A TronMoji is a pixel-based image represented by a hexadecimal string. This string is written to the TRX transaction memo field. Below are the technical details on how a TronMoji image is constructed and interpreted by code:

1. TronMoji Hexadecimal String

• The TronMoji image is encoded as a hexadecimal string.
• Each character in the string represents a color value for a single pixel and occupies a half byte.
• The hexadecimal string is 256 pixels, 128 bytes, and 256 hexadecimal characters long. Each byte is 2 hexadecimal characters.
• The hexadecimal string is always prepended with the prefix `tronmoji:` in the memo field. This brings the total bytes to 137.

2. Color Encoding

The color of each pixel is represented by a single hexadecimal digit (0-9, a-f).

The color values are mapped as follows:

• `0`: Transparent
• `1`: Black
• `2`: White
• `3-f`: Various colors in the HSL color space, calculated as `hsl((value - 2) * 27.6923, 100%, 50%)`.

3. Grid Dimensions

The grid dimensions (number of pixels in X and Y directions) are assumed to be 16x16.

Example: A 16x16 grid would have 256 pixels, requiring a 256-character hexadecimal string, prepended with 18-character hexadecimal string of 'tronmoji:', totaling 274 hexadecimal characters (274/2, 137 bytes).

4. UTF8 Violations

TronMojis violate UTF8 encoding, and as such must be written into both the memo and raw_hex fields manually.

When using TronWeb to create a transaction with a memo (stored in transaction.raw_data.data), the transaction.raw_data_hex representation of the transaction will include some prepended bytes before the actual memo data. These bytes are Protobuf encoding metadata, and they follow Protocol Buffers (ProtoBuf) varint encoding rules.

• Field Number and Wire Type
  • The first byte indicates the field number and wire type.
  • In Protobuf, a field is encoded as: (Field Number << 3) | Wire Type.
  • The memo's field number is 6, and the wire type for bytes is 2.
  • Thus, the first byte is: (6 << 3) | 2 = 0x32.
  • 6 << 3 shifts the field number left by 3 bits (0b00110000 or 0x30).
  • OR-ing with 0b00000010 (wire type 2 for length-delimited fields) results in 0x32.
• Length of the Memo (Varint-Encoded)
  • The next byte(s) indicate the length of the memo string in bytes.
  • This is encoded as a varint (a flexible-length encoding for small integers).
  • If the memo is short (≤127 bytes), this is just 1 byte.
  • If the memo is longer, multiple bytes are used (continuation bit set for values ≥ 128).

* For clarification: The memo field is 256 bytes, which would contain 512 individual hex 'characters' (0-f).