In this paragraph we will introduce the operation of Unwrapping. The Unwrap process is very important when it is necessary to accurately map textures on the surface of a 3D model, as in the field of texturing models for videogames. Essentially, through the unwrap we will “open” the entire surface of a mesh, making it flat, so that each point is identifiable by the coordinates: U horizontal and V vertical, so called to differentiate from the classic XY pair already used for the coordinates of 3D space. Let’s insert the Suzanne mesh into the scene and then switch to the UV Editing workspace.
You will find yourself with the layout divided into two windows (image above): on the right the 3D View in edit mode and on the left the UV Editor. Each primitive of Blender has a UV Map already ready to use. In the UV editor, all the faces of the model appear and we can operate in a completely analog way as we usually do in the 3D View. It is possible to zoom the view using the mouse wheel and there is a grid that behaves identically to the 3D View in Ortho mode. We also find a 2D cursor that positions itself in the point of the window where we will click with the left mouse button after activating the cursor mode in the toolbar.
The UV layout can be modified in the UV Editor analogously to how a mesh is modified in edit mode, so it is possible to select the vertices, edges, faces or islands (composed of faces) through one of these icons from left to right then we will click with the left button on the element that interests us. You will have the same selection tools already known for edit/object mode, that is the keys: A, B (box), C (circle) and Lasso. So you can grab and move the selected elements with the G key, rotate them with R, scale them with S, choosing their center point or the 2D Cursor as the pivot for the transformations. During each transformation we can observe the relative changes in real time in the Viewport (with the modes that make the mapped Textures visible). It is also possible to export the UV Layout from the UV menu > Export UV Layout at the desired resolution (.png) or directly in vector (.svg) format in order to process the textures using any 2D graphics software. Imagine now your texture adapted to a square (if it is not already) and visible as the background of the UV layout; you will understand that every point of any face of the model can correspond to a pixel of the texture (obviously using the UV coordinates). Below you will find two images that make it clear what the importance and function of UV Maps are. In fact, we can use a single texture to map an entire model regardless of its complexity. If the primitives of Blender, and the models exported from MakeHuman, already have adequate unwrapping, in all other cases and for our creations we must find the best way to open the model choosing between two different paths.
After selecting the faces of the model, we can use some unwrap techniques (U key) valid for certain types of shape:
- Cube projection
(sharp objects, as if composed of several cubes).
- Cylinder Projection
(closed curved surfaces similar to tubes).
- Spherical Projection
(objects with many curved surfaces or approximable to more or less deformed spheres).
We also find some automatic solutions such as the Smart UV Project with a logic capable of adapting to many simple and complex models. Increasing the Angle Limit value will give us an unwrap with less distortion and more presence of small groups of faces. Increasing the Island Margin, we will get more space between the islands/groups.
For all other situations, we will have to act differently. Let’s take for example the cube primitive equipped with this uv layout:
which is the classic geometric development of the cube; in fact, on some occasions the various known developments for each type of three-dimensional solid might be useful. In edit mode and with all the faces of the cube selected, we start the UV Mapping menu (U key) and reset the layout with the last option on the list: Reset. This will bring up a single square face that covers the entire layout (in reality it is the six faces of the cube overlapped) in the UV Editor window. At this point, in edit mode we select the edges of the cube as shown in the image
and always from the UV Mapping menu (U) we choose the Mark Seam option (also available in the Edge menu of the 3D View header). In this way, we have applied seams to the model. All that remains is to select all the faces of the cube, go to the UV Mapping menu, and here choose the Unwrap option. We will get the cross development seen earlier again. The Unwrap option is therefore an algorithm capable of cutting and opening the mesh organically, following the application of seams. First of all, we need to think about how to open the model, then apply the seams, and finally use the Unwrap to create the UV layout.
From the image above, depicting the Suzanne mesh, we understand that applying a modifier such as subsurf, the unwrapping is transformed consistently with the mesh.
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