This specification describes a format for including machine-readable metadata in an assembled Bedrock program.
Program metadata takes the form of a structured table of pointers in the first 24 bytes of a Bedrock program. The first ten bytes are a metadata identifier, and the remaining fourteen bytes represent seven pointers to data stored elsewhere in the program. A pointer with a value of zero indicates that the associated item has not been provided.
| Address | Bytes | Name | Description |
|---|---|---|---|
0x0000 |
10 | Identifier | 41 00 18 42 45 44 52 4F 43 4B |
0x000a |
2 | Name | Program name and version |
0x000c |
2 | Authors | Names of program authors |
0x000e |
2 | Description | Short program description |
0x0010 |
2 | Background colour | Icon background colour |
0x0012 |
2 | Foreground colour | Icon foreground colour |
0x0014 |
2 | Small icon | 24x24 pixel monochrome icon |
0x0016 |
2 | Large icon | 64x64 pixel monochrome icon |
Identifier
The identifier is a ten-byte sequence at the start of the file that identifies an assembled Bedrock program from any other type of file. The value of the sequence must be 41 00 18 42 45 44 52 4F 43 4B. If the first ten bytes of a file do not match this sequence, the following bytes cannot be parsed as metadata, and the file is not necessarily a Bedrock program.
The first three bytes of the identifier 41 00 18 are the assembled bytes of the Bedrock instruction JMP:0018, which will prevent the metadata from being executed when the program is run. They also prevent the Bedrock program from being interpreted as a text file, as the 00 byte is a null terminator and the 18 byte is a non-printable character. The remaining seven bytes of the identifier are the ASCII-encoded string BEDROCK, which can provide a human-readable clue if a Bedrock program is found without any accompanying instructions or documentation.
String values
String values are stored as UTF-8 encoded null-terminated byte sequences.
Name
The value at address 0x000a is a big-endian 16-bit pointer that points to a null-terminated UTF-8 string representing the name and version of the program. A pointer value of zero indicates that a name hasn’t been provided.
The format of the string is the program name, followed by the slash character 0x2F, followed by the program version. The program version is not required to fit any particular format, but it is recommended that it is not prefixed with v or version.
Authors
The value at address 0x000c is a big-endian 16-bit pointer that points to a null-terminated UTF-8 string representing a list of authors of the program. A pointer value of zero indicates that a list of authors hasn’t been provided.
The format of the string is a list of author names, with each name separated from the next by the newline character 0A. A newline character following the final name is optional.
Description
The value at address 0x000e is a big-endian 16-bit pointer that points to a null-terminated UTF-8 string representing a short description of the program. A pointer value of zero indicates that a description hasn’t been provided.
The program description should be a short sentence that concisely describes the category or purpose of the program.
Colour values
Colour values are stored as big-endian 16-bit values that each encode a 12-bit, 4-bits-per-channel RGB colour.
The 0x0f00 bits of a colour value hold the red component, the 0x00f0 bits hold the green component, and the 0x000f bits hold the blue component. The 0xf000 bits of a colour value are ignored.
Background colour
The value at address 0x0010 is a big-endian 16-bit pointer that points to a big-endian 16-bit colour value representing the background colour of the program icon. A pointer value of zero indicates that a background colour hasn’t been provided.
Foreground colour
The value at address 0x0012 is a big-endian 16-bit pointer that points to a big-endian 16-bit colour value representing the foreground colour of the program icon. A pointer value of zero indicates that a foreground colour hasn’t been provided.
Icon values
Icons are stored as a sequence of 1-bit sprites. Each sprite is an 8-byte sequence that represents an 8x8 pixel monochrome bitmap. Each byte represents an 8-pixel row ordered from top to bottom. Each bit from highest to lowest represents the state of each pixel from left to right, with a set bit being drawn as the foreground colour and an unset bit being drawn as the background colour.
The sequence of sprites making up an icon are grouped left-to-right in rows, with the rows ordered top-to-bottom.
Small icon
The value at address 0x0014 is a big-endian 16-bit pointer that points to a 72 byte array representing a 3x3 sprite, 24x24 pixel, monochrome icon. A pointer value of zero indicates that a small icon hasn’t been provided.
Large icon
The value at address 0x0016 is a big-endian 16-bit pointer that points to a 512 byte array representing an 8x8 sprite, 64x64 pixel, monochrome icon. A pointer value of zero indicates that a large icon hasn’t been provided.