Reset currentX and currentY when encoded data is not written

Add provided unit test slightly modified

refers to #29

src/NetTopologySuite.IO.VectorTiles.Mapbox/MapboxTileWriter.cs

@@ -280,6 +280,10 @@ private static void EncodeTo(List<uint> destination, CoordinateSequence sequence
             // skipping the last point for rings since ClosePath is used instead
             int count = ring ? sequence.Count - 1 : sequence.Count;
 
+            // In case we decide to ditch encoded data, we must reset currentX and currentY
+            int initialCurrentX = currentX;
+            int initialCurrentY = currentY;
+
             // If the sequence is empty there is nothing we can do with it.
             if (count == 0)
                 return;
@@ -326,14 +330,22 @@ private static void EncodeTo(List<uint> destination, CoordinateSequence sequence
                 if (destination.Count - initialSize - 2 >= 6)
                     destination.Add(GenerateCommandInteger(MapboxCommandType.ClosePath, 1));
                 else
+                {
+                    currentX = initialCurrentX;
+                    currentY = initialCurrentY;
                     destination.RemoveRange(initialSize, destination.Count - initialSize);
+                }
             }
             else
             {
                 // A line has 1 MoveTo and 1 LineTo command.
                 // A line is valid if it has at least 2 points
                 if (destination.Count - initialSize - 2 < 4)
+                {
+                    currentX = initialCurrentX;
+                    currentY = initialCurrentY;
                     destination.RemoveRange(initialSize, destination.Count - initialSize);
+                }
             }
         }
 

test/NetTopologySuite.IO.VectorTiles.Tests/Issues/Issue29.cs

@@ -0,0 +1,56 @@
+using NetTopologySuite.Features;
+using NetTopologySuite.Geometries;
+using NetTopologySuite.IO.VectorTiles.Tiles;
+using NetTopologySuite.IO.VectorTiles.Mapbox;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace NetTopologySuite.IO.VectorTiles.Tests.Issues
+{
+    public class Issue29
+    {
+        [Fact]
+        public void MvtWriterGeometryIssue()
+        {
+            writeTile(8, 6, 4);
+            writeTile(34, 24, 6);
+        }
+
+        private static void writeTile(int x, int y, int z)
+        {
+            var geometry = new WKTReader().Read(ItalyWkt);
+            var feature = new Feature(geometry, new AttributesTable(new Dictionary<string, object>()
+        {
+            { "id", 1 }
+        }));
+            var tileDefinition = new VectorTiles.Tiles.Tile(x, y, z);
+            var vectorTile = new VectorTile { TileId = tileDefinition.Id };
+            var layer = new Layer { Name = "layer1" };
+            vectorTile.Layers.Add(layer);
+            layer.Features.Add(feature);
+
+            byte[] result;
+            MemoryStream? ms;
+            using (ms = new MemoryStream(1024 * 32))
+            {
+                vectorTile.Write(ms);
+                result = ms.ToArray();
+            }
+
+            File.WriteAllBytes($"{x}_{y}_{z}.mvt", result);
+        }
+
+        private static string ItalyWkt
+        {
+            get
+            {
+                return File.ReadAllText(Path.Combine("Issues", $"{typeof(Issue29).Name}.wkt"));
+            }
+        }
+    }
+}

test/NetTopologySuite.IO.VectorTiles.Tests/NetTopologySuite.IO.VectorTiles.Tests.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>net6.0</TargetFramework>
@@ -31,4 +31,10 @@
     </None>
   </ItemGroup>
 
+  <ItemGroup>
+    <None Update="Issues\Issue29.wkt">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
 </Project>