[generator] Reduce coastlines detalisation on World map z6-9

Signed-off-by: Konstantin Pastbin <konstantin.pastbin@gmail.com>

generator/feature_sorter.cpp

@@ -11,6 +11,7 @@
 
 #include "routing/routing_helpers.hpp"
 
+#include "indexer/classificator.hpp"
 #include "indexer/dat_section_header.hpp"
 #include "indexer/feature_impl.hpp"
 #include "indexer/scales.hpp"
@@ -157,6 +158,11 @@ public:
       Polygons const & polys = fb.GetGeometry();
       bool const isCoast = fb.IsCoastCell();
 
+      static uint32_t const desertType = classif().GetTypeByPath({"natural", "desert"});
+      static uint32_t const glacierType = classif().GetTypeByPath({"natural", "glacier"});
+      // Reduce detalisation of glaciers and deserts on World map.
+      bool const isLowDetail = !IsCountry() && isArea && (fb.HasType(desertType, 2) || fb.HasType(glacierType, 2));
+
       int const scalesStart = static_cast<int>(m_header.GetScalesCount()) - 1;
       for (int i = scalesStart; i >= 0; --i)
       {
@@ -167,15 +173,17 @@ public:
                                  scales::PatchMaxDrawableScale(level)))
         {
           // Increment zoom level for coastline polygons (check and simplification)
-          // for better visual quality in the first geometry batch or whole WorldCoasts.
+          // to workaround visual artifacts on low zooms https://github.com/organicmaps/organicmaps/issues/2429
           /// @todo Probably, better to keep 3 zooms (skip trg0 with fallback to trg1)?
-          if (isCoast)
+          if (isCoast && (level <= 1))
           {
-            if (level <= scales::GetUpperWorldScale())
-              ++level;
+            // Effectively change simplification zooms to {5, 6, 7, 8} from {3, 5, 7, 9}
+            ++level;
             if (i == 0)
               ++level;
           }
+          if (isLowDetail && (level <= scales::GetUpperWorldScale()))
+            --level;
 
           // Simplify and serialize geometry.
           // The same line simplification algo is used both for lines

generator/world_map_generator.hpp

@@ -176,6 +176,7 @@ public:
     case feature::GeomType::Area:
     {
       /// @todo Initial area threshold to push area objects into World.mwm
+      /// @todo(pastk) Apply an older lower detail threshold of 0.01 to glaciers, deserts and coastlines (islets)
       auto const & geometry = fb.GetOuterGeometry();
       if (GetPolygonArea(geometry.begin(), geometry.end()) < 0.0025)
         return false;