fix: correct PolygonLayer.useAltRenderer renderer when Polygons have multiple holes

lib/src/layer/polygon_layer/painter.dart

@@ -22,13 +22,17 @@ base class _PolygonPainter<R extends Object>
   /// Whether to draw labels last and thus over all the polygons
   final bool drawLabelsLast;
 
+  /// See [PolygonLayer.debugAltRenderer]
+  final bool debugAltRenderer;
+
   /// Create a new [_PolygonPainter] instance.
   _PolygonPainter({
     required this.polygons,
     required this.triangles,
     required super.camera,
     required this.polygonLabels,
     required this.drawLabelsLast,
+    required this.debugAltRenderer,
     required super.hitNotifier,
   }) : bounds = camera.visibleBounds;
 
@@ -113,6 +117,50 @@ base class _PolygonPainter<R extends Object>
             }
             final vertices = Vertices.raw(VertexMode.triangles, points);
             canvas.drawVertices(vertices, BlendMode.src, paint);
+
+            if (debugAltRenderer) {
+              for (int i = 0; i < trianglePoints.length; i += 3) {
+                canvas.drawCircle(
+                  trianglePoints[i],
+                  5,
+                  Paint()..color = const Color(0x7EFF0000),
+                );
+                canvas.drawCircle(
+                  trianglePoints[i + 1],
+                  5,
+                  Paint()..color = const Color(0x7E00FF00),
+                );
+                canvas.drawCircle(
+                  trianglePoints[i + 2],
+                  5,
+                  Paint()..color = const Color(0x7E0000FF),
+                );
+
+                final path = Path()
+                  ..addPolygon(
+                    [
+                      trianglePoints[i],
+                      trianglePoints[i + 1],
+                      trianglePoints[i + 2],
+                    ],
+                    true,
+                  );
+
+                canvas.drawPath(
+                  path,
+                  Paint()
+                    ..color = const Color(0x7EFFFFFF)
+                    ..style = PaintingStyle.fill,
+                );
+
+                canvas.drawPath(
+                  path,
+                  Paint()
+                    ..color = const Color(0xFF000000)
+                    ..style = PaintingStyle.stroke,
+                );
+              }
+            }
           } else {
             canvas.drawPath(filledPath, paint);
           }
@@ -151,6 +199,25 @@ base class _PolygonPainter<R extends Object>
             polygonTriangles != null ? projectedPolygon.holePoints : null,
       );
 
+      if (debugAltRenderer) {
+        const offsetsLabelStyle = TextStyle(
+          color: Color(0xFF000000),
+          fontSize: 16,
+        );
+
+        for (int i = 0; i < fillOffsets.length; i++) {
+          TextPainter(
+            text: TextSpan(
+              text: i.toString(),
+              style: offsetsLabelStyle,
+            ),
+            textDirection: TextDirection.ltr,
+          )
+            ..layout(maxWidth: 100)
+            ..paint(canvas, fillOffsets[i]);
+        }
+      }
+
       // The hash is based on the polygons visual properties. If the hash from
       // the current and the previous polygon no longer match, we need to flush
       // the batch previous polygons.
@@ -293,6 +360,7 @@ base class _PolygonPainter<R extends Object>
     final isSolid = polygon.pattern == const StrokePattern.solid();
     final isDashed = polygon.pattern.segments != null;
     final isDotted = polygon.pattern.spacingFactor != null;
+
     if (isSolid) {
       final SolidPixelHiker hiker = SolidPixelHiker(
         offsets: offsets,

lib/src/layer/polygon_layer/polygon_layer.dart

@@ -42,6 +42,12 @@ class PolygonLayer<R extends Object> extends StatefulWidget {
   /// above before enabling.
   final bool useAltRendering;
 
+  /// Whether to overlay a debugging tool when [useAltRendering] is enabled to
+  /// display triangulation results
+  ///
+  /// Ignored when not in debug mode.
+  final bool debugAltRenderer;
+
   /// Whether to cull polygons and polygon sections that are outside of the
   /// viewport
   ///
@@ -76,15 +82,17 @@ class PolygonLayer<R extends Object> extends StatefulWidget {
     super.key,
     required this.polygons,
     this.useAltRendering = false,
+    bool debugAltRenderer = false,
     this.polygonCulling = true,
     this.simplificationTolerance = 0.5,
     this.polygonLabels = true,
     this.drawLabelsLast = false,
     this.hitNotifier,
-  }) : assert(
+  })  : assert(
           simplificationTolerance >= 0,
           'simplificationTolerance cannot be negative: $simplificationTolerance',
-        );
+        ),
+        debugAltRenderer = kDebugMode && debugAltRenderer;
 
   @override
   State<PolygonLayer<R>> createState() => _PolygonLayerState<R>();
@@ -175,10 +183,10 @@ class _PolygonLayerState<R extends Object> extends State<PolygonLayer<R>> {
                       : points.elementAt(ii ~/ 2).y,
                   growable: false,
                 ),
-                // Not sure how just this works but it seems to :D
                 holeIndices: culledPolygon.holePoints.isEmpty
                     ? null
-                    : [culledPolygon.points.length],
+                    : _generateHolesIndices(culledPolygon)
+                        .toList(growable: false),
               );
             },
             growable: false,
@@ -192,13 +200,23 @@ class _PolygonLayerState<R extends Object> extends State<PolygonLayer<R>> {
           camera: camera,
           polygonLabels: widget.polygonLabels,
           drawLabelsLast: widget.drawLabelsLast,
+          debugAltRenderer: widget.debugAltRenderer,
           hitNotifier: widget.hitNotifier,
         ),
         size: Size(camera.size.x, camera.size.y),
       ),
     );
   }
 
+  Iterable<int> _generateHolesIndices(_ProjectedPolygon<R> polygon) sync* {
+    var prevValue = polygon.points.length;
+    yield prevValue;
+
+    for (int i = 0; i < polygon.holePoints.length - 1; i++) {
+      yield prevValue += polygon.holePoints[i].length;
+    }
+  }
+
   List<_ProjectedPolygon<R>> _computeZoomLevelSimplification({
     required MapCamera camera,
     required List<_ProjectedPolygon<R>> polygons,