Read polygon and polyline objects from Tiled maps

The polygon field of MapObject is not public, so the map reader skipped it:
every polygon object came as an empty rectangle. In the tiled demo the boat
in the water spawned as a Wall without costume or hitbox and showed the
missing-costume marker, and never blocked the player. The reader now fills
both fields; a polyline's points are a string as Tiled writes them.

Author: mikebarkmin

.changeset/tiled-polygons.md

@@ -0,0 +1,9 @@
+---
+type: patch
+---
+
+Polygon objects of a Tiled map keep their shape: `MapObject.getShape()` and
+`TiledMap.spawn` used to see them as an empty rectangle, because the polygon
+was never read from the map file. A wall drawn as a polygon now blocks, and a
+spawned sprite without a costume no longer shows the missing-costume marker.
+Polylines are read as well.

src/main/java/org/openpatch/scratch/extensions/tiled/MapObject.java

@@ -64,9 +64,13 @@ public void setClassName(String className) {
   public Object point;
 
   /** A Polygon object representing a polygon shape. */
+  // read from the map file although it is not public (the reader only fills
+  // public fields by itself, so polygon objects used to come without their shape)
+  @com.fasterxml.jackson.annotation.JsonProperty("polygon")
   protected Polygon polygon;
 
   /** A Polyline object representing a polyline shape. */
+  @com.fasterxml.jackson.annotation.JsonProperty("polyline")
   protected Polyline polyline;
 
   /**

src/main/java/org/openpatch/scratch/extensions/tiled/Point.java

@@ -1,23 +1,18 @@
 package org.openpatch.scratch.extensions.tiled;
 
-import java.util.List;
-
 /**
- * The Polyline class represents a polyline object in Tiled. It includes a list
- * of points that make
- * up the polyline.
+ * The Polyline class represents a polyline object in Tiled: its points as
+ * Tiled writes them.
  *
  * <p>
  * Example usage:
  *
  * <pre>{@code
  * Polyline p = new Polyline();
- * p.points = new ArrayList<Point>();
- * p.points.add(new Point(0, 0));
- * p.points.add(new Point(10, 10));
+ * p.points = "0,0 10,10";
  * }</pre>
  */
 class Polyline {
-  /** The list of points that make up the polyline. */
-  public List<Point> points;
+  /** The points of the polyline as Tiled writes them: "x,y x,y ...". */
+  public String points;
 }

src/main/java/org/openpatch/scratch/extensions/tiled/Polyline.java

@@ -2,6 +2,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -50,6 +51,25 @@ private static byte[] gids(long... values) {
     return buffer.array();
   }
 
+  @Test
+  void polygonObjectsKeepTheirShape() throws Exception {
+    Map m = load(map("""
+        <objectgroup id="2" name="Objects">
+          <object id="1" type="Wall" x="10" y="20">
+            <polygon points="0,0 30,0 30,-10"/>
+          </object>
+          <object id="2" type="Fence" x="0" y="0">
+            <polyline points="0,0 5,5"/>
+          </object>
+        </objectgroup>
+        """));
+    MapObject wall = TiledMap.objectsFromLayer(m, "Objects")[0];
+    assertNotNull(wall.polygon, "the polygon is read");
+    assertEquals(3, wall.polygon.getPoints().length);
+    assertEquals(org.openpatch.scratch.Polygon.class, wall.getShape().getClass());
+    assertNotNull(TiledMap.objectsFromLayer(m, "Objects")[1].polyline, "the polyline is read");
+  }
+
   @Test
   void csvWithFlipBitsLoadsAndKeepsTheFlips() throws Exception {
     long flipped = 0x80000000L | 3; // horizontal flip of tile 3