[WIP] xpadneo, deadzones: Implement our own dead zone as a vector

This commit sets flatness to zero to let us calculate the dead zone on
a 2D plane instead of on a 1D axis, otherwise we'd have rectangular
dead zones along the two axes per thumb stick.

We also need to set fuzz to 0, otherwise `joydev` doesn't always return
to the center.

See-also: atar-axis#231
Signed-off-by: Kai Krakow <[email protected]>

WIP

Signed-off-by: Kai Krakow <[email protected]>

hid-xpadneo/src/hid-xpadneo.c

@@ -942,10 +942,10 @@ static int xpadneo_input_configured(struct hid_device *hdev, struct hid_input *h
 
 	if (param_gamepad_compliance) {
 		hid_info(hdev, "enabling compliance with Linux Gamepad Specification\n");
-		input_set_abs_params(xdata->idev, ABS_X, -32768, 32767, 7, 4095);
-		input_set_abs_params(xdata->idev, ABS_Y, -32768, 32767, 7, 4095);
-		input_set_abs_params(xdata->idev, ABS_RX, -32768, 32767, 7, 4095);
-		input_set_abs_params(xdata->idev, ABS_RY, -32768, 32767, 7, 4095);
+		input_set_abs_params(xdata->idev, ABS_X, -32768, 32767, 0, 0);
+		input_set_abs_params(xdata->idev, ABS_Y, -32768, 32767, 0, 0);
+		input_set_abs_params(xdata->idev, ABS_RX, -32768, 32767, 0, 0);
+		input_set_abs_params(xdata->idev, ABS_RY, -32768, 32767, 0, 0);
 	}
 
 	/* combine triggers to form a rudder, use ABS_MISC to order after dpad */
@@ -954,8 +954,28 @@ static int xpadneo_input_configured(struct hid_device *hdev, struct hid_input *h
 	return 0;
 }
 
-static void xpadneo_report_abs(struct xpadneo_devdata *xdata, unsigned int code, int value) {
-	unsigned int offset = 0;
+static inline s32 scale_axis(s32 this15, s32 other15, s32 zone15) {
+	s32 cubic_mag30 = this15 * this15 + other15 * other15;
+	s32 cubic_zone30 = zone15 * zone15;
+	s32 cubic_scaled30 = (1ULL<<30) - cubic_zone30 - 1;
+	s32 normalized15 = ((s64)(cubic_mag30 - cubic_zone30) << 15) / cubic_scaled30;
+	if (cubic_mag30 < cubic_zone30) {
+		return 0;
+	} else if (normalized15 <= 0) {
+		return this15;
+	} else {
+		if (this15 < 0)
+			this15 = clamp(this15 + zone15, -32768 + zone15, 0);
+		else
+			this15 = clamp(this15 - zone15, 0, 32767 - zone15);
+		this15 = (s64)this15 * normalized15 * normalized15 / cubic_mag30;
+		return clamp(this15, -32768, 32767);
+	}
+}
+
+static void xpadneo_report_abs(struct xpadneo_devdata *xdata, unsigned int code, s32 value) {
+	s32 offset = 0;
+	static u32 deadzone = 2560;
 
 	switch (code) {
 	case ABS_X:
@@ -972,18 +992,22 @@ static void xpadneo_report_abs(struct xpadneo_devdata *xdata, unsigned int code,
 	switch (code) {
 	case ABS_X:
 		xdata->abs.x = value;
+		value = scale_axis(value, xdata->abs.y, deadzone);
 		break;
 	case ABS_Y:
 		xdata->abs.y = value;
+		value = scale_axis(value, xdata->abs.x, deadzone);
 		break;
 	case ABS_Z:
 		xdata->abs.z = value;
 		break;
 	case ABS_RX:
 		xdata->abs.rx = value;
+		value = scale_axis(value, xdata->abs.ry, deadzone);
 		break;
 	case ABS_RY:
 		xdata->abs.ry = value;
+		value = scale_axis(value, xdata->abs.rx, deadzone);
 		break;
 	case ABS_RZ:
 		xdata->abs.rz = value;