rough, this is a waste of tokens...

core/src/main/java/dev/quoije/umd/rco/object/BasePositionObject.java

@@ -64,26 +64,14 @@ public class BasePositionObject extends BaseObject {
 
     @Override
     public int getWidth() {
-        float w = width.getFloatValue();
+        // A zero authored size means "use the image's natural size"; the
-        if (w == 0f) {
+        // renderer falls back to the decoded image dimensions when this is 0.
-            Object image = getImage();
+        return Math.round(width.getFloatValue() * scaleWidth.getFloatValue());
-            if (image == null) {
-                w = 0f;
-            }
-        }
-        return Math.round(w * scaleWidth.getFloatValue());
     }
 
     @Override
     public int getHeight() {
-        float h = height.getFloatValue();
+        return Math.round(height.getFloatValue() * scaleHeight.getFloatValue());
-        if (h == 0f) {
-            Object image = getImage();
-            if (image == null) {
-                h = 0f;
-            }
-        }
-        return Math.round(h * scaleHeight.getFloatValue());
     }
 
     @Override

core/src/main/java/dev/quoije/umd/rco/vsmx/interpreter/VsmxInterpreter.java

@@ -458,9 +458,23 @@ public final class VsmxInterpreter {
 
     /** Runs the script's main body, populating the given global variables object. */
     public synchronized void run(VsmxObject globalVariables) {
+        // This can be invoked re-entrantly (Controller.changeResource loads and
+        // runs a new resource while the previous resource's script is still on
+        // the stack), so the outer execution state must be preserved and
+        // restored exactly like interpretFunction does. Without this, the
+        // nested run clobbers pc/exit/stack/callStates and the outer script
+        // crashes with a null operand stack after the nested run returns.
+        int savedPc = pc;
+        boolean savedExit = exit;
+        Deque<VsmxBaseObject> savedStack = stack;
+        Deque<VsmxCallState> savedCallStates = callStates;
+        VsmxCallState savedCallState = callState;
+
         pc = 0;
         exit = false;
         callStates = new ArrayDeque<>();
+        stack = null;
+        callState = null;
         pushCallState(VsmxNull.singleton, 0, false, true);
         this.globalVariables = globalVariables;
 
@@ -470,8 +484,16 @@ public final class VsmxInterpreter {
 
         interpret();
 
-        callStates.clear();
+        pc = savedPc;
-        callState = null;
+        exit = savedExit;
+        stack = savedStack;
+        callStates = savedCallStates;
+        callState = savedCallState;
+    }
+
+    /** Requests the currently-running script to stop after the current instruction. */
+    public void stop() {
+        exit = true;
     }
 
     private void callFunction(VsmxFunction function, VsmxBaseObject thisObject, VsmxBaseObject[] arguments,

core/src/main/java/dev/quoije/umd/rco/vsmx/objects/Controller.java

@@ -68,6 +68,10 @@ public class Controller extends BaseNativeObject {
         if (!resource.equals(resourceName)) {
             resource = resourceName;
             menuHost.changeResource(resourceName);
+            // The resource switch abandons this interpreter; stop the script
+            // that requested it so it does not keep running against a stale
+            // menu (the PSP drops the old resource's script at this point).
+            interpreter.stop();
         }
         return VsmxBoolean.getValue(true);
     }

core/src/main/java/dev/quoije/umd/rco/vsmx/objects/GlobalVariables.java

@@ -50,7 +50,7 @@ public class GlobalVariables extends BaseNativeObject {
     }
 
     public void writeln(VsmxBaseObject object, VsmxBaseObject s1, VsmxBaseObject s2, VsmxBaseObject s3) {
-        log.append(s1.getStringValue()).append(s3.getStringValue()).append('\n');
+        log.append(s1.getStringValue()).append(s2.getStringValue()).append(s3.getStringValue()).append('\n');
     }
 
     public VsmxBaseObject parseFloat(VsmxBaseObject object, VsmxBaseObject value) {

core/src/main/java/dev/quoije/umd/rco/vsmx/objects/Timer.java

@@ -76,7 +76,10 @@ public class Timer extends BaseNativeObject {
             if (due != null) {
                 if (due.function instanceof VsmxFunction f) {
                     synchronized (callbackLock) {
-                        interpreter.interpretFunction(f, due.object, due.params);
+                        // Fire on the interpreter that compiled the callback so
+                        // timers survive a resource switch (each resource owns
+                        // its own interpreter).
+                        f.getInterpreter().interpretFunction(f, due.object, due.params);
                     }
                 }
                 continue;

ui/src/main/java/dev/quoije/umd/ui/PlayerApp.java

@@ -72,6 +72,17 @@ public final class PlayerApp extends Application {
     private volatile VsmxNativeObject controllerObject;
     private long lastMenuKeyNanos = 0;
 
+    /** The open disc image, kept for the lifetime of the app so menu resources
+     *  (RCO files) can be switched at runtime. */
+    private volatile UmdIsoReader iso;
+    private volatile String isoPath;
+    private volatile Playlist playlist;
+    /** The script global scope, shared across resource switches so globals
+     *  (e.g. {@code g_nResChangeInfo}) survive. */
+    private volatile VsmxNativeObject globalVariables;
+    /** False until the first resource has run; later loads fire onChangeResource. */
+    private boolean resourceInitialized;
+
     /** The active decode engine, closed when a new stream starts. */
     private volatile PlaybackEngine currentEngine;
     /** Bumped each time playback starts so stale streams stop themselves. */
@@ -173,25 +184,55 @@ public final class PlayerApp extends Application {
     }
 
     private void loadMenu(String isoPath) {
-        try (UmdIsoReader iso = new UmdIsoReader(Path.of(isoPath))) {
+        try {
-            Playlist playlist = Playlist.parse(iso);
+            this.iso = new UmdIsoReader(Path.of(isoPath));
-            byte[] rcoData = readFile(iso, "UMD_VIDEO/RESOURCE/EN100000.RCO");
+            this.isoPath = isoPath;
+            this.playlist = Playlist.parse(iso);
+            this.resourceInitialized = false;
+            loadResource("EN100000");
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
+    /** Loads (or switches to) a menu resource and starts its script. */
+    private void loadResource(String resourceName) {
+        UmdIsoReader disc = iso;
+        if (disc == null) {
+            return;
+        }
+
+        try {
+            byte[] rcoData = readFile(disc, "UMD_VIDEO/RESOURCE/" + resourceName + ".RCO");
             if (rcoData == null) {
-                System.err.println("EN100000.RCO not found");
+                System.err.println("Menu resource not found: " + resourceName + ".RCO");
                 return;
             }
 
             RcoFile rco = new RcoFile(rcoData);
             if (!rco.isValid()) {
-                System.err.println("RCO invalid");
+                System.err.println("RCO invalid: " + resourceName);
                 return;
             }
 
-            Vsmx vsmx = new Vsmx(rco.vsmxData(), "main");
+            // Each resource gets a fresh interpreter so that switching
+            // resources never swaps the bytecode out from under an already
+            // running script (the old script keeps its own code and state).
             VsmxInterpreter interpreter = new VsmxInterpreter();
+            Vsmx vsmx = new Vsmx(rco.vsmxData(), "main");
             interpreter.setVsmx(vsmx);
+            this.menuInterpreter = interpreter;
+            if (this.globalVariables == null) {
+                this.globalVariables = GlobalVariables.create(interpreter, SCREEN_WIDTH, SCREEN_HEIGHT);
+            }
 
+            if (renderer == null) {
                 renderer = new RcoRenderer(menuCanvas);
+            } else {
+                // The previous resource's object tree belongs to a different
+                // script; drop it before the new page tree is registered.
+                renderer.changeResource();
+            }
 
             MenuHost menuHost = new MenuHost() {
                 @Override
@@ -199,7 +240,7 @@ public final class PlayerApp extends Application {
                                       int audioFlag, int subtitleNumber, int subtitleFlag) {
                     Playlist.Stream stream = playlist.streamForPlayListNumber(playListNumber);
                     if (stream != null) {
-                        startPlayback(isoPath, stream, playListNumber);
+                        startPlayback(PlayerApp.this.isoPath, stream, playListNumber);
                     }
                 }
 
@@ -214,26 +255,32 @@ public final class PlayerApp extends Application {
                 }
 
                 @Override
-                public void changeResource(String resourceName) {
+                public void changeResource(String newResource) {
+                    loadResource(newResource);
                 }
             };
 
-            VsmxNativeObject globals = GlobalVariables.create(interpreter, SCREEN_WIDTH, SCREEN_HEIGHT);
+            VsmxNativeObject controllerObject = Controller.create(interpreter, menuHost, resourceName);
-            VsmxNativeObject controllerObject = Controller.create(interpreter, menuHost, "EN100000");
             VsmxNativeObject movieplayer = MoviePlayer.create(interpreter, menuHost, controllerObject);
             VsmxNativeObject resource = Resource.create(interpreter, renderer, controllerObject, rco);
             VsmxNativeObject math = Math.create(interpreter);
-            globals.setPropertyValue(Controller.objectName, controllerObject);
+            globalVariables.setPropertyValue(Controller.objectName, controllerObject);
-            globals.setPropertyValue(MoviePlayer.objectName, movieplayer);
+            globalVariables.setPropertyValue(MoviePlayer.objectName, movieplayer);
-            globals.setPropertyValue(Resource.objectName, resource);
+            globalVariables.setPropertyValue(Resource.objectName, resource);
-            globals.setPropertyValue(Math.objectName, math);
+            globalVariables.setPropertyValue(Math.objectName, math);
+
+            interpreter.run(globalVariables);
 
-            interpreter.run(globals);
             controller = (Controller) controllerObject.getObject();
             moviePlayer = (MoviePlayer) movieplayer.getObject();
-            menuInterpreter = interpreter;
             this.controllerObject = controllerObject;
+
+            if (!resourceInitialized) {
+                resourceInitialized = true;
                 controller.callCallback(interpreter, "onAutoPlay", null);
+            } else {
+                controller.callCallback(interpreter, "onChangeResource", null);
+            }
         } catch (Exception e) {
             e.printStackTrace();
         }

ui/src/main/java/dev/quoije/umd/ui/RcoRenderer.java

@@ -11,6 +11,7 @@ import javafx.application.Platform;
 import javafx.scene.canvas.Canvas;
 import javafx.scene.canvas.GraphicsContext;
 import javafx.scene.image.Image;
+import javafx.scene.image.WritableImage;
 
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
@@ -158,10 +159,28 @@ public final class RcoRenderer implements Display {
         if (data == null || data.length == 0) {
             return null;
         }
+        // Decode synchronously through ImageIO. JavaFX's `new Image(InputStream)`
+        // loads in the background and `GraphicsContext.drawImage` silently skips
+        // images whose pixels have not been uploaded yet, which leaves the whole
+        // menu invisible even though the image headers are readable.
         try (ByteArrayInputStream in = new ByteArrayInputStream(data)) {
-            return new Image(in);
+            java.awt.image.BufferedImage buffered = javax.imageio.ImageIO.read(in);
+            if (buffered == null) {
+                return null;
+            }
+            return toFxImage(buffered);
         } catch (IOException e) {
             return null;
         }
     }
+
+    private static Image toFxImage(java.awt.image.BufferedImage buffered) {
+        int w = buffered.getWidth();
+        int h = buffered.getHeight();
+        int[] argb = new int[w * h];
+        buffered.getRGB(0, 0, w, h, argb, 0, w);
+        WritableImage image = new WritableImage(w, h);
+        image.getPixelWriter().setPixels(0, 0, w, h, javafx.scene.image.PixelFormat.getIntArgbInstance(), argb, 0, w);
+        return image;
+    }
 }