x25, 0x01,                    //   Logical Maximum (1)               38
	0x95, 0x01,                    //   Report Count (1)                  40
	0x81, 0x02,                    //   Input (Data,Var,Abs)              42
	0x95, 0x02,                    //   Report Count (2)                  44
	0x81, 0x03,                    //   Input (Cnst,Var,Abs)              46
	0x75, 0x10,                    //   Report Size (16)                  48
	0x95, 0x01,                    //   Report Count (1)                  50
	0x35, 0x00,                    //   Physical Minimum (0)              52
	0xa4,                          //   Push                              54
	0x05, 0x01,                    //   Usage Page (Generic Desktop)      55
	0x09, 0x30,                    //   Usage (X)                         57
	0x65, 0x13,                    //   Unit (EnglishLinear: in)          59
	0x55, 0x0d,                    //   Unit Exponent (-3)                61
	0x46, 0xff, 0x34,              //   Physical Maximum (13567)          63
	0x26, 0xff, 0x7f,              //   Logical Maximum (32767)           66
	0x81, 0x02,                    //   Input (Data,Var,Abs)              69
	0x09, 0x31,                    //   Usage (Y)                         71
	0x46, 0x20, 0x21,              //   Physical Maximum (8480)           73
	0x26, 0xff, 0x7f,              //   Logical Maximum (32767)           76
	0x81, 0x02,                    //   Input (Data,Var,Abs)              79
	0xb4,                          //   Pop                               81
	0x09, 0x30,                    //   Usage (Tip Pressure)              82
	0x45, 0x00,                    //   Physical Maximum (0)              84
	0x26, 0xff, 0x3f,              //   Logical Maximum (16383)           86
	0x81, 0x42,                    //   Input (Data,Var,Abs,Null)         89
	0x09, 0x3d,                    //   Usage (X Tilt)                    91
	0x15, 0x81,                    //   Logical Minimum (-127)            93
	0x25, 0x7f,                    //   Logical Maximum (127)             95
	0x75, 0x08,                    //   Report Size (8)                   97
	0x95, 0x01,                    //   Report Count (1)                  99
	0x81, 0x02,                    //   Input (Data,Var,Abs)              101
	0x09, 0x3e,                    //   Usage (Y Tilt)                    103
	0x15, 0x81,                    //   Logical Minimum (-127)            105
	0x25, 0x7f,                    //   Logical Maximum (127)             107
	0x81, 0x02,                    //   Input (Data,Var,Abs)              109
	0xc0,                          //  End Collection                     111
	0xc0,                          // End Collection                      112
};

SEC(HID_BPF_RDESC_FIXUP)
int BPF_PROG(hid_fix_rdesc_xppen_artistpro16gen2, struct hid_bpf_ctx *hctx)
{
	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */);

	if (!data)
		return 0; /* EPERM check */

	__builtin_memcpy(data, fixed_rdesc, sizeof(fixed_rdesc));

	/* Fix the Physical maximum values for different sizes of the device
	 * The 14" screen device descriptor size is 11.874" x 7.421"
	 */
	if (hctx->hid->product == PID_ARTIST_PRO14_GEN2) {
		data[63] = 0x2e;
		data[62] = 0x62;
		data[73] = 0x1c;
		data[72] = 0xfd;
	} else if (hctx->hid->product == PID_ARTIST_PRO19_GEN2) {
		/* 19" screen reports 16.101" x 9.057" */
		data[63] = 0x3e;
		data[62] = 0xe5;
		data[73] = 0x23;
		data[72] = 0x61;
	}

	return sizeof(fixed_rdesc);
}

static int xppen_16_fix_eraser(struct hid_bpf_ctx *hctx)
{
	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 10 /* size */);

	if (!data)
		return 0; /* EPERM check */

	if ((data[1] & 0x29) != 0x29) /* tip switch=1 invert=1 inrange=1 */
		return 0;

	/* xor bits 0,3 and 4: convert Tip Switch + Invert into Eraser only */
	data[1] ^= 0x19;

	return 0;
}

/*
 * Static coordinate offset table based on positive only angles
 * Two tables are needed, because the logical coordinates are scaled
 *
 * The table can be generated by Python like this:
 * >>> full_scale = 11.874 # the display width/height in inches
 * >>> tip_height = 0.055677699 # the center of the pen coil distance from screen in inch (empirical)
 * >>> h = tip_height * (32767 / full_scale) # height of the coil in logical coordinates
 * >>> [round(h*math.sin(math.radians(d))) for d in range(0, 128)]
 * [0, 13, 26, ....]
 */

/* 14" inch screen 11.874" x 7.421" */
static const __u16 angle_offsets_horizontal_14[128] = {
	0, 3, 5, 8, 11, 13, 16, 19, 21, 24, 27, 29, 32, 35, 37, 40, 42, 45, 47, 50, 53,
	55, 58, 60, 62, 65, 67, 70, 72, 74, 77, 79, 81, 84, 86, 88, 90, 92, 95, 97, 99,
	101, 103, 105, 107, 109, 111, 112, 114, 116, 118, 119, 121, 123, 124, 126, 127,
	129, 130, 132, 133, 134, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146,
	147, 148, 148, 149, 150, 150, 151, 151, 152, 152, 153, 153, 153, 153, 153, 154,
	154, 154, 154, 154, 153, 153, 153, 153, 153, 152, 152, 151, 151, 150, 150, 149,
	148, 148, 147, 146, 145, 144, 143, 142, 141, 140, 139, 138, 137, 136, 134, 133,
	132, 130, 129, 127, 126, 124, 123
};
static const __u16 angle_offsets_vertical_14[128] = {
	0, 4, 9, 13, 17, 21, 26, 30, 34, 38, 43, 47, 51, 55, 59, 64, 68, 72, 76, 80, 84,
	88, 92, 96, 100, 104, 108, 112, 115, 119, 123, 127, 130, 134, 137, 141, 145, 148,
	151, 155, 158, 161, 165, 168, 171, 174, 177, 180, 183, 186, 188, 191, 194, 196,
	199, 201, 204, 206, 208, 211, 213, 215, 217, 219, 221, 223, 225, 226, 228, 230,
	231, 232, 234, 235, 236, 237, 239, 240, 240, 241, 242, 243, 243, 244, 244, 245,
	245, 246, 246, 246, 246, 246, 246, 246, 245, 245, 244, 244, 243, 243, 242, 241,
	240, 240, 239, 237, 236, 235, 234, 232, 231, 230, 228, 226, 225, 223, 221, 219,
	217, 215, 213, 211, 208, 206, 204, 201, 199, 196
};

/* 16" inch screen 13.567" x 8.480" */
static const __u16 angle_offsets_horizontal_16[128] = {
	0, 2, 5, 7, 9, 12, 14, 16, 19, 21, 23, 26, 28, 30, 33, 35, 37, 39, 42, 44, 46, 48,
	50, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 86, 88, 90,
	92, 93, 95, 97, 98, 100, 101, 103, 105, 106, 107, 109, 110, 111, 113, 114, 115,
	116, 118, 119, 120, 121, 122, 123, 124, 125, 126, 126, 127, 128, 129, 129, 130,
	130, 131, 132, 132, 132, 133, 133, 133, 134, 134, 134, 134, 134, 134, 134, 134,
	134, 134, 134, 134, 134, 133, 133, 133, 132, 132, 132, 131, 130, 130, 129, 129,
	128, 127, 126, 126, 125, 124, 123, 122, 121, 120, 119, 118, 116, 115, 114, 113,
	111, 110, 109, 107
};
static const __u16 angle_offsets_vertical_16[128] = {
	0, 4, 8, 11, 15, 19, 22, 26, 30, 34, 37, 41, 45, 48, 52, 56, 59, 63, 66, 70, 74,
	77, 81, 84, 88, 91, 94, 98, 101, 104, 108, 111, 114, 117, 120, 123, 126, 129, 132,
	135, 138, 141, 144, 147, 149, 152, 155, 157, 160, 162, 165, 167, 170, 172, 174,
	176, 178, 180, 182, 184, 186, 188, 190, 192, 193, 195, 197, 198, 199, 201, 202,
	203, 205, 206, 207, 208, 209, 210, 210, 211, 212, 212, 213, 214, 214, 214, 215,
	215, 215, 215, 215, 215, 215, 215, 215, 214, 214, 214, 213, 212, 212, 211, 210,
	210, 209, 208, 207, 206, 205, 203, 202, 201, 199, 198, 197, 195, 193, 192, 190,
	188, 186, 184, 182, 180, 178, 176, 174, 172
};

/* 19" inch screen 16.101" x 9.057" */
static const __u16 angle_offsets_horizontal_19[128] = {
	0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 25, 27, 29, 31, 33, 35, 37, 39, 41,
	42, 44, 46, 48, 50, 51, 53, 55, 57, 58, 60, 62, 63, 65, 67, 68, 70, 71, 73, 74, 76,
	77, 79, 80, 82, 83, 84, 86, 87, 88, 89, 90, 92, 93, 94, 95, 96, 97, 98, 99, 100,
	101, 102, 103, 104, 104, 105, 106, 106, 107, 108, 108, 109, 109, 110, 110, 111,
	111, 112, 112, 112, 112, 113, 113, 113, 113, 113, 113, 113, 113, 113, 113, 113,
	113, 113, 112, 112, 112, 112, 111, 111, 110, 110, 109, 109, 108, 108, 107, 106,
	106, 105, 104, 104, 103, 102, 101, 100, 99, 98, 97, 96, 95, 94, 93, 92, 90
};
static const __u16 angle_offsets_vertical_19[128] = {
	0, 4, 7, 11, 14, 18, 21, 25, 28, 32, 35, 38, 42, 45, 49, 52, 56, 59, 62, 66, 69, 72,
	75, 79, 82, 85, 88, 91, 95, 98, 101, 104, 107, 110, 113, 116, 118, 121, 124, 127,
	129, 132, 135, 137, 140, 142, 145, 147, 150, 152, 154, 157, 159, 161, 163, 165, 167,
	169, 171, 173, 174, 176, 178, 179, 181, 183, 184, 185, 187, 188, 189, 190, 192, 193,
	194, 195, 195, 196, 197, 198, 198, 199, 199, 200, 200, 201, 201, 201, 201, 201, 201,
	201, 201, 201, 201, 201, 200, 200, 199, 199, 198, 198, 197, 196, 195, 195, 194, 193,
	192, 190, 189, 188, 187, 185, 184, 183, 181, 179, 178, 176, 174, 173, 171, 169, 167,
	165, 163, 161
};

static void compensate_coordinates_by_tilt(__u8 *data, const __u8 idx,
		const __s8 tilt, const __u16 (*compensation_table)[128])
{
	__u16 coords = data[idx+1];

	coords <<= 8;
	coords += data[idx];

	__u8 direction = tilt > 0 ? 0 : 1; /* Positive tilt means we need to subtract the compensation (vs. negative angle where we need to add) */
	__u8 angle = tilt > 0 ? tilt : -tilt;

	if (angle > 127)
		return;

	__u16 compensation = (*compensation_table)[angle];

	if (direction == 0) {
		coords = (coords > compensation) ? coords - compensation : 0;
	} else {
		const __u16 logical_maximum = 32767;
		__u16 max = logical_maximum - compensation;

		coords = (coords < max) ? coords + compensation : logical_maximum;
	}

	data[idx] = coords & 0xff;
	data[idx+1] = coords >> 8;
}

static int xppen_16_fix_angle_offset(struct hid_bpf_ctx *hctx)
{
	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 10 /* size */);

	if (!data)
		return 0; /* EPERM check */

	/*
	 * Compensate X and Y offset caused by tilt.
	 *
	 * The magnetic center moves when the pen is tilted, because the coil
	 * is not touching the screen.
	 *
	 * a (tilt angle)
	 * |  /... h (coil distance from tip)
	 * | /
	 * |/______
	 *         |x (position offset)
	 *
	 * x = sin a * h
	 *
	 * Subtract the offset from the coordinates. Use the precomputed table!
	 *
	 * bytes 0   - report id
	 *       1   - buttons
	 *       2-3 - X coords (logical)
	 *       4-5 - Y coords
	 *       6-7 - pressure (ignore)
	 *       8   - tilt X
	 *       9   - tilt Y
	 */

	__s8 tilt_x = (__s8) data[8];
	__s8 tilt_y = (__s8) data[9];

	switch (hctx->hid->product) {
	case PID_ARTIST_PRO14_GEN2:
		compensate_coordinates_by_tilt(data, 2, tilt_x, &angle_offsets_horizontal_14);
		compensate_coordinates_by_tilt(data, 4, tilt_y, &angle_offsets_vertical_14);
		break;
	case PID_ARTIST_PRO16_GEN2:
		compensate_coordinates_by_tilt(data, 2, tilt_x, &angle_offsets_horizontal_16);
		compensate_coordinates_by_tilt(data, 4, tilt_y, &angle_offsets_vertical_16);
		break;
	case PID_ARTIST_PRO19_GEN2:
		compensate_coordinates_by_tilt(data, 2, tilt_x, &angle_offsets_horizontal_19);
		compensate_coordinates_by_tilt(data, 4, tilt_y, &angle_offsets_vertical_19);
		break;
	}

	return 0;
}

SEC(HID_BPF_DEVICE_EVENT)
int BPF_PROG(xppen_artist_pro_16_device_event, struct hid_bpf_ctx *hctx)
{
	int ret = xppen_16_fix_angle_offset(hctx);

	if (ret)
		return ret;

	return xppen_16_fix_eraser(hctx);
}

HID_BPF_OPS(xppen_artist_pro_16) = {
	.hid_rdesc_fixup = (void *)hid_fix_rdesc_xppen_artistpro16gen2,
	.hid_device_event = (void *)xppen_artist_pro_16_device_event,
};

SEC("syscall")
int probe(struct hid_bpf_probe_args *ctx)
{
	/*
	 * The device exports 3 interfaces.
	 */
	ctx->retval = ctx->rdesc_size != 113;
	if (ctx->retval)
		ctx->retval = -EINVAL;

	/* ensure the kernel isn't fixed already */
	if (ctx->rdesc[17] != 0x45) /* Eraser */
		ctx->retval = -EINVAL;

	return 0;
}

char _license[] SEC("license") = "GPL";