CNavArea::ComputeApproachAreas(): fix hang on *.nav generating (#913)

regamedll/game_shared/bot/nav_area.cpp

@@ -4431,6 +4431,7 @@ inline bool IsAreaVisible(const Vector *pos, const CNavArea *area)
 // Determine the set of "approach areas".
 // An approach area is an area representing a place where players
 // move into/out of our local neighborhood of areas.
+// @todo Optimize by search from eye outward and modifying pathfinder to treat all links as bi-directional
 void CNavArea::ComputeApproachAreas()
 {
 	m_approachCount = 0;
@@ -4452,6 +4453,18 @@ void CNavArea::ComputeApproachAreas()
 	enum { MAX_PATH_LENGTH = 256 };
 	CNavArea *path[MAX_PATH_LENGTH];
 
+	enum SearchType
+	{
+		FROM_EYE,		///< start search from our eyepoint outward to farArea
+		TO_EYE,			///< start search from farArea beack towards our eye
+		SEARCH_FINISHED
+	};
+
+	// In order to *completely* enumerate all of the approach areas, we
+	// need to search from our eyepoint outward, as well as from outwards
+	// towards our eyepoint
+	for (int searchType = FROM_EYE; searchType != SEARCH_FINISHED; searchType++)
+	{
 		// In order to enumerate all of the approach areas, we need to
 		// run the algorithm many times, once for each "far away" area
 		// and keep the union of the approach area sets
@@ -4463,10 +4476,7 @@ void CNavArea::ComputeApproachAreas()
 			if (IsAreaVisible(&eye, farArea))
 				continue;
 
-		// make first path to far away area
 			ApproachAreaCost cost;
-		if (NavAreaBuildPath(this, farArea, nullptr, cost) == false)
-			continue;
 
 			//
 			// Keep building paths to farArea and blocking them off until we
@@ -4475,20 +4485,55 @@ void CNavArea::ComputeApproachAreas()
 			//
 			while (m_approachCount < MAX_APPROACH_AREAS)
 			{
+				CNavArea *from, *to;
+
+				if (searchType == FROM_EYE)
+				{
+					// find another path *to* 'farArea'
+					// we must pathfind from us in order to pick up one-way paths OUT OF our area
+					from = this;
+					to = farArea;
+				}
+				else // TO_EYE
+				{
+					// find another path *from* 'farArea'
+					// we must pathfind to us in order to pick up one-way paths INTO our area
+					from = farArea;
+					to = this;
+				}
+
+				// build the actual path
+				if (NavAreaBuildPath(from, to, NULL, cost) == false)
+					break;
+
 				// find number of areas on path
 				int count = 0;
 				CNavArea *area;
-			for (area = farArea; area; area = area->GetParent())
+				for (area = to; area; area = area->GetParent())
 					count++;
 
 				if (count > MAX_PATH_LENGTH)
 					count = MAX_PATH_LENGTH;
 
-			// build path in correct order - from eye outwards
+				// if the path is only two areas long, there can be no approach points
-			int i = count;
+				if (count <= 2)
-			for (area = farArea; i && area; area = area->GetParent())
+					break;
+
+				// build path starting from eye
+				int i = 0;
+
+				if (searchType == FROM_EYE)
 				{
-				path[--i] = area;
+					for(area = to; i < count && area; area = area->GetParent())
+					{
+						path[count - i - 1] = area;
+						++i;
+					}
+				}
+				else // TO_EYE
+				{
+					for(area = to; i < count && area; area = area->GetParent())
+						path[i++] = area;
 				}
 
 				// traverse path to find first area we cannot see (skip the first area)
@@ -4510,15 +4555,15 @@ void CNavArea::ComputeApproachAreas()
 					// (blocking farArea will cause all subsequent pathfinds to fail)
 					int block = (path[i] == farArea) ? i - 1 : i;
 
-				BlockedID[BlockedIDCount++] = path[block]->GetID();
-
 					if (block == 0)
-					break;
+						continue;
+
+					BlockedID[BlockedIDCount++] = path[block]->GetID();
 
 					// store new approach area if not already in set
 					int a;
 					for (a = 0; a < m_approachCount; a++)
-					if (m_approach[a].here.area == path[block - 1])
+						if (m_approach[a].here.area == path[block-1])
 							break;
 
 					if (a == m_approachCount)
@@ -4534,13 +4579,6 @@ void CNavArea::ComputeApproachAreas()
 					// we are done with this path
 					break;
 				}
-
-			// find another path to 'farArea'
-			ApproachAreaCost cost;
-			if (NavAreaBuildPath(this, farArea, nullptr, cost) == false)
-			{
-				// can't find a path to 'farArea' means all exits have been already tested and blocked
-				break;
 			}
 		}
 	}