MDEV-34141: Implements the function ST_Simplify

The GIS function ST_Simplify takes ad input a geometry and a double. It
applies the Ramer-Douglas-Peucker algorithm on the geometry and returns
the resulting geometry. The tests have been cherry-picked from the MySQL
implementation of this function to grant compatibility among the two
implementations.
Co-authored-by: David Zhao <david.zhao@oracle.com>
Co-authored-by: Pavan Naik <pavan.naik@oracle.com>
Co-authored-by: Norvald H. Ryeng <norvald.ryeng@oracle.com>
Co-authored-by: Erlend Dahl <erlend.dahl@oracle.com>
Co-authored-by: Jon Hauglid <jon.hauglid@oracle.com>
Co-authored-by: Hans H Melby <hans.h.melby@oracle.com>
Co-authored-by: Tor Didriksen <tor.didriksen@oracle.com>

sql/item_geofunc.cc

@@ -2140,6 +2140,69 @@ longlong Item_func_issimple::val_int()
 }
 
 
+String *Item_func_simplify::val_str(String *str)
+{
+  DBUG_ENTER("Item_func_simplify::val_str");
+  String *res= args[0]->val_str(&tmp_value);
+  double max_distance= (double) args[1]->val_real();
+  Geometry_buffer buffer;
+  Geometry *geometry;
+  uint32 num_points;
+
+  null_value= 1;
+  if ((null_value= (args[0]->null_value || args[1]->null_value)) ||
+       !(geometry= Geometry::construct(&buffer, res->ptr(), res->length())))
+  {
+    null_value= 1;
+    DBUG_RETURN(NULL);
+  }
+
+  if (max_distance <= 0)
+  {
+    my_error(ER_WRONG_ARGUMENTS, MYF(0), func_name());
+    null_value= 1;
+    DBUG_RETURN(NULL);
+  }
+
+  uint32 srid= uint4korr(res->ptr());
+  if (srid != 0)
+  {
+    my_error(ER_NOT_IMPLEMENTED_FOR_GEOGRAPHIC_SRS, MYF(0), func_name());
+    null_value= 1;
+    DBUG_RETURN(NULL);
+  }
+
+  if (geometry->get_class_info()->m_type_id == Geometry::wkb_point ||
+      geometry->get_class_info()->m_type_id == Geometry::wkb_multipoint)
+  {
+    str = res;
+    DBUG_RETURN(str);
+  }
+
+  if (geometry->get_class_info()->m_type_id == Geometry::wkb_linestring)
+  {
+    if (geometry->num_points(&num_points))
+    {
+      null_value= 1;
+      DBUG_RETURN(NULL);
+    }
+
+    if (num_points < 3)
+    {
+      str = res;
+      DBUG_RETURN(str);
+    }
+  }
+
+  if (geometry->simplify(str, max_distance))
+  {
+    null_value= 1;
+    DBUG_RETURN(NULL);
+  }
+  DBUG_RETURN(str);
+}
+
+
 longlong Item_func_isclosed::val_int()
 {
   DBUG_ASSERT(fixed());
@@ -4243,6 +4306,22 @@ class Create_func_issimple : public Create_func_arg1
 };
 
 
+class Create_func_simplify : public Create_func_arg2
+{
+public:
+  Item *create_2_arg(THD *thd, Item *arg1, Item *arg2) override
+  {
+    return new (thd->mem_root) Item_func_simplify(thd, arg1, arg2);
+  }
+
+  static Create_func_simplify s_singleton;
+
+protected:
+  Create_func_simplify() = default;
+  ~Create_func_simplify() override = default;
+};
+
+
 class Create_func_numgeometries : public Create_func_arg1
 {
 public:
@@ -4515,6 +4594,7 @@ Create_func_isempty Create_func_isempty::s_singleton;
 Create_func_isvalid Create_func_isvalid::s_singleton;
 Create_func_isring Create_func_isring::s_singleton;
 Create_func_issimple Create_func_issimple::s_singleton;
+Create_func_simplify Create_func_simplify::s_singleton;
 Create_func_mbr_contains Create_func_mbr_contains::s_singleton;
 Create_func_mbr_coveredby Create_func_mbr_coveredby::s_singleton;
 Create_func_mbr_disjoint Create_func_mbr_disjoint::s_singleton;
@@ -4585,6 +4665,7 @@ static Native_func_registry func_array_geom[] =
   { { STRING_WITH_LEN("ISVALID") }, GEOM_BUILDER(Create_func_isvalid)},
   { { STRING_WITH_LEN("ISRING") }, GEOM_BUILDER(Create_func_isring)},
   { { STRING_WITH_LEN("ISSIMPLE") }, GEOM_BUILDER(Create_func_issimple)},
+  { { STRING_WITH_LEN("SIMPLIFY") }, GEOM_BUILDER(Create_func_simplify)},
   { { STRING_WITH_LEN("LINEFROMTEXT") }, GEOM_BUILDER(Create_func_geometry_from_text)},
   { { STRING_WITH_LEN("LINEFROMWKB") }, GEOM_BUILDER(Create_func_geometry_from_wkb)},
   { { STRING_WITH_LEN("LINESTRINGFROMTEXT") }, GEOM_BUILDER(Create_func_geometry_from_text)},
@@ -4669,6 +4750,7 @@ static Native_func_registry func_array_geom[] =
   { { STRING_WITH_LEN("ST_ISVALID") }, GEOM_BUILDER(Create_func_isvalid)},
   { { STRING_WITH_LEN("ST_ISRING") }, GEOM_BUILDER(Create_func_isring)},
   { { STRING_WITH_LEN("ST_ISSIMPLE") }, GEOM_BUILDER(Create_func_issimple)},
+  { { STRING_WITH_LEN("ST_SIMPLIFY") }, GEOM_BUILDER(Create_func_simplify)},
   { { STRING_WITH_LEN("ST_LENGTH") }, GEOM_BUILDER(Create_func_glength)},
   { { STRING_WITH_LEN("ST_LINEFROMTEXT") }, GEOM_BUILDER(Create_func_geometry_from_text)},
   { { STRING_WITH_LEN("ST_LINEFROMWKB") }, GEOM_BUILDER(Create_func_geometry_from_wkb)},

sql/item_geofunc.h

@@ -971,6 +971,29 @@ class Item_func_issimple: public Item_long_func_args_geometry
   { return get_item_copy<Item_func_issimple>(thd, this); }
 };
 
+class Item_func_simplify: public Item_geometry_func_args_geometry
+{
+  String tmp_value;
+  Gcalc_heap collector;
+  Gcalc_function func;
+  Gcalc_scan_iterator scan_it;
+public:
+  Item_func_simplify(THD *thd, Item *a, Item *b)
+   :Item_geometry_func_args_geometry(thd, a, b) {}
+  LEX_CSTRING func_name_cstring() const override
+  {
+    static LEX_CSTRING name= {STRING_WITH_LEN("st_simplify") };
+    return name;
+  }
+  String *val_str(String *) override;
+  const Type_handler *type_handler() const override
+  {
+    return &type_handler_geometry;
+  }
+  Item *do_get_copy(THD *thd) const override
+  { return get_item_copy<Item_func_simplify>(thd, this); }
+};
+
 class Item_func_isclosed: public Item_long_func_args_geometry
 {
 public:

sql/share/errmsg-utf8.txt

@@ -12291,3 +12291,5 @@ WARN_SORTING_ON_TRUNCATED_LENGTH
 ER_INCORRECT_COLUMN_NAME_COUNT
         eng "Incorrect column name count for derived table"
         chi "派生表的列名计数不正确"
+ER_NOT_IMPLEMENTED_FOR_GEOGRAPHIC_SRS
+        eng "%s has not been implemented for geographic spatial reference systems."

sql/spatial.h

@@ -32,7 +32,7 @@ const uint32 SRID_PLACEHOLDER= 0;
 const uint SIZEOF_STORED_DOUBLE= 8;
 const uint BYTE_ORDER_SIZE= 1;
 const uint POINT_DATA_SIZE= (SIZEOF_STORED_DOUBLE * 2);
-const uint WKB_HEADER_SIZE= 1+4;
+const uint WKB_HEADER_SIZE= BYTE_ORDER_SIZE + 4;
 const uint32 GET_SIZE_ERROR= ((uint32) -1);
 
 struct st_point_2d
@@ -293,6 +293,7 @@ class Geometry
   virtual int area(double *ar, const char **end) const { return -1;}
   virtual int is_closed(int *closed) const { return -1; }
   virtual int is_valid(int *valid) const { return -1; }
+  virtual int simplify(String* result, double max_distance) const { return -1; }
   virtual int num_interior_ring(uint32 *n_int_rings) const { return -1; }
   virtual int num_points(uint32 *n_points) const { return -1; }
   virtual int num_geometries(uint32 *num) const { return -1; }
@@ -396,7 +397,7 @@ class Geometry
 
 
 /***************************** Point *******************************/
- 
+
 class Gis_point: public Geometry
 {
 public:
@@ -411,6 +412,7 @@ class Gis_point: public Geometry
                         const char **end) const override;
   bool get_mbr(MBR *mbr, const char **end) const override;
   int is_valid(int *valid) const override;
+
   int get_xy(double *x, double *y) const
   {
     const char *data= m_data;
@@ -483,6 +485,7 @@ class Gis_line_string: public Geometry
   int geom_length(double *len, const char **end) const override;
   int area(double *ar, const char **end) const override;
   int is_closed(int *closed) const override;
+  int simplify(String* result, double max_distance) const override;
   int num_points(uint32 *n_points) const override;
   int is_valid(int *valid) const override;
   int start_point(String *point) const override;
@@ -517,6 +520,7 @@ class Gis_polygon: public Geometry
   bool get_mbr(MBR *mbr, const char **end) const override;
   int is_valid(int *valid) const override;
   int area(double *ar, const char **end) const override;
+  int simplify(String* result, double max_distance) const override;
   int exterior_ring(String *result) const override;
   int num_interior_ring(uint32 *n_int_rings) const override;
   int interior_ring_n(uint32 num, String *result) const override;
@@ -590,6 +594,7 @@ class Gis_multi_line_string: public Geometry
   int geometry_n(uint32 num, String *result) const override;
   int geom_length(double *len, const char **end) const override;
   int is_closed(int *closed) const override;
+  int simplify(String* result, double max_distance) const override;
   bool dimension(uint32 *dim, const char **end) const override
   {
     *dim= 1;
@@ -620,6 +625,7 @@ class Gis_multi_polygon: public Geometry
   int num_geometries(uint32 *num) const override;
   int geometry_n(uint32 num, String *result) const override;
   int area(double *ar, const char **end) const override;
+  int simplify(String* result, double max_distance) const override;
   int centroid(String *result) const override;
   bool dimension(uint32 *dim, const char **end) const override
   {
@@ -651,6 +657,7 @@ class Gis_geometry_collection: public Geometry
   int is_valid(int *valid) const override;
   bool get_mbr(MBR *mbr, const char **end) const override;
   int area(double *ar, const char **end) const override;
+  int simplify(String* result, double max_distance) const override;
   int geom_length(double *len, const char **end) const override;
   int num_geometries(uint32 *num) const override;
   int geometry_n(uint32 num, String *result) const override;