# Model Definition
The 3D geometry of a model: its vertices, the triangles between them, and the colour, texture
and transparency of each of those.

The cache holds three generations of the format, which {ref}`TModelDefinition.Create` tells
apart and decodes.


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## ModelDefinition.DetectFormat
```pascal
function TModelDefinition.DetectFormat(const data: TByteArray): Integer; static;
```
Which of the model formats `data` is in: `0` for the original one, or `2` or `3` for the two
that came after it.

The newer formats mark themselves with a two byte tag at the very end of the buffer. The
original one has no tag, so anything without a recognised one is assumed to be it.


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## ModelDefinition.DecodeOldFormat
```pascal
function TModelDefinition.DecodeOldFormat(id: Integer; const data: TByteArray): TModelDefinition; static;
```
Decodes a model in the original format. Use {ref}`TModelDefinition.Create` rather than calling
this directly.

A model is not stored as one stream but as several parallel ones, and the header at the end of
the buffer gives the length of each so that the cursors into them can be positioned before
anything is read. Vertices are deltas from the vertex before, and face indices are deltas from
the face before, in one of four ways that the compression type per face selects between.


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## ModelDefinition.DecodeType2
```pascal
function TModelDefinition.DecodeType2(id: Integer; const data: TByteArray): TModelDefinition; static;
```
Decodes a model in format 2, which adds vertex skinning groups. Use
{ref}`TModelDefinition.Create` rather than calling this directly.

It is laid out like the original format - see {ref}`TModelDefinition.DecodeOldFormat` - with the
flags in the trailing header rearranged and the animation groups added.


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## ModelDefinition.DecodeType3
```pascal
function TModelDefinition.DecodeType3(id: Integer; const data: TByteArray): TModelDefinition; static;
```
Decodes a model in format 3, the current one. Use {ref}`TModelDefinition.Create` rather than
calling this directly.

The layout follows {ref}`TModelDefinition.DecodeType2`, with textures given their own stream and
their mapping described per texture rather than per face.


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## ModelDefinition.Create
```pascal
function TModelDefinition.Create(id: Integer; const data: TByteArray): TModelDefinition; static;
```
Decodes a model's geometry: its vertices, the triangles between them, and the colour, texture
and transparency of each of those.

Which of the three formats to decode is worked out by {ref}`TModelDefinition.DetectFormat`.


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## ModelDefinition.Recolor
```pascal
procedure TModelDefinition.Recolor(findColor, replaceColor: Integer);
```
Repaints every face currently coloured `findColor`.

This is how one model serves many items: the cache stores the recolours an item wants alongside
it rather than storing a separate model per colour.


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## ModelDefinition.Retexture
```pascal
procedure TModelDefinition.Retexture(findTex, replaceTex: Integer);
```
{ref}`TModelDefinition.Recolor` for textures rather than flat colours.


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## ModelDefinition.Resize
```pascal
procedure TModelDefinition.Resize(x, y, z: Integer);
```
Scales the model along each axis, where `128` is its original size.