Image: Move Edge class to its own namespace

The Edge class is an implementation detail of the scan-line polygon filling algorithm.
Tuck it away in the newly created PolygonFill namespace.

src/zm_image.cpp

@@ -2469,7 +2469,7 @@ void Image::Fill(Rgb colour, int density, const Polygon &polygon) {
 
   size_t n_coords = polygon.GetVertices().size();
 
-  std::vector<Edge> global_edges;
+  std::vector<PolygonFill::Edge> global_edges;
   global_edges.reserve(n_coords);
   for (size_t j = 0, i = n_coords - 1; j < n_coords; i = j++) {
     const Vector2 &p1 = polygon.GetVertices()[i];
@@ -2487,9 +2487,9 @@ void Image::Fill(Rgb colour, int density, const Polygon &polygon) {
                               d.x_ / static_cast<double>(d.y_));
 
   }
-  std::sort(global_edges.begin(), global_edges.end(), Edge::CompareYX);
+  std::sort(global_edges.begin(), global_edges.end(), PolygonFill::Edge::CompareYX);
 
-  std::vector<Edge> active_edges;
+  std::vector<PolygonFill::Edge> active_edges;
   active_edges.reserve(global_edges.size());
 
   int32 scan_line = global_edges[0].min_y;
@@ -2513,7 +2513,7 @@ void Image::Fill(Rgb colour, int density, const Polygon &polygon) {
         ++it;
       }
     }
-    std::sort(active_edges.begin(), active_edges.end(), Edge::CompareX);
+    std::sort(active_edges.begin(), active_edges.end(), PolygonFill::Edge::CompareX);
 
     if (!(scan_line % density)) {
       for (auto it = active_edges.begin(); it != active_edges.end(); ++it) {
@@ -2555,10 +2555,6 @@ void Image::Fill(Rgb colour, int density, const Polygon &polygon) {
   }
 }
 
-void Image::Fill(Rgb colour, const Polygon &polygon) {
-  Fill(colour, 1, polygon);
-}
-
 void Image::Rotate(int angle) {
   angle %= 360;
 

src/zm_image.h

@@ -278,7 +278,7 @@ class Image {
     void Fill( Rgb colour, const Box *limits=0 );
     void Fill( Rgb colour, int density, const Box *limits=0 );
     void Outline( Rgb colour, const Polygon &polygon );
-    void Fill(Rgb colour, const Polygon &polygon);
+    void Fill(Rgb colour, const Polygon &polygon) { Fill(colour, 1, polygon); };
     void Fill(Rgb colour, int density, const Polygon &polygon);
 
     void Rotate( int angle );
@@ -292,6 +292,31 @@ class Image {
     void Deinterlace_4Field(const Image* next_image, unsigned int threshold);
 };
 
+// Scan-line polygon fill algorithm
+namespace PolygonFill {
+class Edge {
+ public:
+  Edge() = default;
+  Edge(int32 min_y, int32 max_y, double min_x, double _1_m) : min_y(min_y), max_y(max_y), min_x(min_x), _1_m(_1_m) {}
+
+  static bool CompareYX(const Edge &e1, const Edge &e2) {
+    if (e1.min_y == e2.min_y)
+      return e1.min_x < e2.min_x;
+    return e1.min_y < e2.min_y;
+  }
+
+  static bool CompareX(const Edge &e1, const Edge &e2) {
+    return e1.min_x < e2.min_x;
+  }
+
+ public:
+  int32 min_y;
+  int32 max_y;
+  double min_x;
+  double _1_m;
+};
+}
+
 #endif // ZM_IMAGE_H
 
 /* Blend functions */

src/zm_poly.h

@@ -23,28 +23,6 @@
 #include "zm_box.h"
 #include <vector>
 
-class Edge {
- public:
-  Edge() = default;
-  Edge(int32 min_y, int32 max_y, double min_x, double _1_m) : min_y(min_y), max_y(max_y), min_x(min_x), _1_m(_1_m) {}
-
-  static bool CompareYX(const Edge &e1, const Edge &e2) {
-    if (e1.min_y == e2.min_y)
-      return e1.min_x < e2.min_x;
-    return e1.min_y < e2.min_y;
-  }
-
-  static bool CompareX(const Edge &e1, const Edge &e2) {
-    return e1.min_x < e2.min_x;
-  }
-
- public:
-  int32 min_y;
-  int32 max_y;
-  double min_x;
-  double _1_m;
-};
-
 // This class represents convex or concave non-self-intersecting polygons.
 class Polygon {
  public: