# GEM RTS Binary File Formats

Most of the binary files GEM RTS are chunk-based containers.

Any chunk starts with a four-byte magic identifier (`Chunk_ID`), usually a human-readable combination of four ascii chars, and the following data is optional.

Chunks do not have size, so a parsing program should calculate it based on a certain structure.

## File name

<table><thead><tr><th width="135.3125">File name</th><th>Description</th></tr></thead><tbody><tr><td><code>.mesh</code></td><td>Container file that stores one or more mesh resources in <code>.ply</code> format. Used to reduce the number of individual files in the file system.</td></tr><tr><td><code>.cmesh</code></td><td>Container file that stores one or more collision and physics mesh resources in <code>.vol</code> format. Used to reduce the number of individual files in the file system.</td></tr><tr><td><code>.animation</code></td><td>Container file that stores one or more animation resources in <code>.anm</code> format. Used to reduce the number of individual files in the file system.</td></tr></tbody></table>

## File extensions

<table><thead><tr><th width="121.28125">Extension</th><th>Description</th></tr></thead><tbody><tr><td><code>.ply</code></td><td>Mesh resource stored inside a <code>.mesh</code> container.</td></tr><tr><td><code>.anm</code></td><td>Animation resource stored inside a <code>.animation</code> container.</td></tr><tr><td><code>.vol</code></td><td>Collision and physics mesh resource stored inside a <code>.cmesh</code> container.</td></tr></tbody></table>

## Data types

<table><thead><tr><th>Type</th><th width="328.2109375">Description</th><th>Size</th></tr></thead><tbody><tr><td>chunk</td><td>Quadruple byte magic identifier, four ASCII symbols.</td><td>4</td></tr><tr><td>int8 / uint8</td><td>Single byte signed / unsigned integer.</td><td>1</td></tr><tr><td>int16 / uint16</td><td>Double byte signed / unsigned integer.</td><td>2</td></tr><tr><td>int32 / uint32</td><td>Quadruple byte signed / unsigned integer.</td><td>4</td></tr><tr><td>float</td><td>Quadruple byte floating point number.</td><td>4</td></tr><tr><td>string8</td><td><p>Short string:</p><ul><li>uint8 length</li><li>char - uint8[length] symbols, <strong>no null terminator</strong>.</li></ul></td><td>1+</td></tr><tr><td>string8/24<br>or <br>string24</td><td><p>Smart long string.<br>For short strings, where length is less than 255, the structure is the same as string8. <br>If length is greater than or equal to 255:</p><ul><li>uint8 signature </li><li>0xFF - uint24 long_length</li><li>char - uint8[long_length] symbols, <strong>no null terminator.</strong></li></ul></td><td>1+</td></tr><tr><td>string32</td><td><p>Legacy format: </p><ul><li>uint32 long_length</li><li>char - uint8[long_length] symbols, <strong>no null terminator</strong>.</li></ul></td><td>4+</td></tr></tbody></table>

## Other conventions

| **Convention**     | **Description**                                                                                                                           |
| ------------------ | ----------------------------------------------------------------------------------------------------------------------------------------- |
| struct             | Nested data structure.                                                                                                                    |
| `<type>[<number>]` | Fixed-size array of type `<type>` containing `<number>` elements.                                                                         |
| `<type>[<name>]`   | Variable-size array of type `<type>`. The number of elements is specified by the value stored in field `<name>`.                          |
| `unorm8`           | Representation of fractional floating-point values in the range \[0..1] using an 8-bit unsigned integer (`uint8`) in the range \[0..255]. |
| Little-endian      | Byte order convention used for multi-byte integer values. The least significant byte is stored first.                                     |


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