evdev: Detect whether input devices are accelerometers

Anything with X, Y and Z axes but no buttons is probably an
accelerometer (this is the assumption made in udev).

Signed-off-by: Simon McVittie <[email protected]>

src/core/linux/SDL_evdev_capabilities.c

@@ -33,6 +33,24 @@ SDL_EVDEV_GuessDeviceClass(unsigned long bitmask_ev[NBITS(EV_MAX)],
     int devclass = 0;
     unsigned long keyboard_mask;
 
+    /* X, Y, Z axes but no buttons probably means an accelerometer */
+    if (test_bit(EV_ABS, bitmask_ev) &&
+        test_bit(ABS_X, bitmask_abs) &&
+        test_bit(ABS_Y, bitmask_abs) &&
+        test_bit(ABS_Z, bitmask_abs) &&
+        !test_bit(EV_KEY, bitmask_ev)) {
+        return SDL_UDEV_DEVICE_ACCELEROMETER;
+    }
+
+    /* RX, RY, RZ axes but no buttons also probably means an accelerometer */
+    if (test_bit(EV_ABS, bitmask_ev) &&
+        test_bit(ABS_RX, bitmask_abs) &&
+        test_bit(ABS_RY, bitmask_abs) &&
+        test_bit(ABS_RZ, bitmask_abs) &&
+        !test_bit(EV_KEY, bitmask_ev)) {
+        return SDL_UDEV_DEVICE_ACCELEROMETER;
+    }
+
     if (test_bit(EV_ABS, bitmask_ev) &&
         test_bit(ABS_X, bitmask_abs) && test_bit(ABS_Y, bitmask_abs)) {
         if (test_bit(BTN_STYLUS, bitmask_key) || test_bit(BTN_TOOL_PEN, bitmask_key)) {

src/core/linux/SDL_evdev_capabilities.h

@@ -37,7 +37,8 @@ typedef enum
     SDL_UDEV_DEVICE_KEYBOARD    = 0x0002,
     SDL_UDEV_DEVICE_JOYSTICK    = 0x0004,
     SDL_UDEV_DEVICE_SOUND       = 0x0008,
-    SDL_UDEV_DEVICE_TOUCHSCREEN = 0x0010
+    SDL_UDEV_DEVICE_TOUCHSCREEN = 0x0010,
+    SDL_UDEV_DEVICE_ACCELEROMETER = 0x0020
 } SDL_UDEV_deviceclass;
 
 #define BITS_PER_LONG           (sizeof(unsigned long) * 8)