Houdini - UV
Vieport display options
Open the vieport display option dialog (press D over the viewport)
- Markers tab > Vertices > UV Overlap
- Displays the overlap in red (in the UV view)
- Add a uv flatten node
- Under the section Flattening Constraints > Rectify Group
- type *
Target Assignment (UDIM)
To force specific primitives to a specific UDIM we can use a primitive attr to specify which one.
- Create a poly tube with end caps.
- Create groups for the top, btm and the “mid”
- One way to do this is to use the group by normal for the top and btm and for the mid a group combine with “equals all but” the top and btm.
- Append a UV Texture, in the group field set top and btm. Orthographic in the y-axis is fine to create uvs for the caps.
- Append another UV Texture for the mid group using Cylindrical projection
- Create an integer Primitive attribute called udim on each of the groups. We will set the attr to be 1001 for the mid group, 1002 for the top and 1003 for the btm.
- Append a UV Layout
- Enable Overrides > Target Assignment > Target Attribute and set to udim
- Enable Scale Islands to Match Their Surface Area
- Set Targets > Pack Into > UDIM Tiles
Note by default the UV Layout node defines islands by connectivity of UV attribute values across polygon edges. If they do they will not be distributed to the UDIM tiles that we would expect. To fix this we could offset the uv texture so the edges do not align before going into the uv layout node or by using separator edges and or the island attribute. Read more in the docs.
- Select edge loop
- Hold A + MMB click the edge