ozone: evdev: Add gamepad support

ui/events/event.h

Index: ui/events/event.h
diff --git a/ui/events/event.h b/ui/events/event.h
index 16dce04e3a44e5133e15b5ddc442d38b83d6c56f..f69b416cf4eff159b3b11492c6bc0db4f51daced 100644
--- a/ui/events/event.h
+++ b/ui/events/event.h
@@ -35,6 +35,7 @@ class Transform;
 namespace ui {
 class CancelModeEvent;
 class EventTarget;
+class GamepadEvent;
 class KeyEvent;
 class LocatedEvent;
 class MouseEvent;
@@ -117,6 +118,12 @@ class EVENTS_EXPORT Event {
     return type_ == ET_CANCEL_MODE;
   }
 
+  bool IsGamepadEvent() const {
+    return type_ == ET_GAMEPAD_BTN_PRESSED ||
+           type_ == ET_GAMEPAD_BTN_RELEASED || type_ == ET_GAMEPAD_ABS_MOVED ||
+           type_ == ET_GAMEPAD_FRAME;
+  }
+
   bool IsKeyEvent() const {
     return type_ == ET_KEY_PRESSED || type_ == ET_KEY_RELEASED;
   }
@@ -241,6 +248,9 @@ class EVENTS_EXPORT Event {
   GestureEvent* AsGestureEvent();
   const GestureEvent* AsGestureEvent() const;
 
+  GamepadEvent* AsGamepadEvent();
+  const GamepadEvent* AsGamepadEvent() const;
+
   // Convenience methods to cast |this| to a KeyEvent. IsKeyEvent()
   // must be true as a precondition to calling these methods.
   KeyEvent* AsKeyEvent();
@@ -760,6 +770,26 @@ class EVENTS_EXPORT PointerEvent : public LocatedEvent {
   PointerDetails details_;
 };
 
+// A Gamepad event is very straignt forward. It contains the event type,
+// timestamp, event code and value. The code and vaule should follow w3c
+// "standard" gamepad.
+class EVENTS_EXPORT GamepadEvent : public Event {
+ public:
+  GamepadEvent(EventType type,
+               double value,
+               uint16_t code,
+               base::TimeTicks timestamp);
+
+  GamepadEvent(const GamepadEvent& gamepad_event);
+
+  double get_value() const { return value_; }
+  uint16_t get_code() const { return code_; }
+
+ private:
+  double value_;
+  uint16_t code_;

[sadrul, 2017/04/12 18:03:58]

Can you document what |value_| and |code_| represent? I went over
https://www.w3.org/TR/gamepad/, and couldn't figure out their meaning.

[jkwang, 2017/04/12 20:51:55]

Interface is here.
interface Gamepad {
    readonly attribute DOMString           id;
    readonly attribute long                index;
    readonly attribute boolean             connected;
    readonly attribute DOMHighResTimeStamp timestamp;
    readonly attribute GamepadMappingType  mapping;
    readonly attribute double[]            axes;
    readonly attribute GamepadButton[]     buttons;
};

Code is the index of axes or button, value is the axes value or button value.
The meaning is defined in ui/events/webgamepad_constants.h	. I will add more
comments here.

+};

[sadrul, 2017/04/10 18:14:05]

I feel like this should simply be a PointerEvent, with type set to a new 
POINTER_TYPE_GAMEPAD.

[jkwang, 2017/04/10 18:19:08]

Would it be confusing?

[dtapuska, 2017/04/10 19:13:35]

Game pad logically has no pointer position does it?

Gamepad isn't combined in W3C land so I guess the question is what similarities
exist between a pointing device and a gamepad device. I think a keyboard might
have more similarities to a gamepad device than a pointer (keys dowm,
repetition, etc). So I'm on the fence. 

I think to be a pointer you need a logical x/y location presented by the
hwd/device. I don't think a gamepad device presents that.

[jkwang, 2017/04/10 20:07:47]

Mostly, gamepad report EV_ABS and EV_KEY. So mapping it to "generic axis moving"
and Key event won't be a bad idea. (If my memory is correct, it is what was done
in android.) However, the event_converter part of gamepad does not really fit
into the keyboard event_converter. To map gamepads to w3c standard, we sometimes
need to map axis to button. With that said, I did not find a "generic axis
event". AND, the w3c gamepad button carry a double value
(https://www.w3.org/TR/gamepad/ )! If we are going to reuse KeyEvent, we need to
do some invasive change. I really want to avoid that.

+
 // A KeyEvent is really two distinct classes, melded together due to the
 // DOM legacy of Windows key events: a keystroke event (is_char_ == false),
 // or a character event (is_char_ == true).