Android: Add system menu

The system menu opens with 3-finger touch. Currently, it can only exit
the game.

android/app/src/main/java/io/github/kichikuou/system3/GameActivity.kt

@@ -22,6 +22,10 @@ import android.media.MediaPlayer
 import android.os.Bundle
 import android.text.InputType
 import android.util.Log
+import android.view.ContextMenu
+import android.view.Menu
+import android.view.MenuItem
+import android.view.View
 import android.widget.EditText
 import org.libsdl.app.SDLActivity
 import java.io.File
@@ -44,6 +48,7 @@ class GameActivity : SDLActivity() {
         super.onCreate(savedInstanceState)
         gameRoot = File(intent.getStringExtra(EXTRA_GAME_ROOT))
         cdda = CddaPlayer(File(gameRoot, Launcher.PLAYLIST_FILE))
+        registerForContextMenu(mLayout)
     }
 
     override fun onStop() {
@@ -97,6 +102,34 @@ class GameActivity : SDLActivity() {
                 .show()
     }
 
+    private var menuShown = false
+    private fun openMenu() {
+        if (menuShown)
+            return
+        openContextMenu(mLayout)
+        menuShown = true
+    }
+
+    override fun onCreateContextMenu(menu: ContextMenu?, v: View?, menuInfo: ContextMenu.ContextMenuInfo?) {
+        super.onCreateContextMenu(menu, v, menuInfo)
+        menuInflater.inflate(R.menu.game_menu, menu)
+    }
+
+    override fun onContextItemSelected(item: MenuItem): Boolean {
+        return when (item.itemId) {
+            R.id.quit_game -> {
+                finish()
+                true
+            }
+            else -> super.onOptionsItemSelected(item)
+        }
+    }
+
+    override fun onContextMenuClosed(menu: Menu?) {
+        super.onContextMenuClosed(menu)
+        menuShown = false
+    }
+
     // The functions below are called in the SDL thread by JNI.
     @Suppress("unused") fun cddaStart(track: Int, loop: Boolean) = cdda.start(track, loop)
     @Suppress("unused") fun cddaStop() = cdda.stop()
@@ -118,6 +151,10 @@ class GameActivity : SDLActivity() {
         }
         return result[0]
     }
+
+    @Suppress("unused") fun popupMenu() {
+        runOnUiThread { openMenu() }
+    }
 }
 
 private class CddaPlayer(private val playlistPath: File) {