How to implement Left and Right Analog Triggers in a HID Gamepad for Android

Question

I am working on a HID gamepad with 4 axis(14 Bit), 16 Buttons, 2 Analog Triggers(1 Byte) and a Hat Switch. I am currently using Axis X and Y for the left analog stick, axis Rx and Ry for right analog stick and axis Z and Rz for left and right triggers. I am able to register all buttons and analog readings(which have been tested with Gamepad tester in android and jstest-gtk in linux), but the problem is that in (Android)games the triggers are supposed to be axis 7 and axis 8 and in my case the Z and Rz are assigned axes 14 and 15. I have also tried using Acceleration(axis:11), Brake(axis:12), Rudder(axis:9) and Throttle(axis:10) but the axes 7 and 8(which are the default trigger axes) are not getting assigned.

Here is my HID Report Descriptor:-

0x05, 0x01,                    // USAGE_PAGE (Generic Desktop)
0x09, 0x05,                    // USAGE (Game Pad)
0xa1, 0x01,                    // COLLECTION (Application)

0x85, 0x01,                    //   REPORT_ID (1)
0x09, 0x01,                    //   USAGE (Pointer)
0xa1, 0x00,                    //   COLLECTION (Physical)
0x09, 0x30,                    //     USAGE (X) - Left Analog Left(-ve),Right(+ve)
0x09, 0x31,                    //     USAGE (Y) - Left Analog Up(-ve), Down(+ve)
0x09, 0x33,                    //     USAGE (Rx) - Right Analog Left(-ve), Right(+ve)
0x09, 0x34,                    //     USAGE (Ry) - Right Analog Up(-ve), Down(+ve)
0x16, 0x01, 0xE0,              //     LOGICAL_MINIMUM (-8191)
0x26, 0xFF, 0x1F,              //     LOGICAL_MAXIMUM (8191)        
0x75, 0x10,                    //     REPORT_SIZE (16)
0x95, 0x04,                    //     REPORT_COUNT (4)
0x81, 0x02,                    //     INPUT (Data,Var,Abs)
0xc0,                          //   END_COLLECTION
0x05, 0x01,                    //     USAGE_PAGE (Generic Desktop) 
0x15, 0x00,                    //     LOGICAL_MINIMUM (0)
0x26, 0xFF, 0x00,              //     LOGICAL_MAXIMUM (255)
0x09, 0x32,                    //     USAGE (Z) - L2 Trigger(Shoulderpads Trigger)
0x09, 0x35,                    //     USAGE (Rz) - R2 Trigger(Shoulderpads Trigger)    
0x75, 0x08,                    //     REPORT_SIZE (8)    
0x95, 0x02,                    //     REPORT_COUNT (2)    
0x81, 0x02,                    //     INPUT (Data,Var,Abs)    

0x05, 0x09,                    //   USAGE_PAGE (Button)
0x19, 0x01,                    //   USAGE_MINIMUM (Button 1)    
0x29, 0x10,                    //   USAGE_MAXIMUM (Button 16)
0x15, 0x00,                    //   LOGICAL_MINIMUM (0)
0x25, 0x01,                    //   LOGICAL_MAXIMUM (1)     
0x95, 0x10,                    //   REPORT_COUNT (16)
0x75, 0x01,                    //   REPORT_SIZE (1)
0x81, 0x02,                    //   INPUT (Data,Var,Abs)

0x05, 0x01,                    //   USAGE_PAGE (Generic Desktop)
0x09, 0x39,                    //   USAGE (Hat switch)
0x15, 0x00,                    //   LOGICAL_MINIMUM (0)
0x25, 0x07,                    //   LOGICAL_MAXIMUM (7)
0x35, 0x00,                    //   PHYSICAL_MINIMUM (0)
0x46, 0x3b, 0x01,              //   PHYSICAL_MAXIMUM (315)
0x65, 0x14,                    //   UNIT (Eng Rotation:Centimeter)
0x75, 0x04,                    //   REPORT_SIZE (4)
0x95, 0x01,                    //   REPORT_COUNT (1)
0x81, 0x42,                    //   INPUT (Data,Var,Abs,Null)
0x95, 0x01,                    //   REPORT_COUNT (1)
0x75, 0x04,                    //   REPORT_SIZE (4)
0x81, 0x43,                    //   INPUT (Cnst,Var,Abs,Null)

0xc0                           // END_COLLECTION

Any Help will be deeply appreciated, Thank You.

Edit:- Here is the new report descriptor I tried based on the Anrdoid CDD document specified by Nipo:-

0x05, 0x01,                    // USAGE_PAGE (Generic Desktop)
0x09, 0x05,                    // USAGE (Game Pad)
0xa1, 0x01,                    // COLLECTION (Application)
0x85, 0x01,                    //   REPORT_ID (1)
0x09, 0x01,                    //   USAGE (Pointer)
0xa1, 0x00,                    //   COLLECTION (Physical)
0x05, 0x01,                    //     USAGE_PAGE (Generic Desktop)
0x09, 0x30,                    //     USAGE (X) - Left Analog Left(-ve),Right(+ve)
0x09, 0x31,                    //     USAGE (Y) - Left Analog Up(-ve), Down(+ve)
0x09, 0x32,                    //     USAGE (Z) - Right Analog X
0x09, 0x35,                    //     USAGE (Rz) - Right Analog Y
0x15, 0x81,                    //     LOGICAL_MINIMUM (-127)
0x25, 0x7F,                    //     LOGICAL_MAXIMUM (127)       
0x75, 0x08,                    //     REPORT_SIZE (8)
0x95, 0x04,                    //     REPORT_COUNT (4)
0x81, 0x02,                    //     INPUT (Data,Var,Abs)
0x05, 0x02,                    // USAGE_PAGE (Simulation Control)            
0x15, 0x00,                    //     LOGICAL_MINIMUM (0)
0x26, 0xFF, 0x00,              //     LOGICAL_MAXIMUM (255)        
0x09, 0xC4,                    //     USAGE(Acceleration)
0x09, 0xC5,                    //     USAGE(Brake)        
0x75, 0x08,                    //     REPORT_SIZE (8)
0x95, 0x02,                    //     REPORT_COUNT (2)    
0x81, 0x02,                    //     INPUT (Data,Var,Abs)
0x05, 0x09,                    //   USAGE_PAGE (Button)
0x09, 0x01,                    //   USAGE(Button 1)
0x09, 0x02,                    //   USAGE(Button 2)
0x09, 0x04,                    //   USAGE(Button 4)
0x09, 0x05,                    //   USAGE(Button 5)
0x09, 0x07,                    //   USAGE(Button 7)
0x09, 0x08,                    //   USAGE(Button 8)
0x09, 0x0E,                    //   USAGE(Button 14)
0x09, 0x0F,                    //   USAGE(Button 15)
0x15, 0x00,                    //   LOGICAL_MINIMUM (0)
0x25, 0x01,                    //   LOGICAL_MAXIMUM (1)     
0x95, 0x08,                    //   REPORT_COUNT (8)
0x75, 0x01,                    //   REPORT_SIZE (1)
0x81, 0x02,                    //   INPUT (Data,Var,Abs)           
0x05, 0x01,                    //   USAGE_PAGE (Generic Desktop)
0x09, 0x39,                    //   USAGE (Hat switch)
0x15, 0x00,                    //   LOGICAL_MINIMUM (0)
0x25, 0x07,                    //   LOGICAL_MAXIMUM (7)
0x35, 0x00,                    //   PHYSICAL_MINIMUM (0)
0x46, 0x3b, 0x01,              //   PHYSICAL_MAXIMUM (315)
0x65, 0x14,                    //   UNIT (Eng Rotation:Centimeter)
0x75, 0x04,                    //   REPORT_SIZE (4)
0x95, 0x01,                    //   REPORT_COUNT (1)
0x81, 0x42,                    //   INPUT (Data,Var,Abs,Null)
0x65, 0x00,                    // Unit (None)
/*!@ The below section is taken from the page 31 of the document given
  in the link below.
  https://www.silabs.com/documents/public/application-notes/AN993.pdf
 */
0x05, 0x0C,                    //   USAGE_PAGE (Consumer)
0x0A, 0x23, 0x02,              //   USAGE (AC Home)
0x0A, 0x24, 0x02,              //   USAGE (AC Back)
0x75, 0x01,                    //   REPORT_SIZE(1)
0x95, 0x02,                    //   REPORT_COUNT(2)
0x15, 0x00,                    //   LOGICAL_MINIMUM (0)
0x25, 0x01,                    //   LOGICAL_MAXIMUM (1)
0x35, 0x00,                    //   PHYSICAL_MINIMUM (0)
0x45, 0x01,                    //   PHYSICAL_MAXIMUM (1)
0x81, 0x42,                    //   INPUT (Data,Var,Abs,Null)
0x95, 0x01,                    //   REPORT_COUNT (2)
0x75, 0x02,                    //   REPORT_SIZE (1)
0x81, 0x43,                    //   INPUT (Cnst,Var,Abs,Null)
0xc0,                          //   END_COLLECTION
0xc0,                          //   END_COLLECTION

Have you looked into paragraph 7.2.6.1 of [Android CDD](https://source.android.com/compatibility/android-cdd.pdf) ? — Nipo, Feb 11 '20 at 13:02
@Nipo Thanks for the reply, I will test the configuration given in the document and post the results, Thanks again — jibin_raj24, Feb 11 '20 at 16:26
@Nipo Hi, tried the descriptor configuration in the document but the axes(0x00C4-AXIS_RTRIGGER/ACCELERATION and 0x00C5-AXIS_LTRIGGER/BRAKE) are detected as axis 12 and axis 13. The document clearly specifies to use these two axes, so I think there is something wrong with the descriptor. — jibin_raj24, Feb 13 '20 at 09:56

score 1 · Answer 1 · answered May 28 '20 at 08:10

private static float getCenteredAxis(MotionEvent event,
                                     InputDevice device, int axis, int historyPos) {
    final InputDevice.MotionRange range =
            device.getMotionRange(axis, event.getSource());
    if (range != null) {
        final float flat = range.getFlat();
        final float value =
                historyPos < 0 ? event.getAxisValue(axis):
                        event.getHistoricalAxisValue(axis, historyPos);
        if (Math.abs(value) > flat) {
            return value;
        }
    }
    return 0;
}



    // trigger_l
    float l = getCenteredAxis(event, mInputDevice,
            MotionEvent.AXIS_BRAKE, historyPos);
    textjoy7.setText(String.valueOf(l));

    if (l == 0) {
        l = getCenteredAxis(event, mInputDevice,
                MotionEvent.AXIS_LTRIGGER, historyPos);
    }
    //trigger_x
    float r = getCenteredAxis(event, mInputDevice,
            MotionEvent.AXIS_GAS, historyPos);
    textjoy8.setText(String.valueOf(r));

    if (r == 0) {
        r = getCenteredAxis(event, mInputDevice,
                MotionEvent.AXIS_RTRIGGER, historyPos);
    }

Thanks for your answer, looking at your answer it seems that the code provided is to read the gamepad inputs from the android side. In my case I was developing an HID gamepad and I was not able to get the analog triggers be detected in the games. After some time it was found that the issue was due to the library used by the particular game developer(3 games I tested were from the same developer) and some games which uses the native android gamepad library worked without any configuration. For the descriptor see my answer. — jibin_raj24, May 29 '20 at 14:21

score 0 · Accepted Answer · answered Mar 04 '20 at 17:02

Here is the Report Descriptor that worked for me:-

0x05, 0x01,                    // USAGE_PAGE (Generic Desktop)
0x09, 0x05,                    // USAGE (Game Pad)
0xa1, 0x01,                    // COLLECTION (Application)    

0x85, 0x01,                    //   REPORT_ID (1)
0x09, 0x01,                    //   USAGE (Pointer)
0xa1, 0x00,                    //   COLLECTION (Physical)    
0x05, 0x01,                    //     USAGE_PAGE (Generic Desktop)
0x09, 0x30,                    //     USAGE (X) - Left Analog Left(-ve),Right(+ve)
0x09, 0x31,                    //     USAGE (Y) - Left Analog Up(-ve), Down(+ve)    
0x09, 0x32,                    //     USAGE (Z) - Right Analog Left(-ve)Right(+ve)
0x09, 0x35,                    //     USAGE (Rz)- Right Analog Up(-ve), Down(+ve)
0x15, 0x81,                    //     LOGICAL_MINIMUM (-127)
0x25, 0x7f,                    //     LOGICAL_MAXIMUM (127)
0x75, 0x08,                    //     REPORT_SIZE (8)
0x95, 0x04,                    //     REPORT_COUNT (4)
0x81, 0x02,                    //     INPUT (Data,Var,Abs)
0xc0,                          //   END_COLLECTION

0x05, 0x02,                    //     USAGE_PAGE (Simulation Control)
0x15, 0x00,                    //     LOGICAL_MINIMUM (0)
0x26, 0xFF, 0x00,              //     LOGICAL_MAXIMUM (255)
0x09, 0xC4,                    //     USAGE(Acceleration)
0x09, 0xC5,                    //     USAGE(Brake)           
0x75, 0x08,                    //     REPORT_SIZE (8)
0x95, 0x02,                    //     REPORT_COUNT (2)
0x81, 0x02,                    //     INPUT (Data,Var,Abs)

0x05, 0x09,                    //   USAGE_PAGE (Button)
0x19, 0x01,                    //   USAGE_MINIMUM (Button 1)
0x29, 0x10,                    //   USAGE_MAXIMUM (Button 16)
0x15, 0x00,                    //   LOGICAL_MINIMUM (0)
0x25, 0x01,                    //   LOGICAL_MAXIMUM (1)
0x95, 0x10,                    //   REPORT_COUNT (16)
0x75, 0x01,                    //   REPORT_SIZE (1)
0x81, 0x02,                    //   INPUT (Data,Var,Abs)

0x05, 0x01,                    //   USAGE_PAGE (Generic Desktop)
0x09, 0x39,                    //   USAGE (Hat switch)
0x15, 0x00,                    //   LOGICAL_MINIMUM (0)
0x25, 0x07,                    //   LOGICAL_MAXIMUM (7)
0x35, 0x00,                    //   PHYSICAL_MINIMUM (0)
0x46, 0x3b, 0x01,              //   PHYSICAL_MAXIMUM (315)
0x65, 0x14,                    //   UNIT (Eng Rotation:Centimeter)
0x75, 0x04,                    //   REPORT_SIZE (4)
0x95, 0x01,                    //   REPORT_COUNT (1)
0x81, 0x42,                    //   INPUT (Data,Var,Abs,Null)
0x95, 0x01,                    //   REPORT_COUNT (1)
0x75, 0x04,                    //   REPORT_SIZE (4)
0x81, 0x43,                    //   INPUT (Cnst,Var,Abs,Null)
0x65, 0x00,                    //   Unit (None)

0x05, 0x0C,                    //   USAGE_PAGE (Consumer)
0x0A, 0x23, 0x02,              //   USAGE (AC Home)
0x0A, 0x24, 0x02,              //   USAGE (AC Back)
0x75, 0x01,                    //   REPORT_SIZE(1)
0x95, 0x02,                    //   REPORT_COUNT(2)
0x15, 0x00,                    //   LOGICAL_MINIMUM (0)
0x25, 0x01,                    //   LOGICAL_MAXIMUM (1)
0x35, 0x00,                    //   PHYSICAL_MINIMUM (0)
0x45, 0x01,                    //   PHYSICAL_MAXIMUM (1)
0x81, 0x42,                    //   INPUT (Data,Var,Abs,Null)

0x95, 0x01,                    //   REPORT_COUNT (2)
0x75, 0x02,                    //   REPORT_SIZE (1)
0x81, 0x43,                    //   INPUT (Cnst,Var,Abs,Null)

0xc0                           // END_COLLECTION

Here are some findings that I was able to see while testing:-

But the above descriptor will not work in every game, what I was able to find is that some games in Android has the option to configure/customize the button mapping like the DEAD TRIGGER 2 - Zombie Survival Shooter FPS, but in such games the default axis for the right joystick is the Rx and Ry, so in such games the right joystick and the triggers(the axes used for triggers is still a mystery) must be mapped explicitly.
But in games where there is no option to change the buttons mapping this HID descriptor will work correctly even the triggers(this made me believe that this is the correct way to define the descriptor).

How to implement Left and Right Analog Triggers in a HID Gamepad for Android

2 Answers2