ClassicWorld file format

ClassicWorld is a level format devised by tyteen4a03 with input from fragmer for use by custom Minecraft Classic servers. Originally designed for cloudBox, it is extensible enough to be used by any server. Metadata allows to attach software-specific data, and to easily share Classic Protocol Extension settings.

Specification

Basic structure

All tags are required, unless noted otherwise. Also note that ordering of named tags cannot always be guaranteed in NBT libraries. Therefore, when reading files, do not assume a specific order of named tags within a compound tag. However, when writing files, do try to stick to this order if possible.

TAG_Compound("ClassicWorld"): 14 entries {
  TAG_Byte("FormatVersion")
  TAG_String("Name")
  TAG_Byte_Array("UUID")
  TAG_Short("X")
  TAG_Short("Y")
  TAG_Short("Z")
  TAG_Compound("CreatedBy"): 2 entries {
    TAG_String("Service")
    TAG_String("Username")
  }
  TAG_Compound("MapGenerator"): 2 entries {
    TAG_String("Software")
    TAG_String("MapGeneratorName")
  }
  TAG_Long("TimeCreated")
  TAG_Long("LastAccessed")
  TAG_Long("LastModified")
  TAG_Compound("Spawn"): 5 entries {
    TAG_Short("X")
    TAG_Short("Y")
    TAG_Short("Z")
    TAG_Byte("H")
    TAG_Byte("P")
  }
  TAG_Byte_Array("BlockArray")
  TAG_Compound("Metadata") {}
}

• FormatVersion is a constant, currently at 1
• Name should be limited to 64 characters in length, and contain only characters that can be displayed in Minecraft.
• UUID is a unique 128-bit identifier for this map (for example a GUID), saved as a 16-byte array. Must be set when the map is originally generated, and must be preserved intact when loading/saving worlds. UUID stands for Universally Unique Identifier.
• X is the width (first horizontal dimension) of the map.
• Y is the height (vertical dimension) of the map.
• Z is the length (second horizontal dimension) of the map.
• TimeCreated is a UTC Unix timestamp that's set when the map is originally generated.
• LastModified is a UTC Unix timestamp that's set when the map's blocks are modified. Changes to spawn point or metadata should not affect this date. Optional.
• LastAccessed is a UTC Unix timestamp that's set when the map is accessed by any player. Optional.
• Spawn compound tag defines the point where players spawn on the map. All coordinates are in player-position units (32 units per block).
  • X is the first horizontal component of player's position.
  • Y is the vertical component of player's position.
  • Z is the second horizontal component of player's position.
  • H is the heading (yew) component of player's orientation.
  • P is the pitch component of player's orientation.
• CreatedBy identifies the creator of this map. Optional compound.
  • Username is the name of a player.
  • Service can be "Minecraft" (for Minecraft.net usernames) or "ClassiCube" (for ClassiCube.net usernames).
• MapGenerator contains information related to map generation. Optional compound.
  • Software is the name of software that originally generated this map (e.g. "cloudBox" or "fCraft").
  • MapGeneratorName is the name of a specific generation method used by the software (e.g. "Realistic" or "Flat").
• BlockArray contains the actual block data, 1 byte per block. Same packing order as in LevelDataChunk packets.
• Metadata contains all kinds of software- and plugin-specific data.

Metadata structure

The Metadata compound tag must contain zero or more named compound tags, each named after a specific software that produced them. Each of those compound tags should contain zero or more named compound tags, one for each logical grouping (e.g. for each plugin or subsystem). An example metadata tag, with two softwares and 3 groups, is shown here:

TAG_Compound("Metadata") {
  TAG_Compound("(SomeSoftware)") {
    TAG_Compound("(OneGroup)") {
      ...implementation-specific contents...
    }
    TAG_Compound("(AnotherGroup)") {
      ...implementation-specific contents...
    }
  }
  TAG_Compound("(OtherSoftware)") {
    TAG_Compound("(Group)") {
      ...implementation-specific contents...
    }
  }
}

Metadata implementation suggestions

Non-spatial metadata

For metadata that does not refer to specific blocks, any tag structure within a group tag is fine.

Sparse metadata for some blocks/coordinates

For metadata that refers to several specific blocks/coordinates, ClassicWorld format suggests the following format.

TAG_Compound("(SomeSoftware)") {
  TAG_Compound("(SomeGroup)") {
    TAG_Int_Array("BlockIndices")
    TAG_List("BlockMetadata") {}
  }
}

• BlockIndices is an array of block indices, each referring to a position in the BlockArray.
• BlockMetadata is a list of unnamed tags, of the same length and order as BlockIndices. Each tag in BlockMetadata refers to a coordinate in BlockIndices.

Data for every block/coordinate

In the common case of 1 byte or 1 integer being attached to every block/coordinate on the map, simply use a ByteArray/IntArray tag of the same length and order as BlockArray.

When more fixed-length data is needed, use one or more List tags, each of the same length and order as BlockArray.

When a variable amount of information is needed to be stored for every block/coordinate, use a List of Compound tags. Again, same length and order as BlockArray should be used.

TAG_Compound("(SomeSoftware)") {
  TAG_Compound("(SomeGroup)") {
    TAG_Byte_Array("OneByteForEveryBlock")
    TAG_Int_Array("OneIntForEveryBlock")
    TAG_List("CustomDataForEveryBlock")
  }
}

Classic Protocol Extension metadata

Metadata name "CPE" is reserved for Classic Protocol Extension data, and has standardized contents. Any or all of the below sections may be present, each corresponding to a CPE extension. Each group contains an Int tag named ExtensionVersion.

ClickDistance

Stores world-specific setting for ClickDistance extension. Note that Distance should be in player-position units (32 units per block).

TAG_Compound("ClickDistance"): 2 entries {
  TAG_Int("ExtensionVersion")
  TAG_Short("Distance")
}

CustomBlocks

Stores world-specific setting for CustomBlocks extension.

TAG_Compound("CustomBlocks"): 3 entries {
  TAG_Int("ExtensionVersion")
  TAG_Short("SupportLevel")
  TAG_Byte_Array("Fallback"): [256 bytes]
}

The purpose of the Fallback array is to allow servers with lower SupportLevel to load maps created by servers with higher SupportLevel. In such cases, any unsupported block IDs can be substituted using Fallback mapping. For instance, when a [hypothetical] block ID 200 is encountered, loading software should substitute it with the value of Fallback[200].

EnvColors

Stores world-specific setting for EnvColors extension. Color variables that are simply set to "default" (-1,-1,-1) may be omitted.

TAG_Compound("EnvColors"): 6 entries {
  TAG_Int("ExtensionVersion")
  TAG_Compound("Sky"): 3 entries {
    TAG_Short("R")
    TAG_Short("G")
    TAG_Short("B")
  }
  TAG_Compound("Cloud"): 3 entries {
    TAG_Short("R")
    TAG_Short("G")
    TAG_Short("B")
  }
  TAG_Compound("Fog"): 3 entries {
    TAG_Short("R")
    TAG_Short("G")
    TAG_Short("B")
  }
  TAG_Compound("Ambient"): 3 entries {
    TAG_Short("R")
    TAG_Short("G")
    TAG_Short("B")
  }
  TAG_Compound("Sunlight"): 3 entries {
    TAG_Short("R")
    TAG_Short("G")
    TAG_Short("B")
  }
}

EnvMapAppearance

Stores world-specific setting for EnvMapAppearance extension.

TAG_Compound("EnvMapAppearance"): 5 entries {
  TAG_Int("ExtensionVersion")
  TAG_String("TextureURL")
  TAG_Byte("SideBlock")
  TAG_Byte("EdgeBlock")
  TAG_Short("SideLevel")
}

Support

These custom servers plan to add support for CW World Format: cloudBox, fCraft