UV Unwrapping and Mapping

This next phase in character development involves preparing your model to be textured. As I briefly explained earlier, a model consists of a large number of points called vertices, and these points are connected via edges to make up a mesh object. Every vertex in 3D space has an X, Y, and Z

Table 1.2 3D Modeling File Types Used by Popular Modeling Software

Program

Type

File Extension

Notes

3ds Max

Scene file

MAX

3ds Max

Mesh file

3DS

3ds Max

AutoCAD drawing file

DXF

Maya

Binary model file

MB

Used with DOOM 3

Maya

ASCII scene file

MA

SoftImage

Scene file

SCN

SoftImage

Image file

SI

gameSpace

Scene file

SCN

gameSpace

Object file

COB

Same for trueSpace

WaveFront

Object file

OBJ

LightWave 3D

Object file

LWO

LightWave 3D

Scene file

LWS

ZBrush

ZTool native file

ZTL

Blender 3D

Image file

BLEND

(universal)

Stereo lithography image file

STL

Used for error checking

(universal)

Microsoft Direct3D object file

X

coordinate that defines its location in that space. When a mesh is created in a modeling program, a duplicate set of invisible vertices is also created, called texture coordinates, or UVs. By default, these vertices occupy the same space as the mesh vertices and are used to define how the texture bitmap wraps onto the model.

The letters u and v (and sometimes w) are initially the same coordinate values of the X, Y, and Z coordinates of a 3D model. After you've finished creating your character model, it is your job in 3ds Max to create a UV texture map so that you can use a program like Photoshop to paint a texture using this map as a reference. A texture map is two-dimensional; the X coordinate is horizontal and the Y coordinate is vertical, just like in planar geometry. In Max, UV mapping involves taking apart the texture coordinates and projecting them flat on a texture map plane. This is analogous to cutting a t-shirt at the seams and laying the pieces flat on a square surface.

During the UV process, a model's texture coordinates have been separated at "seams" and laid flat on a UV workspace. When the points here are no longer in 3D space, they do not have a third dimension, or W value—hence the term UV. From here, you can copy this map to Photoshop, paint it, and use the image in Max to texture your model. At this point, when any texture map is applied to your model, it is wrapped around the model according to the new UV layout. Also note that the model's vertices are unaffected by the UV coordinate manipulation process.

UV mapping is somewhat complex because you must take time to properly cut apart the UV vertices at hidden areas called seams. For instance, if you cut the front of a t-shirt up the middle, the texture will display a visible seam right up the middle because this is the start and end point around which the texture is wrapped. It is ideal to instead cut the vertices along the sides of the model so that the seams are not quite visible to the player.

Sometimes vertices might be crossed or the geometry might be invalid, causing kinks or errors in the UV map. It is also common practice to create a checkerboard map, to make it easier to view these errors.

Notice from Figure 1.1 at the beginning of this chapter that the UV mapping process bounces back and forth between modeling and texturing. You'll be doing this as you preview your texture and make model adjustments to finalize your character.

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