Validate constraint: #polygons per tile (recastnavigation#449)

* Validate constraint: #polygons per tile

When adding a tile to a NavMesh, ensure that the number of polygons in that tile fit in the poly ID address space.

* Improve dtNavMeshParams field documentation

Detour/Include/DetourNavMesh.h

@@ -329,8 +329,8 @@ struct dtNavMeshParams
 	float orig[3];					///< The world space origin of the navigation mesh's tile space. [(x, y, z)]
 	float tileWidth;				///< The width of each tile. (Along the x-axis.)
 	float tileHeight;				///< The height of each tile. (Along the z-axis.)
-	int maxTiles;					///< The maximum number of tiles the navigation mesh can contain.
-	int maxPolys;					///< The maximum number of polygons each tile can contain.
+	int maxTiles;					///< The maximum number of tiles the navigation mesh can contain. This and maxPolys are used to calculate how many bits are needed to identify tiles and polygons uniquely.
+	int maxPolys;					///< The maximum number of polygons each tile can contain. This and maxTiles are used to calculate how many bits are needed to identify tiles and polygons uniquely.
 };
 
 /// A navigation mesh based on tiles of convex polygons.

Detour/Source/DetourNavMesh.cpp

@@ -914,6 +914,13 @@ dtStatus dtNavMesh::addTile(unsigned char* data, int dataSize, int flags,
 		return DT_FAILURE | DT_WRONG_MAGIC;
 	if (header->version != DT_NAVMESH_VERSION)
 		return DT_FAILURE | DT_WRONG_VERSION;
+
+#ifndef DT_POLYREF64
+	// Do not allow adding more polygons than specified in the NavMesh's maxPolys constraint.
+	// Otherwise, the poly ID cannot be represented with the given number of bits.
+	if (m_polyBits < dtIlog2(dtNextPow2((unsigned int)header->polyCount)))
+		return DT_FAILURE | DT_INVALID_PARAM;
+#endif
 
 	// Make sure the location is free.
 	if (getTileAt(header->x, header->y, header->layer))