Render GL viewport on demand instead of every frame

openglfx with fps=-1.0 repaints every JavaFX pulse (~60fps), allocating and
rendering continuously even when idle. Set fps=0.0 so a frame is drawn only
when repaint() is called (every state change and input already does), and add
canvas resize listeners to repaint on size changes. Idle now allocates nothing.

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

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

@@ -36,7 +36,7 @@ public class GLViewport {
     private volatile int[] lastIndices;
     private volatile boolean wireframe = false;
     private volatile boolean cull = false;
-    private volatile float pointScale = 14f;
+    private volatile float pointScale = 20f;
     private volatile float lineScale = 4f;
 
     // highlight marker data, uploaded on the GL thread when dirty
@@ -56,8 +56,10 @@ public class GLViewport {
     private double lastY;
 
     public GLViewport() {
-        // args: executor, profile, flipY=false, msaa=4 -> request a 4x multisampled framebuffer for AA
-        canvas = new GLCanvas(new JOGLExecutor(), GLProfile.CORE, false, 4);
+        // args: executor, profile, flipY=false, msaa=4, fps=0.0
+        // fps=0 -> on-demand rendering: a frame is drawn only when repaint() is called (every state
+        // change / input does so), so an idle viewport allocates and renders nothing.
+        canvas = new GLCanvas(new JOGLExecutor(), GLProfile.CORE, false, 4, 0.0);
         canvas.addOnInitEvent(ev -> {
             // GL context (re)created: shaders/buffers from any previous context are gone. Drop our
             // handles and re-queue the current scene so it is re-uploaded into the new context.
@@ -69,6 +71,9 @@ public class GLViewport {
         });
         canvas.addOnRenderEvent(ev -> render((JOGLRenderEvent) ev));
         canvas.addOnReshapeEvent(ev -> { /* aspect handled per-frame from width/height */ });
+        // on-demand mode: repaint when the canvas is resized so the framebuffer tracks the new size
+        canvas.widthProperty().addListener((obs, ov, nv) -> canvas.repaint());
+        canvas.heightProperty().addListener((obs, ov, nv) -> canvas.repaint());
         installInputHandlers();
     }