Merge pull request #1412 from mathics/polygon-fill-rule

WL uses evenodd fill rule for polygons

Author: rocky

mathics/builtin/graphics.py

@@ -1532,15 +1532,23 @@ def extent(self):
 class Polygon(Builtin):
     """
     <dl>
-    <dt>'Polygon[{$point_1$, $point_2$ ...}]'
-        <dd>represents the filled polygon primitive.
-    <dt>'Polygon[{{$p_11$, $p_12$, ...}, {$p_21$, $p_22$, ...}, ...}]'
-        <dd>represents a number of filled polygon primitives.
+      <dt>'Polygon[{$point_1$, $point_2$ ...}]'
+      <dd>represents the filled polygon primitive.
+
+      <dt>'Polygon[{{$p_11$, $p_12$, ...}, {$p_21$, $p_22$, ...}, ...}]'
+      <dd>represents a number of filled polygon primitives.
     </dl>
 
+    A Right Triangle:
     >> Graphics[Polygon[{{1,0},{0,0},{0,1}}]]
     = -Graphics-
 
+    Notice that there is a line connecting from the last point to the first one.
+
+    A point is an element of the polygon if a ray from the point in any direction in the plane crosses the boundary line segments an odd number of times.
+    >> Graphics[Polygon[{{150,0},{121,90},{198,35},{102,35},{179,90}}]]
+    = -Graphics-
+
     >> Graphics3D[Polygon[{{0,0,0},{0,1,1},{1,0,0}}]]
     = -Graphics3D-
     """

mathics/formatter/svg.py

@@ -303,11 +303,15 @@ def polygonbox(self, **options):
             ]
             mesh.append(data)
         svg += '<meshgradient data="%s" />' % json.dumps(mesh)
+
+    # Perhaps one day this c
+    fill_rule="evenodd"
+
     for line in self.lines:
-        svg += '<polygon points="%s" style="%s" />' % (
-            " ".join("%f,%f" % coords.pos() for coords in line),
-            style,
-        )
+        svg += f"""
+  <polygon points="{" ".join("%f,%f" % coords.pos() for coords in line)}"
+           fill-rule="{fill_rule}"
+           style="{style}" />"""
     # print("XXX PolygonBox", svg)
     return svg