found a bug on uiFixture and the only solution would be creating a cut-down copy of the original ui

src/net/torvald/terrarum/Terrarum.kt

@@ -713,7 +713,7 @@ fun printStackTrace(obj: Any, out: PrintStream = System.out) {
 }
 
 class UIContainer {
-    private val data = ArrayList<Any>()
+    internal val data = ArrayList<Any>()
     fun add(vararg things: Any) {
         things.forEach {
             if (it is UICanvas || it is Id_UICanvasNullable)
@@ -741,8 +741,28 @@ class UIContainer {
             else throw IllegalArgumentException("Unacceptable type ${it.javaClass.name}, instance of ${it.javaClass.superclass.name}")
         }
     }
+    fun iterator2() = object : Iterator<Pair<Int, UICanvas?>> {
+        private var cursor = 0
+
+        override fun hasNext() = cursor < data.size
+
+        override fun next(): Pair<Int, UICanvas?> {
+            val it = data[cursor]
+            // whatever the fucking reason when() does not work
+            if (it is UICanvas) {
+                cursor += 1
+                return (cursor - 1) to it
+            }
+            else if (it is Id_UICanvasNullable) {
+                cursor += 1
+                return (cursor - 1) to it.get()
+            }
+            else throw IllegalArgumentException("Unacceptable type ${it.javaClass.name}, instance of ${it.javaClass.superclass.name}")
+        }
+    }
 
     fun forEach(operation: (UICanvas?) -> Unit) = iterator().forEach(operation)
+    fun forEachIndexed(operation: (Pair<Int, UICanvas?>) -> Unit) = iterator2().forEach(operation)
     fun countVisible(): Int {
         var c = 0
         forEach { if (it?.isVisible == true) c += 1 }

src/net/torvald/terrarum/TerrarumPostProcessor.kt

@@ -11,9 +11,11 @@ import com.jme3.math.FastMath
 import net.torvald.random.HQRNG
 import net.torvald.terrarum.App.IS_DEVELOPMENT_BUILD
 import net.torvald.terrarum.gamecontroller.KeyToggler
+import net.torvald.terrarum.savegame.toHex
 import net.torvald.terrarum.ui.BasicDebugInfoWindow
 import net.torvald.terrarum.ui.Toolkit
 import net.torvald.terrarum.weather.WeatherMixer
+import net.torvald.unsafe.UnsafeHelper
 
 /**
  * Must be called by the App Loader
@@ -150,7 +152,7 @@ object TerrarumPostProcessor : Disposable {
                         // print UIs under cursor
                         App.fontSmallNumbers.draw(it, "${ccY}UIs under mouse:", 2f, 15f)
                         Terrarum.ingame?.uiContainer?.UIsUnderMouse?.forEachIndexed { i, ui ->
-                            App.fontSmallNumbers.draw(it, "${ccY}-$ccG ${ui.javaClass.simpleName}", 2f, 28f + 13*i)
+                            App.fontSmallNumbers.draw(it, "${ccY}-$ccG ${ui.javaClass.simpleName} (0x${UnsafeHelper.addressOf(ui).toHex()})", 2f, 28f + 13*i)
                         }
                     }
                 }

src/net/torvald/terrarum/modulebasegame/TerrarumIngame.kt

@@ -1011,6 +1011,8 @@ open class TerrarumIngame(batch: FlippingSpriteBatch) : IngameInstance(batch) {
             filterVisibleActors()
         }
 
+        if (uiInventoryPlayer == uiFixture) throw IllegalStateException("Do NOT use InventoryPlayer as a UIFixture, the engine cannot handle this situation XwX")
+
         uiContainer.forEach {
 
             // suppress inventory opening if fixture inventory is opened

src/net/torvald/unsafe/UnsafePtr.kt

@@ -58,6 +58,20 @@ internal object UnsafeHelper {
      * @return offset from the array's base memory address (aka pointer) that the actual data begins.
      */
     fun getArrayOffset(obj: Any) = unsafe.arrayBaseOffset(obj.javaClass).toLong()
+
+
+    fun addressOf(o: Any): Long {
+        val array = arrayOf(o)
+
+        val baseOffset = unsafe.arrayBaseOffset(Array<Any>::class.java).toLong()
+        val addressSize = unsafe.addressSize()
+        val objectAddress = when (addressSize) {
+            4 -> unsafe.getInt(array, baseOffset).toLong()
+            8 -> unsafe.getLong(array, baseOffset)
+            else -> throw Error("unsupported address size: $addressSize")
+        }
+        return (objectAddress)
+    }
 }
 
 /**