Export built-in fonts as j3o to remove PNG loader dependency in jme3-core (#2832)

* Initial plan

* Export Default.fnt and Console.fnt as j3o with embedded image data

The fonts Default.fnt and Console.fnt reference PNG textures (Default.png,
Console.png) which require StbImageLoader from jme3-plugins to load.
jme3-android and jme3-ios include General.cfg (which registers StbImageLoader)
but only depend on jme3-core, not jme3-plugins, causing failures when the
engine tries to display the default stats/UI.

Fix: export both fonts as .j3o binary files with the texture image data
embedded directly (no asset key, so no PNG loader needed at runtime).
Update all jme3-core load sites to use the .j3o variants.

Add DefaultFontJ3oTest to verify Default.j3o loads without a PNG loader.

* Add Console.j3o test and refactor DefaultFontJ3oTest helper

* Remove unnecessary loader registrations from DefaultFontJ3oTest

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

jme3-core/src/main/java/com/jme3/app/DetailedProfilerState.java

@@ -108,8 +108,8 @@ protected void initialize(Application app) {
 
         ui.attachChild(darkenStats);
         ui.setLocalTranslation(app.getCamera().getWidth() - PANEL_WIDTH, app.getCamera().getHeight(), 0);
-        font = app.getAssetManager().loadFont("Interface/Fonts/Console.fnt");
-        bigFont = app.getAssetManager().loadFont("Interface/Fonts/Default.fnt");
+        font = app.getAssetManager().loadFont("Interface/Fonts/Console.j3o");
+        bigFont = app.getAssetManager().loadFont("Interface/Fonts/Default.j3o");
         prof.setRenderer(app.getRenderer());
         rootLine = new StatLineView("Frame");
         rootLine.attachTo(ui);

jme3-core/src/main/java/com/jme3/app/SimpleApplication.java

@@ -248,7 +248,7 @@ public void setShowSettings(boolean showSettings) {
      * @return the loaded BitmapFont
      */
     protected BitmapFont loadGuiFont() {
-        return assetManager.loadFont("Interface/Fonts/Default.fnt");
+        return assetManager.loadFont("Interface/Fonts/Default.j3o");
     }
 
     @Override

jme3-core/src/main/java/com/jme3/app/StatsAppState.java

@@ -155,7 +155,7 @@ public void initialize(AppStateManager stateManager, Application app) {
         }
 
         if (guiFont == null) {
-            guiFont = app.getAssetManager().loadFont("Interface/Fonts/Default.fnt");
+            guiFont = app.getAssetManager().loadFont("Interface/Fonts/Default.j3o");
         }
 
         loadFpsText();

jme3-core/src/main/java/com/jme3/app/StatsView.java

@@ -82,7 +82,7 @@ public StatsView(String name, AssetManager manager, Statistics stats) {
         statLabels = statistics.getLabels();
         statData = new int[statLabels.length];
 
-        BitmapFont font = manager.loadFont("Interface/Fonts/Console.fnt");
+        BitmapFont font = manager.loadFont("Interface/Fonts/Console.j3o");
         statText = new BitmapText(font);
         statText.setLocalTranslation(0, statText.getLineHeight() * statLabels.length, 0);
         attachChild(statText);

jme3-core/src/main/java/com/jme3/input/virtual/VirtualJoystickTheme.java

@@ -45,7 +45,7 @@
  */
 public class VirtualJoystickTheme implements Savable {
 
-    private static final String DEFAULT_FONT = "Interface/Fonts/Default.fnt";
+    private static final String DEFAULT_FONT = "Interface/Fonts/Default.j3o";
 
     public enum TextureKey {
         BUTTON,

jme3-core/src/main/resources/Interface/Fonts/Console.j3o

@@ -0,0 +1,47 @@
+package com.jme3.asset;
+
+import com.jme3.asset.plugins.ClasspathLocator;
+import com.jme3.export.binary.BinaryLoader;
+import com.jme3.font.BitmapFont;
+import com.jme3.material.plugins.J3MLoader;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+/**
+ * Verifies that Default.j3o (with embedded image data) can be loaded using only
+ * the loaders available in jme3-core, without depending on the PNG loader from
+ * jme3-plugins. This is needed for Android/iOS which don't depend on jme3-plugins.
+ */
+public class DefaultFontJ3oTest {
+
+    private static DesktopAssetManager createCoreOnlyAssetManager() {
+        DesktopAssetManager assetManager = new DesktopAssetManager(false);
+        assetManager.registerLocator("/", ClasspathLocator.class);
+        assetManager.registerLoader(BinaryLoader.class, "j3o", "j3f");
+        assetManager.registerLoader(J3MLoader.class, "j3m", "j3md");
+        return assetManager;
+    }
+
+    private static void assertFontLoaded(DesktopAssetManager assetManager, String path) {
+        BitmapFont font = assetManager.loadFont(path);
+        assertNotNull(font, path + " should load without a PNG loader");
+        assertNotNull(font.getPage(0), path + " should have at least one material page");
+        assertNotNull(font.getPage(0).getTextureParam("ColorMap"),
+                path + " material page should have a ColorMap texture");
+        assertNotNull(font.getPage(0).getTextureParam("ColorMap").getTextureValue().getImage(),
+                path + " texture should have embedded image data (no key needed)");
+    }
+
+    @Test
+    public void testDefaultFontJ3oLoadsWithoutPngLoader() {
+        // This should succeed: Default.j3o has embedded image data (no PNG loader needed)
+        assertFontLoaded(createCoreOnlyAssetManager(), "Interface/Fonts/Default.j3o");
+    }
+
+    @Test
+    public void testConsoleFontJ3oLoadsWithoutPngLoader() {
+        // This should succeed: Console.j3o has embedded image data (no PNG loader needed)
+        assertFontLoaded(createCoreOnlyAssetManager(), "Interface/Fonts/Console.j3o");
+    }
+}