Enhancing polygon splitting

With this enhancement, the area ratio in DRC can
be configured as a negative value. This indicates
to take the outer manhattan approximation of the
polygons. This way, skinny diagonals are not
resolved into many small triangles.

src/db/db/dbDeepShapeStore.cc

@@ -405,7 +405,7 @@ private:
 // ----------------------------------------------------------------------------------
 
 DeepShapeStoreState::DeepShapeStoreState ()
-  : m_threads (1), m_max_area_ratio (3.0), m_max_vertex_count (16), m_reject_odd_polygons (false), m_text_property_name (), m_text_enlargement (-1), m_subcircuit_hierarchy_for_nets (false)
+  : m_threads (1), m_max_area_ratio (-3.0), m_max_vertex_count (16), m_reject_odd_polygons (false), m_text_property_name (), m_text_enlargement (-1), m_subcircuit_hierarchy_for_nets (false)
 {
   //  .. nothing yet ..
 }

src/db/db/dbHierarchyBuilder.cc

@@ -654,7 +654,7 @@ ReducingHierarchyBuilderShapeReceiver::reduce (const db::Polygon &poly, db::prop
 
   //  NOTE: only halfmanhattan polygons are guaranteed not to generate grid snap artefacts when splitting.
   //  This is important to maintain the connection integrity of shape clusters.
-  if (poly.is_halfmanhattan () && ((m_max_vertex_count >= 4 && poly.vertices () > m_max_vertex_count) || (m_area_ratio > 2.0 && poly.area_ratio () > m_area_ratio))) {
+  if (poly.is_halfmanhattan () && db::suggest_split_polygon (poly, m_max_vertex_count, m_area_ratio)) {
 
     std::vector <db::Polygon> split_polygons;
     db::split_polygon (poly, split_polygons);

src/db/db/dbLayoutUtils.cc

@@ -689,8 +689,7 @@ scale_and_snap (db::Layout &layout, db::Cell &cell, db::Coord g, db::Coord m, db
 
 static bool split_polygon (bool first, db::Polygon &poly, size_t max_vertex_count, double max_area_ratio, std::vector<db::Polygon> &parts)
 {
-  if ((max_vertex_count > 0 && poly.vertices () > max_vertex_count) ||
-      (max_area_ratio > 0 && poly.area_ratio () > max_area_ratio)) {
+  if (db::suggest_split_polygon (poly, max_vertex_count, max_area_ratio)) {
 
     std::vector<db::Polygon> sp;
     db::split_polygon (poly, sp);

src/db/db/dbLocalOperationUtils.cc

@@ -58,7 +58,7 @@ PolygonSplitter::PolygonSplitter (PolygonSink &sink, double max_area_ratio, size
 void
 PolygonSplitter::put (const db::Polygon &poly)
 {
-  if ((m_max_vertex_count > 0 && poly.vertices () > m_max_vertex_count) || (m_max_area_ratio > 0.0 && poly.area_ratio () > m_max_area_ratio)) {
+  if (db::suggest_split_polygon (poly, m_max_vertex_count, m_max_area_ratio)) {
 
     std::vector <db::Polygon> split_polygons;
     db::split_polygon (poly, split_polygons);

src/db/db/dbPolygon.h

@@ -785,6 +785,14 @@ public:
     return area2 () / 2;
   }
 
+  /**
+   *  @brief The upper bound area for a manhattan approximation of the contour times
+   */
+  area_type area_upper_manhattan_bound () const
+  {
+    return area_upper_manhattan_bound2 () / 2;
+  }
+
   /**
    *  @brief The area of the contour times 2
    *  For integer area types, this is the more precise value as the division
@@ -807,6 +815,52 @@ public:
     return a;
   }
 
+  /**
+   *  @brief The upper bound area for a manhattan approximation of the contour times 2
+   *  This area takes non-manhattan edges as being manhattan-interpolated to the outside.
+   */
+  area_type area_upper_manhattan_bound2 () const
+  {
+    size_type n = size ();
+    if (n < 3) {
+      return 0;
+    }
+
+    area_type a = 0;
+    point_type pl = (*this) [n - 1];
+    for (size_type p = 0; p < n; ++p) {
+
+      point_type pp = (*this) [p];
+
+      int sdx = pp.x () < pl.x () ? -1 : (pp.x () == pl.x () ? 0 : 1);
+      int sdy = pp.y () < pl.y () ? -1 : (pp.y () == pl.y () ? 0 : 1);
+
+      if (sdx != 0 && sdy != 0) {
+
+        point_type pm;
+
+        //  determine an interpolation point
+        if (sdx * sdy < 0) {
+          pm = point_type (pp.x (), pl.y ());
+        } else {
+          pm = point_type (pl.x (), pp.y ());
+        }
+
+        a += db::vprod (pm - point_type (), pl - point_type ());
+        a += db::vprod (pp - point_type (), pm - point_type ());
+
+      } else {
+
+        a += db::vprod (pp - point_type (), pl - point_type ());
+
+      }
+
+      pl = pp;
+
+    }
+    return a;
+  }
+
   /**
    *  @brief The perimeter of the contour
    */
@@ -1747,6 +1801,26 @@ public:
     }
   }
 
+  /**
+   *  @brief Returns the area ratio between the polygon's bounding box and upper manhattan approximation bound
+   *
+   *  This number is a measure how well the polygon is approximated by the bounding box,
+   *  while assuming an outer manhattan approximation is a good measure for the polygon's
+   *  area.
+   *  Values are bigger than 1 for well-formed polygons. Bigger values mean worse
+   *  approximation.
+   */
+  double area_upper_manhattan_bound_ratio () const
+  {
+    area_type a = this->area_upper_manhattan_bound2 ();
+    if (a == 0) {
+      //  By our definition, an empty polygon has an area ratio of 0
+      return 0.0;
+    } else {
+      return double (box ().area ()) / (0.5 * a);
+    }
+  }
+
   /**
    *  @brief The hull "begin" point iterator
    *
@@ -2193,6 +2267,21 @@ public:
     return a;
   }
 
+  /**
+   *  @brief The area of the polygon - upper manhattan bound
+   *
+   *  This gives the upper area bound for a manhattan approximation of the
+   *  polygon.
+   */
+  area_type area_upper_manhattan_bound () const
+  {
+    area_type a = 0;
+    for (typename contour_list_type::const_iterator h = m_ctrs.begin (); h != m_ctrs.end (); ++h) {
+      a += h->area_upper_manhattan_bound ();
+    }
+    return a;
+  }
+
   /**
    *  @brief The area of the polygon times 2
    *  For integer area types, this is the more precise value as the division
@@ -2207,6 +2296,21 @@ public:
     return a;
   }
 
+  /**
+   *  @brief The area of the polygon - upper manhattan bound times 2
+   *
+   *  This gives the upper area bound for a manhattan approximation of the
+   *  polygon.
+   */
+  area_type area_upper_manhattan_bound2 () const
+  {
+    area_type a = 0;
+    for (typename contour_list_type::const_iterator h = m_ctrs.begin (); h != m_ctrs.end (); ++h) {
+      a += h->area_upper_manhattan_bound2 ();
+    }
+    return a;
+  }
+
   /**
    *  @brief The perimeter of the polygon
    */
@@ -2966,6 +3070,17 @@ public:
     return m_hull.area ();
   }
 
+  /**
+   *  @brief The area of the polygon - upper manhattan bound
+   *
+   *  This gives the upper area bound for a manhattan approximation of the
+   *  polygon.
+   */
+  area_type area_upper_manhattan_bound () const
+  {
+    return m_hull.area_upper_manhattan_bound ();
+  }
+
   /**
    *  @brief The area of the polygon times 2
    *  For integer area types, this is the more precise value as the division
@@ -2976,6 +3091,17 @@ public:
     return m_hull.area2 ();
   }
 
+  /**
+   *  @brief The area of the polygon - upper manhattan bound times 2
+   *
+   *  This gives the upper area bound for a manhattan approximation of the
+   *  polygon.
+   */
+  area_type area_upper_manhattan_bound2 () const
+  {
+    return m_hull.area_upper_manhattan_bound2 ();
+  }
+
   /**
    *  @brief The perimeter of the polygon
    */
@@ -3101,6 +3227,26 @@ public:
     }
   }
 
+  /**
+   *  @brief Returns the area ratio between the polygon's bounding box and upper manhattan approximation bound
+   *
+   *  This number is a measure how well the polygon is approximated by the bounding box,
+   *  while assuming an outer manhattan approximation is a good measure for the polygon's
+   *  area.
+   *  Values are bigger than 1 for well-formed polygons. Bigger values mean worse
+   *  approximation.
+   */
+  double area_upper_manhattan_bound_ratio () const
+  {
+    area_type a = this->area_upper_manhattan_bound2 ();
+    if (a == 0) {
+      //  By our definition, an empty polygon has an area ratio of 0
+      return 0.0;
+    } else {
+      return double (box ().area ()) / (0.5 * a);
+    }
+  }
+
   void mem_stat (MemStatistics *stat, MemStatistics::purpose_t purpose, int cat, bool no_self = false, void *parent = 0) const
   {
     db::mem_stat (stat, purpose, cat, m_hull, no_self, parent);

src/db/db/dbPolygonTools.cc

@@ -633,6 +633,32 @@ template<> DB_PUBLIC void cut_polygon_internal (const db::DSimplePolygon &polygo
 }
 
 
+// -------------------------------------------------------------------------
+//  Implementation of suggest_split_polygon
+
+template <class PolygonType>
+bool
+suggest_split_polygon (const PolygonType &polygon, size_t max_vertex_count, double max_area_ratio)
+{
+  size_t v = polygon.vertices ();
+  if (v <= 4) {
+    return false;
+  } else if (max_vertex_count > 0 && v > max_vertex_count) {
+    return true;
+  } else if (max_area_ratio > 0 && polygon.area_ratio () > max_area_ratio) {
+    return true;
+  } else if (max_area_ratio < 0 && polygon.area_upper_manhattan_bound_ratio () > -max_area_ratio) {
+    return true;
+  } else {
+    return false;
+  }
+}
+
+template DB_PUBLIC bool suggest_split_polygon<> (const db::Polygon &polygon, size_t max_vertex_count, double max_area_ratio);
+template DB_PUBLIC bool suggest_split_polygon<> (const db::SimplePolygon &polygon, size_t max_vertex_count, double max_area_ratio);
+template DB_PUBLIC bool suggest_split_polygon<> (const db::DPolygon &polygon, size_t max_vertex_count, double max_area_ratio);
+template DB_PUBLIC bool suggest_split_polygon<> (const db::DSimplePolygon &polygon, size_t max_vertex_count, double max_area_ratio);
+
 // -------------------------------------------------------------------------
 //  Implementation of split_polygon
 

src/db/db/dbPolygonTools.h

@@ -129,6 +129,21 @@ void cut_polygon (const PolygonType &input, const typename PolygonType::edge_typ
 template <class PolygonType>
 void DB_PUBLIC split_polygon (const PolygonType &polygon, std::vector<PolygonType> &output);
 
+/**
+ *  @brief Determines whether a polygon needs to be split according to the given max_vertex and area_ratio criteron
+ *
+ *  If max_vertex is 0, there is no vertex limit.
+ *  If max_vertex is >0, the function returns true, if the vertex limit is exceeded.
+ *
+ *  If area_ratio is 0, there is no area ratio limit.
+ *  If area_ratio is >0, the function returns true, if the bounding box area is larger than area_ratio times the polygon area.
+ *  If area_ratio is <0, the function returns true, if the bounding box area is larger than -area_ratio times the polygon
+ *    manhattan approximation upper area bound.
+ *  (the latter definition is useful to prevent splitting of thin diagonal lines).
+ */
+template <class PolygonType>
+bool DB_PUBLIC suggest_split_polygon (const PolygonType &polygon, size_t max_vertex, double area_ratio);
+
 /**
  *  @brief Determines whether a polygon and a box interact
  *

src/db/db/dbRegionProcessors.cc

@@ -266,8 +266,7 @@ void TrapezoidDecomposition::process (const db::Polygon &poly, std::vector<db::P
 
 void PolygonBreaker::process (const db::Polygon &poly, std::vector<db::Polygon> &result) const
 {
-  if ((m_max_vertex_count > 0 && poly.vertices () > m_max_vertex_count) ||
-      (m_max_area_ratio > 0 && poly.area_ratio () > m_max_area_ratio)) {
+  if (db::suggest_split_polygon (poly, m_max_vertex_count, m_max_area_ratio)) {
 
     std::vector<db::Polygon> split_polygons;
     db::split_polygon (poly, split_polygons);

src/db/db/gsiDeclDbPolygon.cc

@@ -42,8 +42,7 @@ static std::vector<C> split_poly (const C *p)
 template <class C>
 static void break_polygon (const C &poly, size_t max_vertex_count, double max_area_ratio, std::vector<C> &result)
 {
-  if ((max_vertex_count > 0 && poly.vertices () > max_vertex_count) ||
-      (max_area_ratio > 0 && poly.area_ratio () > max_area_ratio)) {
+  if (db::suggest_split_polygon (poly, max_vertex_count, max_area_ratio)) {
 
     std::vector<C> split_polygons;
     db::split_polygon (poly, split_polygons);
@@ -222,6 +221,26 @@ struct simple_polygon_defs
     return poly->area2 ();
   }
 
+#if defined(HAVE_64BIT_COORD)
+  //  workaround for missing 128bit binding of GSI
+  static double area_upper_manhattan_bound (const C *poly)
+#else
+  static area_type area_upper_manhattan_bound (const C *poly)
+#endif
+  {
+    return poly->area_upper_manhattan_bound ();
+  }
+
+#if defined(HAVE_64BIT_COORD)
+  //  workaround for missing 128bit binding of GSI
+  static double area_upper_manhattan_bound2 (const C *poly)
+#else
+  static area_type area_upper_manhattan_bound2 (const C *poly)
+#endif
+  {
+    return poly->area_upper_manhattan_bound2 ();
+  }
+
   static std::vector<tl::Variant> extract_rad (const C *sp)
   {
     db::polygon<coord_type> p, pnew;
@@ -572,6 +591,12 @@ struct simple_polygon_defs
       "\n"
       "This method has been introduced in version 0.26.1\n"
     ) +
+    method_ext ("area_upper_manhattan_bound", &area_upper_manhattan_bound,
+      "@hide"  //  too special
+    ) +
+    method_ext ("area_upper_manhattan_bound2", &area_upper_manhattan_bound2,
+      "@hide"  //  too special
+    ) +
     method ("perimeter", &C::perimeter,
       "@brief Gets the perimeter of the polygon\n"
       "The perimeter is sum of the lengths of all edges making up the polygon."
@@ -1091,6 +1116,26 @@ struct polygon_defs
     return poly->area2 ();
   }
 
+#if defined(HAVE_64BIT_COORD)
+  //  workaround for missing 128bit binding of GSI
+  static double area_upper_manhattan_bound (const C *poly)
+#else
+  static area_type area_upper_manhattan_bound (const C *poly)
+#endif
+  {
+    return poly->area_upper_manhattan_bound ();
+  }
+
+#if defined(HAVE_64BIT_COORD)
+  //  workaround for missing 128bit binding of GSI
+  static double area_upper_manhattan_bound2 (const C *poly)
+#else
+  static area_type area_upper_manhattan_bound2 (const C *poly)
+#endif
+  {
+    return poly->area_upper_manhattan_bound2 ();
+  }
+
   static std::vector<tl::Variant> extract_rad (const C *p)
   {
     C pnew;
@@ -1592,6 +1637,12 @@ struct polygon_defs
       "\n"
       "This method has been introduced in version 0.26.1\n"
     ) +
+    method_ext ("area_upper_manhattan_bound", &area_upper_manhattan_bound,
+      "@hide"  //  too special
+    ) +
+    method_ext ("area_upper_manhattan_bound2", &area_upper_manhattan_bound2,
+      "@hide"  //  too special
+    ) +
     method ("perimeter", &C::perimeter,
       "@brief Gets the perimeter of the polygon\n"
       "The perimeter is sum of the lengths of all edges making up the polygon.\n"

src/drc/drc/built-in-macros/_drc_engine.rb

@@ -1298,7 +1298,26 @@ module DRC
     # In deep mode, polygons with a bounding box to polygon area ratio bigger than the given number
     # will be split into smaller chunks to optimize performance (which gets better if the polygon's
     # bounding boxes do not cover a lot of empty space).
-    # The default threshold is 3.0 which means fairly compact polygons. Use this method with a numeric 
+    #
+    # The area ratio is a signed value. Negative values indicate a area ratio, taking the outer
+    # manhattan approximation of the polygons for the area ratio. 
+    # The sign of the value indicates the mode (manhattan approximation or real polygon) - the actual area 
+    # ratio checked is the absolute value.
+    #
+    # For manhattan polygons, an area ratio of -3.0 gives the same results than a positive 3.0. 
+    # For non-manhattan polygons, the area used for the polygon is larger than
+    # the actual polygon area. So splitting is less likely in these cases. This avoids degeneration
+    # of the split polygon which can otherwise happen for thin diagonal lines. These are often 
+    # resolved into a large number of small triangles which does not provide any benefit for 
+    # the algorithms.
+    #
+    # With a negative area ratio, triangles are equivalent to their bounding box and always
+    # have an area ratio of 1.0.
+    #
+    # The default threshold is -3.0 which gives fairly compact polygons and using their outer
+    # manhattan approximation. Skinny diagonals will be maintained.
+    #
+    # Use this method with a numeric 
     # argument to set the value and without an argument to get the current maximum area ratio.
     # Set the value to zero to disable splitting by area ratio.
     # 

src/drc/unit_tests/drcSimpleTests.cc

@@ -1978,3 +1978,8 @@ TEST(131d_edge_pair_interactions)
 {
   run_test (_this, "131", true);
 }
+
+TEST(132d_sensitive_breaking)
+{
+  run_test (_this, "132", true);
+}

src/plugins/tools/net_tracer/db_plugin/dbNetTracer.cc

@@ -1451,7 +1451,7 @@ NetTracer::determine_interactions (const db::Polygon &seed, const NetTracerShape
 {
   int area_ratio = 2;
 
-  db::Polygon::area_type poly_area = seed.area ();
+  db::Polygon::area_type poly_area = seed.area_upper_manhattan_bound ();
   db::Polygon::area_type box_area = seed.box ().area ();
 
   if (poly_area == box_area && seed.vertices () == 4) {