- UI refinement, button position ui file as source no dirty drafting anymore

src/fluency/rendering/occ_renderer.py

@@ -1013,7 +1013,7 @@ class OCCRenderer(Renderer):
     #   • Left button drag   → orbit (rotate around target)
     #   • Middle button drag → pan
     #   • Right button       → (reserved for future use)
-    #   • Wheel              → zoom toward cursor
+    #   • Wheel              → zoom centered on viewport
     #   • Double-click left  → fit all  (handled by the widget)
 
     def _qt_buttons(self, event) -> Any:
@@ -1079,20 +1079,19 @@ class OCCRenderer(Renderer):
             self._nav_mode = None
 
     def handle_wheel(self, event) -> None:
-        """Zoom toward the cursor on scroll."""
+        """Zoom centered on the viewport (body midpoint) on scroll.
+
+        Uses the view's scale factor so the zoom is always centered
+        on the viewport centre — the body never drifts to an edge.
+        """
         if self._view is None:
             return
-        # Qt6: QWheelEvent has no .x()/.y(); use position().toPoint().
-        pos = event.position().toPoint() if hasattr(event, "position") else event.pos()
-        x, y = pos.x(), pos.y()
         delta = event.angleDelta().y()
         if delta == 0:
             return
-        # ZoomAtPoint(startX, startY, endX, endY): move the cursor anchor
-        # by a few pixels to drive a smooth zoom centered on the pointer.
-        step = 30 if delta > 0 else -30
-        self._view.ZoomAtPoint(x, y, x, y - step)
-        self._view.ZFitAll()
+
+        factor = 1.15 if delta > 0 else 1.0 / 1.15
+        self._view.SetScale(self._view.Scale() * factor)
 
     def handle_resize(self, w: int, h: int) -> None:
         """Resize the OCC view when the widget is resized."""