UV map

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• UV Mapping is the process of aligning and adjusting how a Texture (VTF) is applied to a specific Polygonal Mesh. (I'm using the term "mesh" for both brush and model geometry.)
  • To UV map Models use XSI Texture Editor.
  • To UV map Brushes use Hammer Face Edit Dialog.
  • Valve Material Type files can also specify UV mapping adjustments for each VTF used by a particular material, via the $basetexturetransform, $bumptransform, etc VMT parameters.
    • Todo: confirm: these only work for VMTs applied to Brushes, not to Models?
    • UV coordinates (eg "center" and/or "translate" <integer U> <integer V> ?)
    • UV angles (eg "rotate" <angles> ?)
    • UV divisors (eg "scale" <float U> <float V> ?)

• Models tend to have a more complex mesh than brushes, which makes UV mapping much more fiddly. Model VTFs therefore tend to be created specially to map easily and efficiently onto one specific model only. Models may use multiple (alternative) skins, so long as the layout of each VTF corresponds to the model's UV map.

• A model's UV map is an index specifying which area of the relevant VTFs to apply to each specific polygon of the mesh. The UV map itself does not contain any pixel values (colour, etc), it only indexes the mesh's XYZ vertices to corresponding texture UV coordinates. Each UV map is therefore specific to a mesh rather than a texture file, and so it is stored as part of the mesh file. A mesh may only have one UV map, but it can use multiple or alternate skins, so long as the layout (coordinates) of each VTF skin is the same.

• Todo: confirm: "Texture Mapping" means "UV mapping" and a "Texture Map" is a "UV map"?

• See wikipedia:UV mapping for the theory.
• See wikipedia:UVW mapping (used in 3DS Max only?)