Modeling with Subdivision Surfaces/ Assigning Materials to Faces

Assigning Materials to Faces

You can attach textures and materials to SDS objects in several ways:

  • Using geometric mapping objects, such as the parallel and the sphere mapping. This method is suitable for procedurally defined (3D volume) materials. The disadvantage is that rigid mapping coordinates cannot follow deforming SDS objects in animations.
  • With a default mapping object, which uses a vertex channel to define the texture or shader coordinates. The number of vertex channels is not limited: in addition to the UV Coordinates channel, which is available in every SDS object, the user can add his/her own channels 'myuv1', 'myuv2' etc. The disadvantage of vertex channels in surface texturing is that it is often difficult or impossible to unfold a complex, branching surface into a UV plane continuously enough. Two points that are close in 3D space may get dislocated in UV space.
  • With face materials or textures. These are attached using a private set of UV coordinates for each face, which approach solves the unfolding problems of vertex channels. On the other hand, interpolation of face material UVs is less continuous as vertex channel interpolation, because neighbor faces do not contribute.
  • With UV set objects. UV sets are sub meshes of SDS objects defined in UV coordinate space. You can use any number of UV sets to split the parent mesh geometry into suitable UV areas (e.g into front and back projections). Each UV set can contain any number of disconnected face groups.

Assigning Materials to Faces Using Drag & Drop

The easiest way to attach materials to faces is using drag & drop.

1. Put the SDS object into the face edit mode.

2. Select the target faces

3. Zoom and rotate the view so that target faces are relatively parallel to the view window and fill it. UV coordinates for face materials will be the projection of vertices into the view.

4. Drag & drop a suitable material into the view window. This assigns the material to the selected faces. 

 
'Granite' material assigned to the selected faces.  

You can assign any number of materials to a single face. Materials are evaluated in the order in which they are assigned.  
 
 

Editing Texture Coordinates in UV Editor

Each material gets an unique set of texture coordinates through which you can control the position and size of the texture. You can edit these texture coordinates in the UV Editor window. 

The UV editor allows you to edit the UV coordinates of the currently selected face material (there can be any number of materials per face, but the current face material allows you to select which one of them is shown in the UV editor).  

When you open the UV editor for the first time, it automatically evaluates the current face material to a bit map image which is then shown as a backdrop image in the UV Editor. 

Note: evaluating the backdrop image can take several seconds depending on the size of the UV editor window. However, this process is run as a separate thread so you can start using the UV editor as soon as it opens.  

Through the UV editor you can edit the UV coordinates of the currently selected face material. Use any transformation or deformation tools, such as Scale, Rotate, Mirror, Bend etc. to modify the UV coordinates.  

UV editor also supports compass menus. You can put frequently needed UV manipulation tools (mirror faces etc.) to compass menus. The default startup project defines an example compass menu for the SDS objects.  

  
The UV editor and a SDS specific compass menu  

Pressing the Delete key on the UV Editor window removes the current face material from the selected faces (deletes the selected UV faces).  

Most of the standard modifiers also work in the UV Editor. For example, all selection modifiers (Shift = Add to selection, Ctrl = Intersection, Alt = Remove from selection) etc. work. When modifying faces, Shift activates angle grid and so on.  

When modifying the UV coordinates in the UV Editor, 3D view windows update in real time.  

There is also a context sensitive pop-up menu associated with the UV View.  

Just like in 3D views, there are three editing modes available: Points, Edges and Faces. However, edge editing is not avalaible for face materials, only for vertex channels.

The following menu options control which faces are shown on the UV Editor (note that only faces that contain the selected face material can be shown):  

  1. "Show all faces"  - Shows all the faces that contain the current face material
  2. "Hide all faces"  - Hides all faces
  3. "Show selected faces"   - Shows the selected faces (+ currently visible faces)
  4. "Hide selected faces"   - Hides the selected faces
To show only the currently selected faces you can use the "Hide all faces" and "Show selected faces" menu items in succession.  

The popup menu can also be used to select the current UV and the current face material name of the selected SDS object. The UV:s are listed first and the face material names last (there is a delimiter between the two groups).  
  
The SDS specific menu of the UV editor window allows you to detach materials from faces:  

  1. Detach - detaches the current face material from the selected faces.
  2. Detach from all faces - detaches a face material from all faces. The face material is selected from the sub menu.
You can animate face uv coordinates by modifying them in animation recording mode.  
  

The Properties item in the UV View's pop-up menu allows you to open the property window for the UV View. Through this window you can control options like the contrast (weight) of the backdrop image, grid, rendering options and compass menus.  

  
UV editor's property window compass tab  
 
Note that you can record all options in this window to macros and bind those macros to desired keys, compass menus or icons for faster access.  
 

Editing Face Materials through the Property Window

The object specific part (the 'Spec' tab') of the property window shows you the materials assigned to the selected faces. Click the desired material to make it the current face material. Use drag & drop to change the order in which the materials are evaluated. The pop-up menu allows you to remove materials from faces.  

  
In the Property window/Spec tab you can select the current face material, delete materials and change the order in which materials are applied.  
  
The SDS property gadget has a checkbox 'Selected faces only' inside the Faces frame. If checked, the Material list works as before: shows the materials of the first selected face and its Detach popup menu removes the selected face material from the selected faces. If not checked, the Material list shows all face materials and Detach removes the selected face material from all faces.  
  
 
 

Map2Obj

This tool provides you with more control over assigning face specific materials.   

Map2Obj tool (located in the Materials tab) allows you assign materials to faces and define face specific UV coordinates using any mapping object, such as the parallel map. For example, you can use a parallel mapping to attach an 'eye' texture to the faces representing an eye of a head.    

  1. Select the desired SDS faces 
  2. Create a parallel mapping object (from any material) 
  3. Multiselect the SDS object and the parallel mapping object and activate the Map2Obj tool 
  4. Set 'Target' to 'Selected Faces' or 'All Faces', select the material to be assigned using the 'Destination Material' field and click Accept. 
 
Assign 'marble' material to 'Selected Faces' using the Map2Obj tool  
 
 

Previewing Face Materials in OpenGL

To preview a single face material in OpenGL, open the property window, go to the Wire tab and set the Material Rendering option to Single. Specify also a suitable texture quality. Material Rendering=Full evaluates all mapped materials and is usually slower.  

  
Define texture quality through the Property window's 'Wire' tab  

After the texture quality is specified, the system converts the current face material to a bit map image (texture map). You can find the generated images from the 'temp' folder. The image is named as 'materialname_texture.bmp'.  Next time you attach the material to a face, OpenGL will be able to show the result instantly.