Add decrement operators in ChunkIndex for calculation of parent index

modules/globebrowsing/chunk/chunkindex.cpp

@@ -58,6 +58,26 @@ namespace openspace {
         return ChunkIndex(x / 2, y / 2, level - 1);
     }
 
+    ChunkIndex& ChunkIndex::operator--() {
+        x /= 2;
+        y /= 2;
+        level--;
+        return *this;
+    }
+
+    ChunkIndex ChunkIndex::operator--(int) {
+        ChunkIndex tmp(*this);
+        --(*this);
+        return tmp;
+    }
+
+    ChunkIndex& ChunkIndex::operator-=(unsigned int levels) {
+        x <<= levels;
+        y <<= levels;
+        level -= levels;
+        return *this;
+    }
+
 
     /**
     Gets the tile at a specified offset from this tile.

modules/globebrowsing/chunk/chunkindex.h

@@ -71,6 +71,11 @@ struct ChunkIndex {
     }
 
     ChunkIndex parent() const;
+    
+    ChunkIndex& operator--();
+    ChunkIndex operator--(int);
+
+    ChunkIndex& operator-=(unsigned int levels);
 
     bool isWestChild() const {
         return x % 2 == 0;
@@ -88,6 +93,7 @@ struct ChunkIndex {
         return y % 2 == 1;
     }
 
+
     ChunkIndex child(Quad q) const;