UV editor and FaceSelect
Relevant to Blender v2.31
Introduction
The UV-Editor allows you to map textures directly onto the faces of meshes. Each face can have individual texture coordinates and an individual image assigned to it, and can be combined with vertex colors to make the texture brighter or darker or to give it a color.
By using the UV-Editor each face of the Mesh is assigned two extra features:
four UV coordinates - These coordinates define the way an image or a texture is mapped onto the face. These are 2D coordinates, which is why they're called UV, to distinguish them from XYZ coordinates. These coordinates can be used for rendering or for realtime OpenGL display.
a link to an Image - Every face in Blender can have a link to a different image. The UV coordinates define how this image is mapped onto the face. This image then can be rendered or displayed in realtime.
A 3D window has to be in "Face Select" mode to be able to assign Images or change UV coordinates of the active Mesh Object.
Assigning Images to faces
First add a Mesh Object to your Scene, then enter the FaceSelect choosing the UV face select entry in the Mode menu (Figure 38).
Your Mesh will now be drawn Z-buffered. If you enter the Textured draw mode (ALT-Z, also called "potato mode") you will see your Mesh drawn in white, which indicates that there is currently no Image assigned to these faces.
Press AKEY and all of the faces of the Mesh will be selected and highlighted by dotted lines.
Change one window into the Image Window with SHIFT-F10. Here you can load or browse an image with the Load button. Images have to be multiples of 64 pixels (64x64, 128x64 etc.) to be able to drawn in realtime (note: most 3D cards don't support images larger than 256x256 pixels). However, Blender can render all assigned images regardless of size when creating stills or animations.
Loading or browsing an image in FaceSelect automatically assigns the image to the selected faces. You can immediately see this in the 3D window (when in Textured view mode - Figure 39).
Selecting faces
You can select faces with RightMouse or with BorderSelect (BKEY) in the 3D window. If you have problems with selecting the desired faces, you can also enter EditMode and select the vertices you want. After leaving EditMode the faces defined by the selected vertices should be selected as well.
Only one face is active. Or in other words: the Image Window only displays the image of the active face. As usual within Blender, only the last selected face is active and selection is done with RMB.
Editing UV coordinates
In the ImageWindow you will see a representation of your selected faces as yellow or purple vertices connected with dotted lines. You can use the same techniques here as in the Mesh EditMode to select, move, rotate, scale, and so on. With the Lock button pressed you will also see realtime feedback in 3D of what you are doing.
In the 3D window, you can press UKEY in FaceSelect mode to get a menu to calculate UV coordinates for the selected faces (Figure 40).
Cube - This determines cubical mapping. A number requester asks for a scaling property.
Cylinder, Sphere - Cylindrical/spherical mapping, calculated from the center of the selected faces.
Bounds to 1/8, 1/4, 1/2, 1/1 - UV Coordinates are calculated using the projection as displayed in the 3D window, then scaled to the given fraction of the image texture.
Standard 1/8, 1/4, 1/2, 1/1 - Each face gets a set of default square UV coordinates which are then scaled to the requested fraction of the image texture.
From Window - UV coordinates are calculated using the projection as displayed in the 3D window.
In the ImageWindow Toolbar (Figure 41) the third button keeps your UV polygons square while editing them, while the fourth clips them to the size of the image.
Some tips:
Press RKEY in the 3D window to get a menu that allows rotation of the UV coordinates.
It is sometimes necessary to move image files to a new location on your harddisk. To do so, press the Replace button in the ImageWindow header to get a "Replace Image name" window. You can fill in the old directory name, and the new one. Pressing "OK" changes the paths of all images used in Blender using the old directory. (Note: use as new directory the code "//" to indicate the directory where the Blender file is).
You can also use FaceSelect and VertexPaint (VKEY) simultaneously. Vertex painting then only works on the selected faces. This feature is especially useful to paint faces as if they don't share vertices. Note that the vertex colors are used to modulate the brightness or color of the applied image texture.
Rendering and UV coordinates
Even without an image assigned to faces, you can render textures utilizing the UV coordinates using the green "UV" button in the MaterialButtons (F5) menu.
To render the assigned Image texture as well, press the "TexFace" button in the MaterialButtons. Combine this with the "VertexCol" option to use vertex colors too.