Do not render air only blocks. Nice performance speed up! :-)

common/block.go

@@ -47,6 +47,7 @@ type (
 		MapContent []byte
 		AirId      int32
 		IgnoreId   int32
+		AirOnly    bool
 		IndexMap   map[int32]int32
 	}
 )
@@ -136,6 +137,7 @@ func NewDecodedBlock(data []byte, nameIndex map[string]int32) (db *DecodedBlock,
 
 	airId, ignoreId := int32(-1), int32(-1)
 	indexMap := make(map[int32]int32)
+	var airOnly bool
 	if version >= 22 {
 		offset++
 		numMappings := int(binary.BigEndian.Uint16(data[offset:]))
@@ -160,6 +162,7 @@ func NewDecodedBlock(data []byte, nameIndex map[string]int32) (db *DecodedBlock,
 				}
 			}
 		}
+		airOnly = airId != -1 && len(indexMap) == 0
 	}
 
 	db = &DecodedBlock{
@@ -167,6 +170,7 @@ func NewDecodedBlock(data []byte, nameIndex map[string]int32) (db *DecodedBlock,
 		MapContent: mapContent,
 		AirId:      airId,
 		IgnoreId:   ignoreId,
+		AirOnly:    airOnly,
 		IndexMap:   indexMap}
 
 	return

common/renderer.go

@@ -182,6 +182,11 @@ func (r *Renderer) RenderBlock(block *Block, nameIndex map[string]int32) (err er
 		return
 	}
 
+	if db.AirOnly {
+		r.Rejected++
+		return
+	}
+
 	w := r.width << 4
 	ofs := int(bz)*w<<4 + int(bx)<<4
 	yB := r.yBuffer