Map generation limit: Rewrite

The previous implementation applied the setting to blockpos_over_limit(),
objectpos_over_limit() and in createSector(), causing many bugs near the
world edge.

First revert the previous implementation.
Rename blockpos_over_limit() to blockpos_over_max_limit() for clarity.
Add a new function to mapblock.h called blockpos_over_mapgen_limit() that
checks against the map_generation_limit setting, and call this only from
the code that decides where mapgen stops.
Use MAX_MAP_GENERATION_LIMIT in objectpos_over_limit() to reduce the
chance of bugs, there is no need to use map_generation_limit here.

src/clientiface.cpp

@@ -238,9 +238,9 @@ void RemoteClient::GetNextBlocks (
 				continue;
 
 			/*
-				Do not go over-limit
+				Do not go over max mapgen limit
 			*/
-			if (blockpos_over_limit(p))
+			if (blockpos_over_max_limit(p))
 				continue;
 
 			// If this is true, inexistent block will be made from scratch

src/emerge.cpp

@@ -606,7 +606,7 @@ void *EmergeThread::run()
 			continue;
 		}
 
-		if (blockpos_over_limit(pos))
+		if (blockpos_over_max_limit(pos))
 			continue;
 
 		bool allow_gen = bedata.flags & BLOCK_EMERGE_ALLOW_GEN;

src/map.cpp

@@ -1380,9 +1380,9 @@ bool ServerMap::initBlockMake(v3s16 blockpos, BlockMakeData *data)
 	v3s16 full_bpmin = bpmin - extra_borders;
 	v3s16 full_bpmax = bpmax + extra_borders;
 
-	// Do nothing if not inside limits (+-1 because of neighbors)
-	if (blockpos_over_limit(full_bpmin) ||
-		blockpos_over_limit(full_bpmax))
+	// Do nothing if not inside mapgen limits (+-1 because of neighbors)
+	if (blockpos_over_mapgen_limit(full_bpmin) ||
+			blockpos_over_mapgen_limit(full_bpmax))
 		return false;
 
 	data->seed = getSeed();
@@ -1549,25 +1549,14 @@ ServerMapSector *ServerMap::createSector(v2s16 p2d)
 #endif
 
 	/*
-		Do not create over-limit.
-		We are checking for any nodes of the mapblocks of the sector being beyond the limit.
-		A sector is a vertical column of mapblocks, so sectorpos is like a 2D blockpos.
-
-		At the negative limit we are checking for
-			block minimum nodepos < -mapgenlimit.
-		At the positive limit we are checking for
-			block maximum nodepos > mapgenlimit.
-
-		Block minimum nodepos = blockpos * mapblocksize.
-		Block maximum nodepos = (blockpos + 1) * mapblocksize - 1.
+		Do not create over max mapgen limit
 	*/
-	const u16 map_gen_limit = MYMIN(MAX_MAP_GENERATION_LIMIT,
-		g_settings->getU16("map_generation_limit"));
-	if (p2d.X * MAP_BLOCKSIZE < -map_gen_limit
-			|| (p2d.X + 1) * MAP_BLOCKSIZE - 1 > map_gen_limit
-			|| p2d.Y * MAP_BLOCKSIZE < -map_gen_limit
-			|| (p2d.Y + 1) * MAP_BLOCKSIZE - 1 > map_gen_limit)
-		throw InvalidPositionException("createSector(): pos. over limit");
+	const s16 max_limit_bp = MAX_MAP_GENERATION_LIMIT / MAP_BLOCKSIZE;
+	if (p2d.X < -max_limit_bp ||
+			p2d.X >  max_limit_bp ||
+			p2d.Y < -max_limit_bp ||
+			p2d.Y >  max_limit_bp)
+		throw InvalidPositionException("createSector(): pos. over max mapgen limit");
 
 	/*
 		Generate blank sector
@@ -1708,10 +1697,10 @@ MapBlock * ServerMap::createBlock(v3s16 p)
 			FUNCTION_NAME, p.X, p.Y, p.Z);
 
 	/*
-		Do not create over-limit
+		Do not create over max mapgen limit
 	*/
-	if (blockpos_over_limit(p))
-		throw InvalidPositionException("createBlock(): pos. over limit");
+	if (blockpos_over_max_limit(p))
+		throw InvalidPositionException("createBlock(): pos. over max mapgen limit");
 
 	v2s16 p2d(p.X, p.Z);
 	s16 block_y = p.Y;
@@ -2655,7 +2644,7 @@ void MMVManip::initialEmerge(v3s16 blockpos_min, v3s16 blockpos_max,
 		if(block_data_inexistent)
 		{
 
-			if (load_if_inexistent && !blockpos_over_limit(p)) {
+			if (load_if_inexistent && !blockpos_over_max_limit(p)) {
 				ServerMap *svrmap = (ServerMap *)m_map;
 				block = svrmap->emergeBlock(p, false);
 				if (block == NULL)

src/mapblock.h

@@ -669,41 +669,37 @@ typedef std::vector<MapBlock*> MapBlockVect;
 
 inline bool objectpos_over_limit(v3f p)
 {
-	// MAP_BLOCKSIZE must be subtracted to avoid an object being spawned just
-	// within the map generation limit but in a block and sector that extend
-	// beyond the map generation limit.
-	// This avoids crashes caused by sector over limit in createSector().
-	const float object_limit = (MYMIN(MAX_MAP_GENERATION_LIMIT,
-		g_settings->getU16("map_generation_limit")) - MAP_BLOCKSIZE) * BS;
-	return (p.X < -object_limit
-		|| p.X > object_limit
-		|| p.Y < -object_limit
-		|| p.Y > object_limit
-		|| p.Z < -object_limit
-		|| p.Z > object_limit);
+	const float max_limit_bs = MAX_MAP_GENERATION_LIMIT * BS;
+	return p.X < -max_limit_bs ||
+		p.X >  max_limit_bs ||
+		p.Y < -max_limit_bs ||
+		p.Y >  max_limit_bs ||
+		p.Z < -max_limit_bs ||
+		p.Z >  max_limit_bs;
 }
 
-/*
-	We are checking for any node of the mapblock being beyond the limit.
-
-	At the negative limit we are checking for
-		block minimum nodepos < -mapgenlimit.
-	At the positive limit we are checking for
-		block maximum nodepos > mapgenlimit.
+inline bool blockpos_over_max_limit(v3s16 p)
+{
+	const s16 max_limit_bp = MAX_MAP_GENERATION_LIMIT / MAP_BLOCKSIZE;
+	return p.X < -max_limit_bp ||
+		p.X >  max_limit_bp ||
+		p.Y < -max_limit_bp ||
+		p.Y >  max_limit_bp ||
+		p.Z < -max_limit_bp ||
+		p.Z >  max_limit_bp;
+}
 
-	Block minimum nodepos = blockpos * mapblocksize.
-	Block maximum nodepos = (blockpos + 1) * mapblocksize - 1.
-*/
-inline bool blockpos_over_limit(v3s16 p)
+inline bool blockpos_over_mapgen_limit(v3s16 p)
 {
-	const u16 map_gen_limit = MYMIN(MAX_MAP_GENERATION_LIMIT,
-		g_settings->getU16("map_generation_limit"));
-	return (p.X * MAP_BLOCKSIZE < -map_gen_limit
-		|| (p.X + 1) * MAP_BLOCKSIZE - 1 > map_gen_limit
-		|| p.Y * MAP_BLOCKSIZE < -map_gen_limit
-		|| (p.Y + 1) * MAP_BLOCKSIZE - 1 > map_gen_limit
-		|| p.Z * MAP_BLOCKSIZE < -map_gen_limit
-		|| (p.Z + 1) * MAP_BLOCKSIZE - 1 > map_gen_limit);
+	const s16 mapgen_limit_bp = rangelim(
+		g_settings->getS16("map_generation_limit"), 0, MAX_MAP_GENERATION_LIMIT) /
+		MAP_BLOCKSIZE;
+	return p.X < -mapgen_limit_bp ||
+		p.X >  mapgen_limit_bp ||
+		p.Y < -mapgen_limit_bp ||
+		p.Y >  mapgen_limit_bp ||
+		p.Z < -mapgen_limit_bp ||
+		p.Z >  mapgen_limit_bp;
 }
 
 /*