In this Blender tutorial I will introduce you to the concept of UV mapping in Blender.
Introduction
UV mapping is how we take a 3D mesh to a 2D space in order to texture the model
Think of it as unfolding a box and laying it out flat
The 2D UV maps correspond to the vertices, edges, and faces of the 3D mesh
The UV map is based upon a U (or the horizontal axis) and Y (or vertical axis) coordinate systems
When you have a mesh unwrapped, you can select vertices, edges, and faces just like you can on the 3D mesh
You can also select an entire island using the L-key or box-selection
You are also able to scale or rotate an island
You can check for stretching in a couple ways
You can use a UV grid which will produce a series of squares on the mesh where any stretched faces will appears as stretched squares [generated type]
A second method is by using the overlays dropdown menu and choosing “display stretch”
The darker the blue of the island, the less stretching there is – in the case of this mesh, there is some slight stretching on a few of the islands (as seen by the teal color)
If you turn on the UV sync selection and choose one of those teal colored islands, you can see which of the faces of the mesh is stretched
You want to avoid stretching at all costs – the only time this isn’t a problem is when you are using flat colors
Smart UV Project
There are multiple ways to UV unwrap a mesh within Blender but I will only be talking about the two most common ways in this tutorial
The quickest and easiest way to UV unwrap a mesh is by using smart UV project
This option means that Blender will cut the mesh based on the angles of the mesh
If I select the mesh and enter edit mode, I can UV unwrap the mesh
I make sure I have everything selected, use the U-key to open the UV unwrapping menu, and then select “smart UV project”
I now have a dialogue box where I can make some changes before I unwrap the mesh
Angle limit controls how the faces of the mesh are grouped with higher limits resulting in small groups of faces but lower distortion
If I use the default and unwrap the mesh, I now have 13 islands
However, if I cut the angle limit in half and unwrap the mesh, I now have more islands
The island margin determines how close the faces (or islands) are grouped
It is important to allow for some space between the islands so the materials will not bleed from one island to the next
If I set the island margin to a high number – such as 1 – you will see a lot of space between the islands
If, however, I use a small number such as 0.05 – you will see a smaller space between the islands
What you use as your margin is up to you
I would really recommend watching Grant Abbitt’s tutorial if you want to learn more about island margine
Area weight is the weight associated with the projection of the UV face
To be honest, I never change this option
Correct aspect means that the image aspect is taken into account
Scale to Bounds means that if the UV map is larger than the 0 to 1 ranges, the entire UV map will be scaled to fit inside
For example, if I scale the islands so they are larger than the UV map, and then use the “scale to bounds” option, you will notice that the islands are scaled down to fit within the UV map area
If I now add a material to this mesh, you can see some stretching of the brick pavers that correspond to the light-blue area of the islands
Unwrap (Seams)
The unwrap option is used in combination with seams to unwrap the mesh
To mark seams, select the mesh and tab into edit mode
In edge mode, select the edges where you want to add a seam, then right-click and choose “mark seam”
To clear a seam, select the edges, right-click and choose “clear seam”
Once you have a seam marked, simply select the entire mesh and use the U-key to open the UV mapping menu, and choose “unwrap”
Continue to add seams until you have the desired look – this would be a good time to either have the grid option or the display stretch option enabled
It is also important to remember that using this method may produce seams on your material so be careful about where you add seams – if they can be hidden or on the back or bottom of the mesh, that would be ideal
Once I get to the point where there is little or no stretching, I am done with unwrapping the mesh
Now when I add the paving stone material to the mesh, I can see there is no stretching like the previous smart UV project unwrap
There are two options under the UV menu that you should be aware of – average island scale and pack UV islands
The average island scale option will scale each UV island so they are approximately the same scale
The pack UV islands option will pack the UV islands in the best configuration to take up the most amount of space available on the UV map – you may need to adjust the options to make sure there is no stretching or overlapping islands
It is also important to remember that you must save the UV maps separately before closing the Blender file or you will lose them
One option to avoid this is by packing the UV islands within the Blender file
This can be done by choosing “pack” from the image menu