Mgv6 mudflow: Remove decoration if 'dirt with grass' below flows away (#5798)

Mudflow of a neighbouring mapchunk extends into a mapchunk's edge, and could
remove 'dirt with grass' from under a decoration, creating unsupported
decorations.

Remove any decoration above if a 'dirt with grass' node is removed by mudflow.

diff --git a/src/mapgen_v6.cpp b/src/mapgen_v6.cpp
index f3e893f58757ea3f7b72a9359f5dc0d514d12ad2..ff0d93496a568e5a841b1e45d4fff66d4a1f1715 100644 (file)
--- a/src/mapgen_v6.cpp
+++ b/src/mapgen_v6.cpp
@@ -836,13 +836,17 @@ void MapgenV6::flowMud(s16 &mudflow_minpos, s16 &mudflow_maxpos)
                                        v3s16(-1, 0, 0), // left
                                };
 
-                               // Check that upper is air or doesn't exist.
-                               // Cancel dropping if upper keeps it in place
+                               // Check that upper is walkable. Cancel
+                               // dropping if upper keeps it in place.
                                u32 i3 = i;
                                vm->m_area.add_y(em, i3, 1);
-                               if (vm->m_area.contains(i3) == true &&
-                                               ndef->get(vm->m_data[i3]).walkable)
-                                       continue;
+                               MapNode *n3 = NULL;
+
+                               if (vm->m_area.contains(i3)) {
+                                       n3 = &vm->m_data[i3];
+                                       if (ndef->get(*n3).walkable)
+                                               continue;
+                               }
 
                                // Drop mud on side
                                for (u32 di = 0; di < 4; di++) {
@@ -885,10 +889,18 @@ void MapgenV6::flowMud(s16 &mudflow_minpos, s16 &mudflow_maxpos)
                                        if (!dropped_to_unknown) {
                                                *n2 = *n;
                                                // Set old place to be air (or water)
-                                               if (old_is_water)
+                                               if (old_is_water) {
                                                        *n = MapNode(c_water_source);
-                                               else
+                                               } else {
                                                        *n = MapNode(CONTENT_AIR);
+                                                       // Upper (n3) is not walkable or is NULL. If it is
+                                                       // not NULL and not air and not water it is a
+                                                       // decoration that needs removing, to avoid
+                                                       // unsupported decorations.
+                                                       if (n3 && n3->getContent() != CONTENT_AIR &&
+                                                                       n3->getContent() != c_water_source)
+                                                               *n3 = MapNode(CONTENT_AIR);
+                                               }
                                        }
 
                                        // Done