Provide a library interface to the virtual touchpad service.

And make VrWindowManager pay for^H^H^H^H^H^H^H^H use it. The library
interface is a step toward moving 2D embedding into VrCore because it
hides the binder connection that isn't directly accessible to VrCore.

As a matter of implementation, the touchpad-service client library
and the low-level evdev touchpad are derived from the same interface.

Bug: b/35990873
Test: VirtualTouchpad_test; integration TBD.
Change-Id: Ic922ff223ddd5a44f6fb4433a271f8341e93a0e7
diff --git a/services/vr/virtual_touchpad/VirtualTouchpadEvdev.h b/services/vr/virtual_touchpad/VirtualTouchpadEvdev.h
new file mode 100644
index 0000000..c763529
--- /dev/null
+++ b/services/vr/virtual_touchpad/VirtualTouchpadEvdev.h
@@ -0,0 +1,59 @@
+#ifndef ANDROID_DVR_VIRTUAL_TOUCHPAD_EVDEV_H
+#define ANDROID_DVR_VIRTUAL_TOUCHPAD_EVDEV_H
+
+#include <memory>
+
+#include "VirtualTouchpad.h"
+#include "EvdevInjector.h"
+
+namespace android {
+namespace dvr {
+
+class EvdevInjector;
+
+// VirtualTouchpadEvdev implements a VirtualTouchpad by injecting evdev events.
+//
+class VirtualTouchpadEvdev : public VirtualTouchpad {
+ public:
+  static sp<VirtualTouchpad> Create();
+
+  // VirtualTouchpad implementation:
+  status_t Touch(float x, float y, float pressure) override;
+  status_t ButtonState(int buttons) override;
+
+ protected:
+  VirtualTouchpadEvdev() {}
+  ~VirtualTouchpadEvdev() {}
+  status_t Initialize();
+
+  // Must be called only between construction and Initialize().
+  inline void SetEvdevInjectorForTesting(EvdevInjector* injector) {
+    injector_ = injector;
+  }
+
+ private:
+  // Except for testing, the |EvdevInjector| used to inject evdev events.
+  std::unique_ptr<EvdevInjector> owned_injector_;
+
+  // Active pointer to |owned_injector_| or to a testing injector.
+  EvdevInjector* injector_ = nullptr;
+
+  // Previous (x, y) position in device space, to suppress redundant events.
+  int32_t last_device_x_ = INT32_MIN;
+  int32_t last_device_y_ = INT32_MIN;
+
+  // Records current touch state (0=up 1=down) in bit 0, and previous state
+  // in bit 1, to track transitions.
+  int touches_ = 0;
+
+  // Previous injected button state, to detect changes.
+  int32_t last_motion_event_buttons_ = 0;
+
+  VirtualTouchpadEvdev(const VirtualTouchpadEvdev&) = delete;
+  void operator=(const VirtualTouchpadEvdev&) = delete;
+};
+
+}  // namespace dvr
+}  // namespace android
+
+#endif  // ANDROID_DVR_VIRTUAL_TOUCHPAD_EVDEV_H