Update cell local map on different neighbour cells

Save which neighbour cells were active when local map for a cell is rendered.
Update when intersection of currently loaded cells is different from stored. If
map was rendered when all neighbours were loaded no more updates will happen.

apps/openmw/mwrender/localmap.cpp

@@ -189,17 +189,18 @@ namespace MWRender
         int cellY = cell->getCell()->getGridY();
 
         MapSegment& segment = mExteriorSegments[std::make_pair(cellX, cellY)];
-        if (!segment.needUpdate)
+        const std::uint8_t neighbourFlags = getExteriorNeighbourFlags(cellX, cellY);
+        if ((segment.mLastRenderNeighbourFlags & neighbourFlags) == neighbourFlags)
             return;
         requestExteriorMap(cell, segment);
-        segment.needUpdate = false;
+        segment.mLastRenderNeighbourFlags = neighbourFlags;
     }
 
     void LocalMap::addCell(MWWorld::CellStore* cell)
     {
         if (cell->isExterior())
-            mExteriorSegments[std::make_pair(cell->getCell()->getGridX(), cell->getCell()->getGridY())].needUpdate
+            mExteriorSegments.emplace(
-                = true;
+                std::make_pair(cell->getCell()->getGridX(), cell->getCell()->getGridY()), MapSegment{});
     }
 
     void LocalMap::removeExteriorCell(int x, int y)
@@ -211,7 +212,9 @@ namespace MWRender
     {
         saveFogOfWar(cell);
 
-        if (!cell->isExterior())
+        if (cell->isExterior())
+            mExteriorSegments.erase({ cell->getCell()->getGridX(), cell->getCell()->getGridY() });
+        else
             mInteriorSegments.clear();
     }
 
@@ -568,6 +571,25 @@ namespace MWRender
         }
     }
 
+    std::uint8_t LocalMap::getExteriorNeighbourFlags(int cellX, int cellY) const
+    {
+        constexpr std::tuple<NeighbourCellFlag, int, int> flags[] = {
+            { NeighbourCellTopLeft, -1, -1 },
+            { NeighbourCellTopCenter, 0, -1 },
+            { NeighbourCellTopRight, 1, -1 },
+            { NeighbourCellMiddleLeft, -1, 0 },
+            { NeighbourCellMiddleRight, 1, 0 },
+            { NeighbourCellBottomLeft, -1, 1 },
+            { NeighbourCellBottomCenter, 0, 1 },
+            { NeighbourCellBottomRight, 1, 1 },
+        };
+        std::uint8_t result = 0;
+        for (const auto& [flag, dx, dy] : flags)
+            if (mExteriorSegments.contains(std::pair(cellX + dx, cellY + dy)))
+                result |= flag;
+        return result;
+    }
+
     void LocalMap::MapSegment::createFogOfWarTexture()
     {
         if (mFogOfWarTexture)

apps/openmw/mwrender/localmap.hpp

@@ -1,6 +1,7 @@
 #ifndef GAME_RENDER_LOCALMAP_H
 #define GAME_RENDER_LOCALMAP_H
 
+#include <cstdint>
 #include <map>
 #include <set>
 #include <vector>
@@ -107,6 +108,18 @@ namespace MWRender
         typedef std::set<std::pair<int, int>> Grid;
         Grid mCurrentGrid;
 
+        enum NeighbourCellFlag : std::uint8_t
+        {
+            NeighbourCellTopLeft = 1,
+            NeighbourCellTopCenter = 1 << 1,
+            NeighbourCellTopRight = 1 << 2,
+            NeighbourCellMiddleLeft = 1 << 3,
+            NeighbourCellMiddleRight = 1 << 4,
+            NeighbourCellBottomLeft = 1 << 5,
+            NeighbourCellBottomCenter = 1 << 6,
+            NeighbourCellBottomRight = 1 << 7,
+        };
+
         struct MapSegment
         {
             void initFogOfWar();
@@ -114,12 +127,11 @@ namespace MWRender
             void saveFogOfWar(ESM::FogTexture& fog) const;
             void createFogOfWarTexture();
 
+            std::uint8_t mLastRenderNeighbourFlags = 0;
+            bool mHasFogState = false;
             osg::ref_ptr<osg::Texture2D> mMapTexture;
             osg::ref_ptr<osg::Texture2D> mFogOfWarTexture;
             osg::ref_ptr<osg::Image> mFogOfWarImage;
-
-            bool needUpdate = true;
-            bool mHasFogState = false;
         };
 
         typedef std::map<std::pair<int, int>, MapSegment> SegmentMap;
@@ -147,6 +159,8 @@ namespace MWRender
 
         bool mInterior;
         osg::BoundingBox mBounds;
+
+        std::uint8_t getExteriorNeighbourFlags(int cellX, int cellY) const;
     };
 
 }