Graphics Programs Reference
In-Depth Information
will assume the grid is 256 pixels across and give
coordinates on that scale. You can turn this feature
off by pressing N to bring up the Properties region
of the UV Image editor and checking Normalized
in the Display panel, which will then give UV coor-
dinates between 0 and 1. The UV Image editor fol-
lows the same conventions as the 3D Viewport: You
can move, rotate, and scale any selected vertices
using the same keys as in the 3D Viewport, and you
can use the X and Y keys to constrain operators to
the horizontal and vertical axes of the UV grid. By
default, a mesh will not have any UV coordinates, so
there will be nothing to select until you unwrap it.
When you map an image to a mesh using its UV
coordinates, the image is scaled to fill the UV grid,
and each point of the mesh is then mapped to the
corresponding point in the image. Beyond the edges
of the UV grid, the image is repeated or extended so
that UV coordinates outside the grid are mapped to
part of the image as well. This allows you to repeat a
tileable texture (one that can be repeated side by side
and top to bottom without any discontinuity) over
the surface of your mesh by unwrapping the mesh to
be much bigger than the UV grid. Conversely, you
can unwrap a whole mesh (or even multiple meshes)
so that all the UV coordinates fit within the UV grid
Editing uV Coordinates
To edit UV coordinates, we use Blender's UV Image
editor along with the 3D Viewport. In general, when
working with UV coordinates, it's useful to switch
to Blender's UV editing layout using the drop-down
menu in the Info editor header (see Figure 8-2).
This brings up the UV Image editor shown on the
left and the 3D Viewport on the right.
It's helpful to add a Properties editor between
the UV Image editor and the 3D Viewport by right-
clicking the border between them and choosing Split
Area. When you set the new area as a Properties edi-
tor, you can access the Object Data tab for switching
between different UV coordinate sets and the Render
tab for accessing Texture Baking controls.
The UV Grid
We'll use the UV Grid in the Image editor to deter-
mine which portion of a texture or image is applied
to part of a mesh. The grid has coordinates that run
from 0 to 1, with the origin at the bottom left. By
default, these coordinates are multiplied by the size
of the image you select in order to give a number
in pixels. If you have no image selected, Blender
Layout dropdown
Mesh (in edit mode)
Image properties
UV unwrap
operators
UV grid
UV islands
Active
UV group
Active image
(click new to add)
Figure 8-2: A slightly modified UV Image editor layout. You can save this as the default layout by setting up your windows like
this in a new .blend file and choosing Save User Settings from the File menu.
 
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