[NOT FOR MERGE] Add opt-in virtual mouse pointer for touch devices

Provide a trackpad-style on-screen cursor for touch environments (mainly
Android), where touching the screen previously jumped the pointer to the
touched location (absolute) and SDL hardware cursors are invisible.

When enabled, a finger drag moves an arrow cursor relatively, a tap
left-clicks (held briefly so polling games detect it), two fingers
right-click, and a stationary long press starts a left-button drag. Real
mouse motion is ignored (including the spurious startup (0,0) event), and
program-driven cursor moves are followed via the internal pointer location
instead of warping the OS cursor.

The feature is disabled by default and enabled via the -virtualpointer
command-line option, the virtualpointer profile setting, or the "Virtual
mouse pointer" toggle in the Android launcher (persisted in
SharedPreferences and passed to the engine as -virtualpointer).

The gesture handling lives in event.c and the cursor rendering in the new
platform-independent virtual_pointer module, so it works on any touch
target.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

android/app/src/main/java/io/github/kichikuou/xsystem35/GameActivity.kt

@@ -61,9 +61,13 @@ class GameActivity : SDLActivity() {
     }
 
     override fun getArguments(): Array<String> {
-        return arrayOf(
+        val args = mutableListOf(
             "-gamedir", intent.getStringExtra(EXTRA_GAME_ROOT)!!,
             "-savedir", intent.getStringExtra(EXTRA_SAVE_DIRECTORY)!!)
+        val prefs = getSharedPreferences(Launcher.PREFS_NAME, MODE_PRIVATE)
+        if (prefs.getBoolean(Launcher.PREF_VIRTUAL_POINTER, false))
+            args.add("-virtualpointer")
+        return args.toTypedArray()
     }
 
     override fun setTitle(title: CharSequence?) {

android/app/src/main/java/io/github/kichikuou/xsystem35/Launcher.kt

@@ -42,6 +42,8 @@ interface LauncherObserver {
 class Launcher private constructor(private val rootDir: File) {
     companion object {
         const val SAVE_DIR = "save"
+        const val PREFS_NAME = "settings"
+        const val PREF_VIRTUAL_POINTER = "virtual_pointer"
         const val TITLE_FILE = "title.txt"
         const val GAMEDIR_FILE = "game_directory.txt"
         const val PLAYLIST_FILE = "playlist.txt"

android/app/src/main/java/io/github/kichikuou/xsystem35/LauncherActivity.kt

@@ -92,6 +92,9 @@ class LauncherActivity : Activity(), LauncherObserver {
 
     override fun onCreateOptionsMenu(menu: Menu): Boolean {
         menuInflater.inflate(R.menu.launcher_menu, menu)
+        val prefs = getSharedPreferences(Launcher.PREFS_NAME, MODE_PRIVATE)
+        menu.findItem(R.id.virtual_pointer).isChecked =
+            prefs.getBoolean(Launcher.PREF_VIRTUAL_POINTER, false)
         return true
     }
 
@@ -143,6 +146,13 @@ class LauncherActivity : Activity(), LauncherObserver {
                 startActivity(intent)
                 true
             }
+            R.id.virtual_pointer -> {
+                val enabled = !item.isChecked
+                item.isChecked = enabled
+                getSharedPreferences(Launcher.PREFS_NAME, MODE_PRIVATE).edit()
+                    .putBoolean(Launcher.PREF_VIRTUAL_POINTER, enabled).apply()
+                true
+            }
             else -> super.onOptionsItemSelected(item)
         }
     }

android/app/src/main/res/menu/launcher_menu.xml

@@ -12,6 +12,10 @@
     <item
         android:id="@+id/clear_savedata"
         android:title="@string/action_clear_save_data" />
+    <item
+        android:id="@+id/virtual_pointer"
+        android:checkable="true"
+        android:title="@string/action_virtual_pointer" />
     <item
         android:id="@+id/help"
         android:title="@string/action_help" />

android/app/src/main/res/values-ja/strings.xml

@@ -7,6 +7,7 @@
     <string name="action_install_from_zip">ZIPからインストール</string>
     <string name="action_licenses">オープンソースライセンス</string>
     <string name="action_clear_save_data">セーブデータをクリア</string>
+    <string name="action_virtual_pointer">仮想マウスポインタ</string>
     <string name="cancel">キャンセル</string>
     <string name="cannot_find_ald">System 3.x のファイル (*.ald) が見つかりません。</string>
     <string name="choose_a_file">ファイルを選択</string>

android/app/src/main/res/values/strings.xml

@@ -6,6 +6,7 @@
     <string name="action_import_save_data">Import Save Files</string>
     <string name="action_install_from_zip">Install from ZIP</string>
     <string name="action_licenses">Open source licenses</string>
+    <string name="action_virtual_pointer">Virtual mouse pointer</string>
     <string name="cancel">Cancel</string>
     <string name="cannot_find_ald">Cannot find System 3.x game files (*.ald).</string>
     <string name="choose_a_file">Choose a file</string>