Support coupled GL viewports for the dual-view healer

Add OrbitCamera.copyOrbitFrom (sync orbit/zoom/pan, keep per-viewport aspect),
and GLViewport interaction listener + requestRedraw + clearScene so two
viewports can share camera movement and be cleared/redrawn independently.

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

CityDoctorParent/Extensions/CityDoctorGUI/src/main/java/de/hft/stuttgart/citydoctor2/gui/gl/GLViewport.java

@@ -56,6 +56,10 @@ public class GLViewport {
     private double lastX;
     private double lastY;
 
+    // optional hook invoked after a camera interaction (orbit/pan/zoom) so a coupled viewport can be
+    // kept in sync and redrawn (used by the dual-viewport healer)
+    private Runnable interactionListener;
+
     // on-demand render request. openglfx can drop a repaint() that arrives while a frame is rendering
     // (its requestRepaint is an unconditional notify with no pending flag), so a single repaint is not
     // reliable. This flag + pump re-deliver repaint() each pulse until a frame consumes the request,
@@ -120,6 +124,19 @@ public class GLViewport {
 
     public OrbitCamera camera() { return camera; }
 
+    /** Hook invoked after a camera interaction so a coupled viewport can sync and redraw. */
+    public void setInteractionListener(Runnable listener) { this.interactionListener = listener; }
+
+    /** Public redraw trigger (e.g. for a coupled viewport). */
+    public void requestRedraw() { requestRender(); }
+
+    /** Clears the displayed geometry (draws nothing) until a new scene is set. */
+    public void clearScene() {
+        currentScene = null;
+        lastIndices = new int[0];
+        setIndexSet(new int[0]);
+    }
+
     /**
      * Requests a redraw. Sets the render flag, wakes the canvas immediately (best effort), and starts
      * the pump so the request is re-delivered until a frame actually consumes it. Call on the FX thread.
@@ -257,12 +274,20 @@ public class GLViewport {
                 camera.pan(-dx * speed, dy * speed);
             }
             requestRender();
+            notifyInteraction();
         });
         canvas.setOnScroll(e -> {
             camera.zoom(e.getDeltaY() < 0 ? 1.05 : 0.95);
             requestRender();
+            notifyInteraction();
         });
     }
 
     public void resetCamera() { camera.reset(); requestRender(); }
+
+    private void notifyInteraction() {
+        if (interactionListener != null) {
+            interactionListener.run();
+        }
+    }
 }

CityDoctorParent/Extensions/CityDoctorGUI/src/main/java/de/hft/stuttgart/citydoctor2/gui/gl/OrbitCamera.java

@@ -6,8 +6,8 @@ package de.hft.stuttgart.citydoctor2.gui.gl;
  */
 public class OrbitCamera {
 
-    private static final double INITIAL_AZIMUTH = 120.0;
-    private static final double INITIAL_ELEVATION = 20.0;
+    private static final double INITIAL_AZIMUTH = 180.0;
+    private static final double INITIAL_ELEVATION = -60.0;
     private static final double INITIAL_DISTANCE = 100.0;
     private static final double FOVY_RAD = Math.toRadians(30);
     private static final float NEAR = 0.1f;
@@ -57,6 +57,15 @@ public class OrbitCamera {
         panY = 0;
     }
 
+    /** Copies the orbit/zoom/pan state from another camera (but not its aspect ratio). */
+    public void copyOrbitFrom(OrbitCamera other) {
+        this.azimuthDeg = other.azimuthDeg;
+        this.elevationDeg = other.elevationDeg;
+        this.distance = other.distance;
+        this.panX = other.panX;
+        this.panY = other.panY;
+    }
+
     public double distance() { return distance; }
 
     /** Current azimuth (rotation about Z) in degrees. */