[Android] Simple haptic feedback

HapticFeedbackConstants.KEYBOARD_TAP on all keypress and touchpad down
events triggered by QML.

Fixes #115

core/os/os-android.cpp

@@ -155,3 +155,33 @@ char *android_basename(const char *path)
 
     return nullptr;
 }
+
+void androidVibrate()
+{
+    QAndroidJniEnvironment env;
+
+    // Call activity.getWindow().getDecorView().perforHapticFeedback(KEYBOARD_TAP);
+    QAndroidJniObject window = QtAndroid::androidActivity()
+            .callObjectMethod("getWindow", "()Landroid/view/Window;");
+
+    QAndroidJniObject decorView = window.callObjectMethod("getDecorView", "()Landroid/view/View;");
+
+    if (env->ExceptionCheck())
+    {
+        env->ExceptionDescribe();
+        env->ExceptionClear();
+        return;
+    }
+
+    bool success = decorView.callMethod<jboolean>("performHapticFeedback", "(I)Z", 3); // HapticFeedbackConstants.KEYBOARD_TAP
+
+    if (env->ExceptionCheck())
+    {
+        env->ExceptionDescribe();
+        env->ExceptionClear();
+        return;
+    }
+
+    if (!success)
+        qInfo() << "Haptic feedback failed";
+}

core/os/os.h

@@ -25,6 +25,8 @@ FILE *fopen_utf8(const char *filename, const char *mode);
 #if defined(__ANDROID__)
 /* Returns an allocated string or NULL on failure. */
 char *android_basename(const char *path);
+/* KEYBOARD_TAP vibration for the current View. */
+void androidVibrate();
 #endif
 
 void *os_reserve(size_t size);

qmlbridge.cpp

@@ -256,13 +256,23 @@ void QMLBridge::setButtonState(int id, bool state)
 {
     int col = id % KEYPAD_COLS, row = id / KEYPAD_COLS;
 
+#ifdef Q_OS_ANDROID
+    if (state)
+        androidVibrate();
+#endif
+
     ::keypad_set_key(row, col, state);
 }
 
 void QMLBridge::setTouchpadState(qreal x, qreal y, bool contact, bool down)
 {
     ::touchpad_set_state(x, y, contact, down);
 
+#ifdef Q_OS_ANDROID
+    if (down)
+        androidVibrate();
+#endif
+
     touchpadStateChanged();
 }