fix pinch zoom on mobile

lib/filament_gesture_detector.dart

@@ -83,8 +83,35 @@ class _FilamentGestureDetectorState extends State<FilamentGestureDetector> {
   Widget build(BuildContext context) {
     return Stack(children: [
       Positioned.fill(
+          // pinch zoom on mobile
+          // couldn't find any equivalent for pointerCount in Listener so we use two widgets:
+          // - outer is a GestureDetector only for pinch zoom
+          // - inner is a Listener for all other gestures
+          child: GestureDetector(
+              onScaleStart: (d) async {
+                if (d.pointerCount == 2) {
+                  await widget.controller.zoomEnd();
+                  await widget.controller.zoomBegin();
+                }
+              },
+              onScaleEnd: (d) async {
+                if (d.pointerCount == 2) {
+                  _lastScale = 0;
+                  await widget.controller.zoomEnd();
+                }
+              },
+              onScaleUpdate: (d) async {
+                if (d.pointerCount == 2) {
+                  if (_lastScale != 0) {
+                    await widget.controller
+                        .zoomUpdate(100 * (_lastScale - d.scale));
+                  }
+                }
+                _lastScale = d.scale;
+              },
               child: Listener(
                   onPointerSignal: (pointerSignal) async {
+                    // scroll-wheel zoom on desktop
                     if (pointerSignal is PointerScrollEvent) {
                       _scrollTimer?.cancel();
                       await widget.controller.zoomBegin();
@@ -98,50 +125,19 @@ class _FilamentGestureDetectorState extends State<FilamentGestureDetector> {
                       print(pointerSignal);
                     }
                   },
-              onPointerPanZoomStart: (pzs) {
+                  onPointerPanZoomStart: (pzs) {},
-                print(pzs);
-              },
                   onPointerDown: (d) async {
-                await _functionStart(d.localPosition.dx, d.localPosition.dy);
+                    await _functionStart(
+                        d.localPosition.dx, d.localPosition.dy);
                   },
                   onPointerMove: (d) async {
-                await _functionUpdate(d.localPosition.dx, d.localPosition.dy);
+                    await _functionUpdate(
+                        d.localPosition.dx, d.localPosition.dy);
                   },
                   onPointerUp: (d) async {
                     await _functionEnd();
                   },
-              // on
+                  child: widget.child))),
-              //   onScaleStart: (d) async {
-              //     print("SCALE START");
-              //     if (d.pointerCount == 2) {
-              //       await widget.controller.zoomEnd();
-              //       await widget.controller.zoomBegin();
-              //     } else {
-              //       await _functionStart(d.focalPoint.dx, d.focalPoint.dy);
-              //     }
-              //   },
-              //   onScaleEnd: (d) async {
-              //     print("SCALE END");
-
-              //     if (d.pointerCount == 2) {
-              //       _lastScale = 0;
-              //       await widget.controller.zoomEnd();
-              //     } else {
-              //       await _functionEnd();
-              //     }
-              //   },
-              //   onScaleUpdate: (d) async {
-              //     if (d.pointerCount == 2) {
-              //       if (_lastScale != 0) {
-              //         await widget.controller
-              //             .zoomUpdate(100 * (_lastScale - d.scale));
-              //       }
-              //     } else {
-              //       await _functionUpdate(d.focalPoint.dx, d.focalPoint.dy);
-              //     }
-              //     _lastScale = d.scale;
-              //   },
-              child: widget.child)),
       widget.showControls
           ? Align(
               alignment: Alignment.bottomRight,